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We examined the effect of L364718, a new cholecystokinin (CCK) receptor antagonist, on amylase release stimulated by CCK or different secretagogues in isolated rat pancreatic acini. L364718 caused a parallel rightward shift of the dose-response curve of CCK8. Schild plots showed a slope of 1.05 +/- 0.15 and a pA2 value of 10.01 +/- 0.31. L364718 inhibited maximally stimulated amylase release by CCK in a dose-dependent manner, with half maximal inhibition (ID50) at 1.7 nM and complete inhibition at 30 nM. Asperlicin, a prototype compound of L364718, also caused dose-dependent inhibition, but L364718 was approximately 400 times more potent than asperlicin (ID50 = 761 nM). L364718 significantly inhibited amylase release in response to CCK33 and CCK8 but had no effect on amylase release stimulated by other receptor secretagogues or agents by passing receptors. The results indicate that L364718 acts as an extremely potent, competitive, and specific antagonist of CCK's action on pancreatic acini.

The effects of L-364,718, a new CCK receptor antagonist, on food-stimulated exocrine pancreatic secretion and plasma levels of PP, insulin, CCK, and gastrin were examined in four conscious dogs with pancreatic fistulas. Intravenous injections of L-364,718 (20 nmol/kg) significantly inhibited pancreatic protein and enzyme responses by food (33% inhibition) but not juice volume output. Both rapid and secondary prolonged postprandial rises of plasma PP were also significantly suppressed by L-364,718 (50% inhibition); however, plasma levels of insulin were not altered. Postprandial levels of gastrin were not affected by L-364,718 administration, whereas 3-hr integrated CCK response was significantly enhanced by L-364,718. This study indicates that L-364,718 inhibits pancreatic protein and enzyme secretion and the release of pancreatic polypeptide stimulated by food in conscious dogs. This inhibition might be due to the selective blockage of receptor binding of circulating CCK molecules. The results suggest that L-364,718 may be useful for the physiological and pathophysiological studies associated with CCK.

This study was undertaken to investigate the mechanisms of action of nicotine on receptor mediated enzyme secretion in isolated rat pancreatic acini. Acinar cells were isolated from untreated and nicotine treated rats by collagenase digestion and differential centrifugation. Cells from the untreated animals were incubated with either varying concentrations of nicotine (range 10 microM to 30 mM) or with a fixed dose of 10 mM nicotine with varying concentrations of carbachol(10nM to 100 microM). Cells from the nicotine treated animals(16 weeks in drinking water) were incubated with either a fixed dose of CCK-8(10(-10) M) or carbachol(10(-5) M). All incubations were conducted at 37 C for 30 min. Amylase released in the media was measured by spectrophotometry. In pancreatic acinar cells isolated from control rats, amylase release stimulated by carbachol was inhibited by nicotine. Acinar cells isolated from rats treated with nicotine at nicotine concentrations of 1.23 mM also showed significant inhibition of amylase release in response to CCK-8 and carbachol compared to their identical controls. Nicotine induced inhibition curves of amylase release stimulated by carbachol were non-parallel suggesting that the effect of nicotine on acinar cells is regulated by mechanisms other than carbachol receptors. Nicotine may have a direct inhibitory effect on the intracellular mechanisms of pancreatic enzyme secretion. We conclude that the mechanism by which nicotine inhibits pancreatic enzyme secretion is complex.

Little is known regarding the mechanism by which peptide YY exerts an inhibitory effect on exocrine pancreatic secretion. The purpose of this study is to determine if peptide YY affects pancreatic blood flow with simultaneous measurement of exocrine pancreatic secretion in dogs. Pancreatic blood flow was measured by a laser Doppler flowmeter which allows continuous measurement of tissue blood flow. Natural peptide YY (0.1, 0.5, 1 microgram/kg) was infused intravenously as a bolus under background infusion of secretin (1 unit/kg/hr) in combination with cholecystokinin-octapeptide (0.1 microgram/kg/hr). Peptide YY caused a reduction of pancreatic blood flow in a dose-dependent manner as well as inhibition of pancreatic protein output, attaining the maximal reduction (28 +/- 4%) and inhibition (45 +/- 9%) at a dose of 1 microgram/kg, respectively. Simultaneous and continuous observation on tissue blood flow and exocrine secretion of the pancreas revealed that there was a highly significant correlation between the percent reduction of pancreatic blood flow and that of volume of pancreatic juice in response to peptide YY (r = 0.849, P less than 0.001). This study provides evidence that the mechanism of peptide YY-induced inhibition of exocrine pancreatic secretion is mediated, at least partly, through the decreased pancreatic blood flow.

We have examined the effect of neuromedin C on exocrine pancreatic secretion both in vivo and in vitro, and compared its bioactivity with those of related peptides. In anesthetized dogs, neuromedin C caused a dose-dependent initial reduction of pancreatic blood flow and an increase in secretin-stimulated exocrine pancreatic secretion, and had almost the same potency as gastrin-releasing peptide (GRP) in decreasing pancreatic blood flow. A potent stimulatory effect on exocrine pancreatic secretion was found in conscious dogs accompanied by a significant elevation in the circulating cholecystokinin (CCK) levels. In isolated rat pancreatic acini, amylase was released dose-dependently in response to neuromedin C. This study demonstrates that neuromedin C (a smaller molecular form of GRP) possesses potent bioactivity on exocrine pancreas and suggests that two factors may be involved in the mechanism by which this peptide effects exocrine secretion, namely; direct stimulation on acinar cells and stimulation of CCK release.

Neuromedin C, the smaller molecular form of gastrin releasing peptide (GRP [18–27]), has been recently identified from canine intestinal muscle and porcine spinal cord. This study was conducted to determine if this newly identified peptide retains biological activity on canine pancreas in vivo. Intravenous injection of graded doses of synthetic Neuromedin C caused a marked increase of systematic blood pressure and initial reduction of pancreatic blood flow in eleven anesthetized dogs, as measured by Laser Doppler Flowmetry. Flow volume and protein output of pancreatic juice were also increased by Neuromedin C in a dose-related manner in six dogs. These results suggest that this peptide is one of the biologically active forms of mammalian bombesin-like peptides and may possess physiological significance as a novel neuropeptide.

In anesthetized cats, immunoreactive cholecystokinin (CCK), pancreatic polypeptide (PP), and gastrin were released in response to bombesin both before and after small bowel resection. Total small bowel resection significantly decreased bombesin-stimulated release of cholecystokinin and pancreatic polypeptide without affecting the release of gastrin. Integrated analysis showed that CCK, pancreatic polypeptide, and gastrin were released in significant quantities after small bowel resection. The results show that total small bowel resection caused significant inhibition of bombesin-stimulated release of cholecystokinin and pancreatic polypeptide; in contrast, gastrin release remained unaffected. The data further indicate that extra bowel sources of cholecystokinin exist in cats and the release of CCK from those sources occurred following bombesin stimulation.

The physiology of pancreatic blood flow has been poorly understood because of the difficulty in measuring it since there is an abundance of anastomoses between the branches of the vessels supplying blood flow to the pancreas. Furthermore, very little information is available regarding the physiology of pancreatic blood flow in the conscious state.

Pancreatic secretion and plasma levels of cholecystokinin-33/39 (CCK) were measured for 5 h after a meal in dogs with and without exclusion of pancreatic juice. Significant and prolonged increases in pancreatic secretion and plasma CCK levels were observed irrespective of pancreatic juice exclusion. The integrated responses of pancreatic protein output (2.6 +/- 0.6 g/300 min), plasma CCK (1.3 +/- 0.5 nmol.l-1 .300 min) with exclusion of pancreatic juice showed no significant differences from those without exclusion (2.8 +/- 0.3 g/300 min and 1.3 +/- 0.3 nmol.l-1.300 min for protein output and CCK, respectively). These results suggest that the CCK-mediated feedback mechanism of pancreatic enzyme secretion does not work, at least not in the postprandial state in dogs.

A new porcine gastrointestinal 29-residue peptide, galanin, was synthesized in a satisfactory yield by assembling seven peptide fragments followed by deprotection with 1 M trifluoromethane-sulfonic acid-thioanisole in trifluoroacetic acid. Nin-Mesitylenesulfonyltryptophan was employed to suppress indole alkylation during Na-deprotection. β-Cycloheptylaspartate was employed to suppress base-catalyzed succinimide formation. The synthetic peptide exhibited a powerful contractile activity on rat ileum, but not on guinea pig ileum and caused sustained hyperglycemia in dogs.

L364,718, a potent and specific antagonist for peripheral cholecystokinin (CCK) receptors, was used to determine its effect on plasma levels of pancreatic polypeptide (PP) after administration of 2-deoxy-D-glucose (2-DG, a central vagal activator) and of bethanechol (a cholinergic receptor agonist). Six conscious dogs were used in this study. Intravenous injection of 2-DG (75 mg/kg) caused significant increases in plasma levels of PP and gastrin, but there was no significant rise in plasma levels of immunoreactive and bioactive CCK. Intravenous injection of L364,718 (20 nmol/kg) significantly inhibited the PP response stimulated by 2-DG injection by approximately 60% but did not affect gastrin. Plasma levels of PP were increased dose dependently by bethanechol infusion and were not altered significantly by injections of L364,718. The results indicate that L364,718 inhibits PP response stimulated by a central vagal activator (2-DG) but not by cholinergic receptor agonist (bethanechol). This study suggests that CCK might be involved in the neural control of PP release as a neurotransmitter but probably not as a final activator of PP cells in dogs.

A new gastrointestinal polypeptide, galanin, which consists of 29 amino acids, was synthesized using the trifluoromethanesulphonic acid deprotecting procedure: two new amino acid derivatives, Trp(Mts)[Mts =Ni mesitylene-2-sulphonyl] and Asp(OChp)[Chp =β-cycloheptyl], were employed for this synthesis to suppress possible side reactions, i.e., indole-alkylation and succinimide formation respectively; the synthetic peptide exhibited contractile activity in isolated rat ileum and hyperglycemic activity in dogs.

A new gastrointestinal polypeptide, galanin, which consists of 29 amino acids, was synthesized using the trifluoromethanesulphonic acid deprotecting procedure: two new amino acid derivatives, Trp(Mts)[Mts =Ni mesitylene-2-sulphonyl] and Asp(OChp)[Chp =β-cycloheptyl], were employed for this synthesis to suppress possible side reactions, i.e., indole-alkylation and succinimide formation respectively; the synthetic peptide exhibited contractile activity in isolated rat ileum and hyperglycemic activity in dogs.