V. Schusdziarra

Pancreatic and Gastric Somatostatin Release in Response to Intragastric and Intraduodenal Nutrients and HCl in the Dog

The effects of the instillation of glucose, fat, casein hydrolysate, and HCl into the gastrointestinal tract upon plasma levels of somatostatin-like immunoreactivity (SLI) in the venous effluent of the pancreas, fundus and antrum of the stomach, and in the inferior vena cava (IVC) were determined in normal laparotomized dogs. Fasting SLI levels in the effluent plasma from these sites were significantly greater than IVC levels. The intragastric administration of glucose elicited a prompt and significant rise in SLI levels in pancreatic, fundic and antral venous plasma, and in IVC plasma; intraduodenal glucose elicited smaller increments. After intragastric fat, a smaller, more gradual increase in the pancreatic and fundic effluents was observed, whereas the rise in antral SLI was minute, and IVC SLI did not rise significantly. Intraduodenal fat elicited a prompt increase in the pancreatic and antral vein SLI levels, and a small but significant increase in fundic and IVC plasma which suggests faster release of enteric factors that influence SLI secretion in the pancreas and antrum. Intragastric casein hydrolysate elicited a prompt increase in SLI in both the pancreatic and fundic veins, the latter being marked, but the antral SLI response was small; IVC SLI rose significantly within 15 min. Intragastric HCl provoked a prompt and marked rise in pancreaticoduodenal and antral vein SLI but no increase in fundic vein SLI; IVC SLI levels rose significantly within 20 min. Intraduodenal HCl elicited an even more prompt and marked pancreatic SLI response, and SLI rose significantly in both the fundic and antral venous effluents; IVC SLI also rose more promptly. In dogs with a gastric fistula that prevented intraduodenal entry of HCl, intragastric HCl elicited only a very small and transient rise in pancreaticoduodenal vein SLI, markedly stimulated the antral SLI response, but completely suppressed fundic venous SLI levels. The results indicate that all three nutrients stimulate SLI release from the pancreas and stomach. The greater SLI response to intragastric, as opposed to intraduodenal, glucose suggests that unidentified local factors are of importance. The responses to the intraduodenal instillation of HCl and fat suggest a role of enteric hormones in the release of SLI from the pancreas and fundus and antrum of the stomach. Additionally, there is evidence of direct effects of HCl upon gastric SLI release.

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.

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.

Properties of endogenous somatostatin-like immunoreactivity and synthetic somatostatin in dog plasma.

Somatostatin-like immunoreactivity (SLI) in the peripheral venous plasma of dogs and in their pancreatic and gastric venous effluents was characterized and compared with synthetic somatostatin. Both endogenuous plasma SLI and somatostatin added to plasma were eluted from Sephadex gels at pH 8.8 in the 150,000--200,000-mol wt region but at pH 2.5 both appeared in the 1,500--2,000-mol wt region. The SLI released from the isolated dog pancreas perfused with plasma-free buffer was eluted entirely as a 1,600-dalton polypeptide, but when the pancreas was perfused with plasma, SLI was eluted in the 150,000--200,000-mol wt zone. Affinity chromatography of plasma samples on immobilized antibodies directed against the central portion of the somatostatin molecule (residues 5--9 and 11) removed approximately equal to 90% of both endogenous SLI and somatostatin added to plasma, but neither was removed by affinity chromatography on antibodies directed against the NH2-terminal region of somatostatin (residues 1--4). The SLI from plasma and from pancreas perfusate isolated by affinity chromatography was identical in molecular size, charge, and immunometric properties to synthetic somatostatin. It is concluded that endogenous SLI is secreted by the pancreas and stomach in a form not distinguishable from synthetic somatostatin, but circulates in plasma bound to large molecular weight components; the NH2-terminal residues of somatostatin appear to be important in this binding.

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.

Oral administration of somatostatin reduces postprandial plasma triglycerides, gastrin and gut glucagon-like immunoreactivity

Abstract The present study was designed to determine if orally administered somatostatin can reduce the postprandial rise in plasma triglycerides, gastrin, gut glucagon-like immunoreactivity (GLI) and the pancreatic hormones insulin and glucagon. Ten overnight fasted dogs were fed a fat-protein meal with or without 2 mg synthetic somatostatin, followed by another 2 mg somatostatin 90 min later. After the meal with somatostatin, postprandial plasma triglyceride levels were significantly lower for 5 hours, GLI levels for 3.5 hours and gastrin levels for 1 hour compared to the controls. Plasma insulin, glucagon and somatostatin-like immunoreactivity was not different from the control experiments. It is concluded that orally administered somatostatin lowers the postprandial levels of triglycerides, GLI and gastrin in dogs. This may have therapeutic implications for the management of gastrointestinal and metabolic disorders.

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.

Insulin inhibits somatostatin-like immunoreactivity release stimulated by intragastric HCL

To determine the effect of an increase in insulin levels within the range occuring under physiologic conditions on the protein- and acid-induced release of splanchnic somatostatin, insulin was infused in dogs for 1 h following the intragastric instillation of a neutral protein load (20% liver extract at pH 7), a weak stimulus of somatostatin-like immunoreactivity (SLI), and after an intragastric HCI, a strong stimulus of SLI release, instilled 30 min later. Insulin levels between 50 and 60 μU/ml significantly reduced the rise in peripheral venous SLI levels elicited by the acid load from a mean integrated incremental value of 1705 ±182 pg/ml in controls to 840 ± 312 in the insulininfused group (P < 0.05). Prevention of the insulininduced hypoglycemia and the secondary rise in glucagon, a known stimulus of pancreatic somatostatin secretion, by means of a concomitant infusion of glucose, did not modify the reduction in acid-induced increase in plasma SLI concentration associated with hyperinsulinemia. Insulin-glucose infusion significantly lowered the SLI in the pancreaticoduodenal vein, and in the gastroepiploic vein draining the antrum (P < 0.02; P < 0.05), but not in the short gastric veins draining the fundus of the stomach in response to the acid load. It is concluded that a physiologic elevation of insulin levels causes significantly reduced response of SLI to an intragastric acid load in dogs. This reduction is explained by a diminished increment of SLI in the venous effluent of the pancreas and the antrum.

TRIGLYCERIDE LOWERING EFFECT OF SOMATOSTATIN AND ITS ANALOGS

Volker SCHUSDZIARRA+, Marvin BROWN#, Jean RIVIER#, Wylie VALE#, Richard DOBBS+, Philip RASKIN* and Roger H. UNGER+ + Veterans Administration Hospital, 4500 South Lancaster Road, Dallas, Texas 75216 and the University of Texas Southwestern Medical School, Department of Internal Medicine, 5323 Harry Hines Boulevard, Da&s Texas 7523.5 and #Salk Institute, PO Box 1809, San Diego, California 921 I2 and *Clinical Investigator, Dallas Veterans Administration Hospital, USA