V. Harris

Amylin secretion from the rat pancreas and its selective loss after streptozotocin treatment.

Amylin, a peptide copackaged with insulin in beta-cell granules, was measured in the effluent of the perfused rat pancreases by means of a newly developed specific radioimmunoassay. Its secretion parallels that of insulin in response to 20 mM glucose, 10 mM arginine, or the combination thereof. The relative molar amount of secreted amylin was estimated to be 25-37% that of insulin. Treatment with a borderline diabetogenic dose of streptozotocin reduced amylin response without significantly changing the insulin response. A severely diabetogenic dose of streptozotocin totally abolished amylin release and markedly reduced insulin release. The selective impairment of amylin secretion in streptozotocin-treated rats could represent an early manifestation of beta-cell depletion or injury.

Measurements of somatostatin-like immunoreactivity in plasma

Abstract The validity of measurements of somatostatin-like immunoreactivity (SLI) in canine plasma has been examined. The radioimmunoassay employed had a minimal sensitivity of 50 pg/ml and a discriminatory sensitivity of 15 pg/ml above this. The coefficient of variation within and between assays was 6% and 18%, respectively. There was no cross-reaction with any of 9 other peptide hormones tested. Significant incubation damage by canine plasma to the [125I]-tyrosine1-somatostatin tracer was effectively prevented by Trasylol and EDTA, and recovery of synthetic somatostatin added to canine plasma and incubated for 3 h at 20°C was 96%. Subcutaneous injections of somatostatin were followed by a prompt rise in plasma SLI that was significantly correlated with decrease in plasma glucagon levels. Serial dilutions of plasma specimens containing high levels of either endogenous SLI or injected synthetic somatostatin gave proportional readings and their slopes paralleled those of synthetic somatostatin in plasma-free buffer. Ninety-five percent of endogenous plasma SLI was removed by passage of plasma specimens through a column of immobilized somatostatin antibodies. Both endogenous SLI in plasma and synthetic somatostatin added to plasma were eluted in the void volume of Biogel P-10 columns, but following isolation by affinity chromatography the molecular size of both was approx. 1600, suggesting that both endogenous SLI and synthetic somatostatin circulate in plasma bound to larger molecules. It is concluded that this radioimmunoassay permits valid measurements of endogenous SLI in canine plasma.

The effects of gastrin, gastric inhibitory polypeptide, secretin, and the octapeptide of cholecystokinin upon immunoreactive somatostatin release by the perfused canine pancreas.

The effects of gastrin, gastric inhibitory polypeptide, secretin, and the octapeptide of pancreozymin-cholecystokinin on immunoreactive somatostatin release were studied in the isolated perfused dog pancreas. Gastrin at a concentration of 65 ng/ml and the octapeptide of pancreozymin-cholecystokinin at a concentration of 25 ng/ml produced a prompt, but transient statistically significant, twofold rise in mean somatostatin concentration. Secretion at a concentration of 0.3 U/ml and gastric inhibitory polypeptide concentration of 58 ng/ml produced a prompt two- to threefold rise in mean somatostatin release, which persisted throughout the perfusion period. With all four polypeptides the pattern of the somatostatin response resembled that of insulin. It appears that pancreatic somatostatin release is stimulated by gastrointestinal hormones that influence the secretion of insulin and glucagon.

Immunoreactive somatostatin levels in plasma of normal and alloxan diabetic dogs

The recent discovery by Luft and associates [l] and by Dubois [2] of somatostatin-containing islet cells, subsequently identified as D-cells [3-51, has opened a new phase in the physiology and pathophysiology of the endocrine pancreas. It is,now recognized that diabetes resulting from a deficiency of insulin-secreting cells, such as human juvenile type diabetes and streptozotocin diabetes in rats, is characterized by an apparent increase in somatostatincontaining D-cells per islet [6] and that the content of immunoassayable somatostatin in the islets of such rats is high [7]. However, it has not been determined if these abnormalities in the islets are reflected by hypersomatostatinemia indeed, it is not known if under normal circumstances somatostatin is released into the circulation from those tissues in which its presence has been demonstrated [8,9]. In this study, we attemped to determine, first, if the levels of immunoreactive somatostatin-like material (IRS) in the venous plasma of organs with a substantial somatostatin content are higher than in peripheral venous plasma and, second, if hypersomatostatinemia is present in dogs with alloxan-induced deficiency of B-cells.

Gastric and Pancreatic Release of Somatostatin-like Immunoreactivity During the Gastric Phase of a Meal: Effects of Truncal Vagotomy and Atropine in the Anesthetized Dog

The postprandial release of gastric and pancreatic somatostatin-like immunoreactivity (SLI) was examined in anesthetized dogs during the gastric phase of a meal, and the role of vagal and atropine-sensitive mechanisms in the responses was assessed. The intragastric instillation of liver extract at pH 7 elicited a significant rise in antral vein SLI (∼300 pg/ml) and gastrin concentration. After truncal vagotomy, both baseline and postprandial antral vein SLI and gastrin concentration increased significantly compared with the control group. The infusion of atropine (100 μg/kg/h) abolished the postprandial rise in antral vein SLI but not in gastrin. The liver meal at pH 2 elicited a sustained sixfold greater rise of antral SLI (∼2000 pg/ml) than that at pH 7, while gastrin concentrations did not rise significantly. The latter antral SLI response was not influenced by truncal vagotomy, but atropine infusion reduced it by about 50%. In response to the meal at pH 7, fundic vein SLI concentrations rose by about 300 pg/ml. The rise was augmented slightly by truncal vagotomy but was abolished completely by atropine infusion. In response to the meal at pH 2, fundic SLI decreased sharply below baseline levels. The response was not altered significantly by vagotomy, but was reversed completely by atropine infusion, during which fundic vein SLI concentrations rose significantly. Pancreatic vein SLI concentrations rose by about 350 pg/ml in response to the gastric meal at pH 7. That rise was not altered significantly by vagotomy but was abolished by atropine infusion. In response to the meal at pH 2, pancreatic SLI concentrations rose by about 1000 pg/ml above baseline, significantly greater than the response to the meal at pH 7. The pancreatic vein SLI response to the meal at pH 2 was not altered by vagotomy. It was reduced considerably by atropine infusion. It is concluded that SLI is released from the antrum, fundus, and pancreas during the gastric phase of a meal and that these responses are modified by acidification of the intragastric contents and by truncal vagotomy and atropine infusion. The greatly augmented release of antral SLI in response to the acidified meal raises the possibility of a role for somatostatin in acid-induced suppression of gastrin release.

Effect of bombesin upon plasma somatostatin-like immunoreactivity, insulin and glucagon in normal and chemically sympathectomized dogs.

The present study was designed to determine the effects of intravenously infused bombesin (10 ng/kg/min) upon basal and postprandial plasma somatostatin-like immunoreactivity (SLI), glucagon, insulin and triglyceride levels in normal (n = 12) and chemically sympathectomized (n = 11) dogs. Basal plasma SLI, glucagon and insulin levels rose significantly during the infusion of bombesin in the normal dogs, and this was not altered by chemical sympathectomy. Bombesin infusion enhanced the postprandial SLI response, while attenuating the postprandial glucagon response by 50% and the insulin response in the early postprandial phase of the meal. Sympathectomy did not significantly alter the basal levels of these polypeptides, but augmented the postprandial plasma SLI response during the first 90 min, and reduced the postprandial glucagon response during the infusion of bombesin. The postprandial insulin response was not affected by sympathectomy. In both normal and chemically sympathectomized dogs the rise in postprandial triglyceride levels was attenuated by bombesin infusion.

Role of histamine H2-receptors in gastric and pancreatic release of somatostatin-like immunoreactivity during the gastric phase of a meal

The present study was designed to determine the role of H2-receptors in the postprandial release of somatostatin-like immunoreactivity (SLI) from the gastric fundus and antrum and from the pancreas. In dogs subjected to laparotomy, the pylorus was bisected and a gastric fistula was created, following which 250 ml 20% liver extract (LE) at pH 7 or 2 were instilled intragastrically. In the fundic vein the incremental SLI rise in response to LE at pH 7 was 2423 plus or minus 540 pg/ml during a control infusion of saline and 4780 plus or minus 863 pg/ml during the infusion of cimetidine (1 mg/kg per h) (P less than 0.05). In the antral vein the incremental SLI in response to LE at pH 7 was 2182 plus or minus 530 pg/ml during the saline control but did not rise significantly during cimetidine infusion. In the pancreatic vein the incremental SLI level after LE at pH 7 was 1953 plus or minus 358 pg/ml in the control experiments and 4430 plus or minus 1024 pg/ml during cimetidine infusion (P less than 0.025). The incremental inferior vena cava SLI level was approximately 925 pg/ml in both groups (not significant). The instillation of LE at pH 2 during the saline control lowered fundic vein SLI by 500 pg/ml; this decline was abolished during cimetidine infusion. In the antral vein the incremental SLI level of 15 750 plus or minus 2514 pg/ml during saline was lowered to only 6728 plus or minus 2257 pg/ml during cimetidine (P less than 0.025). After LE at pH 2 the incremental pancreatic vein SLI level of 5641 plus or minus 1175 pg/ml during the control infusion was also significantly reduced to 2392 plus or minus 559 pg/ml by cimetidine (P less than 0.05). The incremental SLI in the inferior vena cava was reduced from 1270 plus or minus 280 pg/ml during saline to 680 plus or minus 190 pg/ml when cimetidine was infused (P less than 0.05). The present data suggest a histaminergic influence via stimulation of H2-receptors upon the regulation of gastric and pancreatic somatostatin release during the gastric phase of a meal.