Ian L. Taylor

The effect of 15(R)-15-methyl prostaglandin E2 on meal-stimulated gastric acid secretion, serum gastrin, and pancreatic polypeptide in duodenal ulcer patients

The effects of 100-μg doses of 15(R)-15-methyl prostaglandin E2 on meal-stimulated acid secretion, serum gastrin, and pancreatic polypeptide concentrations were measured in patients with duodenal ulcer. The drug given in encapsulated or unencapsulated form significantly reduced gastric acid secretion by 59% or 70%, respectively. Rises in serum gastrin and pancreatic polypeptide concentrations after the meal were significantly blunted by 15(R)-15-methyl prostaglandin E2. This dose of prostaglandin led to no side effects and merits clinical evaluation in the treatment of peptic ulcer disease.

Effects of Prostaglandin and Indomethacin on Diet-Induced Acute Pancreatitis in Mice

This study was performed to determine the effects of exogenous prostaglandin and a prostaglandin synthetase inhibitor on experimental pancreatitis in mice. An ethionine-supplemented choline-deficient diet was used to induce pancreatitis in 4-6-wk-old Swiss Webster mice. Mice were injected subcutaneously with 16,16-dimethyl prostaglandin E2 (0.1, 1.0, 10 micrograms X kg-1 X day-1), indomethacin (0.05, 0.5, 5 mg X kg-1 X day-1), or saline for 7 days. The ethionine-supplemented choline-deficient diet was introduced 24 h after the first injection, and animals ate the test diet for 48 h. A 55% mortality was observed in control animals (n = 100) treated with carrier alone. Treatment with 10 micrograms X kg-1 X day-1 of 16,16-dimethyl prostaglandin E2 significantly decreased (p less than 0.01) mortality to 12% (n = 100). Improved survival was accompanied by a significant (p less than 0.05) decrease in the pancreatic content of free chymotrypsin and a decrease in histologic damage. Treatment with 5 mg X kg-1 X day-1 of indomethacin (n = 30) significantly (p less than 0.01) increased mortality in diet-treated rats from a control rate of 55% to 100%. These studies demonstrate a protective effect of prostaglandin on the pancreas and suggest a role for endogenous prostaglandins in the pathophysiology of pancreatitis.

Pancreatic Polypeptide Enhances Postcontractile Gallbladder Filling in the Prairie Dog

The hypothesis that pancreatic polypeptide promotes postcontractile gallbladder filling was tested in the prairie dog model. Fifteen animals underwent laparotomy with catheter placement into the gallbladder, distal common bile duct (vent), and femoral vein. The gallbladder was perfused with [14C]polyethylene glycol labeled lactated Ringers solution at 0.03 ml/min and vent effluent was collected at 2.5-min intervals. All animals received a 20-min intravenous infusion of cholecystokinin-octapeptide, 2.5 ng/kg X min, immediately followed by 60-min infusions of either lactated Ringers solution or bovine pancreatic polypeptide (PP), 10 or 50 ng/kg X min. Gallbladder emptying and intragallbladder pressure were similar for all three groups after cholecystokinin-octapeptide. When lactated Ringers was administered after cholecystokinin-octapeptide, gallbladder filling increased by 15.6% with a minimal change in gallbladder pressure. In contrast, infusion of PP10 resulted in a significant (p less than 0.02) increase in gallbladder filling, 64.1% +/- 17.1%, and a significant (p less than 0.05) decrease in intragallbladder pressure, as compared to controls. Similar findings were noted with PP50. These data indicate that exogenous PP significantly increases gallbladder filling after cholecystokinin-induced gallbladder contraction. This enhanced filling results from gallbladder relaxation as manifested by decreased intraluminal pressure. These findings coupled with the observation that serum PP levels remain elevated for up to 6 h after a meal suggest that PP may play a role in the regulation of postprandial gallbladder filling.

Pancreatic polypeptide release following gastric surgery

Although there is little doubt that the release of pancreatic polypeptide (PP) in response to a meal is vagal-cholinergic dependent (1), the exact nervous and hormonal pathways which mediate this response are largely undetermined. The demonstration of Stern et al in the present issue that truncal vagotomy markedly inhibits the PP response to food suggests an important role for the vagi in PP release. Although this study confirms the findings of two other groups (2, 3), there are other studies (4, 5) which suggest that truncal vagotomy has little effect on the PP response to food. These apparently contradictory findings spawned two theories of PP release, ie, that PP release is largely mediated through the vagus (2), and that gastrointestinal hormones play the major role in PP release (4). We found ourselves in the somewhat embarrassing situation of having one study in each camp (3, 5) and sought to explain this paradox in terms of differences in methodology. In the studies (2, 3) which demonstrated a marked inhibition of PP release by vagotomy, the PP response to a meal was measured in the same subject before vagotomy and then once again within the 6-week period following surgery. In the studies (4, 5) showing no effect, two separate groups were investigated. One group consisted of unoperated duodenal ulcer patients; the other of patients who had had a vagotomy several years before. These differences led us to suggest (5) that the inhibition of meal-stimulated PP release by truncal vagotomy might be time dependent, ie, that the response was initially inhibited by truncal vagotomy but that it returned towards normal with time. At first sight, this

Pancreatic polypeptide release by intraluminal fatty acids

The question of whether the response of pancreatic polypeptide to intestinal fatty acids is influenced by the site of intestinal perfusion or the chain length of the fatty acid was investigated. Six dogs with chronic gastric, pancreatic, and intestinal fistulas were studied. Proximal perfusates were administered at the pylorus and diverted via a Foley catheter in the orad stoma of an intestinal fistula placed 45 cm beyond the pancreatic cannula. Distal perfusates were administered into the caudal stoma of the intestinal cannula. Three experimental protocols were used: proximal fatty acid perfusion (20, 40, or 80 mmol/L) combined with distal saline perfusion; distal fatty acid perfusion (20, 40, or 80 mmol/l) combined with proximal saline perfusion; or distal fatty acid perfusion combined with proximal fatty acid perfusion of 80 mmol/L. Each dose of fatty acid was given in random order and the two fatty acids (dodecanoate and oleate) were tested on different days. Blood samples were drawn for pancreatic polypeptide radioimmunoassay, and pancreatic secretion was collected for determination of bicarbonate and protein outputs. Pancreatic polypeptide responses to perfusion of both proximal and distal segments with oleate exceeded (P less than 0.05) those evoked by dodecanoate. The responses of pancreatic polypeptide to dodecanoate administration into either the proximal segment or the distal intestine were not significantly different. In contrast, perfusion of the proximal intestinal segment with oleate release significantly (P less than 0.05) less pancreatic polypeptide than did distal intestinal perfusion with oleate.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic polypeptide and peptide YY inhibit the denervated canine pancreas.

Pancreatic polypeptide and peptide YY are inhibitors of pancreatic exocrine secretion in vivo but not in vitro, which suggests secondarily mediated mechanism(s) of action. To determine the role of extrinsic neural and intrinsic cholinergic elements on this inhibitory effect, a total of nine dogs underwent two-stage extrapancreatic denervation and creation of a chronic pancreatic fistula. After recovery, pancreatic polypeptide or peptide YY (400 pmol/kg/h) was administered during the intermediate hour of a 3-hour secretin (125 ng/kg/h)/cholecystokinin (50 ng/kg/h) infusion. Exocrine secretion during pancreatic polypeptide or peptide YY hours was compared with that of the first and third hours. The studies were then repeated during infusion of atropine (10 μg/kg/h). Despite extrinsic denervation, pancreatic polypeptide and peptide YY significantly inhibited secretinlcholecystokinin-induced pancreatic output. Although less profound, significant inhibition persisted in the presence of an atropine background. Pancreatic polypeptide or peptide YY infusion also decreased the exocrine response to meal stimulation. We conclude that the inhibitory effects of pancreatic polypeptide and peptide YY are not mediated by extrapancreatic, and possibly not by intrapancreatic cholinergic, neural pathways.

Beneficial effect of pancreatic polypeptide in experimental pancreatitis

Two animal models have been employed to examine the role of pancreatic polypeptide, a potent and selective inhibitor of pancreatic exocrine secretion, in the treatment of acute pancreatitis. In one model pancreatitis was induced by feeding young female Swiss Webster mice an ethionine-supplemented, choline-deficient diet for 48 hr. Animals (N=30 per group) were injected subcutaneously every 8 hr for 7 days with pancreatic polypeptide (0, 2, 20, and 200 μg/kg/day). Treatment with 20 and 200 μg/kg/day pancreatic polypeptide significantly (P<0.05) reduced moriality from a control rate of 70% to 42% and 33%, respectively. Treated animals also exhibited significant (P<0.05) decreases in pancreatic content of activated chymotrypsin and an improvement in pancreatic histology. Pancreatic polypeptide was effective whether treatment was started before or at the same time the test diet was introduced. In contrast, pancreatic polypeptide failed to protect dogs with acute pancreatitis induced by retrograde injection of the pancreas with bile, which may reflect the rapid and mechanical nature of pancreatic damage in this animal model.

Potential Methodologic Problems with in Vivo Immunoneutralization of Pancreatic Polypeptide

Dogs with chronic pancreatic fistulae were given 0.5 ml of nonimmune rabbit serum or antibody S5, an antibody raised against the C-terminal pancreatic polypeptide (PP) hexapeptide. A 3-h infusion of secretin (125 ng/kg/ h) and CCK8 (50 ng/kg/h) was started 30 min after injecting serum. Exogenous BPP (400 pmol/kg/h) was administered during the middle secretin/CCK hour. In a second protocol, 30 min after injecting nonimmune serum or PP-antiserum, the animals were fed 15 g/kg cooked ground beef. Pretreatment with S5 enhanced secretin/CCK-induced bicarbonate outputs; protein outputs did not differ. Exogenous BPP inhibited pancreatic secretion, even in S5-treated animals. Meal-induced pancreatic secretion was not altered by S5 pretreatment. Significant increments in PP were measured by radioimmunoassay during administration of secretin/CCK and during BPP infusion. Anti-PP pretreatment abolished the former and significantly decreased, but did not abolish, the latter. The meal evoked significant postprandial increments in PP which were essentially abolished following S5 pretreatment. A physiological role for PP cannot be proved or refuted because antiserum pretreatment failed to block the effects of exogenous hormone. The latter must be established before excluding a peptides physiological role based on negative in vivo immunoneutralization data.

Meal-induced pancreatic polypeptide release in a validated pancreatic denervation model: a role for the distal pancreas?

In previous studies, postprandial pancreatic polypeptide (PP) release was diminished when pancreatic denervation was combined with distal pancreatectomy in animals without chronic fistulae. In contrast, postprandial PP release was reported to be unchanged when the pancreas was denervated without performing a distal pancreatectomy. These findings were unexpected given that the distal pancreas is a PP-poor region. To clarify this issue, we performed extrinsic pancreatic denervation, distal pancreatectomy, and insertion of chronic pancreatic fistulae in nine mongrel dogs. Insulin (0.5 U/kg) and meal-stimulated PP release were measured pre- and postoperatively. In addition, insulin- and meal-induced exocrine secretion was measured postoperatively. Preoperatively, insulin-induced hypoglycemia stimulated significant PP release (80,553 ± 18,540 pg/min/ml). This response was completely abolished postoperatively (− 1,669 ± 5,054 pg/min/ml). Exocrine secretion did not increase above basal levels after administration of insulin in postoperative animals. These findings suggest adequate pancreatic denervation. Ingestion of a meal evoked significant PP response preoperatively (97,909 ± 18,394 pg/min/ml). Postoperatively, the response was significantly blunted (17,23 1 ± 6,407 pg/min/ml). This finding is in contrast to a previous report using a similar experimental preparation without distal pancreatic resection. We speculate that although the distal pancreas is PP-poor, it may play a role in the regulation of PP release from the PP-rich pancreatic head.

Role of the distal pancreas in pancreatic polypeptide release

In two previous studies, postprandial pancreatic polypeptide (PP) release was inhibited when pancreatic denervation was combined with distal pancreatectomy. In contrast, postprandial PP release was unaffected by pancreatic denervation without a distal pancreatectomy. These findings suggested a role for the distal pancreas in regulation of postprandial PP release. To examine this possibility, we performed distal pancreatectomy on four mongrel dogs. Pancreatic polypeptide response to i.v. insulin (0.5 U/kg), a meal, and an infusion of cholecystokinin octapeptide (CCK-8; 50 ng/kg/h) were measured in conscious dogs before and after distal pancreatectomy. Insulin-induced hypoglycemia stimulated PP release both preoperatively (47.0 ± 8.8 ng. [0–120]min/ml) and postoperatively (61.6 ± 9.2 ng. [0–120]min/ml). Ingestion of a meal also evoked significant PP release preoperatively (85.8 ± 22.1 ng. [0–180]min/ml) and postoperatively (105.8 ± 42.2 ng. [0–180]min/ml). CCK-8 elicited only a small increase in circulating PP, which was not influenced by distal pancreatectomy. These findings demonstrate that distal pancreatectomy does not alter PP response to insulin, a meal, or CCK-8.