Clinical and Experimental Pharmacology and Physiology (1976) 3, 59-55.
Effects of glucagon on pancreatic secretion in the dog K. Iwatsuki, H. On0 and K. Hashimoto Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan
(Received 27 June 1975)
SUMMARY
1. The effects of glucagon on the secretion of pancreatic juice were investigated using blood-perfused canine pancreas preparations. 2. Intravenous administration of glucagon (3-30 pg/kg) to the donor dog elicited a dose-dependent increase in pancreatic secretion. Intra-arterial administration of glucagon (10-100 pg) into the perfused pancreas also elicited increased secretion. 3. There were slight increases in amylase concentration of the pancreatic juice with the largest doses of glucagon given by either route. 4. Glucagon-induced secretion was not modified by treatment with phentolamine, propranolol, atropine, guanethidine, tetrodotoxin, haloperidol, prostaglandin F,, or calcitonin. 5. The results suggest that glucagon acts directly on the exocrine cells of the canine pancreas.
Key words :glucagon, pancreatic secretion, pancreozymin, secretin.
INTRODUCTION It is well known that pancreatic exocrine secretion is regulated by two hormones, secretin and pancreozymin. Secretin is a principal stimulant for electrolyte secretion and pancreozymin for enzyme secretion (Harper, 1967). Since glucagon has a similar structure to secretin (Jorpes, 1968), it is possible that these two substances act in a similar manner. In fact, glucagon and secretin have similar actions on the gastrointestinal tract; thus, both produce inhibition of gastric acid secretion (Lin & Spray, 1968; Dyck et al., 1969), inhibition of gastric movement (Stunkard, Van Itallie & Reiss, 1955) and stimulation of bile outflow (Fritz & Brooks, 1963). In a previous paper, we reported that glucagon caused an increase in the outflow of pancreatic juice (Takeuchi, Satoh & Hashimoto, 1974). In the present study, the effects of glucagon on pancreatic exocrine secretion have been compared with those of secretin and pancreozymin, using a blood-perfused canine pancreas preparation. Correspondence :Professor Koroku Hashimoto, Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan 980.
59
60
K . Iwatsuki, H . Ono and K . Hashimoto METHODS
Eighteen adult mongrel dogs of either sex weighing 12-16 kg were used. They were fasted for 24 h and anaesthetized with pentobarbitone sodium (30 mg/kg, i.v.). During the experimental procedures, anaesthesia was maintained by additional injections of pentobarbitone sodium (5 mg/kg, i.m.) at hourly intervals. The dogs were respired artificially with air with a Harvard respirator (Model 607). The supranavel abdomen was opened by a midline incision. A polyethylene tube was inserted into the main pancreatic duct for collection of the pancreatic juice. The accessory pancreatic duct was ligated. The cystic duct was ligated and bile was drained through a tube inserted into the bile duct in order to observe the bile production. Polyethylene cannulae were inserted into the gastroduodenal arteries through which the pancreas was perfused with the dog’s own blood, conducted from the left femoral artery and maintained at a constant pressure of 100 mmHg by means of a Harvard peristaltic pump (Model 1215). The splenic artery was also cannulated and perfused retrogradely with blood from the femoral artery. The experimental procedure has been previously described in detail (Hashimoto, Satoh & Takeuchi, 1971). A dose of 300 U/kg of sodium heparin was given at the beginning of perfusion and maintenance doses of 2,000 U were given hourly. The rate of secretion of pancreaticjuice was monitored by a drop counter and the volume was measured with a graduated cylinder. The amylase concentration in the juice was determined by the Caraway method (Caraway, 1959). Drugs used in this study were glucagon hydrochloride (Novo), secretin (Boots), pancreozymin (Boots), phentolamine mesylate (Ciba), (-)-adrenaline (Merck), (+)-isoprenaline hydrochloride (ICN), atropine sulphate (Torii), acetylcholine chloride (Daiichi), guanethidine sulphate (Ciba), tetrodotoxin (Sankyo), haloperidol (Searle), prostaglandin F,, (Nippon Upjon) and calcitonin (Teikoku Hormone). Drug solutions were injected into a rubber tube connected to the right femoral vein, in six experiments, or to the shank of the arterial cannula, in twelve experiments, over a period of 4 s using an injector (Terumo).
RESULTS
EfSect of intravenous administration of glucagon on pancreatic exocrine secretion A single injection of glucagon (3-30 pg/kg) caused a dose-dependent outflow of the pancreatic juice after a delay of 30 s as shown in Fig. 1. Secretin (0.03-0.3 U/kg) or pancreozymin (0.1-1.0 U/kg) also elicited a profuse outflow of the juice. The threshold dose of glucagon required to increase the secretion was approximately 3 pg/kg; threshold doses of secretin and pancreozymin were 0.01 U/kg and 0-03 U/kg, respectively. Table 1 shows the volume and the duration of the secretory responses to glucagon, secretin or pancreozymin obtained from six experiments. Although the duration of the secretory response to 10 pg/kg of i.v. glucagon was similar to that obtained with 0.1 U/kg of secretin or 0.3 U/kg of pancreozymin, the total volume in response to the dose of glucagon was significantly less than with secretin (0.1 U/kg) or pancreozymin (0.3 U/kg). With higher dose of glucagon (30 pg/kg), the systemic blood pressure decreased. None of these drugs affected bile production. Efects of glucagon (i.a.) on pancreatic exocrine secretion and vascular bed Glucagon (10-100 pg) given intra-arterially caused a dose-dependent outflow of the pan-
61
Glucagon and canine pancreatic secretion 5 rnin blood pressure 100
Drops of bile
Drops of pancreatic juice
4 3(pg/kg)
1
I IO(pg/kg
I
1
30(Pg/kg)
O.I(U/ kg 1
Glucagon
03(U/kg)
Secretin
Pancreazymin
FIG.1. Typical secretory responses of the canine pancreas to glucagon, secretin and pancreozymin, injected intravenously.
creatic juice after a delay of 10-20 s. The response to glucagon reached a maximum in 1-2 min and disappeared after 5-10 min (Fig. 2). Secretin (0.1 U) or pancreozymin (0.3 U) also increased the outflow of the pancreatic juice with a similar time course. Concerning the actions of these drugs on the vascular bed, glucagon caused a long-lasting increase in the blood flow rate similar to that of pancreozymin. On the other hand, secretin caused only a slight increase in the blood flow rate. Table 2 shows the secretory and vascular responses of the pancreas to glucagon, secretin and pancreozymin. Efects of blocking agents on the secretion induced by glucagon The blocking agents were given intra-arterially before testing the effects of glucagon. The doses administered were: phentolamine (100 pg), propranolol (300 pg), atropine (100 pg), TABLE 1. Effect of intravenous administration of glucagon, secretin or pancreozymin on the pancreatic secretion Secretory response* Pancreatic juice ( p l )
Duration (s)
Dose
Glucagon
Secretin
Pancreozymin
(pg/kg) 3 10
30 (U/W 0.03 0.1 0.3 (U/kg) 0.1 0.3 1 .o
mean
s.e.m.
mean
s.e.m.
34 132 340
8 28 90
127 483 683
24 46 90
158 456 1740
20 54 252
223 498 893
61 16 108
100 430 1100
41 104 200
234 454 776
58 71 158
* Results from six experiments.
K. Iwatsuki, H. Ono and K . Hashimoto
62
5 min
Drops juice of pancreatic
10
0 k I
I
30
0.1
100
0.3
Secretin (U)
Glucagon (pg)
Poncreozymin (U)
FIG.2. Typical secretory and vascular responses of the canine pancreas to glucagon, secretin and pancreozymin, injected intra-arteriaIly.
guanethidine (30 pg), tetrodotoxin (3 pg), haloperidol (1 mg), prostaglandin F,, (100 pg) and calcitonin (1 U/min). None of these agents appreciably altered the secretory or vascular responses to glucagon. Typical records of observations with phentolamine, propranolol and atropine are illustrated in Fig. 3. Efect of glucagon on the amylase concentration in pancreatic juice Glucagon (30-100 pg) produced a slight increase in the amylase concentration of pancreatic juice. Unlike glucagon, increasing doses of pancreozymin caused marked increases TABLE 2. Effects of intra-arterial administration of glucagon, secretin and pancreozymin on the pancreatic secretion and pancreatic blood flow
Secretory response* Pancreatic juice ( p l )
Vascular response*
Duration (S)
Blood flow (ml/min)
Duration (S)
Dose mean Glucagon
Secretin
Pancreozymin
(Pi) 3 10 30 (U) 0.03 0.1 0.3 (U) 0.1 0.3 1.0
s.e.m.
mean
s.e.m.
mean
s.e.m.
mean
112 254 340
22 46 40
194 258 383
47 34 41
1.9 3.7 4.6
0.3 0.2 0.2
113 164 206
166 366 1254
46 48 78
225 415 543
41 39 55
0.9 1.6 3.3
0.3 0.3 0.4
30 40 88
7.7 6.8 4.0
140 450 844
28 62 138
172 370 518
30 51 50
0.9 2.2 4.1
0.1 0.2 0.5
73 152 275
0.8 18 35
* Results from six experiments.
s.e.m. 71 57 128
63
Glucagon and canine pancreatic secretion Phentolomine IOO@g Drops of pancreatic juice
Drops of pancreatic juice
u s
5 min
t
t
J I I l l INlllllIllIl I I I I ~ I I I I I I I I I L OLlsoprenaiine I b9
Giucagon
Glucogon 3 0 ~ 9
30~9
tsoprenofine I @9
Atropine IOOug Drops of pancreatic juice
-
t
IIIlllllllIImlIllI1III I IIImlllllIIi IIllI1 Acetylcholine 1019
Glucopn 30 w g
Glucogon
30~9
Acetylcholine lOP9
FIG.3. Records illustrating the absence of effects of phentolamine, propranolol and atropine on glucagon-induced pancreatic secretion. Drugs are injected intra-arterially. TABLE 3. Effect of glucagon, secretin and pancreozymin on the amyIase activity of pancreatic juice. When glucagon, secretin or pancreozymin was injected, the pancreatic juice was collected from the beginning until the end of the secretory response Amylase activity* ( x lo00 units/ml) Dose
Glucagon
(Pd 30 100
__
mean
s.e.m.
817 964
50 42
536 513
22 60
1447 2223
89 120
(U)
Secretin
0.03 0.1
Pancreozymin
(U) 0.1 0 3
* Results from six experiments.
K. Iwatsuki, H. Ono and K . Hashimoto in amylase concentration. On the other hand, secretin scarcely changed the amylase concentration of the pancreatic juice. The results obtained are shown in Table 3. DISCUSSION In this study, a single injection of glucagon immediately elicited an increase in the pancreatic exocrine secretion; dose-dependent responses were obtained with increasing doses of glucagon. These actions of glucagon did not resemble those of either secretin or pancreozymin, since the slope of the dose-response curve with glucagon rose more smoothly than those with secretin or pancreozymin. Furthermore, glucagon caused a slight increase in the amylase concentration compared with pancreozymin. On the other hand, secretin had little effect on the amylase concentration, even when the dose of secretin was increased. Necheles (1957) observed that glucagon caused an increase in pancreatic secretion followed by a prolonged inhibition of secretion in dogs. Previously we also reported that glucagon caused an increase in the pancreatic secretion in dogs (Takeuchi et al., 1974). On the other hand it has been reported that glucagon markedly depressed the secretion of pancreatic juice from the secretin/pancreozymin-stimulated gland in dogs with a pancreatic fistula (Dyck et al., 1969). These observations were confirmed in dogs by Nakajima & Magee (1970) and in man by Dyck et al. (1970). Therefore it is suggested that glucagon acts as a partial agonist on the exocrine pancreas. Intravenous injections of parasympathomimetic agents and vagal stimulation caused an increase in pancreatic secretion (Lenninger, 1971). But the possibility that glucagon might act through cholinergic transmitter released from the vagal nerve terminal can be ruled out since the secretion and its vascular response to glucagon were not modified by atropine. Glucagon-induced secretion was not modified appreciably by phentolamine or propranolol, which suggests that the mechanism does not involve adrenergic mechanisms. Tetrodotoxin and guanethidine abolish the adrenergic component of responses to drugs or electrical stimulation (Brodie, Chang & Costa, 1965; Kao, 1966), but neither the secretory nor the vascular responses to glucagon were affected by tetrodotoxin or guanethidine. Thus, it is reasonable to conclude that neural excitation was not involved in the responses. Furthermore, responses to glucagon were not antagonized by haloperidol, a dopamine-receptor blocking agent (McNay & Goldberg, 1966), by prostaglandin F2=,which blocks the action of secretin (Iwatsuki, Furuta & Hashimoto, 1973), or by calcitonin, which regulates the calcium metabolism (Talmage, Neuenschwander & Kraintz, 1965). Furthermore, it has been recognized that glucagon induces a rise in blood sugar. But Crider et al. (1956) demonstrated that the elevation of blood sugar had no effect on the volume of secretion of pancreatic juice. Therefore, it is highly probable that glucagon elicits the pancreatic exocrine secretion and vasodilatation by direct actions on the secretory cells and vasculature. It has been proposed that a number of hormones, including glucagon, exert their effects by an intracellular mediator, adenosine-3’,5’-monophosphate(cyclic AMP) (Sutherland, 1960). Glucagon accelerates the conversion of adenosine triphosphate to cyclic AMP by increasing the activity of the enzyme adenylate cyclase. Cyclic AMP and dibutyryl cyclic AMP have been shown to stimulate pancreatic secretion (Takeuchi et al., 1974). Furthermore, secretin, pancreozymin and acetylcholine cause the concentration of cyclic AMP in pancreatic tissue to rise (Case et al., 1972). Thus, it is proposed that cyclic AMP is a possible intracellular mediator for the stimulant effect of glucagon on pancreatic exocrine secretion.
Glucagon and canine pancreatic secretion
65
ACKNOWLEDGMENTS
The authors wish to thank Kodama Co. Ltd for supplying glucagon and Teikoku Hormone Co. Ltd for calcitonin. REFERENCES
Brodie, B.B., Chang, C.C. & Costa, E. (1965) On the mechanism of action of guanethidine and bretylium. British Journal of Pharmacology, 25, 171-178. Case, R.M., Johnson, M., Scratcherd, T. & Sherratt, H.S.A. (1972) Cyclic adenosine 3’,5’-monophosphate concentration in the pancreas following stimulation by secretin, cholecystokinin-pancreozyminand acetylcholine. Journal of Physiology, 223,669-684. Caraway, W.T. (1959) A stable starch substrate for the determination of amylase in serum and other body fluids. American Journal of Clinical Pathology, 32,97-99. Crider, J.O., Conly, S.S., Dorchester, J.E.C. & Thomas, J.E. (1956) Effect of intravenous injection of hypertonic glucose solution on external secretion of the pancreas. American Journal of Physiology, 186, 187189. Dyck, W.P., Rudick, J., Hoexter, B. & Janowitz, H.D. (1969) Influence of glucagon on pancreatic exocrine secretion. Gastroenterology, 56,531-537. Dyck, W.P., Texter, E.C., Lasater, J.M. & Hightower, N.C. (1970) Influence of glucagon on pancreatic exocrine secretion in man. Gastroenterology, 58, 532-539. Fritz, M.E. & Brooks, F.P. (1963) Control of bile flow in the cholecystectomized dog. American Journal of Physiology, 204,825-828. Harper, A.A. (1967) Hormonal control of pancreatic secretion. Handbook of Physiology, Section 6, Alimentary Canal, volume 11. pp. 969-995, American Physiological Society, Washington, D.C. Hashimoto, K., Satoh, S. & Takeuchi, 0. (1971) Effect of dopamine on pancreatic secretion of the dog. British Journal of Pharmacology, 43,739-746, Iwatsuki, K., Furuta, Y. & Hashimoto, K. (1973) Effects of prostaglandin FZCZ (PCFZa)on the secretion of pancreatic juice induced by secretin and by doparnine. Experientia, 29, 319. Jorpes, J.E. (1968) The isolation and chemistry of secretin and cholecystokinin. Gastroenterology, 55, 157164. Kao, C.Y. (1966) Tetrodotoxin, saxitoxin and their significance in the study of excitation phenomena. Pharmacological Reviews, 18,997-1049. Lenninger, S . (1971) Effects of parasympathomimetic agents and vagal stimulation on the flow in the pancreatic duct of the cat. Acta physiologica scandinavica, 82, 345-353. Lin, T.M. & Spray, G.F. (1968) Effect of glucagon on gastric HCl secretion. Gastroenterology, 54, 1254. McNay, J.L. & Goldberg, L.I. (1966) Comparison of the effects of dopamine, isoproterenol, norepinephrine and bradykinin on canine renal and femoral blood flow. Journal of Pharmacology and Experimental Therapeutics, 151,23-31. Nakajirna, S . & Magee, D.F. (1970) Inhibition of exocrine pancreatic secretion by glucagon and D-glucose given intravenously. Canadian Journal of Physiology and Pharmacology, 48,299-305. Necheles, H. (1957) Effects of glucagon on external secretion of the pancreas. American Journal ofPhysiology, 191, 595-597. Stunkard, A.J., Van Itallie, T.B. & Reiss, B.B. (1955) Mechanism of satiety: effect of glucagon on gastric hunger contractions in man. Proceedings of the Society for Experimental Biology and Medicine, 89, 258-261. Sutherland, E.W. (1960) The relation of adenosine 3’5’-phosphate and phosphorylase to the actions of catecholamines and other hormones. Pharmacological Reviews, 12,265-299. Takeuchi, O., Satoh, S. 81Hashimoto, K. (1974) Secretory and vascular response to various biogenic and foreign substances of the perfused canine pancreas. Japanese Journal of Pharmacology, 24,57-73. Talmage, R.V., Neuenschwander, J. & Kraintz, L. (1965) Evidence for the existence of thyrocalcitonin in the rat. Endocrinology, 76, 103-107.
E
Effects of glucagon on pancreatic secretion in the dog K. Iwatsuki, H. On0 and K. Hashimoto Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan
(Received 27 June 1975)
SUMMARY
1. The effects of glucagon on the secretion of pancreatic juice were investigated using blood-perfused canine pancreas preparations. 2. Intravenous administration of glucagon (3-30 pg/kg) to the donor dog elicited a dose-dependent increase in pancreatic secretion. Intra-arterial administration of glucagon (10-100 pg) into the perfused pancreas also elicited increased secretion. 3. There were slight increases in amylase concentration of the pancreatic juice with the largest doses of glucagon given by either route. 4. Glucagon-induced secretion was not modified by treatment with phentolamine, propranolol, atropine, guanethidine, tetrodotoxin, haloperidol, prostaglandin F,, or calcitonin. 5. The results suggest that glucagon acts directly on the exocrine cells of the canine pancreas.
Key words :glucagon, pancreatic secretion, pancreozymin, secretin.
INTRODUCTION It is well known that pancreatic exocrine secretion is regulated by two hormones, secretin and pancreozymin. Secretin is a principal stimulant for electrolyte secretion and pancreozymin for enzyme secretion (Harper, 1967). Since glucagon has a similar structure to secretin (Jorpes, 1968), it is possible that these two substances act in a similar manner. In fact, glucagon and secretin have similar actions on the gastrointestinal tract; thus, both produce inhibition of gastric acid secretion (Lin & Spray, 1968; Dyck et al., 1969), inhibition of gastric movement (Stunkard, Van Itallie & Reiss, 1955) and stimulation of bile outflow (Fritz & Brooks, 1963). In a previous paper, we reported that glucagon caused an increase in the outflow of pancreatic juice (Takeuchi, Satoh & Hashimoto, 1974). In the present study, the effects of glucagon on pancreatic exocrine secretion have been compared with those of secretin and pancreozymin, using a blood-perfused canine pancreas preparation. Correspondence :Professor Koroku Hashimoto, Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan 980.
59
60
K . Iwatsuki, H . Ono and K . Hashimoto METHODS
Eighteen adult mongrel dogs of either sex weighing 12-16 kg were used. They were fasted for 24 h and anaesthetized with pentobarbitone sodium (30 mg/kg, i.v.). During the experimental procedures, anaesthesia was maintained by additional injections of pentobarbitone sodium (5 mg/kg, i.m.) at hourly intervals. The dogs were respired artificially with air with a Harvard respirator (Model 607). The supranavel abdomen was opened by a midline incision. A polyethylene tube was inserted into the main pancreatic duct for collection of the pancreatic juice. The accessory pancreatic duct was ligated. The cystic duct was ligated and bile was drained through a tube inserted into the bile duct in order to observe the bile production. Polyethylene cannulae were inserted into the gastroduodenal arteries through which the pancreas was perfused with the dog’s own blood, conducted from the left femoral artery and maintained at a constant pressure of 100 mmHg by means of a Harvard peristaltic pump (Model 1215). The splenic artery was also cannulated and perfused retrogradely with blood from the femoral artery. The experimental procedure has been previously described in detail (Hashimoto, Satoh & Takeuchi, 1971). A dose of 300 U/kg of sodium heparin was given at the beginning of perfusion and maintenance doses of 2,000 U were given hourly. The rate of secretion of pancreaticjuice was monitored by a drop counter and the volume was measured with a graduated cylinder. The amylase concentration in the juice was determined by the Caraway method (Caraway, 1959). Drugs used in this study were glucagon hydrochloride (Novo), secretin (Boots), pancreozymin (Boots), phentolamine mesylate (Ciba), (-)-adrenaline (Merck), (+)-isoprenaline hydrochloride (ICN), atropine sulphate (Torii), acetylcholine chloride (Daiichi), guanethidine sulphate (Ciba), tetrodotoxin (Sankyo), haloperidol (Searle), prostaglandin F,, (Nippon Upjon) and calcitonin (Teikoku Hormone). Drug solutions were injected into a rubber tube connected to the right femoral vein, in six experiments, or to the shank of the arterial cannula, in twelve experiments, over a period of 4 s using an injector (Terumo).
RESULTS
EfSect of intravenous administration of glucagon on pancreatic exocrine secretion A single injection of glucagon (3-30 pg/kg) caused a dose-dependent outflow of the pancreatic juice after a delay of 30 s as shown in Fig. 1. Secretin (0.03-0.3 U/kg) or pancreozymin (0.1-1.0 U/kg) also elicited a profuse outflow of the juice. The threshold dose of glucagon required to increase the secretion was approximately 3 pg/kg; threshold doses of secretin and pancreozymin were 0.01 U/kg and 0-03 U/kg, respectively. Table 1 shows the volume and the duration of the secretory responses to glucagon, secretin or pancreozymin obtained from six experiments. Although the duration of the secretory response to 10 pg/kg of i.v. glucagon was similar to that obtained with 0.1 U/kg of secretin or 0.3 U/kg of pancreozymin, the total volume in response to the dose of glucagon was significantly less than with secretin (0.1 U/kg) or pancreozymin (0.3 U/kg). With higher dose of glucagon (30 pg/kg), the systemic blood pressure decreased. None of these drugs affected bile production. Efects of glucagon (i.a.) on pancreatic exocrine secretion and vascular bed Glucagon (10-100 pg) given intra-arterially caused a dose-dependent outflow of the pan-
61
Glucagon and canine pancreatic secretion 5 rnin blood pressure 100
Drops of bile
Drops of pancreatic juice
4 3(pg/kg)
1
I IO(pg/kg
I
1
30(Pg/kg)
O.I(U/ kg 1
Glucagon
03(U/kg)
Secretin
Pancreazymin
FIG.1. Typical secretory responses of the canine pancreas to glucagon, secretin and pancreozymin, injected intravenously.
creatic juice after a delay of 10-20 s. The response to glucagon reached a maximum in 1-2 min and disappeared after 5-10 min (Fig. 2). Secretin (0.1 U) or pancreozymin (0.3 U) also increased the outflow of the pancreatic juice with a similar time course. Concerning the actions of these drugs on the vascular bed, glucagon caused a long-lasting increase in the blood flow rate similar to that of pancreozymin. On the other hand, secretin caused only a slight increase in the blood flow rate. Table 2 shows the secretory and vascular responses of the pancreas to glucagon, secretin and pancreozymin. Efects of blocking agents on the secretion induced by glucagon The blocking agents were given intra-arterially before testing the effects of glucagon. The doses administered were: phentolamine (100 pg), propranolol (300 pg), atropine (100 pg), TABLE 1. Effect of intravenous administration of glucagon, secretin or pancreozymin on the pancreatic secretion Secretory response* Pancreatic juice ( p l )
Duration (s)
Dose
Glucagon
Secretin
Pancreozymin
(pg/kg) 3 10
30 (U/W 0.03 0.1 0.3 (U/kg) 0.1 0.3 1 .o
mean
s.e.m.
mean
s.e.m.
34 132 340
8 28 90
127 483 683
24 46 90
158 456 1740
20 54 252
223 498 893
61 16 108
100 430 1100
41 104 200
234 454 776
58 71 158
* Results from six experiments.
K. Iwatsuki, H. Ono and K . Hashimoto
62
5 min
Drops juice of pancreatic
10
0 k I
I
30
0.1
100
0.3
Secretin (U)
Glucagon (pg)
Poncreozymin (U)
FIG.2. Typical secretory and vascular responses of the canine pancreas to glucagon, secretin and pancreozymin, injected intra-arteriaIly.
guanethidine (30 pg), tetrodotoxin (3 pg), haloperidol (1 mg), prostaglandin F,, (100 pg) and calcitonin (1 U/min). None of these agents appreciably altered the secretory or vascular responses to glucagon. Typical records of observations with phentolamine, propranolol and atropine are illustrated in Fig. 3. Efect of glucagon on the amylase concentration in pancreatic juice Glucagon (30-100 pg) produced a slight increase in the amylase concentration of pancreatic juice. Unlike glucagon, increasing doses of pancreozymin caused marked increases TABLE 2. Effects of intra-arterial administration of glucagon, secretin and pancreozymin on the pancreatic secretion and pancreatic blood flow
Secretory response* Pancreatic juice ( p l )
Vascular response*
Duration (S)
Blood flow (ml/min)
Duration (S)
Dose mean Glucagon
Secretin
Pancreozymin
(Pi) 3 10 30 (U) 0.03 0.1 0.3 (U) 0.1 0.3 1.0
s.e.m.
mean
s.e.m.
mean
s.e.m.
mean
112 254 340
22 46 40
194 258 383
47 34 41
1.9 3.7 4.6
0.3 0.2 0.2
113 164 206
166 366 1254
46 48 78
225 415 543
41 39 55
0.9 1.6 3.3
0.3 0.3 0.4
30 40 88
7.7 6.8 4.0
140 450 844
28 62 138
172 370 518
30 51 50
0.9 2.2 4.1
0.1 0.2 0.5
73 152 275
0.8 18 35
* Results from six experiments.
s.e.m. 71 57 128
63
Glucagon and canine pancreatic secretion Phentolomine IOO@g Drops of pancreatic juice
Drops of pancreatic juice
u s
5 min
t
t
J I I l l INlllllIllIl I I I I ~ I I I I I I I I I L OLlsoprenaiine I b9
Giucagon
Glucogon 3 0 ~ 9
30~9
tsoprenofine I @9
Atropine IOOug Drops of pancreatic juice
-
t
IIIlllllllIImlIllI1III I IIImlllllIIi IIllI1 Acetylcholine 1019
Glucopn 30 w g
Glucogon
30~9
Acetylcholine lOP9
FIG.3. Records illustrating the absence of effects of phentolamine, propranolol and atropine on glucagon-induced pancreatic secretion. Drugs are injected intra-arterially. TABLE 3. Effect of glucagon, secretin and pancreozymin on the amyIase activity of pancreatic juice. When glucagon, secretin or pancreozymin was injected, the pancreatic juice was collected from the beginning until the end of the secretory response Amylase activity* ( x lo00 units/ml) Dose
Glucagon
(Pd 30 100
__
mean
s.e.m.
817 964
50 42
536 513
22 60
1447 2223
89 120
(U)
Secretin
0.03 0.1
Pancreozymin
(U) 0.1 0 3
* Results from six experiments.
K. Iwatsuki, H. Ono and K . Hashimoto in amylase concentration. On the other hand, secretin scarcely changed the amylase concentration of the pancreatic juice. The results obtained are shown in Table 3. DISCUSSION In this study, a single injection of glucagon immediately elicited an increase in the pancreatic exocrine secretion; dose-dependent responses were obtained with increasing doses of glucagon. These actions of glucagon did not resemble those of either secretin or pancreozymin, since the slope of the dose-response curve with glucagon rose more smoothly than those with secretin or pancreozymin. Furthermore, glucagon caused a slight increase in the amylase concentration compared with pancreozymin. On the other hand, secretin had little effect on the amylase concentration, even when the dose of secretin was increased. Necheles (1957) observed that glucagon caused an increase in pancreatic secretion followed by a prolonged inhibition of secretion in dogs. Previously we also reported that glucagon caused an increase in the pancreatic secretion in dogs (Takeuchi et al., 1974). On the other hand it has been reported that glucagon markedly depressed the secretion of pancreatic juice from the secretin/pancreozymin-stimulated gland in dogs with a pancreatic fistula (Dyck et al., 1969). These observations were confirmed in dogs by Nakajima & Magee (1970) and in man by Dyck et al. (1970). Therefore it is suggested that glucagon acts as a partial agonist on the exocrine pancreas. Intravenous injections of parasympathomimetic agents and vagal stimulation caused an increase in pancreatic secretion (Lenninger, 1971). But the possibility that glucagon might act through cholinergic transmitter released from the vagal nerve terminal can be ruled out since the secretion and its vascular response to glucagon were not modified by atropine. Glucagon-induced secretion was not modified appreciably by phentolamine or propranolol, which suggests that the mechanism does not involve adrenergic mechanisms. Tetrodotoxin and guanethidine abolish the adrenergic component of responses to drugs or electrical stimulation (Brodie, Chang & Costa, 1965; Kao, 1966), but neither the secretory nor the vascular responses to glucagon were affected by tetrodotoxin or guanethidine. Thus, it is reasonable to conclude that neural excitation was not involved in the responses. Furthermore, responses to glucagon were not antagonized by haloperidol, a dopamine-receptor blocking agent (McNay & Goldberg, 1966), by prostaglandin F2=,which blocks the action of secretin (Iwatsuki, Furuta & Hashimoto, 1973), or by calcitonin, which regulates the calcium metabolism (Talmage, Neuenschwander & Kraintz, 1965). Furthermore, it has been recognized that glucagon induces a rise in blood sugar. But Crider et al. (1956) demonstrated that the elevation of blood sugar had no effect on the volume of secretion of pancreatic juice. Therefore, it is highly probable that glucagon elicits the pancreatic exocrine secretion and vasodilatation by direct actions on the secretory cells and vasculature. It has been proposed that a number of hormones, including glucagon, exert their effects by an intracellular mediator, adenosine-3’,5’-monophosphate(cyclic AMP) (Sutherland, 1960). Glucagon accelerates the conversion of adenosine triphosphate to cyclic AMP by increasing the activity of the enzyme adenylate cyclase. Cyclic AMP and dibutyryl cyclic AMP have been shown to stimulate pancreatic secretion (Takeuchi et al., 1974). Furthermore, secretin, pancreozymin and acetylcholine cause the concentration of cyclic AMP in pancreatic tissue to rise (Case et al., 1972). Thus, it is proposed that cyclic AMP is a possible intracellular mediator for the stimulant effect of glucagon on pancreatic exocrine secretion.
Glucagon and canine pancreatic secretion
65
ACKNOWLEDGMENTS
The authors wish to thank Kodama Co. Ltd for supplying glucagon and Teikoku Hormone Co. Ltd for calcitonin. REFERENCES
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