J. Phyqiol. (1979), 291, pp. 413-423 With 8 text-figure. Printed in Great Britain
413
GASTRIC EMPTYING AND SECRETION IN THE CALF ON DUODENAL INFUSION OF TRYPTOPHAN, TRYPTAMINE AND 5-HYDROXYTRYPTAMINE
BY F. R. BELL AND D. E. WEBBER From the Department of Medicine, Royal Veterinary College, London NW1 OTU
(Received 7 September 1978) SUMMARY
1. Gastric emptying, gastric acid and pepsinogen secretion were assessed simultaneously in the conscious calf using the test meal and duodenal perfusion technique (Bell & Mostaghni, 1975). 2. When 60 mM-HCl was infused into the duodenum, gastric emptying was arrested but both acid and pepsinogen secretion continued at a low level. Duodenal infusion with isotonic NaHCO3 caused rapid exponential emptying of the test meal and acid and pepsinogen output was more than doubled. 3. Duodenal infusion of amino acids in isotonic NaHCO3 did not affect the rapid emptying, except infusion with tryptophan, which caused a measureable degree of inhibition of emptying, with concomitant effects on acid and pepsinogen secretion 4. Tryptamine and 5-hydroxytryptamine (5-HT) incorporated in low concentration into isotonic NaHCO3 also produced depression of gastric emptying, acid and pepsinogen levels comparable to the response initiated by acid infusate. Tryptophan was effective only in non-physiological amounts while 5-HT and tryptamine were active in smaller doses. 5. Our results suggest that the inhibition of gastric emptying following duodenal infusion of tryptophan noted by Stephens, Woolson & Cooke (1975) may be due to the duodenal synthesis of its biogenic amine derivatives tryptamine and 5-HT. 6. The level of activity of the three gastric functions, emptying, acid secretion and pepsinogen secretion appears to be linked. A single stimulus, therefore, could evoke a duodenal receptor or receptors to mediate or suppress activity of the gastric smooth muscle and secretary cells through interrelated mechanisms. The effect of some duodenal infusates, however, produces some variability in response which suggests differential activation of different receptors with consequent variable motor activity on effector cells. INTRODUCTION
The mechanisms which control gastric emptying, acid secretion and pepsinogen secretion have been examined intensively for many years. Gastric emptying and acid secretion have received most attention and only rarely have all three functions been examined simultaneously. It is accepted that various constituents of gastric chyme when evacuated into the duodenum play a major role in controlling intra0022-3751/79/3920-0720 $01.50 © 1979 The Physiological Society
F. R. BELL AND D. E. WEBBER gastric digestive processes. A dual regulatory mechanism, neural and hormonal, has been shown to be mediated through duodenal receptors responsive to H+, fat, amino acids, ions, monosaccharides, acids and many other substances (Cooke, 1975; Baron, 1976). We have examined the triple response of gastric emptying, acid secretion, and pepsinogen secretion when the duodenum is perfused with either 60 mM-HCl, which is known to retard physiological processes in the stomach, and isotonic NaHCO3 which is known to enhance these processes (Bell & Mostaghni, 1975; Bell & Grivel, 1975; Bell & Watson, 1976). We have also examined a number of individual amino acids by duodenal infusion including tryptophan, noted by Stephens et al. (1975) to be inhibitory to gastric emptying in the dog by an osmotic mechanism. Another possible mechanism which could implicate tryptophan as a gastric inhibitor are the biogenic amines tryptamine and 5-hydroxytryptamine (5-HT) produced from dietary tryptophan (Stacey & Sullivan, 1957; Axelrod & Saavedra, 1974). It is also possible that 5-HT is involved in gastric control when other substances occur in the duodenum since both acid and glucose perfusion of the duodenum are associated with a rise in endogenous 5-HT (O'Hara, Fox & Cole, 1959; Drapanas, McDonald & Stewart, 1962; Kellum & Jaffe, 1976). We have therefore tested the hypothesis that the inhibitory action of tryptophan on gastric emptying may result from its metabolites tryptamine and 5-HT. 414
METHODS Nine Friesian bull calves, 40-50 kg body weight, were used for the experiments. The experi-
mental animals were prepared with abomasal and re-entrant duodenal cannulae when they were 10-14 days old and experiments commenced 6 days later. Experimental procedures were as described previously (Bell & Mostaghni, 1975), except that test meals were 1-5 1. isotonic saline with 70 mg phenol red/l. The abomasal effluent was collected directly from the proximal duodenal cannula during 5 min periods. The loss of phenol red to the effluent and the amount in abomasal samples allowed the volume of meal remaining in the abomasum to be calculated. Acid and pepsin estimation Acid concentration was measured by titrating gastric samples against 0.01 M-NaOH using phenol red as indicator. Pepsin concentration was measured after the method of Anson (1938) using denatured bovine haemoglobin (Sigma) as substrate. Digestion products soluble in trichloracetic acid were alkalinized with NaOH and read at 680 nm on a Beckman spectrophotometer after the addition of Folin and Ciocalteu's phenol reagent (B.D.H.). Absolute values were taken from a standard curve for pepsin, using crystalline hog pepsin (Sigma) as the standard. The empirical unit definition was that 1O sg of reference pesin liberated an amount of split product, the absorption of which corresponded to 0 11 mg L-tyrosine in a final reaction volume of 9 ml., and pepsin outputs were expressed as the increase in the amount of secretion (volume x concentration) for each 5 min interval. The duodenal infusion was maintained at 10 ml./min at 39 0C throughout the test meal period and for 10 min prior to the instillation of the meal. The following substances (B.D.H. Chemicals Limited, 97-5-99 % minimum assay purity) were used as infusates: L-tryptophan (12.5, 25 and 50 mm, equivalent to 0 5, 1 0 and 2-0 mg/kg per min); 5-HT (equivalent to 0*05, 0-1 mg/kg per min); tryptamine (equivalent 0 1 mg/kg per min). These substances were dissolved in isotonic NaHCO3 solution in order to ensure effective isosmolality and a stable pH (osmolality range 260-289 m-osmole/kg; pH range 8.1-8.6). Comparisons were made with isotonic NaHCO3 solution which facilitates emptying, and with 60 mM-HCl, which has a pronounced inhibitory effect on gastric function. A small number of experiments were conducted with the amino acids
DUODENAL INFUSION AND GASTRIC FUNCTION
415
phenylalanine, lysine and leucine (B.D.H.) dissolved in isotonic NaHCO3 solution (50 mM, osmolality range 312-392 m-osmole/kg, pH range 7 9-8 3). Osmolality was measured with an osmometer (Fiske Instruments, Model 330). Experiments were statistically evaluated with Student's t test for unpaired values, P < 0 05 being taken as level of significance. RESULTS
The effect of duodenal infusion of isotonic NaHCO.3 or 60 mM-HCl Gastric emptying. In order to provide an upper and lower limit of abomasal emptying with which to compare gastric acid and pepsinogen secretion, the duodenum was infused with isotonic NaHCO3 or 60 mM-HCl. These infusates have already been shown to produce maximal emptying of a test meal in 45 min on the one hand and complete inhibition of emptying on the other (Bell & Mostaghni, 1975). The results for the present series of experiments are shown in Fig. 1. 100 F
*00
0 . 0 0 0
90 80
x
70 cm
E
60 50
E 0 *
40
30 L I
I
I
I
0
5
10
15
I
I
20 25 Time (min)
-
I
I
30
35
40
45
Fig. 1. The percentage volume of saline test meal remaining in the abomasum when the duodenum was infused with isotonic NaHCO3 solution (X) or 60 mM-HCl (0). The average data for each infusate was from thirteen experiments in six calves.
Gastric acid secretion. In contrast to the exponential effect of gastric emptying evoked by perfusion of the duodenum with isotonic NaHCO3, gastric acid is produced in a linear fashion throughout the test meal period (Fig. 2). A greater apparent production of acid is seen in the first 5 min of the test meal with either bicarbonate or acid infusion of the duodenum (Fig. 2). Following this initial period acid secretion is linear and continues to be so throughout the infusion period. There is no exponential output but the amount of acid produced is much greater with alkali than with acid infusion (Fig. 2). There is a statistically significant difference in the level of acid secretion evoked by the two duodenal perfusates.
F. R. BELL AND D. E. WEBBER Pepsinogen secretion. Acid perfusion of the duodenum is associated with a mean linear production of 1 0 mg/5 min of pepsin throughout the meal period. On perfusion of the duodenum with isotonic NaHCO3 a similar linear pepsin production is evoked but at a higher mean level of 2-5 mg/5 min. The difference between pepsinogen secretion on alkaline and acid perfusion of the duodenum is statistically significant 416
(Fig. 2). **
4
-
3
2
....
.
N H- .
...... ....,.I. .a~t I '''i'.....
...........
....
~ o ~~ ~ ~ ~
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.....
...,....,.....
33. 0
,HC
CD*1 5 0
0
...
5
10
15
25 20 Time (min)
30
35
40
45
Fig. 2. Abomasal acid and pepsin output (mean + s.E. of mean) when the duodenum was infused with isotonic NaHCO, solution (continuous line) or 60 mM-HCl (dotted line). Test meals were instilled at time 0 min. Significant differences in secretion during the same 5 min period with duodenal infusion of NaHCO8 or HCl is shown by * (P < 0.05) or ** (P < 0.01)
There is a clear relationship between the increase of gastric emptying, acid secretion and pepsinogen secretion on alkalinization of the duodenum compared with the inhibition of emptying and the low level of gastric acid and pepsinogen secretion when the duodenum is infused with acid. The effect of duodenal infusion of amino acid The amino acids were dissolved in isotonic NaHCO3 solution to facilitate the disclosure of possible inhibitory effects over the alkaline effect and to maintain the osmolality of the infusates. Gawtric emptying. The effect on gastric emptying of some amino acids is illustrated in Fig. 3. The stimulatory influence of NaHCO3 was maintained in each case despite the presence of a 50 mm concentration of amino acid. Only the highest dose of
DUODENAL INFUSION AND GASTRIC FUNCTION
417
110 *** A 100 90 80 Abe,, 70 _-** -
60
c6
E 50E
:1
T
w403.-T
II
30
10th aminHCi 10
-
~
n= 1 3 C= 6
Trp
Trp
50mm 8 5
25mM 6 4
nt
Trp
Phe
50mM 12-5mm 3 6 5 3 Duodenal infusate
Lys
Leu
50mM 3 2
50mM 3 3
NaHCof C0
13 6
Fig. 3. The percentage of meal remaining in the abomasum on infusion of the duodenum with ammno acids, isotonic NaHCO, and 60 rmm-HC1. Values are the mean + s.E. of the mean percentage of the saline test meal remaining in the abomasum after 45 min. The data presented represents n experiments and c calves. Significant difference compared with isotonic NaHCO3 infusion is shown by ** (P < 0.01) or *** (P < 0.001). 28 26 24 22
E20
:i6-0
LO
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214-
1240. 3 10 0
~0I
4
0
HO
Trp 50mM
Trp 25mM
Trp 12-5mm
Phe 50mM
Lys 50mM
Leu 50mM
NaHCO3
Duodenal infusate
Fig. 4. The effect on abomasal acid output of infusion of amino acids into the duodenum. Values are the mean + s.E. of mean; results for isotonic WaHCO3 and 60 mM-HCl are included for comparison. None of the amino acids significantly affected acid output compared with isotonic NaHCO3, infusion.
tryptophan employed, 50 mm, produced a statistically significant reduction in gastric emptying, although this effect was much less than with 60 mM-HCl infusion. Lower concentration of tryptophan had no detectable effect on gastric emptying. Acid secretion. Consistent acid secretion, similar to that evoked by NaHCO, infusion, was observed irrespective of the amino acid employed (Fig. 4). The higher 14
PHY
291
F. R. BELL AND D. E. WEBBER concentrations of tryptophan did not alter acid output significantly, although mean values were slightly depressed. Pepsinogen secretion. Duodenal infusion of amino acids caused some reduction in pepsinogen output but the levels were not statistically different from those seen when NaHCO3 was infused. Tryptophan, 25 mm, gave a significant depression (P < 0.05) but a wide range of pepsinogen secretary rates occurred, particularly on tryptophan infusion, as shown by the large standard errors of the mean (Fig. 5). 418
26242220-
-
E 18-
E~
14-
CL120
*
10
C
4 2
-
HCl
Trp
Trp
Trp
Phe
Lys
Leu
50mM
25mM
12-5mM
50mM
50mM
50mM
NaHCO3
Duodenal infusate
Fig. 5. The effect on abomasal pepsinogen output when the duodenum was infused with amino acid. Values are the mean + s.E. of mean; results for isotonic NaHCO3 and 60 mM-HCl are included for comparison. Significant difference in pepsinogen output when compared with isotonic NaHCO3 infusion is shown by * (P < 0.05), found only with tryptophan 25 mm infusion.
The effect of duodenal infusion of 5-HT or tryptamine Isotonic NaHCO3 solution was used as the substrate for the introduction into the duodenum of the amine derivatives of tryptophan, 5-HT and tryptamine. Gastric emptying. Incorporation of 5-HT or tryptamine into NaHCO3 solution significantly inhibited gastric emptying, producing a pattern of emptying similar to that seen with HCl infusion (Fig. 6). This observation is particularly remarkable as it was necessary to overcome the stimulatory effect of isotonic NaHCO3 solution. Only the smaller dose of 5-HT employed did not reduce evacuation of the test meal. Both 5-HT and tryptamine were disproportionately effective in slowing gastric emptying compared with tryptophan. Acid secretion. In contrast to the pronounced inhibitory effect of the larger dose of 5-HT on gastric emptying, acid secretion was not affected by either dose of the amine. In contrast, tryptamine was almost as effective as 60 mM-HCl in inhibiting acid secretion (Fig. 7). Pepsinogen secretion. Total pepsin output was significantly reduced by both doses of 5-HT employed in duodenal infusion (Fig. 8). This effect was remarkable as infusion of 5-HT 0.05 mg/kg per min had no effect on gastric emptying or acid output (cf. Figs. 6, 7
DUODENAL INFUSION AND GASTRIC FUNCTION
419
110 100 90
80 70-
.Ca i
60 c -
E
0)
50E 40 4
>0
i
0
.~C
El
*'~
~
10
compared
n=
13
10
8
6
C=
6
4
4
4
waHCO3 13
6
Duodenal infusate
Fig. 6. The retention of saline test meals in the abomasum after the 45 mm test period when the duodenum was infused with 5-HT or tryptamine. Values are the mean + s.E:. of mean; the data presented represents n experiments and c calves. Significant difference compared with isotonic NaHCO, infusion is shown by **(P < 0.001). 26 2422
.2020 Ln 18Z 16-
1412 *-
10
2o
T
HCI~~~ 1O
E
NaHCO3
6
Duodenal infusate
Fig. 7. The effect on abomasal acid output when the duodenum was infused with 5-HT or tryptamine. Values are the mean + .E. of mean and significant difference compared with isotonic NaHCO3 infusion is shown by ** (P < 0.01).
and 8). Tryptamine also significantly reduced pepsin secretion (P < 0.05), thus showan effect of inhibition on the three phases of gastric function comparable to 60 mm-HCl infusion.
ing
DISCUSSION
Gastric emptying and acid secretion are known to be controlled through receptors in the duodenum (Andersson, 1967; Hunt & Knox, 1968) but the control of pepsinogen 14--2
F. R. BELL AND D. E. WEBBER secretion has been less actively investigated. There are few data on the co-ordination of motor and secretary activity of the stomach from duodenal receptors. We have shown that when the three main functions of the gastric viscus are examined simultaneously during duodenal perfusion with 60 mM-HCl, complete inhibition of abomasal emptying occurs and acid and pepsinogen secretion is reduced
420
26
24 22
z20E 18 LO) 16-
*
.14
*
o12
0-10
*
C
IHCI
CoE L~i Doudenal infusate
Fig. 8. The effect on abomasal pepsinogen output when the duodenum was infused with 5-HT or tryptamine. Values are the mean ± 5.E. of mean and significant difference- to NaHCO3 infusion is shown by * (P < 0.05) and ** (P < 0.01).
to a low level. This result indicates that all three gastric functions are inhibited simultaneously. Since it has been shown that inhibition of action potentials of smooth muscle results from acid in the duodenum (Bell &; Grivel, 1975) and is associated with quiescence of the gastric body and antrum (Bell, 1978), then the reduction of gastric secretion to basal levels noted in the present observations may also reflect a similar inhibitory effect from duodenal acid receptors. When the duodenum is perfused with isotonic NaHCO3 the functions ofthe stomach are enhanced, the abomasum empties most of the test meal in 45 min, and gastric acid and pepsinogen secretion is increased by a factor of two to three compared to acid perfusion. Alkaline stimulus to the duodenum generates positive feed-back with activation of gastric smooth muscle and maximal emptying of the viscus (Bell &Z Grivel, 1975). The experiments reported here indicate that when duodenal receptors are stimulated by isotonic NaHCO3 all three phases of gastric function are augmented simultaneously. The effect of isotonic NaHCO3, and the inhibitory effect of 60 mM-HCl on the three components of gastric function thus provide parameters for comparison, so that stimulation or inhibition of gastric activity by other substances might indicate similar or dissimilar mechanisms of gastric effector processes. A preferential action on one or more of these parameters could dissociate or consolidate interdependence of gastric emptying, gastric acid and pepsinogen secretion. We chose to examine tryptophan for possible differential action since it has been shown to cause partial
DUODENAL INFUSION AND GASTRIC FUNCTION 421 inhibition of gastric emptying in the dog (Stephens et al. 1975). In the calf, as in the dog, tryptophan proved to be the only amino acid examined which produced a measure of inhibition of gastric emptying. In addition we have shown that in the calf pepsinogen and acid secretion are not significantly inhibited by tryptophan at the concentration used, except that 25 mM-tryptophan did reduce pepsinogen secretion. Tryptophan therefore, compared to acid, appears to have some differential effect on gastric function, although it should be emphasized that high concentrations of tryptophan (50 mm) were used. In the milk-fed calf the concentration of tryptophan would be approximately 2 mm in the duodenal chyme. The biogenic amine derivatives of tryptophan, 5-HT and tryptamine, however, proved to be much more potent inhibitors of gastric emptying than tryptophan itself, which suggests that conversion of tryptophan may be necessary for it to be effective. Tryptamine and 5-HT have been shown to activate intestinal smooth muscle in vitro (Gaddum, 1953; Feldberg & Smith, 1954; Bulbring & Lin, 1958) and 5-HT has an inhibitory effect on gastric motility in the human subject (Misiewicz, Waller & Eisner, 1966). Although 5-HT is produced on acidification of the duodenum (Kellum & Jaffe, 1976; Jaffe, Kopen & Lazan, 1977), it is not usually regarded as affecting gastric processes since it is removed from the plasma by platelets and the liver. It has been reported, however, that in the dog, acid infusion of the duodenum does cause an endogenous rise in plasma 5-HT levels which produces inhibition of acid secretion (Jaffe et al. 1977). The effects produced by tryptamine and 5-HT are different from the responses produced by tryptophan. Tryptamine, like acid, significantly inhibits both gastric emptying and secretion. By contrast 5-HT does not affect acid secretion significantly but does inhibit pepsinogen output and has a dose-response inhibitory effect on gastric emptying. This differential effect can also be produced by the action of intestinal hormones, for example secretion activates acid secretion but not pepsinogen, whereas motilin stimulates pepsin secretion (Baron, 1976). These differential effects may reflect multifactorial stimuli through neural pathways or enteric hormones on effector organs such as gastric smooth muscle and secreting cells. Duodenal infusion may cause the elaboration of hormones which affect gastric function, for example acid produces an endogenous rise in gastrin (Konturek, Rayford & Thompson, 1977), motilin (Strunz, Mitznegg, Domschke, Subramanian, Domschke & Wunsch, 1977), secretin (Johnson & Grossman, 1968), secretin, motilin and pancreatic glucagon (Bell & Watson, 1976). It would appear that enterogastrone should be regarded as an omnibus entity with collective inhibitory properties which affect various phases of gastric function differentially. The evidence points strongly towards the components of enterogastrone acting synergistically to produce inhibitory effects (Wormsley, 1973; Hendel & Henriksen, 1976). The current experients do not afford information on the effect of individual components of gastric chyme on postulated duodenal receptors such as osmoreceptors or acid chemoreceptors. Thus it is not possible to suggest that gastric control from the duodenum is mediated via a single neural or hormonal process, so that a specific constituent of duodenal chyme affects both contractile and secretary activity of the stomach. There is evidence that activating processes of the abomasum are
422
F. R. BELL AND D. E. WEBBER mediated mainly by neural networks and inhibitory processes through humoral agents released from parent cells in the duodenum (Bell & Watson, 1976). However, motility and secretion are usually affected in the same direction to produce positive active work or inhibition of cellular activity. This work was supported by a grant from the Agricultural Research Council. REFERENCES
ANDERSSON, S. (1967). Gastric and duodenal mechanisms inhibiting gastric secretion of acid. In Handbook of Physiology, section 6: Alimentary Canal. Vol. ii. Secretion, ed. CODE, C. F. Washington D.C.: American Physiological Society.
ANsoN, M. L. (1938). The estimation of pepsin, trypsin, papain and cathepsin with haemoglobin J. gen. Phyeiol. 22, 79-89.
AxELUOD, J. & SAAVEDRA, J. M. (1974). Octopamine, phenylethanolamine, phenylethylamine
and tryptamine in the brain. In Aromatic Amino Acids in the Brain. Ciba Foundation Symposium 22. Amsterdam: Associated Scientific. BARON, J. H. (1976). Inhibition of gastric secretion by intestinal hormones. Scand. Jnl Ga8troenterol. 11, suppl. 42, 17-24. BELL, F. R. (1978). The pressure relationship in the gastric body, antrum and duodenum during gastric (abomasal) emptying in the calf. In Sixth International Sympoeium on Ga8trointestinal Motility, ed. DUTHIE, H. L. Edinburgh: MTP Press. BELL, F. R. & GRIVEL, M.-L. (1975). The effect of duodenal infusion on the electromyogram of gastric muscle during activation and inhibition of gastric emptying. J. Phyeiol. 248, 377391. BELL, F. R. & MosTAaHNI, K. (1975). Duodenal control of gastric emptying in the milk-fed calf. J. Phy8iol. 245, 387-407. BELL, F. R. & WATSON, D. J. (1976). The influence of gastric distension and the duodenal infusate on the pattern of stomach (abomasal) emptying in the preruminant calf. J. Phyeiol. 259, 445-456. BULBRING, E. & Liu, R. C. Y. (1958). The effect of intraluminal application of 5-hydroxytryptamine and 5-hydroxytryptophan on peristalsis; the local production of 5-HT and its release in relation to intraluminal pressure and propulsive activity. J. Phyeiol. 140, 381-407. CooxE, A. R. (1975). Control of gastric emptying and motility. Gastroenterology 68, 804-816. DRAPANAS, T., MCDONALD, J. C. & STEWART, J. D. (1962). Serotonin release following instillation of hypertonic glucose into the proximal intestine. Ann. Surg. 156, 528-536. FELDBERG, W. & Sm=T, A. N. (1954). The role of histamine release for the motor effects of histamine liberators on the guinea-pig's ileum preparation. J. Phyeiol. 124, 219-233. GADDUM, J. H. (1953). Tryptamine receptors. J. Phyeiol. 119, 363-368. HENDEL, L. & HENRIKSEN, F. W. (1976). Inhibition of gastric secretion by combined secretin and CCK and combined glucagon and CCK. Scand. Jnl. Gaatroenterel. 11, supply. 42, 37-39. HUNT, J. N. & KNox, M. T. (1968). Regulation of gastric emptying. In Handbook of Physiology, section 6: Alimentary Canal. Vol. Iv. Motility, ed. CODE, C. F. Washington D.C.: American Physiology Society. JAFFE, B. M., KOPEN, D. F. & LAZAN, D. W. (1977). Endogenous serotonin in the control of gastric acid secretion. Surgery, St Louis 82, 156-163. JOHNSON, L. R. & GiaossMAN, M. I. (1968). Secretin: the enterogastrone released by acid in the
duodenum. Am. J. Physiol. 215, 885-888.
KELLUM, J. M. & JAFFE, B. M. (1976). Release of immunoreactive serotonin following acid perfusion of the duodenum. Ann. Surg. 184, 633-636. KONTuREK, S. J., RAYFORD, P. L. & THOMPSON, J. C. (1977). Effect of pH of gastric and intestinal meals on gastric acid and plasma gastrin and secretin responses in the dog. Am. J. Physiol. 233, E537-543. MISmEwIcz, J. J., WALLER, S. L. & EISNER, M. (1966). Motor responses of human gastrointestinal tract to 5-hydroxytryptamine in vivo and in vitro. Gut. 7, 208-216.
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O'HARA, R. S., Fox, R. 0. & COLE, J. W. (1959). Serotonin release mediated by intraluminal sucrose solutions. Surg. Forum. 10, 215-221. STACEY, R. S. & SULLIVAN, T. J. (1957). Effect of diet and antibiotics on intestinal 5-hydroxytryptamine. J. Physiol. 137, 63P. STEPHENS, J. R., WooLsoN, R. F. & COOKE, A. R. (1975). Effects of essential and nonessential amino acids on gastric emptying in the dog. Gastroenterology 69, 920-927. STRUNZ, U., MITZNEGG, P. DOMsCHKE, W., SUBRAMANIAN, N., DoMscwx , S. & WuNSCH, E. (1977). Acid releases motilin from the human duodenum in vitro. Acta hepato-gastroenterol. 24, 456-457. WORMSLEY, K. G. (1973). Is secretin secreted? Gut 14, 743-751.
413
GASTRIC EMPTYING AND SECRETION IN THE CALF ON DUODENAL INFUSION OF TRYPTOPHAN, TRYPTAMINE AND 5-HYDROXYTRYPTAMINE
BY F. R. BELL AND D. E. WEBBER From the Department of Medicine, Royal Veterinary College, London NW1 OTU
(Received 7 September 1978) SUMMARY
1. Gastric emptying, gastric acid and pepsinogen secretion were assessed simultaneously in the conscious calf using the test meal and duodenal perfusion technique (Bell & Mostaghni, 1975). 2. When 60 mM-HCl was infused into the duodenum, gastric emptying was arrested but both acid and pepsinogen secretion continued at a low level. Duodenal infusion with isotonic NaHCO3 caused rapid exponential emptying of the test meal and acid and pepsinogen output was more than doubled. 3. Duodenal infusion of amino acids in isotonic NaHCO3 did not affect the rapid emptying, except infusion with tryptophan, which caused a measureable degree of inhibition of emptying, with concomitant effects on acid and pepsinogen secretion 4. Tryptamine and 5-hydroxytryptamine (5-HT) incorporated in low concentration into isotonic NaHCO3 also produced depression of gastric emptying, acid and pepsinogen levels comparable to the response initiated by acid infusate. Tryptophan was effective only in non-physiological amounts while 5-HT and tryptamine were active in smaller doses. 5. Our results suggest that the inhibition of gastric emptying following duodenal infusion of tryptophan noted by Stephens, Woolson & Cooke (1975) may be due to the duodenal synthesis of its biogenic amine derivatives tryptamine and 5-HT. 6. The level of activity of the three gastric functions, emptying, acid secretion and pepsinogen secretion appears to be linked. A single stimulus, therefore, could evoke a duodenal receptor or receptors to mediate or suppress activity of the gastric smooth muscle and secretary cells through interrelated mechanisms. The effect of some duodenal infusates, however, produces some variability in response which suggests differential activation of different receptors with consequent variable motor activity on effector cells. INTRODUCTION
The mechanisms which control gastric emptying, acid secretion and pepsinogen secretion have been examined intensively for many years. Gastric emptying and acid secretion have received most attention and only rarely have all three functions been examined simultaneously. It is accepted that various constituents of gastric chyme when evacuated into the duodenum play a major role in controlling intra0022-3751/79/3920-0720 $01.50 © 1979 The Physiological Society
F. R. BELL AND D. E. WEBBER gastric digestive processes. A dual regulatory mechanism, neural and hormonal, has been shown to be mediated through duodenal receptors responsive to H+, fat, amino acids, ions, monosaccharides, acids and many other substances (Cooke, 1975; Baron, 1976). We have examined the triple response of gastric emptying, acid secretion, and pepsinogen secretion when the duodenum is perfused with either 60 mM-HCl, which is known to retard physiological processes in the stomach, and isotonic NaHCO3 which is known to enhance these processes (Bell & Mostaghni, 1975; Bell & Grivel, 1975; Bell & Watson, 1976). We have also examined a number of individual amino acids by duodenal infusion including tryptophan, noted by Stephens et al. (1975) to be inhibitory to gastric emptying in the dog by an osmotic mechanism. Another possible mechanism which could implicate tryptophan as a gastric inhibitor are the biogenic amines tryptamine and 5-hydroxytryptamine (5-HT) produced from dietary tryptophan (Stacey & Sullivan, 1957; Axelrod & Saavedra, 1974). It is also possible that 5-HT is involved in gastric control when other substances occur in the duodenum since both acid and glucose perfusion of the duodenum are associated with a rise in endogenous 5-HT (O'Hara, Fox & Cole, 1959; Drapanas, McDonald & Stewart, 1962; Kellum & Jaffe, 1976). We have therefore tested the hypothesis that the inhibitory action of tryptophan on gastric emptying may result from its metabolites tryptamine and 5-HT. 414
METHODS Nine Friesian bull calves, 40-50 kg body weight, were used for the experiments. The experi-
mental animals were prepared with abomasal and re-entrant duodenal cannulae when they were 10-14 days old and experiments commenced 6 days later. Experimental procedures were as described previously (Bell & Mostaghni, 1975), except that test meals were 1-5 1. isotonic saline with 70 mg phenol red/l. The abomasal effluent was collected directly from the proximal duodenal cannula during 5 min periods. The loss of phenol red to the effluent and the amount in abomasal samples allowed the volume of meal remaining in the abomasum to be calculated. Acid and pepsin estimation Acid concentration was measured by titrating gastric samples against 0.01 M-NaOH using phenol red as indicator. Pepsin concentration was measured after the method of Anson (1938) using denatured bovine haemoglobin (Sigma) as substrate. Digestion products soluble in trichloracetic acid were alkalinized with NaOH and read at 680 nm on a Beckman spectrophotometer after the addition of Folin and Ciocalteu's phenol reagent (B.D.H.). Absolute values were taken from a standard curve for pepsin, using crystalline hog pepsin (Sigma) as the standard. The empirical unit definition was that 1O sg of reference pesin liberated an amount of split product, the absorption of which corresponded to 0 11 mg L-tyrosine in a final reaction volume of 9 ml., and pepsin outputs were expressed as the increase in the amount of secretion (volume x concentration) for each 5 min interval. The duodenal infusion was maintained at 10 ml./min at 39 0C throughout the test meal period and for 10 min prior to the instillation of the meal. The following substances (B.D.H. Chemicals Limited, 97-5-99 % minimum assay purity) were used as infusates: L-tryptophan (12.5, 25 and 50 mm, equivalent to 0 5, 1 0 and 2-0 mg/kg per min); 5-HT (equivalent to 0*05, 0-1 mg/kg per min); tryptamine (equivalent 0 1 mg/kg per min). These substances were dissolved in isotonic NaHCO3 solution in order to ensure effective isosmolality and a stable pH (osmolality range 260-289 m-osmole/kg; pH range 8.1-8.6). Comparisons were made with isotonic NaHCO3 solution which facilitates emptying, and with 60 mM-HCl, which has a pronounced inhibitory effect on gastric function. A small number of experiments were conducted with the amino acids
DUODENAL INFUSION AND GASTRIC FUNCTION
415
phenylalanine, lysine and leucine (B.D.H.) dissolved in isotonic NaHCO3 solution (50 mM, osmolality range 312-392 m-osmole/kg, pH range 7 9-8 3). Osmolality was measured with an osmometer (Fiske Instruments, Model 330). Experiments were statistically evaluated with Student's t test for unpaired values, P < 0 05 being taken as level of significance. RESULTS
The effect of duodenal infusion of isotonic NaHCO.3 or 60 mM-HCl Gastric emptying. In order to provide an upper and lower limit of abomasal emptying with which to compare gastric acid and pepsinogen secretion, the duodenum was infused with isotonic NaHCO3 or 60 mM-HCl. These infusates have already been shown to produce maximal emptying of a test meal in 45 min on the one hand and complete inhibition of emptying on the other (Bell & Mostaghni, 1975). The results for the present series of experiments are shown in Fig. 1. 100 F
*00
0 . 0 0 0
90 80
x
70 cm
E
60 50
E 0 *
40
30 L I
I
I
I
0
5
10
15
I
I
20 25 Time (min)
-
I
I
30
35
40
45
Fig. 1. The percentage volume of saline test meal remaining in the abomasum when the duodenum was infused with isotonic NaHCO3 solution (X) or 60 mM-HCl (0). The average data for each infusate was from thirteen experiments in six calves.
Gastric acid secretion. In contrast to the exponential effect of gastric emptying evoked by perfusion of the duodenum with isotonic NaHCO3, gastric acid is produced in a linear fashion throughout the test meal period (Fig. 2). A greater apparent production of acid is seen in the first 5 min of the test meal with either bicarbonate or acid infusion of the duodenum (Fig. 2). Following this initial period acid secretion is linear and continues to be so throughout the infusion period. There is no exponential output but the amount of acid produced is much greater with alkali than with acid infusion (Fig. 2). There is a statistically significant difference in the level of acid secretion evoked by the two duodenal perfusates.
F. R. BELL AND D. E. WEBBER Pepsinogen secretion. Acid perfusion of the duodenum is associated with a mean linear production of 1 0 mg/5 min of pepsin throughout the meal period. On perfusion of the duodenum with isotonic NaHCO3 a similar linear pepsin production is evoked but at a higher mean level of 2-5 mg/5 min. The difference between pepsinogen secretion on alkaline and acid perfusion of the duodenum is statistically significant 416
(Fig. 2). **
4
-
3
2
....
.
N H- .
...... ....,.I. .a~t I '''i'.....
...........
....
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33. 0
,HC
CD*1 5 0
0
...
5
10
15
25 20 Time (min)
30
35
40
45
Fig. 2. Abomasal acid and pepsin output (mean + s.E. of mean) when the duodenum was infused with isotonic NaHCO, solution (continuous line) or 60 mM-HCl (dotted line). Test meals were instilled at time 0 min. Significant differences in secretion during the same 5 min period with duodenal infusion of NaHCO8 or HCl is shown by * (P < 0.05) or ** (P < 0.01)
There is a clear relationship between the increase of gastric emptying, acid secretion and pepsinogen secretion on alkalinization of the duodenum compared with the inhibition of emptying and the low level of gastric acid and pepsinogen secretion when the duodenum is infused with acid. The effect of duodenal infusion of amino acid The amino acids were dissolved in isotonic NaHCO3 solution to facilitate the disclosure of possible inhibitory effects over the alkaline effect and to maintain the osmolality of the infusates. Gawtric emptying. The effect on gastric emptying of some amino acids is illustrated in Fig. 3. The stimulatory influence of NaHCO3 was maintained in each case despite the presence of a 50 mm concentration of amino acid. Only the highest dose of
DUODENAL INFUSION AND GASTRIC FUNCTION
417
110 *** A 100 90 80 Abe,, 70 _-** -
60
c6
E 50E
:1
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10th aminHCi 10
-
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n= 1 3 C= 6
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Trp
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nt
Trp
Phe
50mM 12-5mm 3 6 5 3 Duodenal infusate
Lys
Leu
50mM 3 2
50mM 3 3
NaHCof C0
13 6
Fig. 3. The percentage of meal remaining in the abomasum on infusion of the duodenum with ammno acids, isotonic NaHCO, and 60 rmm-HC1. Values are the mean + s.E. of the mean percentage of the saline test meal remaining in the abomasum after 45 min. The data presented represents n experiments and c calves. Significant difference compared with isotonic NaHCO3 infusion is shown by ** (P < 0.01) or *** (P < 0.001). 28 26 24 22
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4
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Trp 50mM
Trp 25mM
Trp 12-5mm
Phe 50mM
Lys 50mM
Leu 50mM
NaHCO3
Duodenal infusate
Fig. 4. The effect on abomasal acid output of infusion of amino acids into the duodenum. Values are the mean + s.E. of mean; results for isotonic WaHCO3 and 60 mM-HCl are included for comparison. None of the amino acids significantly affected acid output compared with isotonic NaHCO3, infusion.
tryptophan employed, 50 mm, produced a statistically significant reduction in gastric emptying, although this effect was much less than with 60 mM-HCl infusion. Lower concentration of tryptophan had no detectable effect on gastric emptying. Acid secretion. Consistent acid secretion, similar to that evoked by NaHCO, infusion, was observed irrespective of the amino acid employed (Fig. 4). The higher 14
PHY
291
F. R. BELL AND D. E. WEBBER concentrations of tryptophan did not alter acid output significantly, although mean values were slightly depressed. Pepsinogen secretion. Duodenal infusion of amino acids caused some reduction in pepsinogen output but the levels were not statistically different from those seen when NaHCO3 was infused. Tryptophan, 25 mm, gave a significant depression (P < 0.05) but a wide range of pepsinogen secretary rates occurred, particularly on tryptophan infusion, as shown by the large standard errors of the mean (Fig. 5). 418
26242220-
-
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C
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Trp
Trp
Trp
Phe
Lys
Leu
50mM
25mM
12-5mM
50mM
50mM
50mM
NaHCO3
Duodenal infusate
Fig. 5. The effect on abomasal pepsinogen output when the duodenum was infused with amino acid. Values are the mean + s.E. of mean; results for isotonic NaHCO3 and 60 mM-HCl are included for comparison. Significant difference in pepsinogen output when compared with isotonic NaHCO3 infusion is shown by * (P < 0.05), found only with tryptophan 25 mm infusion.
The effect of duodenal infusion of 5-HT or tryptamine Isotonic NaHCO3 solution was used as the substrate for the introduction into the duodenum of the amine derivatives of tryptophan, 5-HT and tryptamine. Gastric emptying. Incorporation of 5-HT or tryptamine into NaHCO3 solution significantly inhibited gastric emptying, producing a pattern of emptying similar to that seen with HCl infusion (Fig. 6). This observation is particularly remarkable as it was necessary to overcome the stimulatory effect of isotonic NaHCO3 solution. Only the smaller dose of 5-HT employed did not reduce evacuation of the test meal. Both 5-HT and tryptamine were disproportionately effective in slowing gastric emptying compared with tryptophan. Acid secretion. In contrast to the pronounced inhibitory effect of the larger dose of 5-HT on gastric emptying, acid secretion was not affected by either dose of the amine. In contrast, tryptamine was almost as effective as 60 mM-HCl in inhibiting acid secretion (Fig. 7). Pepsinogen secretion. Total pepsin output was significantly reduced by both doses of 5-HT employed in duodenal infusion (Fig. 8). This effect was remarkable as infusion of 5-HT 0.05 mg/kg per min had no effect on gastric emptying or acid output (cf. Figs. 6, 7
DUODENAL INFUSION AND GASTRIC FUNCTION
419
110 100 90
80 70-
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E
0)
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i
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El
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~
10
compared
n=
13
10
8
6
C=
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4
4
waHCO3 13
6
Duodenal infusate
Fig. 6. The retention of saline test meals in the abomasum after the 45 mm test period when the duodenum was infused with 5-HT or tryptamine. Values are the mean + s.E:. of mean; the data presented represents n experiments and c calves. Significant difference compared with isotonic NaHCO, infusion is shown by **(P < 0.001). 26 2422
.2020 Ln 18Z 16-
1412 *-
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2o
T
HCI~~~ 1O
E
NaHCO3
6
Duodenal infusate
Fig. 7. The effect on abomasal acid output when the duodenum was infused with 5-HT or tryptamine. Values are the mean + .E. of mean and significant difference compared with isotonic NaHCO3 infusion is shown by ** (P < 0.01).
and 8). Tryptamine also significantly reduced pepsin secretion (P < 0.05), thus showan effect of inhibition on the three phases of gastric function comparable to 60 mm-HCl infusion.
ing
DISCUSSION
Gastric emptying and acid secretion are known to be controlled through receptors in the duodenum (Andersson, 1967; Hunt & Knox, 1968) but the control of pepsinogen 14--2
F. R. BELL AND D. E. WEBBER secretion has been less actively investigated. There are few data on the co-ordination of motor and secretary activity of the stomach from duodenal receptors. We have shown that when the three main functions of the gastric viscus are examined simultaneously during duodenal perfusion with 60 mM-HCl, complete inhibition of abomasal emptying occurs and acid and pepsinogen secretion is reduced
420
26
24 22
z20E 18 LO) 16-
*
.14
*
o12
0-10
*
C
IHCI
CoE L~i Doudenal infusate
Fig. 8. The effect on abomasal pepsinogen output when the duodenum was infused with 5-HT or tryptamine. Values are the mean ± 5.E. of mean and significant difference- to NaHCO3 infusion is shown by * (P < 0.05) and ** (P < 0.01).
to a low level. This result indicates that all three gastric functions are inhibited simultaneously. Since it has been shown that inhibition of action potentials of smooth muscle results from acid in the duodenum (Bell &; Grivel, 1975) and is associated with quiescence of the gastric body and antrum (Bell, 1978), then the reduction of gastric secretion to basal levels noted in the present observations may also reflect a similar inhibitory effect from duodenal acid receptors. When the duodenum is perfused with isotonic NaHCO3 the functions ofthe stomach are enhanced, the abomasum empties most of the test meal in 45 min, and gastric acid and pepsinogen secretion is increased by a factor of two to three compared to acid perfusion. Alkaline stimulus to the duodenum generates positive feed-back with activation of gastric smooth muscle and maximal emptying of the viscus (Bell &Z Grivel, 1975). The experiments reported here indicate that when duodenal receptors are stimulated by isotonic NaHCO3 all three phases of gastric function are augmented simultaneously. The effect of isotonic NaHCO3, and the inhibitory effect of 60 mM-HCl on the three components of gastric function thus provide parameters for comparison, so that stimulation or inhibition of gastric activity by other substances might indicate similar or dissimilar mechanisms of gastric effector processes. A preferential action on one or more of these parameters could dissociate or consolidate interdependence of gastric emptying, gastric acid and pepsinogen secretion. We chose to examine tryptophan for possible differential action since it has been shown to cause partial
DUODENAL INFUSION AND GASTRIC FUNCTION 421 inhibition of gastric emptying in the dog (Stephens et al. 1975). In the calf, as in the dog, tryptophan proved to be the only amino acid examined which produced a measure of inhibition of gastric emptying. In addition we have shown that in the calf pepsinogen and acid secretion are not significantly inhibited by tryptophan at the concentration used, except that 25 mM-tryptophan did reduce pepsinogen secretion. Tryptophan therefore, compared to acid, appears to have some differential effect on gastric function, although it should be emphasized that high concentrations of tryptophan (50 mm) were used. In the milk-fed calf the concentration of tryptophan would be approximately 2 mm in the duodenal chyme. The biogenic amine derivatives of tryptophan, 5-HT and tryptamine, however, proved to be much more potent inhibitors of gastric emptying than tryptophan itself, which suggests that conversion of tryptophan may be necessary for it to be effective. Tryptamine and 5-HT have been shown to activate intestinal smooth muscle in vitro (Gaddum, 1953; Feldberg & Smith, 1954; Bulbring & Lin, 1958) and 5-HT has an inhibitory effect on gastric motility in the human subject (Misiewicz, Waller & Eisner, 1966). Although 5-HT is produced on acidification of the duodenum (Kellum & Jaffe, 1976; Jaffe, Kopen & Lazan, 1977), it is not usually regarded as affecting gastric processes since it is removed from the plasma by platelets and the liver. It has been reported, however, that in the dog, acid infusion of the duodenum does cause an endogenous rise in plasma 5-HT levels which produces inhibition of acid secretion (Jaffe et al. 1977). The effects produced by tryptamine and 5-HT are different from the responses produced by tryptophan. Tryptamine, like acid, significantly inhibits both gastric emptying and secretion. By contrast 5-HT does not affect acid secretion significantly but does inhibit pepsinogen output and has a dose-response inhibitory effect on gastric emptying. This differential effect can also be produced by the action of intestinal hormones, for example secretion activates acid secretion but not pepsinogen, whereas motilin stimulates pepsin secretion (Baron, 1976). These differential effects may reflect multifactorial stimuli through neural pathways or enteric hormones on effector organs such as gastric smooth muscle and secreting cells. Duodenal infusion may cause the elaboration of hormones which affect gastric function, for example acid produces an endogenous rise in gastrin (Konturek, Rayford & Thompson, 1977), motilin (Strunz, Mitznegg, Domschke, Subramanian, Domschke & Wunsch, 1977), secretin (Johnson & Grossman, 1968), secretin, motilin and pancreatic glucagon (Bell & Watson, 1976). It would appear that enterogastrone should be regarded as an omnibus entity with collective inhibitory properties which affect various phases of gastric function differentially. The evidence points strongly towards the components of enterogastrone acting synergistically to produce inhibitory effects (Wormsley, 1973; Hendel & Henriksen, 1976). The current experients do not afford information on the effect of individual components of gastric chyme on postulated duodenal receptors such as osmoreceptors or acid chemoreceptors. Thus it is not possible to suggest that gastric control from the duodenum is mediated via a single neural or hormonal process, so that a specific constituent of duodenal chyme affects both contractile and secretary activity of the stomach. There is evidence that activating processes of the abomasum are
422
F. R. BELL AND D. E. WEBBER mediated mainly by neural networks and inhibitory processes through humoral agents released from parent cells in the duodenum (Bell & Watson, 1976). However, motility and secretion are usually affected in the same direction to produce positive active work or inhibition of cellular activity. This work was supported by a grant from the Agricultural Research Council. REFERENCES
ANDERSSON, S. (1967). Gastric and duodenal mechanisms inhibiting gastric secretion of acid. In Handbook of Physiology, section 6: Alimentary Canal. Vol. ii. Secretion, ed. CODE, C. F. Washington D.C.: American Physiological Society.
ANsoN, M. L. (1938). The estimation of pepsin, trypsin, papain and cathepsin with haemoglobin J. gen. Phyeiol. 22, 79-89.
AxELUOD, J. & SAAVEDRA, J. M. (1974). Octopamine, phenylethanolamine, phenylethylamine
and tryptamine in the brain. In Aromatic Amino Acids in the Brain. Ciba Foundation Symposium 22. Amsterdam: Associated Scientific. BARON, J. H. (1976). Inhibition of gastric secretion by intestinal hormones. Scand. Jnl Ga8troenterol. 11, suppl. 42, 17-24. BELL, F. R. (1978). The pressure relationship in the gastric body, antrum and duodenum during gastric (abomasal) emptying in the calf. In Sixth International Sympoeium on Ga8trointestinal Motility, ed. DUTHIE, H. L. Edinburgh: MTP Press. BELL, F. R. & GRIVEL, M.-L. (1975). The effect of duodenal infusion on the electromyogram of gastric muscle during activation and inhibition of gastric emptying. J. Phyeiol. 248, 377391. BELL, F. R. & MosTAaHNI, K. (1975). Duodenal control of gastric emptying in the milk-fed calf. J. Phy8iol. 245, 387-407. BELL, F. R. & WATSON, D. J. (1976). The influence of gastric distension and the duodenal infusate on the pattern of stomach (abomasal) emptying in the preruminant calf. J. Phyeiol. 259, 445-456. BULBRING, E. & Liu, R. C. Y. (1958). The effect of intraluminal application of 5-hydroxytryptamine and 5-hydroxytryptophan on peristalsis; the local production of 5-HT and its release in relation to intraluminal pressure and propulsive activity. J. Phyeiol. 140, 381-407. CooxE, A. R. (1975). Control of gastric emptying and motility. Gastroenterology 68, 804-816. DRAPANAS, T., MCDONALD, J. C. & STEWART, J. D. (1962). Serotonin release following instillation of hypertonic glucose into the proximal intestine. Ann. Surg. 156, 528-536. FELDBERG, W. & Sm=T, A. N. (1954). The role of histamine release for the motor effects of histamine liberators on the guinea-pig's ileum preparation. J. Phyeiol. 124, 219-233. GADDUM, J. H. (1953). Tryptamine receptors. J. Phyeiol. 119, 363-368. HENDEL, L. & HENRIKSEN, F. W. (1976). Inhibition of gastric secretion by combined secretin and CCK and combined glucagon and CCK. Scand. Jnl. Gaatroenterel. 11, supply. 42, 37-39. HUNT, J. N. & KNox, M. T. (1968). Regulation of gastric emptying. In Handbook of Physiology, section 6: Alimentary Canal. Vol. Iv. Motility, ed. CODE, C. F. Washington D.C.: American Physiology Society. JAFFE, B. M., KOPEN, D. F. & LAZAN, D. W. (1977). Endogenous serotonin in the control of gastric acid secretion. Surgery, St Louis 82, 156-163. JOHNSON, L. R. & GiaossMAN, M. I. (1968). Secretin: the enterogastrone released by acid in the
duodenum. Am. J. Physiol. 215, 885-888.
KELLUM, J. M. & JAFFE, B. M. (1976). Release of immunoreactive serotonin following acid perfusion of the duodenum. Ann. Surg. 184, 633-636. KONTuREK, S. J., RAYFORD, P. L. & THOMPSON, J. C. (1977). Effect of pH of gastric and intestinal meals on gastric acid and plasma gastrin and secretin responses in the dog. Am. J. Physiol. 233, E537-543. MISmEwIcz, J. J., WALLER, S. L. & EISNER, M. (1966). Motor responses of human gastrointestinal tract to 5-hydroxytryptamine in vivo and in vitro. Gut. 7, 208-216.
DUODENAL INFUSION AND GASTRIC FUNCTION
423
O'HARA, R. S., Fox, R. 0. & COLE, J. W. (1959). Serotonin release mediated by intraluminal sucrose solutions. Surg. Forum. 10, 215-221. STACEY, R. S. & SULLIVAN, T. J. (1957). Effect of diet and antibiotics on intestinal 5-hydroxytryptamine. J. Physiol. 137, 63P. STEPHENS, J. R., WooLsoN, R. F. & COOKE, A. R. (1975). Effects of essential and nonessential amino acids on gastric emptying in the dog. Gastroenterology 69, 920-927. STRUNZ, U., MITZNEGG, P. DOMsCHKE, W., SUBRAMANIAN, N., DoMscwx , S. & WuNSCH, E. (1977). Acid releases motilin from the human duodenum in vitro. Acta hepato-gastroenterol. 24, 456-457. WORMSLEY, K. G. (1973). Is secretin secreted? Gut 14, 743-751.
