Differential Sensitivity to Somatostatin of Pancreatic Polypeptide, Glucagon and Insulin Secretion From the Isolated Perfused Canine Pancreas Kjeld
Hermansen
This dose-response study deals with the relative inhibitory effect of somatostatin on the acetylcholine-stimulated release of pancreatic polypeptide (PP), glucagon, and insulin from the isolated canine pancreas. Somatostatin in picomolar doses potently inhibited insulin and glucagon secretion, whereas PP secretion was relatively insensitive. Also. in the absence of acetylcholine, somatostatin exerted a preferential inhibition of the release of insulin and glucagon compared with PP. These findings point to a physiologically important role of somatostatin for the secretion of insulin and glucagon, but probably not for PP.
OMATOSTATIN inhibits pancreatic horsecretion.‘-* Somatostatin’s inhibitory effect on the secretory function of the endocrine cells is probably at least partly caused by an interference with the cellular calcium handling.‘-13 We have shown that the PP cell function, in contrast with the other endocrine cells in the pancreas, is relatively independent of extracellular calcium.‘4 In this investigation, a doseresponse study was performed in order to investigate somatostatin’s relative inhibitory effect on the release of pancreatic hormones from the isolated canine pancreas.
S mone
MATERIALS
AND
METHODS
Mongrel dogs, fasted overnight and weighing 17-28 kg, were used as pancreas donors. The technique for isolation of the canine pancreas and the perfusion system have previously been described in detaiLI In brief, the preparation consists of the pancreas and the proximal IO cm of the attached duodenum. A non-recirculating medium of Krebs-Ringer bicarbonate buffer pH 7.4 containing 40 g/liter dextran (mol wt 75,000), 2 g/liter bovine albumin, glutamate. fumarate, and pyruvate, each at a concentration of 5 mmol/liter. was pumped through the splenic and the coeliac arteries, and the total portal effluent was collected every minute. The perfusion pressure was 30-40 mm Hg, and the perfusion flow was 18-20 ml/min during the experiments. Substances to be investigated were added to the basic perfusion medium through side-arm syringes. Following are the substances that were used. Acetylcholine chloride (Sigma Chemical, St. Louis, MO.) at a submaximal, stimulatory concentration’6 of 10 -6 mol/liter. Acetylcholine was chosen as stimulus because it is a common stimulator of PP. glucagon, and insulin secretions.‘5 and also because it has only a slight effect on the release of endogenous somatostatin.“.‘* Synthetic cyclic somatostatin (a generous gift from Dr. Norman Grant, Wyeth Laboratories, Philadelphia, Pa.) was infused for 10
Metabolism, Vol. 28, No. 12 (December), 1979
and Thue
W. Schwartz
min with 15min
resting periods between infusions.
The final
concentrations of somatostatin were 31 (one perfusion), 122 (six), 610 (five), 6100 (five). 61,000 pmol/liter (five perfusions). In all but one experiment, the different doses were given in the order of increasing concentration because the somatostatin was slowly washed out of the system after the highest doses. In two perfusions the concentration of somatostatin in the influx was quantitatively checked by radioimmunoassay.” All experiments were performed with a glucose concentration of 100 mg/lOO ml. In three different perfusions, somatostatin, 6.1 x 10’ pmol/liter, was infused at low (25 mg/ 100 ml) and high (150 mg/lOO ml) glucose concentrations without other secretagogues added. Insulin,” glucagon,‘” PP.16 and somatostatin” were measured by specific radioimmunoassays as described in detail previously. The inhibition by somatostatin was calculated in two ways; either as the percent decrease in hormone concentration from pre-inhibitory levels to maximal inhibition, Fig. IA. or as percent decrease in hormone concentration from the previous increment caused by acetylcholine (Fig. I B). The calculations were based on the mean concentration of the last 7 min before inhibition and the last 7 min during inhibition. Student’s t test for paired comparisons was used for statistical analysis, with a 5% significance level. RESULTS
In five perfusion experiments, somatostatin in increasing concentrations caused a dose-related inhibition of secretion of PP, glucagon, and insulin stimulated by acetylcholine (1 pmol/liter). Figure 2 shows a representative experiment. Insulin and glucagon secretion were more readily suppressed than was PP secretion. The 50% inhibitory dose (ID,,) for insulin and glucagon was of the same order of magnitude, 100 and 430 pmol/liter of somatostatin, respectively, whereas the ID,, for PP was 3200 pmol/liter (Fig. 1). At From the Second University Clinic of Internal Medicine, Aarhus Kommunehospital. and Institute of Medical Biochemistry, University of Aarhus. Aarhus, Denmark. Receivedfor publication February 22, 1979. Supported in part by grants from the Danish Medical Researrh Council, the P. Carl Petersen Foundation, and the NOVO Foundation. Address reprint requests to Dr. T. W. Schwartz. Department of Biochemistry, University of Chicago, Chicago, Ill. 60637. 8 I979 by Grune & Stratton, Inc. 0026~495/79/28/220007$01.00/0
1229
HERMANSEN
1230
SOMATOSTATI
N
pmol
AND
SCHWARTZ
II
Fig. 1. Dose-response curves on somatostatin inhibition of the acetylcholine-induced secretion of insulin (U), glucagon @--O), and pancreatic polypeptide (A-A). (A) Inhibition calculated as the percent decrement in hormone concentration caused by the somatostatin from pre-inhibitory levels to the concentration during maximal inhibition. Mean + SE, n = 5. (6) Mean inhibition calculated as percent decrement caused by somatostatin from the previous increment caused by acetylcholine. The somatostatin concentrations indicated at the abscissa is shown in a logarithmic scale.
all doses of somatostatin the inhibition of insulin was slightly greater than the inhibition of glucagon; only reaching statistical significance (2~ < 0.05), however, at a somatostatin concentration of 122 pmol/liter. On the contrary, somatostatin concentrations higher than 122 pmol/liter were needed to cause statistically significant inhibition of PP secretion. The incremental insulin and glucagon release in response to acetylcholine was eliminated by 165 and 820 pmol/liter of somatostatin, whereas the incremental PP secretion was only inhibited by less than 25% (Fig. 1B) by 820 pmol/liter of somatostatin. In the absence of acetylcholine stimulation, somatostatin at the high dose of 6100 pmol/liter inhibited the secretion of all three hormones during perfusion with high and low glucose concentration. Insulin and glucagon secretion were inhibited by about 90% whereas PP secretion was only inhibited by about 35% (Table 1). There was no difference between the somatostatin-induced inhibition of glucagon at high and low glucose concentrations, or of PP secretion at high and low glucose concentration. At the low glucose concentration, insulin secretion was already maximally suppressed. DISCUSSION
In this study we have shown that acetylcholine-induced insulin and glucagon secretion from
the isolated canine pancreas can be suppressed by as little as 31-122 pmol/liter somatostatin added to the influx perfusion medium. Such concentrations are easily achieved in the efflux from this preparation in response to physiologic stimulir’ and must therefore be presumed to be well within the local somatostatin concentrations at the receptor sites. In contrast, the somatostatin concentration needed to inhibit the acetylcholine-stimulated PP secretion is much higher. PP cells are found inside and outside the islets,20~2’ but the majority of the canine PP cells are scattered in the exocrine tissue” and are, in contrast to the A and B cells, not exposed to the high somatostatin concentrations obtained in the islets. Thus, our results point to a physiologically important role for somatostatin in the secretion of insulin and glucagon, but probably not in the secretion of PP. Somatostatin’s almost equipotent inhibitory effect on insulin and glucagon secretion is in agreement with findings in both man and rat by EfendiC and co-workers4 Using a rat pancreas preparation, Gerich and co-workers,3 however, found a slight preferential inhibition of glucagon. The reason for the relative insensitivity of the secretory function of the PP cells to somatostatin is not known. An explanation could be that somatostatin’s inhibitory action on pancreatic
1231
SOMATOSTATIN EFFECT ON PANCREATIC HORMONES
pm4
500
SOMATOSTATIN
1
r500
I 3000
I
I flu/m
INSULIN
1
2000
1000 0
0 Fig. 2. Effect of different doses of somatostatin on the secretion of insulin. glucagon, and pancreatic-polypeptide (PP) from the isolated perfused canine pancreas induced by acetylcholine (1 pmollliter). Concentrations of somatostatin measured in the efflux are shown at the top. One out of five experiments.
w/m 1
GLUCAGON
500
r 100
0-I
I
LJJ _-
W
LO
w/ml
300
PP 1000
200
500
“’ 100
L 3
I1
10
20
II
30
LO
1
50
0
60
10-6
acetylcholine SOMATOSTATIN:
hormone release is at least partly exerted via interference with the calcium handling by the A, B, and PP cells. It has been demonstrated that high calcium concentrations attenuate or reverse the inhibitory effect of somatostatin on
11
70
0.2
1
122
610
1
80
90
”
lco
110
I 0
mol/l 10 6.1 xlo3
100
ng/ml
6.1~10~ pmol/l
insulin9-‘* and glucagon secretion,“.‘” and that somatostatin reduces the 45Ca uptake in pancreatic islets.“.‘3 Moreover, it is known that calcium ions are of principal importance for insulin?2,'3 and glucagon release.24-26 On the
1232
HERMANSEN
Table 1. Inhibitory Effect of Somatostatin pmol/liter)
on the Secretion
(6100
of insulin,
Glucagon. and PP From the Isolated Perfused Canine Pancreas
(Three individual Perfusions)
at Low and High Glucose Concentrations Percent Inhibition+ GlUCOSe
25 mg/lOO
Insulin
ml
(1.4 mmol/liter) Mean (k SE) 150 mg/lOO ml (8.3 mmol/liter) Mean (k SE)
Glucagon
PP
-
87.6
49.5
-
95.0
35.8
-
94.1
-
92.9
+ 2.0
34.7 40.0
f 4.8
94.3
79.8
41.4
97.5
94.4
30.9
87.8
81.5
93.2
? 2.9
85.2
k 4.6
26.9 33.1
* 4.3
results are not at variance with those of this study. Somatostatin is a poor inhibitor of the PP response to intra-arterially administered acetylcholine in vivo in the pig; however, the PP response to electrical stimulation of the vagus in the same animals is more readily inhibited by somatostatin (Schwartz, Fahrenkrug, Holst, and Schaffalitzky de Muckadell, unpublished observations). As suggested by Guillemin,29 somatostatin might act by inhibiting the release of acetylcholine rather than by blocking the effect of the transmitter; or somatostatin may interfere with the action of other transmitters.
*Percent decrease in hormone concentration from preinhibitory level.
contrary, PP secretion is relatively independent of extracellular calcium,‘4 and it is relatively insensitive to inhibition by somatostatin. In vivo, where the PP secretion is dependent on vagal, cholinergic mechanisms,‘6~27~28 somatostatin has been shown to inhibit PP secretion.5-7 Such
AND SCHWARTZ
ACKNOWLEDGMENT We are very grateful to Karen Just, Jette Bach Haulrik, and Evy Dgrge for most conscientious and skillful technical assistance and to Anette Larsen for her expert assistance in typing the manuscript. We are also grateful to R. E. Chance, Lilly Research Laboratory, Indianapolis, Ind., for donating highly purified pancreatic polypeptides and antisera, and to Lise Heding, NOVO Research Laboratory, Copenhagen, for donating highly specific glucagon antiserum. Cyclic somatostatin was generously provided by Norman Grant, Wyeth Laboratories, Philadelphia, Pa.
REFERENCES 1. Alberti KGMM, Christensen SE, lversen J, et al: Inhibition of insulin secretion by somatostatin. Lancet 2:1299-1301, 1973 2. Iversen J: Inhibition of pancreatic glucagon release by somatostatin: In vitro. Stand J Clin Lab Invest 33:125-129, 1974 3. Gerich JE, Lovinger R, Grodsky GM: Inhibition by somatostatin of glucagon and insulin release from the perfused rat pancreas in response to arginine, isoproterenol and theophylline: Evidence for a preferential effect on glucagon secretion. Endocrinology 96:749-754, 1975 4. Efendif S, Claro A, Luft R: Studies on the mechanism of somatostatin action on insulin release. III. Effect of somatostatin on arginine induced release of insulin and glucagon in man and perfused rat pancreas. Acta Endocrinol (Kbh) 81:753-761, 1976 5. Floyd JC, Fajans SS, Pek S, et al: A newly recognized pancreatic polypeptide: Plasma levels in health and disease. Recent Prog Horm Res 33519-570, 1977 6. Marco J, Hedo JA, Villanueva ML: Inhibitory effect of somatostatin on human pancreatic polypeptide secretion. Life Sci 21:789-792, 1977 7. Kayasseh L, Haecki WH, Gyr K, et al: The endogenous release of pancreatic polypeptide by acid and meal in dogs. Effect of somatostatin. Stand J Gastroenterol 13:385-391, 1978 8. Adrian TE, Bloom SR, Hermansen K, et al: Pancreatic polypeptide, glucagon and insulin secretion from the isolated perfused canine pancreas. Diabetologia 14:4 13-4 17, 1978 9. Curry DL, Bennett LL: Reversal of somatostatin inhibition of insulin secretion by calcium. Biochem Biophys Res Commun 60:1015-1019, 1974
10. Taminato T, Seino Y, Goto Y, et al: Interaction of somatostatin and calcium in regulating insulin release from isolated pancreatic islets of rats. Biochem Biophys Res Commun 66:928-934, 1975 11. Bhathena SJ, Perrino PV, Voyles NR, et al: Reversal of somatostatin inhibition of insulin and glucagon secretion. Diabetes 25:1031-1040, 1976 12. Hermansen K, Iversen J: Calcium, glucose and glucagon secretion. Diabetologia 12:398, 1976 13. Oliver JR: Inhibition of calcium uptake by somatostatin in isolated rat islets of Langerhans. Endocrinology 99:91&913, 1976 14. Hermansen K, Schwartz TW: The influence of calcium on the basal and acetylcholine stimulated secretion of pancreatic-polypeptide (PP) from the isolated perfused canine pancreas. Endocrinology (Dec., 1979 in press) 15. Iversen J, Miles DW: Evidence for a feed-back inhibition of insulin on insulin secretion in the isolated, perfused canine pancreas. Diabetes 10: l-9, 197 1 16. Schwartz TW, Holst JJ, Fahrenkrug J, et al: Vagal, cholinergic regulation of pancreatic polypeptide secretion. J Clin Invest 6 1:78 l-789, 1978 17. Hermansen K, Christensen SE, orskov H: Characterization of somatostatin release from the pancreas. The role of calcium and acetylcholine. Diabetologia 16:261-266, 1979 18. Samols EG, Weir GC, Ramseur R, et al: Modulation of pancreatic somatostatin by adrenergic and cholinergic agonism and by hyper- and hypoglycemic sulfonamides. Metabolism 27:1218-1221, 1978 19. @rskov H, Yde H, Thomsen HG: Wick-chromatography for rapid and reliable immunoassay of insulin, glucagon and growth hormone. Nature 219:193-195, 1968
SOMATOSTATIN
EFFECT ON PANCREATIC
HORMONES
1233
20. Larsson LI, Sundler F, Hakanson R: Pancreatic polypeptide-a postulated new hormone: Identification of its cellular storage site by light and electron microscopic immunocytochemistry. Diabetologia 12:21 l-226, 1976
21. Gersell DJ, Gingerich RL, Greider MH: Regional distribution and concentration of pancreatic polypeptide in the human and canine pancreas. Diabetes 28:l l-l 5, 1979 22. Mimer RDG, Hales CN: The role of calcium and magnesium in insulin secretion from rabbit pancreas studied in vitro. Diabetologia 3:47-49, 1967
23. Grodsky GM. Bennett LL: Cation requirements for insulin secretion in the isolated, perfused pancreas. Diabetes 15:910-913,
1966
24. Hermansen
K,
lversen
J: Effect
of verapamil
on
pancreatic glucagon release from the isolated, perfused canine pancreas. Stand J Clin Lab Invest 37: 139-l 42, 1977 25. Iversen J, Hermansen K: Calcium, glucose and glucagon release. Diabetologia 13:297-303. 1977 26. Hermansen K, Iversen J: Dual action of Mn” upon the secretion of insulin and glucagon from the isolated, perfused canine pancreas. Diabetologia 15:475479, 1978 27. Schwartz TW, Rehfeld JF, Stadil F, et al: Pancreaticpolypeptide response to food in duodenal-ulcer patients before and after vagotomy. Lancet I:1 102-l 105, 1976 28. Schwartz TW: Atropine suppression test for pancreatic-polypeptide. Lancet 2:4344, 1978 29. Guillemin R: Somatostatin inhibits the release of acetylcholine induced electrically in the myenteric plexus. Endocrinology 99:1953-1954, 1976
Hermansen
This dose-response study deals with the relative inhibitory effect of somatostatin on the acetylcholine-stimulated release of pancreatic polypeptide (PP), glucagon, and insulin from the isolated canine pancreas. Somatostatin in picomolar doses potently inhibited insulin and glucagon secretion, whereas PP secretion was relatively insensitive. Also. in the absence of acetylcholine, somatostatin exerted a preferential inhibition of the release of insulin and glucagon compared with PP. These findings point to a physiologically important role of somatostatin for the secretion of insulin and glucagon, but probably not for PP.
OMATOSTATIN inhibits pancreatic horsecretion.‘-* Somatostatin’s inhibitory effect on the secretory function of the endocrine cells is probably at least partly caused by an interference with the cellular calcium handling.‘-13 We have shown that the PP cell function, in contrast with the other endocrine cells in the pancreas, is relatively independent of extracellular calcium.‘4 In this investigation, a doseresponse study was performed in order to investigate somatostatin’s relative inhibitory effect on the release of pancreatic hormones from the isolated canine pancreas.
S mone
MATERIALS
AND
METHODS
Mongrel dogs, fasted overnight and weighing 17-28 kg, were used as pancreas donors. The technique for isolation of the canine pancreas and the perfusion system have previously been described in detaiLI In brief, the preparation consists of the pancreas and the proximal IO cm of the attached duodenum. A non-recirculating medium of Krebs-Ringer bicarbonate buffer pH 7.4 containing 40 g/liter dextran (mol wt 75,000), 2 g/liter bovine albumin, glutamate. fumarate, and pyruvate, each at a concentration of 5 mmol/liter. was pumped through the splenic and the coeliac arteries, and the total portal effluent was collected every minute. The perfusion pressure was 30-40 mm Hg, and the perfusion flow was 18-20 ml/min during the experiments. Substances to be investigated were added to the basic perfusion medium through side-arm syringes. Following are the substances that were used. Acetylcholine chloride (Sigma Chemical, St. Louis, MO.) at a submaximal, stimulatory concentration’6 of 10 -6 mol/liter. Acetylcholine was chosen as stimulus because it is a common stimulator of PP. glucagon, and insulin secretions.‘5 and also because it has only a slight effect on the release of endogenous somatostatin.“.‘* Synthetic cyclic somatostatin (a generous gift from Dr. Norman Grant, Wyeth Laboratories, Philadelphia, Pa.) was infused for 10
Metabolism, Vol. 28, No. 12 (December), 1979
and Thue
W. Schwartz
min with 15min
resting periods between infusions.
The final
concentrations of somatostatin were 31 (one perfusion), 122 (six), 610 (five), 6100 (five). 61,000 pmol/liter (five perfusions). In all but one experiment, the different doses were given in the order of increasing concentration because the somatostatin was slowly washed out of the system after the highest doses. In two perfusions the concentration of somatostatin in the influx was quantitatively checked by radioimmunoassay.” All experiments were performed with a glucose concentration of 100 mg/lOO ml. In three different perfusions, somatostatin, 6.1 x 10’ pmol/liter, was infused at low (25 mg/ 100 ml) and high (150 mg/lOO ml) glucose concentrations without other secretagogues added. Insulin,” glucagon,‘” PP.16 and somatostatin” were measured by specific radioimmunoassays as described in detail previously. The inhibition by somatostatin was calculated in two ways; either as the percent decrease in hormone concentration from pre-inhibitory levels to maximal inhibition, Fig. IA. or as percent decrease in hormone concentration from the previous increment caused by acetylcholine (Fig. I B). The calculations were based on the mean concentration of the last 7 min before inhibition and the last 7 min during inhibition. Student’s t test for paired comparisons was used for statistical analysis, with a 5% significance level. RESULTS
In five perfusion experiments, somatostatin in increasing concentrations caused a dose-related inhibition of secretion of PP, glucagon, and insulin stimulated by acetylcholine (1 pmol/liter). Figure 2 shows a representative experiment. Insulin and glucagon secretion were more readily suppressed than was PP secretion. The 50% inhibitory dose (ID,,) for insulin and glucagon was of the same order of magnitude, 100 and 430 pmol/liter of somatostatin, respectively, whereas the ID,, for PP was 3200 pmol/liter (Fig. 1). At From the Second University Clinic of Internal Medicine, Aarhus Kommunehospital. and Institute of Medical Biochemistry, University of Aarhus. Aarhus, Denmark. Receivedfor publication February 22, 1979. Supported in part by grants from the Danish Medical Researrh Council, the P. Carl Petersen Foundation, and the NOVO Foundation. Address reprint requests to Dr. T. W. Schwartz. Department of Biochemistry, University of Chicago, Chicago, Ill. 60637. 8 I979 by Grune & Stratton, Inc. 0026~495/79/28/220007$01.00/0
1229
HERMANSEN
1230
SOMATOSTATI
N
pmol
AND
SCHWARTZ
II
Fig. 1. Dose-response curves on somatostatin inhibition of the acetylcholine-induced secretion of insulin (U), glucagon @--O), and pancreatic polypeptide (A-A). (A) Inhibition calculated as the percent decrement in hormone concentration caused by the somatostatin from pre-inhibitory levels to the concentration during maximal inhibition. Mean + SE, n = 5. (6) Mean inhibition calculated as percent decrement caused by somatostatin from the previous increment caused by acetylcholine. The somatostatin concentrations indicated at the abscissa is shown in a logarithmic scale.
all doses of somatostatin the inhibition of insulin was slightly greater than the inhibition of glucagon; only reaching statistical significance (2~ < 0.05), however, at a somatostatin concentration of 122 pmol/liter. On the contrary, somatostatin concentrations higher than 122 pmol/liter were needed to cause statistically significant inhibition of PP secretion. The incremental insulin and glucagon release in response to acetylcholine was eliminated by 165 and 820 pmol/liter of somatostatin, whereas the incremental PP secretion was only inhibited by less than 25% (Fig. 1B) by 820 pmol/liter of somatostatin. In the absence of acetylcholine stimulation, somatostatin at the high dose of 6100 pmol/liter inhibited the secretion of all three hormones during perfusion with high and low glucose concentration. Insulin and glucagon secretion were inhibited by about 90% whereas PP secretion was only inhibited by about 35% (Table 1). There was no difference between the somatostatin-induced inhibition of glucagon at high and low glucose concentrations, or of PP secretion at high and low glucose concentration. At the low glucose concentration, insulin secretion was already maximally suppressed. DISCUSSION
In this study we have shown that acetylcholine-induced insulin and glucagon secretion from
the isolated canine pancreas can be suppressed by as little as 31-122 pmol/liter somatostatin added to the influx perfusion medium. Such concentrations are easily achieved in the efflux from this preparation in response to physiologic stimulir’ and must therefore be presumed to be well within the local somatostatin concentrations at the receptor sites. In contrast, the somatostatin concentration needed to inhibit the acetylcholine-stimulated PP secretion is much higher. PP cells are found inside and outside the islets,20~2’ but the majority of the canine PP cells are scattered in the exocrine tissue” and are, in contrast to the A and B cells, not exposed to the high somatostatin concentrations obtained in the islets. Thus, our results point to a physiologically important role for somatostatin in the secretion of insulin and glucagon, but probably not in the secretion of PP. Somatostatin’s almost equipotent inhibitory effect on insulin and glucagon secretion is in agreement with findings in both man and rat by EfendiC and co-workers4 Using a rat pancreas preparation, Gerich and co-workers,3 however, found a slight preferential inhibition of glucagon. The reason for the relative insensitivity of the secretory function of the PP cells to somatostatin is not known. An explanation could be that somatostatin’s inhibitory action on pancreatic
1231
SOMATOSTATIN EFFECT ON PANCREATIC HORMONES
pm4
500
SOMATOSTATIN
1
r500
I 3000
I
I flu/m
INSULIN
1
2000
1000 0
0 Fig. 2. Effect of different doses of somatostatin on the secretion of insulin. glucagon, and pancreatic-polypeptide (PP) from the isolated perfused canine pancreas induced by acetylcholine (1 pmollliter). Concentrations of somatostatin measured in the efflux are shown at the top. One out of five experiments.
w/m 1
GLUCAGON
500
r 100
0-I
I
LJJ _-
W
LO
w/ml
300
PP 1000
200
500
“’ 100
L 3
I1
10
20
II
30
LO
1
50
0
60
10-6
acetylcholine SOMATOSTATIN:
hormone release is at least partly exerted via interference with the calcium handling by the A, B, and PP cells. It has been demonstrated that high calcium concentrations attenuate or reverse the inhibitory effect of somatostatin on
11
70
0.2
1
122
610
1
80
90
”
lco
110
I 0
mol/l 10 6.1 xlo3
100
ng/ml
6.1~10~ pmol/l
insulin9-‘* and glucagon secretion,“.‘” and that somatostatin reduces the 45Ca uptake in pancreatic islets.“.‘3 Moreover, it is known that calcium ions are of principal importance for insulin?2,'3 and glucagon release.24-26 On the
1232
HERMANSEN
Table 1. Inhibitory Effect of Somatostatin pmol/liter)
on the Secretion
(6100
of insulin,
Glucagon. and PP From the Isolated Perfused Canine Pancreas
(Three individual Perfusions)
at Low and High Glucose Concentrations Percent Inhibition+ GlUCOSe
25 mg/lOO
Insulin
ml
(1.4 mmol/liter) Mean (k SE) 150 mg/lOO ml (8.3 mmol/liter) Mean (k SE)
Glucagon
PP
-
87.6
49.5
-
95.0
35.8
-
94.1
-
92.9
+ 2.0
34.7 40.0
f 4.8
94.3
79.8
41.4
97.5
94.4
30.9
87.8
81.5
93.2
? 2.9
85.2
k 4.6
26.9 33.1
* 4.3
results are not at variance with those of this study. Somatostatin is a poor inhibitor of the PP response to intra-arterially administered acetylcholine in vivo in the pig; however, the PP response to electrical stimulation of the vagus in the same animals is more readily inhibited by somatostatin (Schwartz, Fahrenkrug, Holst, and Schaffalitzky de Muckadell, unpublished observations). As suggested by Guillemin,29 somatostatin might act by inhibiting the release of acetylcholine rather than by blocking the effect of the transmitter; or somatostatin may interfere with the action of other transmitters.
*Percent decrease in hormone concentration from preinhibitory level.
contrary, PP secretion is relatively independent of extracellular calcium,‘4 and it is relatively insensitive to inhibition by somatostatin. In vivo, where the PP secretion is dependent on vagal, cholinergic mechanisms,‘6~27~28 somatostatin has been shown to inhibit PP secretion.5-7 Such
AND SCHWARTZ
ACKNOWLEDGMENT We are very grateful to Karen Just, Jette Bach Haulrik, and Evy Dgrge for most conscientious and skillful technical assistance and to Anette Larsen for her expert assistance in typing the manuscript. We are also grateful to R. E. Chance, Lilly Research Laboratory, Indianapolis, Ind., for donating highly purified pancreatic polypeptides and antisera, and to Lise Heding, NOVO Research Laboratory, Copenhagen, for donating highly specific glucagon antiserum. Cyclic somatostatin was generously provided by Norman Grant, Wyeth Laboratories, Philadelphia, Pa.
REFERENCES 1. Alberti KGMM, Christensen SE, lversen J, et al: Inhibition of insulin secretion by somatostatin. Lancet 2:1299-1301, 1973 2. Iversen J: Inhibition of pancreatic glucagon release by somatostatin: In vitro. Stand J Clin Lab Invest 33:125-129, 1974 3. Gerich JE, Lovinger R, Grodsky GM: Inhibition by somatostatin of glucagon and insulin release from the perfused rat pancreas in response to arginine, isoproterenol and theophylline: Evidence for a preferential effect on glucagon secretion. Endocrinology 96:749-754, 1975 4. Efendif S, Claro A, Luft R: Studies on the mechanism of somatostatin action on insulin release. III. Effect of somatostatin on arginine induced release of insulin and glucagon in man and perfused rat pancreas. Acta Endocrinol (Kbh) 81:753-761, 1976 5. Floyd JC, Fajans SS, Pek S, et al: A newly recognized pancreatic polypeptide: Plasma levels in health and disease. Recent Prog Horm Res 33519-570, 1977 6. Marco J, Hedo JA, Villanueva ML: Inhibitory effect of somatostatin on human pancreatic polypeptide secretion. Life Sci 21:789-792, 1977 7. Kayasseh L, Haecki WH, Gyr K, et al: The endogenous release of pancreatic polypeptide by acid and meal in dogs. Effect of somatostatin. Stand J Gastroenterol 13:385-391, 1978 8. Adrian TE, Bloom SR, Hermansen K, et al: Pancreatic polypeptide, glucagon and insulin secretion from the isolated perfused canine pancreas. Diabetologia 14:4 13-4 17, 1978 9. Curry DL, Bennett LL: Reversal of somatostatin inhibition of insulin secretion by calcium. Biochem Biophys Res Commun 60:1015-1019, 1974
10. Taminato T, Seino Y, Goto Y, et al: Interaction of somatostatin and calcium in regulating insulin release from isolated pancreatic islets of rats. Biochem Biophys Res Commun 66:928-934, 1975 11. Bhathena SJ, Perrino PV, Voyles NR, et al: Reversal of somatostatin inhibition of insulin and glucagon secretion. Diabetes 25:1031-1040, 1976 12. Hermansen K, Iversen J: Calcium, glucose and glucagon secretion. Diabetologia 12:398, 1976 13. Oliver JR: Inhibition of calcium uptake by somatostatin in isolated rat islets of Langerhans. Endocrinology 99:91&913, 1976 14. Hermansen K, Schwartz TW: The influence of calcium on the basal and acetylcholine stimulated secretion of pancreatic-polypeptide (PP) from the isolated perfused canine pancreas. Endocrinology (Dec., 1979 in press) 15. Iversen J, Miles DW: Evidence for a feed-back inhibition of insulin on insulin secretion in the isolated, perfused canine pancreas. Diabetes 10: l-9, 197 1 16. Schwartz TW, Holst JJ, Fahrenkrug J, et al: Vagal, cholinergic regulation of pancreatic polypeptide secretion. J Clin Invest 6 1:78 l-789, 1978 17. Hermansen K, Christensen SE, orskov H: Characterization of somatostatin release from the pancreas. The role of calcium and acetylcholine. Diabetologia 16:261-266, 1979 18. Samols EG, Weir GC, Ramseur R, et al: Modulation of pancreatic somatostatin by adrenergic and cholinergic agonism and by hyper- and hypoglycemic sulfonamides. Metabolism 27:1218-1221, 1978 19. @rskov H, Yde H, Thomsen HG: Wick-chromatography for rapid and reliable immunoassay of insulin, glucagon and growth hormone. Nature 219:193-195, 1968
SOMATOSTATIN
EFFECT ON PANCREATIC
HORMONES
1233
20. Larsson LI, Sundler F, Hakanson R: Pancreatic polypeptide-a postulated new hormone: Identification of its cellular storage site by light and electron microscopic immunocytochemistry. Diabetologia 12:21 l-226, 1976
21. Gersell DJ, Gingerich RL, Greider MH: Regional distribution and concentration of pancreatic polypeptide in the human and canine pancreas. Diabetes 28:l l-l 5, 1979 22. Mimer RDG, Hales CN: The role of calcium and magnesium in insulin secretion from rabbit pancreas studied in vitro. Diabetologia 3:47-49, 1967
23. Grodsky GM. Bennett LL: Cation requirements for insulin secretion in the isolated, perfused pancreas. Diabetes 15:910-913,
1966
24. Hermansen
K,
lversen
J: Effect
of verapamil
on
pancreatic glucagon release from the isolated, perfused canine pancreas. Stand J Clin Lab Invest 37: 139-l 42, 1977 25. Iversen J, Hermansen K: Calcium, glucose and glucagon release. Diabetologia 13:297-303. 1977 26. Hermansen K, Iversen J: Dual action of Mn” upon the secretion of insulin and glucagon from the isolated, perfused canine pancreas. Diabetologia 15:475479, 1978 27. Schwartz TW, Rehfeld JF, Stadil F, et al: Pancreaticpolypeptide response to food in duodenal-ulcer patients before and after vagotomy. Lancet I:1 102-l 105, 1976 28. Schwartz TW: Atropine suppression test for pancreatic-polypeptide. Lancet 2:4344, 1978 29. Guillemin R: Somatostatin inhibits the release of acetylcholine induced electrically in the myenteric plexus. Endocrinology 99:1953-1954, 1976
