Insulin, glucagon, and somatostatin secretion from isolated perfused rat and chicken pancreas-duodenum

Insulin, glucagon, and somatostatin secretion were evaluated in the following isolated perfused models: rat pancreas-duodenum (both normal and streptozotocin-diabetic animals) and the chicken pancreas with and without duodenum. Insulin secretion in response to glucose or arginine was greater from the normal rat than either the diabetic rat or the chicken. Glucagon release from both species was suppressed by glucose and stimulated by arginine except that poor inhibition by glucose was found in the diabetic rat. Somatostatin could be measured in the effluent from both normal and diabetic rats, but the responses to glucose and arginine were variable and modest. Clear increases of secretion in the rat were only observed in response to a combination of glucose, arginine, theophylline, and isoproterenol. In contrast, the chicken somatostatin secretion was markedly stimulated by glucose and by arginine. In conclusion, the perfused chicken pancreas-duodenum has been shown to secrete large amounts of somatostatin in comparison to the rat and should prove to be a useful system for the study of D-cell regulation.     

Myelin basic protein stimulates insulin and glucagon secretion from rat pancreatic islets in vitro and in vivo

The effect of myelin basic protein on insulin and glucagon secretion from rat pancreatic islets was studied in vivo and in vitro. The myelin basic proteins isolated from bovine, human and rat brains all stimulated insulin secretion in a similar fashion. In a static incubation of isolated pancreatic islets, myelin basic protein at doses of 15.6–250 μg in a 0.5-ml reaction volume (1.7 times 10^-8 to 2.7 times 10^-5 M) significantly stimulated hormone release. Maximal stimulation, obtained at the 250-μg dose, was 6.5-fold greater than control for insulin secretion and 6.7-fold greater than control for glucagon secretion. In the case of glucagon no saturation was observed, but saturation was obvious for insulin release at doses of myelin basic protein of 62.5–250μg, larger doses causing permeabilization of the islet membranes as indicated by leakage of acid phosphatase. At a 100-μg dose the time course of insulin secretion induced by myelin basic protein indicated a fast initial release, and after the first 2 h only a little more insulin was released. At the lower doses of myelin basic protein (11 and 33μg) the secretion rate was nearly constant after the first hour. Significant stimulation of glucagon release by myelin basic protein was seen after 60 min, the rate of release being roughly constant at 33-and 100-μg doses thereafter. At the 11-μg dose significant stimulation of hormone release was observed only after a 4-h incubation. Lowering the temperature from 37 to 27 and 20°C reduced both basal and stimulated hormone secretion, the extent of stimulation over the basal level remaining the same at all temperatures only for insulin secretion at a dose of myelin basic protein of 100 μg. A dose of 10 mg myelin basic protein injected intravenously into anaesthetized rats resulted 15 min after injection in a circulating concentration of myelin basic protein of 34.7 μg ml^-1 (1.7 times 10^-6 M) as measured by our radioimmunoassay. It stimulated insulin secretion (P < 0.01), having no significant effect on plasma glucagon levels. Since myelin basic proteins have been shown to display fusogenic properties in cell-free membrane systems, we propose that myelin basic protein exerts its hormone-releasing effect by aggregating and fusing the hormone-containing vesicles to the cell plasma membranes.     

Myelin basic protein stimulates insulin and glucagon secretion from rat pancreatic islets in vitro and in vivo.

The effect of myelin basic protein on insulin and glucagon secretion from rat pancreatic islets was studied in vivo and in vitro. The myelin basic proteins isolated from bovine, human and rat brains all stimulated insulin secretion in a similar fashion. In a static incubation of isolated pancreatic islets, myelin basic protein at doses of 15.6-250 micrograms in a 0.5-ml reaction volume (1.7 X 10(-6) to 2.7 X 10(-5) M) significantly stimulated hormone release. Maximal stimulation, obtained at the 250-micrograms dose, was 6.5-fold greater than control for insulin secretion and 6.7-fold greater than control for glucagon secretion. In the case of glucagon no saturation was observed, but saturation was obvious for insulin release at doses of myelin basic protein of 62.5-250 micrograms, larger doses causing permeabilization of the islet membranes as indicated by leakage of acid phosphatase. At a 100-micrograms dose the time course of insulin secretion induced by myelin basic protein indicated a fast initial release, and after the first 2 h only a little more insulin was released. At the lower doses of myelin basic protein (11 and 33 micrograms) the secretion rate was nearly constant after the first hour. Significant stimulation of glucagon release by myelin basic protein was seen after 60 min, the rate of release being roughly constant at 33- and 100-micrograms doses thereafter. At the 11-micrograms dose significant stimulation of hormone release was observed only after a 4-h incubation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of glucagon,dibutyrylic cyclic AMP and insulin on bile production in the intact rat and the perfused rat liver

The effect of glucagon, dibutyrylic cyclic AMP (DBcAMP) and insulin on bile flow and composition was studied in fasting, Nembutal anesthetized intact rats and perfused rat livers. In intact rats the infusion of glucagon (0.5 μg · kg b. w^-1· min^-1) resulted in a parallel increase in bile flow and ¹⁴C-erythritol clearance of approx. 20%. The biliary excretion rate of electrolytes increased, whereas the net ductular fluid transport and the excretion rate of bile acids remained unchanged. Thus glucagon choleresis in intact rats appears to be due to a stimulation of the bile acid independent fraction of canalicular bile production. A similar effect was seen when DBcAMP (0.5 μmol · kg b. w.^-1· min^-1) and insulin (1 U · kg b. w.^-1) was given. In the perfused liver glucagon or DBcAMP also increased bile flow. However, bile acid excretion rate also increased and the rise in bile flow was proportional to the rate of taurocholate administration. This effect may be due to uneven distribution of perfusate flow. Insulin was totally without effect on bile production in the perfusion experiments. It is concluded that the choleretic effect of glucagon and insulin is dependent on unknown factors which may be related to extrahepatic actions of the hormones.     

Hepatic insulin and glucagon extraction after their augmented secretion in dogs

Effects of intravenous arginine and cholecystokinin-pancreozymin (CCK-PZ) infusion on hepatic extraction of insulin (EI) and glucagon (EGG) and also on hepatic glucose output (HGO) were studied in anesthetized dogs. Because insulin and glucagon exert antagonistic effects on HGO, insulin:glucagon (I/GG) molar ratios were determined in the portal vein and also in peripheral vessels. During the arginine-CCK-PZ infusion the amount of insulin and glucagon coming to the liver increased 12- and 15-fold, respectively. In contrast EI decreased significantly from a control value of 62 +/- 6% to a nadir of 22 +/- 13%. EGG (control value 19 +/- 9%), however, was unaffected by arginine-CCK-PZ. The absence of any alteration in EGG cannot be attributed to the molecular heterogeneity of the immunoreactive glucagon. HGO increased fourfold in response to the pancreatic stimulation, whereas portal I/GG decreased significantly from 8.2 +/- 0.9 to 5.0 +/- 0.7. The concurrent femoral arterial I/GG (control 3.7 +/- 1.0) and mesenteric venous I/GG (control 2.1 +/- 0.5) increased significantly. These observations indicate that portal, but not peripheral, I/GG measurements reflect hepatic events in anesthetized dogs, probably because of the different extraction patterns for insulin and glucagon.     

Enhancement of insulin and glucagon secretion by arginine after hepatic vagotomy

The hepatic vagus nerve consists of mostly afferent fibers in the rat, and is a major afferent pathway between the liver and the medulla. The present study was carried out to examine the role of the hepatic branch of the vagus nerve in secretion of insulin and glucagon after intraperitoneal injection of arginine (1 g/kg body wt.) in rats. Measurements were made one week after section of this branch. Intraperitoneal arginine enhanced both plasma insulin and glucagon concentrations; more in hepatic-vagotomized than in sham-vagotomized rats. The results suggest that inhibition of the secretion of insulin and glucagon after arginine stimulation is mediated by the hepatic branch of the vagus nerve. The existence of 'sensors' in the liver for arginine, or its derivatives, is proposed as an explanation for the inhibition of the secretion of insulin and glucagon by the hepatic vagus nerve.     

Stimulation of insulin and glucagon secretion by vasoactive intestinal peptide.

In vivo, vasoactive intestinal peptide (VIP) produces simultaneous increases in blood glucose and insulin levels. In order to determine whether VIP, like its homologues, also stimulates insulin secretion directly, studies were made in controlled glucose media employing the vascularly perfused cat pancreas. VIP stimulated insulin secretion significantly in the presence of constant physiological concentrations of glucose. The highest insulin response to VIP (100.3+/-8.1 muU/min) approached the highest insulin response to glucose (119.9 +/- 12.0 muU/min). In the absence of glucose, the insulin response to VIP was insignificant. Unexpectedly, VIP was found to be a more effective stimulant of glucagon than of insulin secretion. The highest glucagon response to VIP (327+/-51% of control levels) was attained in the presence of physiological concentrations of glucose and equalled the glucagon response obtained upon withdrawal of glucose from the perfusate. The glucagon response to VIP was blocked by increasing the glucose in the perfusate. These studies indicate the VIP present in pancreatic islets might play a role in the local control of pancreatic endocrine function.     

Galanin: effects on basal and stimulated insulin and glucagon secretion in the mouse

Galanin was recently demonstrated to be a neuropeptide in intrapancreatic nerves. In this study, the effects of galanin on basal and stimulated insulin and glucagon secretion in the mouse were investigated. Galanin, injected intravenously at dose levels ranging from 0.53 to 8.5 nmol kg-1, markedly lowered basal plasma insulin levels and transiently increased basal plasma glucagon levels. Furthermore, galanin induced hyperglycaemia: plasma glucose levels were 11 +/- 0.2 mmol l-1 2 min after injection of galanin (4.25 nmol kg-1) compared with 9.3 +/- 0.3 mmol-1 in controls (P less than 0.001). Galanin also impaired the plasma insulin response to either glucose or the cholinergic agonist carbachol. Thus, galanin (4.25 nmol kg-1) inhibited the plasma insulin response to glucose by 65% (P less than 0.001), and that to carbachol by 85% (P less than 0.001). Moreover, glucose abolished the galanin-induced plasma glucagon response. Also, galanin and carbachol exerted additive stimulatory effects on glucagon levels. It is concluded from this study in mice that galanin inhibits basal and stimulated insulin secretion, stimulates glucagon secretion, and induces hyperglycaemia. It is suggested that the intrapancreatic neuropeptide galanin is of importance in the regulation of both insulin and glucagon secretion.     

GnRH类似物对大鼠回肠组织胰高血糖素释放的影响

目的 :研究促性腺激素释放激素 (GnRH)类似物 (阿拉瑞林 )对大鼠回肠L细胞释放胰高血糖素的影响。方法 :应用放射免疫分析法对体内和体外大鼠回肠进行观察。结果 :大鼠回肠灌注GnRH类似物后 ,血中及肠液中胰高血糖素的含量较对照组明显升高 ;体外孵育大鼠回肠组织后 ,在一定浓度范围内 ,孵育液中胰高血糖素含量随GnRH类似物浓度升高而升高 ;当浓度高于一定范围时 ,则随浓度升高而降低。GnRH类似物浓度为 1 .0× 1 0 - 4mol/L时孵育液中胰高血糖素含量是升高的。结论 :GnRH可能对大鼠回肠L细胞分泌胰高血糖素呈现双向调节作用。但是GnRH类似物为 1 .0× 1 0 - 4mol/L ,不论是体内还是体外 ,都可能对肠道分泌胰高血糖素表现促进作用     

Effects of alpha- and beta-adrenoceptor stimulation on 45Ca2+ efflux and insulin secretion from perfused rat islets

Exposure to the beta 2-adrenoceptor agonist terbutaline resulted in a transient stimulation of 45Ca2+ efflux from 45Ca2+ preloaded rat islets perfused in 2 mM Ca2+ and 8.3 mM glucose. Concomitantly, an increase in insulin secretion occurred. Under the same experimental conditions, the alpha-adrenoceptor agonist noradrenaline promptly inhibited insulin release without any apparent influence on 45Ca2+ efflux. In contrast, in a medium containing 2 mM Ca2+ and a low glucose concentration (2.8 mM), terbutaline stimulated insulin secretion without any apparent effects on 45Ca2+ efflux. Noradrenaline had no effect on insulin secretion or 45Ca2+ efflux in this medium. When islets were perfused with 8.3 mM glucose in a Ca2+ deficient medium, with or without addition of the chelating agent EGTA, terbutaline induced a marginal stimulation of insulin secretion and a negligible stimulation of 45Ca2+ efflux. On the contrary, noradrenaline stimulated to an immediate and notable 45Ca2+ efflux in these Ca2+ deficient media. Noradrenaline also clearly inhibited insulin secretion, though less markedly and with a slower onset than in islets perfused in 2 mM Ca2+. When the islets were perfused in a Ca2+ deficient medium with 2.8 mM glucose, terbutaline had a slight insulin releasing effect, but stimulated 45Ca2+ efflux potently. Noradrenaline had no influence on insulin secretion but a weak stimulatory effect on 45Ca2+ efflux. The data suggest that the beta 2-adrenoceptor agonist terbutaline has the ability to stimulate insulin secretion in perfused rat islets, requiring extracellular Ca2+ for the full expression of its effects. These effects may be exerted through a Ca2+-Ca2+ exchange over the cell membrane and/or through cAMP and intracellular Ca2+ perturbations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of avian insulin secretion by isolated perfused chicken pancreas.

Chicken insulin secretory responses to glucose, glucagon, tolbutamide, and lack of Mg2+ were measured using isolated perfused in situ chicken pancreata. Although elevating perfusate glucose concentration from 100 to 250 mg/100 ml failed to increase insulin release, 500 mg glucose/100 ml provoked a transient 5-min insulin response. Additionally, 700 mg glucose/100 ml resulted in both a transient response and subsequent elevation in secretory rate that continued throughout the following 50-min stimulatory period. Glucagon (500 microgram/ml) and omission of perfusate Mg2+ potentiated glucose-stimulated insulin output by 6 and 25%, respectively. A faster release of insulin (less than 1 min) occurred during tolbutamide infusion (0.13 mg/ml) than with either 500 or 700 mg glucose per 100 ml (2-3 min); however, secretory rates declined to near basal levels within 5 min. Mammalian-like insulin responses to glucose, glucagon, Mg2+ lack, and tolbutamide suggest similarities between avian and mammalian beta-cell insulin secretory mechanisms. Nevertheless, the relatively high chicken insulin release threshold and low insulin output to glucose indicate that chicken pancreata are relatively glucose insensitive.     

Insulin secretion by isolated perfused rat and mouse pancreas.

A method for isolation and perfusion of a pancreas preparation consisting of pancreas, stomach, proximal duodenum, and spleen is described. Basic characteristics of regulation of insulin secretion from the perfused pancreas isolated from rats, albino mice, obese mice (ob/ob), and black mice were identical. Viability and stability of the pancreas preparation during perfusion were maintained as documented by measurements of oxygen consumption of the pancreas preparation, perfusion pressure, and pH of the perfusion medium. The insulin-secretory capacity of the pancreas of different animal species was compared. Insulin secretion by the perfused rat and obese (ob/ob) mouse pancreas was much more potent than that by the pancreas of lean albino and lean black mice. D-Glucose-induced insulin secretion from the pancreas was decreased after fasting of the animals and was dependent on glucose concentration and presence of calcium in the perfusion medium. D-Glyceraldehyde, tolbutamide, D-mannose, dihydroxyacetone, L-leucine, and L-arginine also induced insulin secretion from the pancreas. D-Fructose, D-galactose, L-glucose, 3-O-methyl-D-glucose, N-acetylglucosamine, D-xylose, D,L-glyceric acid, pyruvate, L-lactate, and theophylline did not provoke insulin secretion.