Action of pancreatic polypeptide on exocrine pancreas and on release of cholecystokinin and secretin

We have studied the effect of exogenous porcine pancreatic polypeptide (PP; 0.8 and 2.1 microgram/kg . h, iv) on endogenously stimulated pancreatic exocrine secretion in five pancreatic-fistula dogs. Plasma levels of cholecystokinin (CCK), secretin, and PP were measured in addition to pancreatic secretion of water, bicarbonate, and protein. Intraduodenal infusions of acid and a mixture of phenylalanine and tryptophan were used to stimulate hormone release. PP caused a dose-dependent inhibition of endogenously stimulated pancreatic secretion, whereas the release of CCK and secretin was not affected. Duodenal acidification and intraduodenal infusion of phenylalanine and tryptophan caused a significant release of PP. This study shows that: 1) PP suppresses pancreatic secretion by means of a mechanism that is probably direct; this effect is not mediated through inhibition of release of CCK or secretin, and 2) phenylalanine and tryptophan, both strong stimulants of CCK release, cause a substantial rise in PP in peripheral blood. The mechanism of PP release may involve CCK (in previous studies, we have shown a rise in circulating PP levels after iv CCK infusion).

Effect of pancreatic polypeptide and its C-terminal hexapeptide on meal and secretin induced pancreatic secretion in dogs

1. Gastric acid and pancreatic bicarbonate and protein secretion as well as immunoreactive serum gastrin and pancreatic polypeptide concentrations in response to a meal and secretin have been measured before and after infusion of bovine pancreatic polypeptide or its C-terminal hexapeptide. 2. Liver extract meal kept in the stomach at pH 5.5 (by intragastric titration) produced a marked increase in gastric acid and pancreatic protein secretion accompanied by a rise in serum gastrin and pancreatic polypeptide levels. Exogenous bovine pancreatic polypeptide caused little change in gastric secretion and serum gastrin but resulted in a profound suppression of pancreatic secretion. 3. Ordinary feeding a liver meal produced a marked increase in pancreatic bicarbonate and protein secretion that was dose-dependently inhibited by bovine pancreatic polypeptide or its C-terminal hexapeptide, the degree of inhibition being closely correlated with the increments in plasma pancreatic polypeptide. 4. Bovine pancreatic polypeptide and its C-terminal hexapeptide also inhibited secretin and caerulein-induced pancreatic secretion in a dose-dependent manner. 5. This study shows that bovine pancreatic polypeptide inhibits pancreatic secretion at least in part by acting directly on the exocrine pancreas and that its biological activity resides in its C-terminal hexapeptide fragment.

Lack of effect of pancreatic polypeptide in the rate of gastric emptying and gut hormone release during breakfast

Bovine pancreatic polypeptide (PP) was infused intravenously in 5 healthy subjects on two separate occasions with mean doses of 1 and 2 pmol kg-1 min-1, respectively, which achieved plasma levels equal to and twice those observed after a normal mixed breakfast. The gastric emptying rate of a carbohydrate-rich breakfast 20 min after the start of each PP infusion was not significantly different from a control infusion of 0.15 M saline. PP is unlikely to be an important physiological modulator of gastric emptying rate in man.

Effects of vasoactive intestinal peptide and pancreatic polypeptide in rabbit intestine

The effects of porcine vasoactive intestinal peptide (VIP) and bovine pancreatic polypeptide (PP) on jejunal, ileal, and colonic fluid transport were studied in the rabbit. VIP produced secretion in the small intestine (jejunum greater than ileum) but did not affect absorption in the colon. PP had no secretory effects in jejunum, ileum, or colon. The small intestinal secretion induced by VIP was not associated with raised cAMP concentrations in the mucosa; this suggests that the secretory effects of VIP in vivo are mediated by a mechanism other than stimulation of adenylate cyclase.

Effects of pancreatic polypeptide on motilin and circulating metabolites in man

Pancreatic polypeptide was infused intravenously in healthy fasting subjects at 1 pmol kg-1 (n = 7) and 4 pmol kg-1 min-1 (n = 10) producing plasma PP concentrations of 223 +/- 37 pmol/l (mean +/- SEM) and 891 +/- 64 pmol/l respectively. These levels are similar to and four-fold higher than those seen after a normal mixed breakfast in healthy young adults. In a separate study five healthy subjects ingested a small breakfast during infusion of PP on different days at 1 pmol kg-1 min-1 and 2 pmol kg-1 min-1 respectively. PP at 1 pmol kg-1 min-1 caused a marked reduction in fasting plasma motilin concentrations to 20% of the basal level (p less than 0.001). There were, however, no significant changes in plasma concentrations of insulin, glucagon, gastrin, secretin, enteroglucagon, gastric inhibitory peptide or neurotensin. Despite previous reports possibly implicating PP in metabolism, there were no significant effects on blood levels of glucose, alanine lactate, 3-hydroxybutyrate, glycerol or non-esterified fatty acids, either in the fasting state or after the ingestion of food. Although it seems unlikely that PP is a major hormonal regulator of intermediary metabolism in man, its ability to suppress motilin at physiological concentrations suggests the possibility of an indirect influence on digestive motor function.

Effect of bovine pancreatic polypeptide on isolated rat liver cells

Pancreatic polypeptide (PP) is a newly isolated protein found in the islets of Langerhans of many species. No clear metabolic function of PP has yet been determined. We have investigated the possible metabolic effect of bovine PP (bPP) on rat liver cells. bPP had no effect on glucose or urea production when liver cells were incubated with a variety of substrates, epinephrine, or glucagon. In addition, there was no appreciable effect of bPP on ketone body production or cAMP levels. Though species differences between the polypeptide and the cells may account for our results, it would seem that further efforts in the search for metabolic actions of PP should be directed toward possible effects on the periphery, i.e. fat and muscle tissue.

Effects of insulin and pancreatic polypeptide on gastric somatostatin release

Effects of arginine and such pancreatic hormones as insulin and pancreatic polypeptide on gastric somatostatin release from the isolated perfused rat stomach were studied. The stomach was isolated from a fasted rat by a modification of the method of Lefébvre and was perfused with 4.6% dextran Krebs-Ringer biocarbonate buffer containing 5.5 mM glucose. Both insulin and pancreatic polypeptide (10(-10), 10(-9), and 10(-8) M) caused a significant decrease in gastric somatostatin secretion. Insulin (10(-10) M), furthermore, inhibited the glucagon (5 x 10(-8) M)-induced somatostatin response. Arginine (10 and 19 mM) failed to elicit any significant change of somatostatin release. These results suggest that gastric somatostatin release is affected by pancreatic hormones.

Effects of gastrointestinal hormones and carbamylcholine on cAMP accumulation in isolated pancreatic duct fragments from the rat

A modification of a technique to isolate kidney tubule fragments and pancreatic acinar cells has been used to prepare a suspension of pancreatic duct fragments from rats with pancreatic lipomatosis due to pretreatment with penicillamine and a copper-free diet. This suspension is 90-95% pure almost without any acinar cell contamination. The accumulation of 3',5'-cyclic adenosine monophosphate (cAMP) in response to various gastrointestinal hormones, hormone-like substances and theophylline was studied in these isolated pancreatic duct fragments. In the absence of theophylline, secretin increased the level of cAMP in a dose-dependent manner with a maximum at 10(-6) M. With supramaximal doses the concentration of cAMP decreased. During maximal stimulation with secretin the level of cAMP was dependent on the concentration of fragments in the incubation mixture. Vasoactive intestinal peptide (VIP) also increased the formation of cAMP. However, VIP was 10 times less effective than secretin on a molar basis. The addition of various concentrations of VIP to a submaximal dose of secretin did not alter cAMP levels as compared to the levels observed with the same concentration of secretin alone. Theophylline (5 x 10(-3) and 10(-2) M) stimulated cAMP accumulation and 5 x 10(-3) M theophylline potentiated the response to secretin and VIP. Pancreozymin (20 and 99% pure), glucagon bovine pancreatic polypeptide and carbamylcholine did not effect the level of cAMP when given alone or in combination with secretin. These data lend support to the hypothesis that cAMP is the intracellular mediator of the action of secretin and VIP on the pancreatic duct cells.

Effects of gastrointestinal hormones on fasting gallbladder storage patterns in man

Gallbladder storage and emptying patterns were studied in fasting normal subjects by a duodenal perfusion technique using indocyanine green as a biliary marker. Fasting gallbladder storage patterns were very variable but a more uniform biliary output with net storage of about 40% of the biliary marker was observed during a simulated interprandial state (2--4 h after meals) produced by a low dose intravenous infusion of secretin and caerulein. With this background hormonal stimulation, infusion of bovine pancreatic polypeptide to achieve physiological interprandial levels promoted further gallbladder storage of bile. Bovine pancreatic polypeptide produced storage by a major effect on the gallbladder rather than on the liver, common bile duct or sphincter of Oddi since a reduction of biliary output was not observed during bovine pancreatic polypeptide infusion in cholecystectomized subjects. Bovine pancreatic polypeptide had a separate effect on the pancreas, reducing trypsin output in both normal and cholecystectomized subjects.

Effects of pancreatic polypeptide and vasoactive intestinal polypeptide on rat ileal and colonic water and electrolyte transport in vivo

Two gastrointestinal peptides, vasoactive intestinal polypeptide (VIP) and pancreatic polypeptide, suspected of being associated with symptoms of WDHA syndrome (pancreatic cholera) were tested on the rat small and large intestine for their effects on water and electrolyte transport. Intravenous infusion of VIP (14.3 microgram/kg/hr) inhibited net absorption of water and electrolytes in the ileum and reversed net absorption to net secretion in the colon. In contrast, bovine pancreatic polypeptide (52 microgram/kg/hr) did not inhibit absorption or stimulate secretion. These data indicate VIP causes colonic secretion in vivo, an effect previously shown only in vitro, and that bovine pancreatic polypeptide (at this dose) is not a secretagogue in the small or large intestine of the rat. Thus, while consistent with VIP being a contributory agent to the secretion of pancreatic cholera, the data do not support the notion that pancreatic polypeptide might be a causative agent in this syndrome.

Pancreatic polypeptide. Metabolism and effect on pancreatic secretion in dogs

In dogs with gastric and pancreatic fistulas, porcine pancreatic polypeptide (PP) was infused intravenously in doses of 50, 100, 200, 400, and 800 pmol kg-1 hr-1 in the basal state and in doses of 100, 200, and 400 pmol kg-1 hr-1 during stimulation with submaximal doses of secretin (125 ng kg-1 hr-1) plus caerulein (50 ng kg-1 hr-1). Plasma concentrations of PP were measured by radioimmunoassay, and pancreatic bicarbonate and protein outputs were monitored. The half-time for disappearance of PP was 5.5 +/- 1.0 min, the metabolic clearance rate was 25.6 +/- 1.0 ml kg-1, and the volume of distribution was 209 +/- 42 ml kg-1. Basal pancreatic flow and protein output were significantly inhibited by the lowest dose of PP tested, 50 pmol kg-1 hr-1. The lowest dose of PP significantly inhibiting stimulated pancreatic secretion was 100 pmol kg-1 hr-1 for bicarbonate output and 200 pmol kg-1 hr-1 for protein output. The mean +/- SE peak increment in PP concentration in response to a meal of meat, 210 +/- 39 pM, was greater than the mean peak increment with the 400 pmol kg-1 hr-1 dose of exogenous PP, 175 +/- 19 PM. We conclude that exogenous doses of PP that produce smaller increments in PP concentration than those seen after feeding inhibit pancreatic bicarbonate and protein secretion stimulated by secretin and caerulein. This suggests that the amount of PP released by a meal is sufficient to inhibit pancreatic secretion.

Effect of bovine pancreatic polypeptide on basal pancreatic and biliary outputs in man

Basal pancreatic and biliary outputs were examined in seven healthy volunteers during intravenous infusion of bovine pancreatic polypeptide (BPP) at a mean dose of 320 pmol/kg/hr. BPP significantly (P less than 0.02) inhibited outputs of trypsin and bilirubin, without affecting bicarbonate. These studies suggest the possibility that pancreatic polypeptide may have a role in the regulation of biliary and pancreatic enzyme secretion in man.

Influence of exogenous avian pancreatic polypeptide on gastrointestinal motility in turkeys

To determine the influence of avian pancreatic polypeptide (APP) on avian GI motility, strain-gauge transducers were implanted on the glandular stomach, thick caudodorsal and thin caudoventral muscles of the muscular stomach, and on the duodenum (cranial tract) of five young turkeys. Implants were also made on the ileum, cecum, and colon (caudal tract) of three other turkeys. Isovolumic injections of APP at six (cranial tract preparations) or four (caudal tract preparations) levels were made via a chronic jugular catheter while recording GI contractile activity in fasted birds. Injections of 2 or 5 micrograms/kg caused no statistically significant change in motility of the cranial tract. Significant depression in contraction frequency during the first 10 min post-injection resulted from an injection of 8 micrograms/kg. Injections of 10, 20, and 30 micrograms/kg depressed motility throughout the entire 30 min post-injection period. Motility of the caudal tract usually was not significantly affected by injections of 5 and 10 micrograms/kg doses. Larger doses (20 and 30 micrograms/kg) significantly depressed caudal tract motility during the first 10 min post-injection but not throughout the 30 min post-injection period. In both cranial and caudal portions of the tract, depression of contractile activity by injections of APP persisted longer following larger doses. The highest plasma APP levels in turkeys, found at about 1 hr post-prandially, were still less than plasma levels following IV injection of 5 micrograms/kg. Since the latter injection caused no apparent alteration in Gi motility, APP may have little or no physiological role in regulation of avian GI motility.

Inhibition of secretin stimulated pancreatic secretion by pancreatic polypeptide

The effect of PP on secretin-stimulated pancreatic secretion was assessed in five healthy subjects. During an intravenous infusion of BPP at a dose which produced plasma levels similar to those seen after meals in healthy young adults the volume and bicarbonate content of duodenal juice was reduced by 25% (p less than 0.05) and 24% (p less than 0.05) respectively, while protein and bilirubin concentrations were more markedly reduced by 68% (p less than 0.0005) and 67% (p less than 0.0005) respectively. PP, thus, may be an important inhibitory factor in the control of bilirubin and pancreatic enzyme secretion in man.