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We investigated the effects of the sensory neuropeptide substance P (SP) on amylase and fluid secretion in the isolated vascularly perfused rat pancreas. SP inhibited CCK-induced amylase release and secretin-induced juice flow via the pancreatic duct in a dose-related fashion. Threshold inhibition occurred following addition of 10(-10) M SP to the perfusate, and maximal inhibition was seen with 10(-8) M SP. The effects of SP were partially blocked by both the neurokinin-1 (NK1) and neurokinin-2 (NK2) receptor antagonists. Atropine and TTX blocked SP-induced effects on both amylase secretion (26 and 63% blockade, respectively) and pancreatic juice flow (21 and 79% blockade, respectively). Excitation of pancreatic sensory nerves using capsaicin (in the absence of SP) inhibited both amylase and pancreatic juice flow via activation of the NK1 receptor. We conclude that SP inhibits exocrine secretion via an indirect neural mechanism.

There is general agreement that the exocrine pancreas derives from the endoderm of the embryonic foregut. The cellular origin of the endocrine pancreas has been debated for a long time. A hypothesis existed that the endocrine cells of the pancreas originated from the neural crest of the embryo. The recent application of microdissection of the mouse embryo and an exquisitely sensitive polymerase chain reaction assay (PCR) indicates that both the exocrine and endocrine cells of the pancreas develop from the endoderm of the foregut as evidenced by the expression of genes responsible for acinar enzymes and islet hormones in the foregut at the site where the future pancreatic diverticulum would form. Furthermore, the mesenchyme surrounding the primitive endoderm cells from which the pancreas would form exerts significant regulation of differentiation of the pancreas. In culture or in vivo explants, these endoderm cells differentiate only into islet cells in the absence of mesenchyme. On the other hand, when these cells are cultured in vitro with mesenchyme, they differentiate to form not only islets but also ducts and acini.

The vagus is a mixed nerve containing cholinerrgic and non-cholinergic neurons. Vagal fibers interact with peptidergic neurons of the enteric nervous system which stain immunohistochemically for cholecystokinin, vasoactive intestinal polypeptide, and gastrin releasing peptide. The contribution of these peptidergic neurons in the pancreatic response to vagal stimulation is unknown. We tested the effect of specific inhibitor of these stimulants against vagally mediated exocrine secretion in rats. The response to vagal stimulation was blocked significantly by each of the following: the ganglionic blocker hexamethonium (100% inhibition); the muscarinic, cholinergic blocker atropine (85% inhibition); the specific cholecystokinin-A receptor blocker (91% inhibition); and a vasoactive intestinal polypeptide polyclonal antibody (89% inhibition). This observation is consistent with the hypothesis that potentiating interactions among several agonists mediate the vagal response. Our study, however, dose not exclude acetylcholine as the final common mediator.

Although cholecystokinin is localized within neuronal fibres of the pancreas, a physiological role for intrapancreatic cholecystokinin has not been identified. The strategy of this study was to elicit pure vagal stimulation electrically, and to use specific receptor antagonists to identify the mediators of exocrine pancreatic secretion. We conclude that vagal stimulation of the rat pancreas involves ganglionic neurotransmission and release of acetylcholine and cholecystokinin from intrapancreatic, postganglionic fibres. To our knowledge, this is the first study to demonstrate a physiological role for intrapancreatic cholecystokinin.

Background: The vagus nerve contains cholinergic and noncholinergic neurons that interact with peptidergic neurons of the enteric nervous system, which stain immunohistochemically for cholecystokinin, vasoactive intestinal polypeptide, and gastrin-releasing peptide., Methods: The role of these pancreatic exocrine secretagogues during electrical vagal stimulation was studied using specific inhibitors in urethane-anesthetized rats., Results: The pancreatic secretory response to vagal stimulation was blocked significantly by each of the following: the ganglionic blocker hexamethonium (100% inhibition); the muscarinic, cholinergic blocker atropine (85% inhibition); the specific cholecystokinin A-receptor antagonist L-364,718 (84% inhibition); a gastrin-releasing peptide-receptor blocker (91% inhibition); and a vasoactive intestinal polypeptide polyclonal antibody (89% inhibition). The response was not altered by a monoclonal antibody to somatostatin. A subthreshold dose of cholecystokinin octapeptide augmented the response to electrical vagal stimulation., Conclusions: Suppression of tonic somatostatin release is not the final common event. The findings that subthreshold cholecystokinin augments vagal stimulation, together with marked inhibition by each antagonist used, are consistent with the hypothesis that potentiating interactions among several agonists mediate the vagal response in anesthetized rats. However, this study does not exclude acetylcholine as the final common mediator. Studies in conscious animals are needed to determine the physiological significance of these observations.

Gastrin expression occurs in the pancreas in only two situations: (1) in cases of gastrinoma and (2) in the embryonic/fetal pancreas. The initiation of gastrin expression in the embryonic pancreas may be recapitulated during gastrinoma tumorigenesis. For this reason, we have tried to identify the point of onset of gastrin expression in the developing pancreas. Previously, determining the point of onset for genes in embryonic tissues has been difficult because of low expression levels and small tissue samples. Using the sensitive polymerase chain reaction assay, we were able to determine, with a sensitivity of 10 molecules of mRNA, the earliest expression of gastrin in the developing pancreas. This expression occurred at 30 somites, or at a gestation of 9.5 to 10 days.

Calcitonin gene-related peptide is a potent inhibitor of stimulated pancreatic exocrine secretion in vivo. The mechanism of this inhibitory action was studied in dogs and rats. The questions examined were: (1) is the inhibitory action of CGRP on pancreatic secretion mediated by somatostatin? (2) is the inhibition direct, via action on acinar cells, or indirect? and (3) is a neuronal mechanism involved, and, if so, by what pathway? In dogs with chronic pancreatic fistulae, CGRP caused significant inhibition of the outputs of pancreatic protein (63-68%) and of pancreatic bicarbonate (74-89%) and a simultaneous dose-related rise (40-102 fmol/ml) in plasma somatostatin-like immunoreactivity. A similar degree of inhibition was found when exogenous somatostatin was infused to achieve similar levels of plasma somatostatin-like immunoreactivity. More direct evidence of somatostatin mediation of CGRP action was sought in conscious rats with pancreatic fistulae using a potent and specific monoclonal antibody to somatostatin. The latter studies suggest that CGRP has both a somatostatin-dependent and a somatostatin-independent mechanism of action. In isolated rat acini, CGRP did not inhibit CCK-stimulated amylase release, suggesting that its in vivo action is indirect. In the isolated vascularly perfused rat pancreas, CGRP (10(-10)-10(-7) M) inhibited in a dose-dependent manner volume and protein output stimulated by a mixture of CCK-8 and secretin. The inhibitory action of CGRP was blocked by tetrodotoxin (10(-7) M) and by atropine (10(-7) M), but not by hexamethonium (10(-7) M). We conclude that CGRP action: (1) is partly explained by release of somatostatin; (2) is indirect; (3) is neurally mediated; and (4) involves cholinergic muscarinic neurons within the pancreas.

The effects of a specific cholecystokinin (CCK) receptor antagonist (L364,718) and a gastrin receptor antagonist (L365,260) on gastrin-releasing peptide-10 (GRP-10)-stimulated pancreatic secretion were investigated in the anesthetized rat. GRP-10 stimulated pancreatic exocrine secretion in a dose-dependent manner. A dose of 1.0 nmol/kg/h elicited a significant increase in pancreatic protein output. L364,718 (2.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous CCK-8 (3.0 nmol/kg/h) on pancreatic secretion, did not suppress the excitatory effect of GRP-10. L365,260 (5.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous gastrin (20 micrograms/kg/h) on gastric acid secretion, did not suppress the excitatory effect of GRP-10 either. We concluded that CCK or gastrin do not mediate the excitatory mechanism of bombesin/GRP on pancreatic secretion. Since CCK and gastrin are the most probable candidates for excitatory mediator of bombesin/GRP, these results support the hypothesis that bombesin/GRP directly stimulates the exocrine pancreas in the rat.

The mechanism by which calcitonin gene-related peptide (CGRP) inhibits exocrine secretion from the rat pancreas was examined in the isolated, vascularly perfused pancreas and in vitro using freshly isolated pancreatic acini. CGRP (10(-10)-10(-7) M) inhibited the volume and protein output from the perfused pancreas, stimulated by a mixture of the cholecystokinin octapeptide CCK8 (10(-10) M) and secretin (10(-8) M). The inhibition by CGRP was dose related and maximal at 10(-8) M (P less than 0.05). CGRP (10(-8) M) failed to inhibit amylase secretion from isolated pancreatic acini, stimulated by graded concentrations of CCK8 (10(-13)-10(-8) M). This implies an indirect mechanism of inhibition. The mechanism of inhibition was investigated in the isolated, vascularly perfused pancreas using tetrodotoxin, atropine and hexamethonium (all 10(-7) M). Tetrodotoxin and atropine but not hexamethonium prevented the inhibition of volume and protein secretion by CGRP (10(-8) M) (P less than 0.05). Tetrodotoxin, atropine and hexamethonium were without effect on exocrine secretion stimulated by CCK8 and secretin (controls). These results indicate that CGRP inhibits pancreatic exocrine secretion by an indirect, neurally mediated mechanism involving cholinergic-muscarinic transmission.

Geranyl-geranyl acetone (GGA), a new acyclic polyisoprenoid, anti-ulcer drug appears to exert its beneficial effect by stimulating bicarbonate secretion from the stomach and pancreas. Its efficacy in stimulating pancreatic bicarbonate is particularly striking, and this study was designed to examine the mechanism for this action. Since it is structurally similar to the side chain of the prostaglandin molecule, its ability to stimulate bicarbonate secretion could be a direct one. On the other hand, the magnitude of pancreatic bicarbonate response (about 50% of maximal response to secretin) suggests it might act by releasing secretin. Two types of experiments were performed in dogs with pancreatic fistulas: first, secretagogue interactions were examined by studying the effect of intraduodenal GGA (8 mg/kg) or its carrier (control) on the dose-response curves to exogenous secretin and cholecystokinin octapeptide (CCK-8); second, the effect of graded doses of intraduodenal GGA on pancreatic bicarbonate and plasma secretin-like immunoreactivity (SLI) responses was tested directly. Pancreatic bicarbonate responses (micromoles per 30 min) were to secretin doses of 32, 125, and 500 ng/kg/h. Without and with GGA, responses were 74 +/- 27, 952 +/- 215, and 2,000 +/- 425 and 599 +/- 110, 1,624 +/- 472, and 2,129 +/- 398 ng/kg/h, respectively. Similarly, the bicarbonate responses to CCK-8 were augmented. Basal plasma SLI was 1.5 +/- 0.6 pM/ml. Peak plasma SLI in response to 2, 4, and 8 mg of GGA intraduodenally were 6.8 +/- 0.7, 8.9 +/- 3.1, and 19.6 +/- 2.7 pM/ml, respectively. It is concluded that GGA is a potent stimulant of pancreatic bicarbonate secretion, and this action appears to be mediated by the release of duodenal secretin.

The mechanism of inhibition of pancreatic exocrine secretion by somatostatin is unknown. We hypothesized that somatostatin acts indirectly, via intrinsic pancreatic neurons, to inhibit pancreatic exocrine secretion. To test this hypothesis, amylase and volume outputs in response to secretin (10(-8) mol/L) and cholecystokinin octapeptide (CCK) (10(-8) mol/L) were studied in the rat isolated, perfused, pancreas model. Somatostatin (10(-7) mol/L) significantly inhibited amylase output by 48% compared with control (352 +/- 57 v 676 +/- 85 U/30 min, P less than .05 by ANOVA). Blockade of axonal neuronal transmission by tetrodotoxin (10(-7) mol/L) completely abolished the inhibitory effect of somatostatin (992 +/- 53 U/30 min). Similar effects were seen on volume output. The inhibitory effect of somatostatin on amylase output was not affected by cholinergic receptor blockade with atropine (328 +/- 65 U/30 min) or by sympathetic ganglionic blockade with hexamethonium (360 +/- 68 U/30 min). This suggests that the intrinsic pancreatic neurons responsible for the inhibitory effect of somatostatin are peptidergic. The possibility that somatostatin acts directly on the acinar cell to inhibit exocrine secretion was tested by incubating varying doses of somatostatin (10(-12) to 10(-7) mol/L) with isolated pancreatic acini in the presence of graded concentrations of CCK (10(-12) to 10(-10) mol/L). In this model, CCK alone is a potent stimulant of amylase release, with a Km of 6 X 10(-12) mol/L and a Vmax of 22 +/- 3% total amylase. In this model, somatostatin had no inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

In seven dogs provided with innervated pouch of the pyloric antrum, gastric fistula, and chronic pancreatic fistula, the effect of graded antral distenion on pancreatic exocrine secretion was studied. The effect of antral distension was tested both when gastrin release was promoted (alkaline distention) and when gastrin release was blocked (acid distension). These studies were performed both before and after transthoracic truncal vagotomy. Graded alkaline antral distension caused graded rise in protein-rich pancreatic secretion and graded increase in the concentration of serum immunoreactive gastrin. A similar pancreatic response was also seen with graded acid distention although this time no rise in serum gastrin concentration occurred. Pancreatic response to antral distension with either alkali or acid is completely inhibited by pretreatment of the animals with systemic atropine. Truncal vagotomy reduced pancreatic response to alkaline antral distension by 90% but completely abolished pancreatic response to distension of the antrum with acid. These studies provide evidence for a pyloropancreatic reflex mechanism for pancreatic secretion that is cholinergic and requires intact long vagal pathways.

The effects of cholecystokinin receptor antagonist, dipentyl-3,4-dichloroproglumide (DDP), on stimulated pancreatic and gastric secretion were studied in the rat. DDP dose-dependently inhibited cholecystokinin-stimulated amylase release from dispersed acinar cells. In vivo, DDP inhibited cholecystokinin octapeptide-stimulated amylase and protein secretion. DDP also inhibited pentagastrin-stimulated gastric acid secretion in vivo. Meal-stimulated acid output was decreased by 34% (DDP 400 micrograms/kg/hr) but responsiveness to histamine or parachlorophenyl-gamma-aminobutyric acid was unchanged.

Cholinergic receptors for cholecystokinin (CCK) have been identified on neurons of the enteric nervous system, including those of the gallbladder. To determine whether any differences exist in the extent to which CCK action depends on muscarinic cholinergic receptors in the pancreas and gallbladder, 11 dogs with pancreatic and 7 dogs with biliary fistulas were given increasing doses of intravenous CCK-8 (15-250 ng X kg-1 X h-1) or intraduodenal sodium oleate (0.1-9 mmol/h) with and without atropine pretreatment. Pancreatic protein response to CCK-8 was dose dependent, reaching a maximal of 448 +/- 76 mg/15 min at the highest dose. Atropine pretreatment caused nonsignificant reduction in the response to the lowest dose but had no effect on the responses to the other doses, with the response to the highest dose of CCK being 473 +/- 82 mg/15 min. In contrast, gallbladder contraction as measured by bile fistula bilirubin output was very sensitive to inhibition by atropine. Bilirubin responses to 16, 32, 62.5, 125, and 250 ng X kg-1 X h-1 were 14 +/- 5, 18 +/- 5, 28 +/- 5, 36 +/- 6, and 52 +/- 12 mg/h, respectively, without atropine and 0 +/- 0, 6 +/- 2, 7 +/- 2, 18 +/- 4, and 18 +/- 4 mg/h with atropine pretreatment. Similarly, pancreatic responses to sodium oleate infusion were less susceptible to inhibition by atropine than were the gallbladder responses. With respect to pancreatic protein secretion, the response to only the lowest dose of sodium oleate was significantly inhibited by atropine.(ABSTRACT TRUNCATED AT 250 WORDS)

We compared the responses of the canine exocrine pancreas to intraduodenal versus intravenous administration of mixed amino acids, fat emulsion, and glucose. Graded doses of amino acid mixture and of fat emulsion gave graded responses in volume, protein, and bicarbonate when administered intraduodenally. In contrast, the same doses of the amino acid mixture and fat emulsion administered by central intravenous infusion caused no significant pancreatic secretion of volume, protein, or bicarbonate. Graded doses of glucose caused no statistically significant pancreatic secretion whether they were given intraduodenally or intravenously. We conclude, contrary to a previously published observation, that amino acids and fats given parenterally do not stimulate pancreatic secretion. As a corollary, it is reasonable to assume that the pancreas is not stimulated during total parenteral nutrition with acute pancreatitis or a pancreatic fistula.

The coexistence of calcitonin gene-related peptide (CGRP) and somatostatin (SS) within the stomach and pancreas and the potent inhibitory effects of both peptides on exocrine secretions from these organs suggest that they are functionally related. To assess the potential role of SS in the mediation of CGRP action, the effects of intravenous human CGRP (64, 132, and 264 pmol.kg-1.h-1) and somatostatin-14 (SS-14; 100, 400, and 800 pmol.kg-1.h-1) on plasma levels of SS immunoreactivity (SS-IR) and on pentagastrin-stimulated gastric and pancreatic secretion were compared in conscious dogs. CGRP caused significant inhibition of gastric acid (85-102%), pancreatic protein (63-86%), and pancreatic bicarbonate (74-89%) outputs and a simultaneous dose-related rise (40-102 fmol/ml) in plasma SS-IR. Cessation of CGRP infusion resulted in prompt return of plasma SS-IR to basal levels and an increase in gastric and pancreatic secretion. Although CGRP is a potent releasor of SS into the circulation, its inhibitory action on gastric acid secretion cannot be explained solely by a rise in plasma SS-IR. In the pancreas, in contrast to the stomach, inhibition appears to be more closely related to a rise in circulating level of SS-IR.

In four dogs with chronic pancreatic and gastric fistulas, dose-response studies of pancreatic bicarbonate and protein secretion were done with intravenous infusions of secretin, octapeptide of cholecystokinin (OP-CCK), and 2-deoxyglucose (2-DG). The pancreatic response to a meal and to duodenal perfusion of graded concentrations of HCl, sodium oleate, and tryptophan were also studied. These observations were repeated after division of both the hepatic and celiac vagal branches to produce extragastric vagotomy, and subsequently after transthoracic truncal vagotomy. The responses to secretin, OP-CCK, and to duodenal perfusion of HCl were either unaltered or only slightly decreased by either extragastric or truncal vagotomy. Basal pancreatic secretion and the responses to duodenal perfusion of oleate and tryptophan were markedly depressed by extragastric vagotomy. These findings indicate that tonic vagal activity contributes to basal pancreatic secretion but has little effect on the response of the pancreas to secretin or CCK or on the release of secretin from the intestine. The decreased pancreatic response to intestinally perfused oleate and tryptophan seen after extragastric vagotomy could be caused either by interruption of reflex paths between gut and pancreas or by interference with CCK release. Extragastric vagotomy reduced pancreatic responses to a meal and to 2-DG and subsequent truncal vagotomy caused still further reduction, possibly, at least in part, by depressing release of antral gastrin.

It is well established that massive small-bowel resection (MSBR) invariably causes hypersecretion of acid in animals with denervated gastric pouches. The effect of MSBR on the secretory responses of both the totally innervated stomach and pancreas have been less well studied. Eighteen adult mongrel dogs were prepared with chronic gastric and pancreatic fistulae. In eight, massive small-bowel resection was performed in addition. Bowel resection did not alter the responses to graded doses of pentagastrin. However, in response to the intragastric titration of a liver extract meal, it had the following effects: (1) profound gastric acid hyposecretion; (2) reduction in pancreatic bicarbonate and protein secretion; and (3) increase in basal and meal-stimulated serum glucagon levels. Hypergastrinemia did not occur after resection. The hyposecretory responses may represent either increased inhibition or decreased secretory stimulation.

Peptide YY is an ileocolonic peptide that inhibits meal-stimulated pancreatic secretion when infused in a dose of 400 pmol/kg X h. In this study pancreatic secretion was monitored in response to increasing doses of secretin or cholecystokinin-octapeptide (62.5, 125, 250, and 500 ng/kg X h) during the simultaneous infusion of either saline or peptide YY (400 pmol/kg X h). Peptide YY significantly (p less than 0.05) inhibited the secretory response to the three lowest doses of each pancreatic secretogogue, reducing the bicarbonate response to the 62.5-ng/kg X h dose of secretin by 86% +/- 6% and the protein response to the same dose of cholecystokinin by 57% +/- 16%. In the second limb of the study, the half-life of peptide YY (11.7 +/- 21 min) and the metabolic clearance rate (13.8 +/- 1.6 ml/kg X min) were found to be similar to those of other gastrointestinal hormones. We conclude that inhibition of meal-stimulated pancreatic secretion by peptide YY can be explained by its ability to decrease the responsiveness of the pancreas to endogenous secretogogues.

In dogs with chronic pancreatic fistulas, pure cholecystokinin (CCK), CCK-variant, 20% pure CCK, octapeptide of CCK, and caerulein all gave the same high maximal protein outputs and low maximal bicarbonate outputs. 10% pure CCK gave higher bicarbonate output that can be achieved with pure CCK. By intestinal perfusion, HCI gave greater protein output than can be achieved with secretine alone, sodium oleate gave greater bicarbonate output than can be achieved with pure CCK alone, and tryptophan gave maximal bicarbonate output less than that of pure CCK. On the hypothesis that intestinally perfused stimulants act solely by release of secretin and CCK, the effects of tryptophan can be accounted for by release of CCK alone, of HCI by release mainly of secretin plus small amounts of CCK, and of oleate by release mainly of CCK plus small amounts of secretin.