Effect of glucose/sulfonylurea interaction on release of insulin, glucagon, and somatostatin from isolated perfused rat pancreas.

The effect of a sulfonylurea, glibenclamide, on the release of insulin, glucagon, and somatostatin was studied in the isolated perfused rat pancreas. At glucose concentrations of 1.1 mM or less, the drug stimulated somatostatin release, whereas glucagon release, after 2-3 min of increase, was markedly inhibited. Insulin release was moderately stimulated, and maximal release occurred relatively late. A moderate glucose load (6.7 mM) inhibited glibenclamide-induced release of somatostatin, whereas the two in combination exerted an additive action on insulin release. Greater glucose loads, which by themselves would stimulate somatostatin release, only marginally suppressed glibenclamide-induced somatostatin release. The insulinogenic effect of these glucose levels was not modified by glibenclamide. Glibenclamide may thus stimulate both the alpha and beta as well as delta cells of the pancreas, depending on glucose concentration. We suggest a paracrine (local) interaction of somatostatin with the alpha and beta cells, which has an important role in the kinetics of insulin and glucagon release induced by sulfonylureas.     

Studies on the mechanism of somatostatin action on insulin release. V. Effect of somatostatin analogues on arginine induced release of insulin and glucagon from the perfused rat pancreas.

Eighteen analogues of somatostatin have been used in order to elucidate the structure-activity relationship of the peptide on the release of insulin and glucagon from the isolated perfused rat pancreas. Neither the amino terminal nor a free carboxyl terminal seemed to be essential for the activity of the cyclic peptide. Addition of amino acids to the amino terminal did not decrease the activity. On the other hand, minor changes in the structure of linear somatostatin, which lead to the loss of ability to form a cyclic peptide, impaired the activity. Deletion of Asn5 was accompanied by decreased action on glucagon but not on insulin release. It seems that the major actions of somatostatin on the pancreas are bound to the amino acid sequence 4-13 in the molecule and to the ability of the molecule to cyclize.     

Effects of K+ and arginine on insulin, glucagon, and somatostatin release from the in vitro perfused rat pancreas

Rat pancreases were perfused in vitro for 5-min periods with K+ alone (8, 10, and 12 mM) or in the presence of arginine (10 mM). Alone, K+ caused bursts of insulin, glucagon, and somatostatin (SRIF) release; with arginine, it caused a burst of insulin and sustained SRIF release, but caused sustained suppression of glucagon. This suppression correlated better with SRIF than insulin release. Therefore, if a paracrine effect is responsible for the inhibition of glucagon secretion under these circumstances, SRIF is a more likely candidate than insulin.     

Effects of glimepiride on insulin and glucagon release from isolated rat pancreas at different glucose concentrations

The effects of glimepiride, the newest sulphonylureic compound, on pancreatic insulin and glucagon secretion were studied using the classical, isolated, perfused rat pancreas model. The influence of four different environmental glucose conditions (during a glycaemic stimulus with glucose increasing from 5 to 8.33 mM and at stable 0, 5 and 2.22 mM glucose levels) on the effects of glimepiride was also assessed. At a pharmacological concentration glimepiride strongly stimulated beta-cell activity, producing a characteristic biphasic insulin release with a sharp first-phase secretory peak, followed by a prolonged and sustained second phase. Environmental glucose concentrations markedly influenced the extent, but not the pattern of glimepiride-induced insulin secretion, as hormone release dropped significantly when the glucose level was reduced. Glimepiride failed to influence alpha-cell activity at any of the environmental glycaemic levels.     

Effects of gamma-aminobutyric acid on insulin, glucagon, and somatostatin release from isolated perfused dog pancreas

The effects of gamma-aminobutyric acid (GABA) on the secretion of insulin, glucagon, and somatostatin were studied in the isolated dog pancreas. Insulin secretion was inhibited in a dose-related fashion for 10 min or more by as little as 1 microM GABA. A prompt but small and transitory rise in somatostatin secretion, lasting only 1 min, occurred at GABA concentrations of 10 and 100 microM, levels that exert inhibitory effects on nervous tissue. Bicuculline, a GABA antagonist, inhibited insulin secretion and did not antagonize GABA-mediated insulin inhibition. The results suggest that GABA in concentrations that are known to exist in islet tissue can influence the secretion of islet hormones.     

Multiple effects of leucine on glucagon, insulin, and somatostatin secretion from the perfused rat pancreas

The effects of increasing concentrations of leucine (0.2, 2.0, and 15.0 mmol/liter) on glucagon secretion from the perfused rat pancreas were examined at various glucose levels (0, 3.3, or 8.3 mmol/liter) and in the absence or presence of either arginine (5.0 mmol/liter) or glutamine (10.0 mmol/liter). At a low glucose concentration (3.3 mmol/liter), leucine caused a dose-related biphasic increase in glucagon output in the absence of arginine, but only a transient increase in the presence of the latter amino acid. These positive responses were markedly reduced and, on occasion, abolished at a high glucose concentration (8.3 mmol/liter). Moreover, at a low glucose concentration (3.3 mmol/liter) and in the presence of arginine, the highest concentration of leucine (15.0 mmol/liter) provoked a sustained and reversible inhibition of glucagon release. Likewise, leucine (15.0 mmol/liter) reversibly inhibited glucagon secretion evoked by glutamine in the absence of glucose. Thus, leucine exerted a dual effect on the secretion of glucagon, the inhibitory effect of leucine prevailing at a high concentration of the branched chain amino acid and when glucagon secretion was already stimulated by arginine or glutamine. At a physiological concentration (0.2 mmol/liter), however, leucine was a positive stimulus for glucagon release, especially in the absence of another amino acid. Concomitantly, leucine was always a positive stimulus for both insulin and somatostatin secretion. The intimate mechanisms involved in the dual effect of leucine on glucagon secretion remain to be elucidated.     

Effects of galanin on the release of insulin, glucagon and somatostatin from the isolated, perfused dog pancreas

Galanin is a 29 amino acid peptide which has been found in intrapancreatic nerves. The effects of galanin, adrenergic and cholinergic blockade as well as somatostatin on the hormone release from the isolated perfused dog pancreas were studied. It was found that galanin dose-dependently inhibited insulin (P less than 0.001) and somatostatin (P less than 0.001) but not glucagon secretion at normal glucose levels. The lowest galanin concentration that caused a significant suppression of insulin and somatostatin secretion was 10(-11) and 10(-10) mol/l, respectively. Similar effects were evident during stimulation with 2.5 mmol/l arginine. Galanin (10(-9) mol/l) caused a more pronounced inhibition of insulin and somatostatin secretion at high (10 mmol/l) and normal (5 mmol/l) than at low glucose (1.3 mmol/l). In contrast, suppression of the glucagon secretion was only seen at low glucose (1.3 mmol/l). Perfusion of 10(-6) mol/l of atropine, phentolamine and propranolol had no effect on the galanin-mediated (10(-10) mol/l) inhibition of insulin and somatostatin secretion. Galanin (10(-12)-10(-10) mol/l) and somatostatin (10(-12)-10(-10) mol/l) were equipotent in inhibiting insulin secretion whereas only somatostatin exerted a suppression of the glucagon secretion at normal glucose. Thus, galanin exerts a differential effect on islet hormone secretion and may participate in the hormonal control of insulin, glucagon and somatostatin secretion.     

Immediate and delayed effects of D-fructose upon insulin, somatostatin, and glucagon release by the perfused rat pancreas

Novel information was recently provided concerning the reciprocal effects of d-glucose and d-fructose upon their respective metabolism in rat pancreatic islets. In the light of such findings, this study aims at comparing the effects of d-glucose and d-fructose on insulin, somatostatin, and glucagon release from the isolated perfused rat pancreas. A rise in d-glucose concentration from 3.3 to 5.0 or 7.3 mM or the administration of d-fructose (17 and 40 mM) in the presence of 3.3 mM d-glucose stimulated insulin release in a concentration-related manner, but failed to affect somatostatin output. The secretion of glucagon was decreased in all cases. The secretory response to l-arginine (5 mM), 25 min after restoring the basal concentration of d-glucose, was more markedly affected, in terms of potentiation of insulin and somatostatin release and reduction of glucagon output, after prior administration of d-fructose than after a prior increase in d-glucose concentration. These findings argue against any major role for a paracrine regulation of hormonal release and, instead, are consistent with a causal link between metabolic and secretory events in the islet cells. Nevertheless, the present results emphasize differences in the response of distinct pancreatic endocrine cell types to the same or distinct hexoses.     

Neurotransmitters partially restore glucose sensitivity of insulin and glucagon secretion from perfused streptozotocin-induced diabetic rat pancreas

Summary To elucidate the mechanisms of insensitivity of hormone secretion to glucose in streptozotocin-induced diabetic rat islets, we investigated the effects of acetylcholine (ACh) and norepinephrine on insulin and glucagon secretion in response to changes in glucose concentration, using perfused pancreas preparations. Basal insulin secretion at a blood glucose level of 5.6 mmol/l was significantly higher and basal glucagon secretion significantly lower in streptozotocin-induced diabetic rats than in controls, and neither high (16.7 mmol/l) nor low (1.4 mmol/l) blood glucose concentrations influenced insulin or glucagon secretion. Addition of 10^–6 mol/l ACh to the perfusate increased glucose-stimulated insulin secretion. Also, 10^–6 mol/l ACh, 10^–7 mol/l norepinephrine, as well as a combination of both, induced marked glucagon secretion, this was suppressed by high blood glucose level. Although simultaneous addition of 10^–6 mol/l ACh and 10^–7 mol/l norepinephrine induced only a slight increase in glucagon secretion in response to glucopenia, there was a significant increase in glucagon secretion in conjunction with an ambient decrease in insulin. Histopathological examination revealed a marked decline in acetylcholinesterase and monoamine-oxidase activities in the islets of streptozotocin-induced diabetic rats. We speculate that reduction of the potentiating effects of ACh and norepinephrine lessens glucose sensitivity of islet beta and alpha cells in this rat model of diabetes.Abbreviations STZ Streptozotocin - STZD streptozotocin-induce diabetic - ACh acetylcholine - AChE acetylcholinesterase - NE norepinephrine - MAO monoamine-oxidase     

Effect of glucagon antibodies on plasma glucose,insulin and somatostatin in the fasting and fed rat

Summary A potent high-titre glucagon antibody pool was used to induce a state of acute glucagon deficiency in order to investigate the importance of glucagon in maintaining euglycaemia in the fed and fasted anaesthetised rat. Binding characteristics of the antiserum and evidence of its neutralisation of the biological effects of exogenous glucagon are described. The amount of antibody administered was capable of neutralising up to 12 times the total content of glucagon (approximately 1nmol) in the rat pancreas. The hyperglycaemic response to 1.43 nmol exogenous glucagon was significantly inhibited in the rat by glucagon antibodies given intravenously or intraperitoneally (p < 0.001). However, no changes in plasma glucose occurred in rats fasted 16 h (4.35±0.1 mmol/l or 24 h (4.0±0.05 mmol/l) after antibody administration. The same dose of glucagon antibodies produced no change in plasma glucose (6.1±0.2 mmol/l), immunoreactive insulin (1.85±0.05 g/l) or immunoreactive somatostatin (110±30 ng/l) in rats after antibody administration. Antibody excess, equivalent to a binding capacity for glucagon of 40 nmol/l in the plasma of recipient animals, was demonstrable at all times after passive immunisation. The absence of any affect on glucose concentrations following immunoneutralisation of glucagon suggests that glucagon secretion may not be a major factor in the maintenance of euglycaemia in the rat.     

Effect of ventromedial hypothalamic lesions on the secretion of somatostatin,insulin, and glucagon by the perfused rat pancreas

Somatostatin, insulin, and glucagon secretion by the perfused pancreas were studied in adult female rats 10 days after ventromedial hypothalamic (VMH) lesions and in sham operated controls to assess the role of their hypothalamic control. Insulin secretion was significantly greater in VMH-lesioned rats both under basal conditions and after stimulation by theophylline and arginine plus theophylline. Basal glucagon secretion was greater in VMH-lesioned rats as was the glucagon response to theophylline alone and in combination with arginine. Basal somatostatin secretion was similar in VMH and control rats but somatostatin secretion induced by theophylline and by arginine plus theophylline was significantly increased in VMH-lesioned rats. Both the pancreatic content and concentration of somatostatin were increased in VMH-lesioned rats. These results indicate the presence of hyperresponsiveness of A, B, and D cells following VMH destruction and provide new evidence for a role of the hypothalamus in the regulation of pancreatic somatostatin secretion.     

Effect of neurotensin on insulin, glucagon, and somatostatin release from isolated pancreatic islets.

The effects of neurotensin on the release of insulin, glucagon, and somatostatin were investigated in isolated pancreatic islets prepared from 3- to 4-day-old rats and maintained in culture for 48 h before use. Islets were incubated for 20 and 60 min in the presence of 3 or 23 mM glucose with or without neurotensin. In 20-min incubations at 3 mM glucose, neurotensin (10-100 nM) increased the release of insulin, glucagon, and somatostatin by 60%, 90%, and 110%, respectively. These increases were not detected in 60-min incubations. Neurotensin (100 nM) inhibited the release of both insulin (by 60-90%) and somatostatin (by 100%) which was induced by 23 mM glucose in 60-min incubations; this inhibitory effect could be detected with neurotensin at a concentration of 1 nM. Neurotensin also significantly inhibited the elevations in glucagon, insulin, and somatostatin release induced by 20 mM arginine. It is concluded that neurotensin exerts a dual effect on the endocrine pancreas in vitro: 1) at low glucose concentration and over short term (20 min) incubations, the peptide stimulates insulin, glucagon, and somatostatin release; and 2) under stimulated conditions (high glucose or arginine), neurotensin inhibits insulin, glucagon, and somatostatin release.     

Role of glucose and insulin in the dynamic regulation of glucagon release by the perfused rat pancreas

The effect of glucose upon the release of glucagon and insulin from the perfused rat pancreas in vitro was studied by varying both the concentration of glucose (from 3.3 to 4.6, 8.5, or 11.1 mmol/l) and the time of exposure to an elevated concentration of the sugar (5, 10 or 23 min). The results suggest that the amount of insulin released during the early period of stimulation could contribute to both the speed and extent of the inhibition in glucagon release. The rate of recovery from inhibition in the A cell, however, appeared to be independent of insulin and was related, in a dose-dependent and time-dependent manner, only to the glucose stimulus. It is suggested that a direct effect of glucose upon the A cell is involved in the physiological regulation of glucagon secretion. An indirect effect of glucose, as mediated via insulin release, may contribute to the rapidity and magnitude of inhibition in A cell secretory activity.     

Inhibition of glucagon and insulin secretion from the perfused rat pancreas by a B-cell-selective somatostatin analog

The isolated perfused rat pancreas was used to study the effects of somatostatin and the analog des-Asn⁵-[D-Trp⁸, D-Ser¹³]-somatostatin on arginine-stimulated insulin and glucagon secretion. Even though the analog was found to inhibit glucagon secretion at concentrations of 10 and 100 ng/ml, it had a relatively more inhibitory effect on the B cell than on the A cell than did somatostatin itself. These data suggest that the A- and B-cell receptors for these two peptides differ.     

Glucose dependency of arginine vasopressin-induced insulin and glucagon release from the perfused rat pancreas

The purpose of this study was to investigate the glucose dependency of arginine vasopressin (AVP)-induced insulin, glucagon, and somatostatin release from the perfused rat pancreas. AVP (30 or 300 pmol/L) was tested in the presence of a glucose concentration of 0, 1.4, 5.5 (basal level), or 20 mmol/L. The rates of insulin release at 0 and 1.4 mmol/L glucose were approximately 70% to 80% and 60% to 70% less, respectively, than that at the baseline level. AVP (30 or 300 pmol/L) failed to change insulin release at 0 and 1.4 mmol/L glucose. At the basal glucose level, AVP (300 pmol/L) induced a biphasic insulin release, a peak followed by a sustained phase. In addition, the combination of glucose (20 mmol/L) and AVP (300 pmol/L) induced a higher insulin peak and sustained phase than 20 mmol/L glucose alone. The rates of glucagon release at 0 and 1.4 mmol/L glucose were about 3- and 2-fold more, respectively, than that at the baseline level. At 0 and 1.4 mmol/L glucose, both 30 and 300 pmol/L AVP caused a higher glucagon peak and sustained phase than 0 and 1.4 mmol/L glucose alone. At the basal glucose level, AVP (30 or 300 pmol/L) induced a biphasic glucagon release, a peak followed by a sustained phase. The rate of glucagon release at 20 mmol/L glucose was approximately 60% to 70% less than that at the baseline level. When AVP (300 pmol/L) was administered in 20 mmol/L glucose, it induced a transient glucagon peak, which was 2.4-fold of the baseline level. At all glucose concentrations tested, AVP (30 or 300 pmol/L) failed to change somatostatin release. These results suggested that (1) hypoglycemia directly increases glucagon and decreases insulin release; (2) AVP induces insulin and glucagon release by a direct action on beta and alpha cells, respectively; (3) AVP induces insulin and glucagon release in a glucose-dependent manner-the higher the glucose concentration, the greater the enhancement of AVP-induced insulin release, whereas the lower the glucose concentration, the higher the enhancement of AVP-induced glucagon release; and (4) alpha cells are more sensitive to AVP than beta cells in hormone release.     

Kisspeptin-13 inhibits insulin secretion without affecting glucagon or somatostatin release: study in the perfused rat pancreas

Kisspeptins are a family of peptides encoded by the KISS1 gene, which binds to G-protein-coupled receptor (GPR54), an orphan GPR54 related to galanin receptors. Endogenous forms composed of 54, 14, and 13 amino acids have been identified. Kisspeptin and GPR54 mRNAs have been detected in pancreatic B and A cells. Furthermore, kisspeptin-54 has been shown to slightly stimulate the last phase of glucose-induced insulin secretion in mouse and human islets and to inhibit insulin release in MIN6 cells. We have investigated the effect of kisspeptin-13 on insulin, glucagon, and somatostatin secretion. The study was performed in the perfused rat pancreas. Glucose, arginine, carbachol, and exendin-4 were used as secretagogues. Hormones were measured by RIA. Kisspeptin-13 reduced glucose-induced insulin secretion in a dose-dependent manner (IC(50)=1.2 nM) and inhibited the insulin responses to both carbachol and exendin-4. Kisspeptin-13 blocked arginine-induced insulin secretion without affecting the glucagon or somatostatin responses to this amino acid, thus indicating that kisspeptin-13 influences B cells directly, rather than through an A- or D-cell paracrine effect. The reduction of the insulin response to exendin-4 induced by kisspeptin-13 was also observed in pertussis toxin-treated rats, thus suggesting an inhibition independent of G(i) proteins. In view of the potent insulinostatic effect of kisspeptin-13, it is tempting to speculate that kisspeptins may be implicated in the regulation of B-cell secretion.     

Effect of a long acting glucagon selective somatostatin analogue on plasma glucose,insulin and glucagon levels in the anaesthetized rat during arginine infusion

Summary The effects of somatostatin and a long acting, glucagon selective somatostatin analog (des-Ala¹Gly²[His^4,5-D-Trp⁸]-somatostatin), were studied during arginine tolerance tests in normal anaesthetized rats. Arginine infusion in control animals resulted in a rapid increase in plasma insulin and glucagon, and an increase of 15±5 mg/dl in plasma glucose. Somatostatin infusion (1 mg/kg/h) resulted in suppression of basal insulin secretion and a decrease in arginine-induced insulin and glucagon release. Glucose levels increased rapidly during the combined arginine-somatostatin infusion reaching a peak of 72±10 mg/dl above basal levels. Similar results were obtained when somatostatin was injected SC (1 mg/kg) at times 0, 15, 30, and 45 minutes (arginine infused from 30–60 minutes). A single injection (1 mg/kg) of the long-acting somatostatin analogue resulted in significant inhibition of basal insulin and glucagon release; during arginine infusion glucagon levels rose only slightly, the insulin response was, however, nearly normal, and only a small arginine-induced increase in glucose levels was observed. Carbohydrate absorption was not influenced by either somatostatin or the analogue.     

Differential sensitivity to somatostatin of pancreatic polypeptide, glucagon and insulin secretion from the isolated perfused canine pancreas

This dose-response study deals with the relative inhibitory effect of somatostatin on the acetylcholine-stimulated release of pancreatic polypeptide (PP), glucagon, and insulin from the isolated canine pancrease. Somatostatin in picomolar doses potently inhibited insulin and glucagon secretion, whereas PP secretion was relatively insensitive. Also, in the absence of acetylcholine, somatostatin exerted a preferential inhibition of the release insulin and glucagon compared with PP. These findings point to a physiologically important role of somatostatin for the secretion of insulin and glucagon, but probably not for PP.