Effect of glucagon antiserum on somatostatin,glucagon and insulin release from the isolated perfused rat pancreas

In order to elucidate the effect of glucagon antiserum on the endocrine pancreas, the release of somatostatin, glucagon, and insulin from the isolated perfused rat pancreas was studied following the infusion of arginine both with and without pretreatment by glucagon antiserum. Various concentrations of arginine in the presence of 5.5 mM glucose stimulated both somatostatin and glucagon secretion. However, the responses of somatostatin and glucagon were different at different doses of arginine. The infusion of glucagon antiserum strongly stimulated basal secretion in the perfusate total glucagon (free + antibody bound glucagon) and also enhanced its response to arginine, but free glucagon was undetectable in the perfusate during the infusion. On the other hand, the glucagon antiserum had no significant effect on either insulin or somatostatin secretion. Moreover, electron microscopic study revealed degrannulation and vacuolization in the cytoplasm of the A cells after exposure to glucagon antiserum, suggesting a hypersecretion of glucagon, but no significant change was found in the B cells or the D cells. We conclude that in a single pass perfusion system glucagon antiserum does not affect somatostatin or insulin secretion, although it enhances glucagon secretion.     

Effect of obestatin on insulin, glucagon and somatostatin secretion in the perfused rat pancreas

Obestatin is a 23-amino acid peptide derived from preproghrelin, purified from stomach extracts and detected in peripheral plasma. In contrast to ghrelin, obestatin has been reported to inhibit appetite and gastric motility. However, these effects have not been confirmed by some groups. Obestatin was originally proposed to be the ligand for GPR39, a receptor related to the ghrelin receptor subfamily, but this remains controversial. Obestatin and GPR39 are expressed in several tissues, including pancreas. We have investigated the effect of obestatin on islet cell secretion in the perfused rat pancreas. Obestatin, at 10 nM, inhibited glucose-induced insulin secretion, while at 1 nM, it potentiated the insulin response to glucose, arginine and tolbutamide. The potentiated effect of obestatin on glucose-induced insulin output was not observed in the presence of diazoxide, an agent that activates ATP-dependent K(+) channels, thus suggesting that these channels might be sensitive to this peptide. Obestatin failed to significantly modify the glucagon and somatostatin responses to arginine, indicating that its stimulation of insulin output is not mediated by an alpha- or delta-cell paracrine effect. Our results allow us to speculate about a role of obestatin in the control of beta-cell secretion. Furthermore, as an insulinotropic agent, its potential antidiabetic effect may be worthy of investigation.     

Action of glibenclamide on glucagon and insulin secretions studied on isolated and perfused pancreas of the rat]

Glibenclamide stimulates the insulin secretion by the isolated and perfused rat pancreas, but does not inhibit glucagon secretion when the perfusion liquid contains 1.5 g/I glucose. In the absence of glucose in the perfusion medium, glibenclamide stimulates both insulin and glucagon secretions.     

Effects of adenosine on the secretions of glucagon and insulin of isolated ad perfused pancreas of the rat

The effects of adenosine on insulin and glucagon secretions were studied using the isolated perfused rat pancreas. The secretion of glucagon was stimulated by adenosine at concentrations ranging from 1.65 to 165 mumol/l, in the presence of glucose 0.5 g/l; the stimulation was immediate, but transient and was dose-dependent. Insulin secretion was not changed by adenosine in the presence of glucose 0.5 g/l; in the presence of glucose 1.5 g/l, adenosine at 1.65 and 16.5 mumol/l did not significantly modify insulin secretion. But at 165 mumol/l adenosine induced a progressive increase in time after the 5th minute. The A cell appears then to be much more sensitive to adenosine than the B cell.     

Effects of pancreastatin on insulin, glucagon and somatostatin secretion by the perfused rat pancreas

Pancreastatin is a novel peptide, isolated from porcine pancreatic extracts, which has been shown to inhibit glucose-induced insulin release "in vitro". To achieve further insight into the influence of pancreastatin on pancreatic hormone secretion, we have studied the effects of this peptide on unstimulated insulin, glucagon and somatostatin output, as well as on the responses of these hormones to glucose and to tolbutamide in the perfused rat pancreas. Pancreastatin strongly inhibited unstimulated insulin release as well as the insulin responses to glucose and to tolbutamide. It did not significantly affect glucagon or somatostatin output under any of the above-mentioned conditions. These findings suggest that pancreastatin inhibits B-cell secretory activity directly, and not through an A-cell or D-cell paracrine effect.     

Adrenergic modulation of insulin and glucagon secretion from the isolated perfused rat pancreas

In order to observe the effect of the adrenergic system on pancreatic glucagon secretion in the isolated perfused rat pancreas, phenylephrine, an alpha-adrenergic agonist, and isoproterenol, a beta-adrenergic agonist, were added to the perfused solution. 1.2 microM phenylephrine suppressed glucagon secretion at 2.8 mM glucose, and it also decreased insulin secretion at 11.1 mM glucose. 240 nM isoproterenol enhanced glucagon secretion not only at 2.8 mM glucose, but also at 11.1 mM glucose, as well as insulin secretion at 11.1 mM. In order to study the role of intra-islet noradrenalin, phentolamine, an alpha-adrenergic antagonist, and propranolol, a beta-adrenergic antagonist, were infused with the perfused solution. 10 and 100 microM phentolamine caused an increase in insulin secretion, and 25 microM propranolol decreased insulin secretion, while they did not cause any change in glucagon secretion. From these results, it can be concluded that alpha-stimulation suppresses not only insulin but also glucagon secretion, while beta-stimulation stimulates glucagon secretion, as well as insulin secretion. Intra-islet catecholamine may have some effect on the B cell, whereas it seems to have no influence on the A cell.     

Effect of exercise training on insulin and glucagon release from perfused rat pancreas

The effect of physical training on insulin and glucagon release in perfused rat pancreas was examined in the spontaneously exercised group running in a wheel cage an average of 1.4 km/day for 3 weeks and in the sedentary control group kept in the cage whose rotatory wheel was fixed on purpose. Pancreatic immunoreactive insulin (IRI) responses to glucose and arginine were reduced by 28% and 47.8% respectively in trained rats compared with untrained rats, while IRI content of the pancreas was similar in these two groups. The demonstrated decrease in insulin secretion of the beta-cell of the trained rats, in response to the glucose and arginine stimulations, may be functional in nature. On the other hand, neither pancreatic glucagon immunoreactivity (GI) response to glucose and arginine nor GI content of the pancreas was modified by exercise training. These results demonstrate that exercise training reduces IRI responses to glucose as well as to arginine stimulations, but does not modify any secretory response of pancreatic GI.     

Effects of neuromedin B on insulin and glucagon release from the isolated perfused rat pancreas

The effect of neuromedin B (NMB) on insulin and glucagon release was studied in isolated perfused rat pancreas. Infusion of NMB (10 nM, 100 nM and 1 microM) did not affect the insulin release under the perusate conditions of 5.5 mM glucose plus 10 mM arginine and 11 mM glucose plus 10 mM arginine, although 10 nM NMB tended to slightly suppress it under the perfusate condition of 5.5 mM glucose alone. The degree of stimulation of insulin release provoked by the addition of 5.5 mM glucose to the perfusate was not affected by the presence of 10 nM NMB. The glucagon release was slightly stimulated by the infusion of 100 nM and 1 microM NMB but not by 10 nM NMB under the perfusate condition of 5.5 mM glucose plus 10 mM arginine. The effect of C-terminal decapeptide of gastrin releasing peptide (GRP-10) was also examined and similar results were obtained; 10 nM and 100 nM GRP-10 did not affect insulin release and 100 nM GRP-10 stimulated glucagon release under the perfusate condition of 5.5 mM glucose plus 10 mM arginine. The present results concerning glucagon release are consistent with the previous results obtained with isolated perfused canine and porcine pancreas. However, the results regarding insulin release are not. Species differences in insulin release are also evident with other neuropeptides such as substance P and the mechanism of such differences remains for be clarified.     

Effect of beta-hydroxybutyrate and acetoacetate on insulin and glucagon secretion from perfused rat pancreas

To elucidate the physiological significance of ketone bodies on insulin and glucagon secretion, the direct effects of beta-hydroxybutyrate (BOHB) and acetoacetate (AcAc) infusion on insulin and glucagon release from perfused rat pancreas were investigated. The BOHB or AcAc was administered at concentrations of 10, 1, or 0.1 mM for 30 min at 4.0 ml/min. High-concentration infusions of BOHB and AcAc (10 mM) produced significant increases in insulin release in the presence of 4.4 mM glucose, but low-concentration infusions of BOHB and AcAc (1 and 0.1 mM) caused no significant changes in insulin secretion from perfused rat pancreas. BOHB (10, 1, and 0.1 mM) and AcAc (10 and 1 mM) infusion significantly inhibited glucagon secretion from perfused rat pancreas. These results suggest that physiological concentrations of ketone bodies have no direct effect on insulin release but have a direct inhibitory effect on glucagon secretion from perfused rat pancreas.     

Effect of the alpha 2-blocker DG-5128 on insulin and somatostatin release from the isolated perfused rat pancreas

2[2-(4.5-Dihydro-1H-imidazol-2-yl)-1-phenylethyl] pyridine dihydrochloride sesquihydrate (DG-5128) is an alpha 2-specific-adrenergic antagonist. We have studied the effect of DG-5128 on insulin and somatostatin release from the isolated perfused rat pancrease. DG-5128 stimulated somatostatin and insulin release not only at a low glucose concentration but also at a high glucose concentration. These findings suggest that an alpha 2-adrenergic receptor plays an important role in the regulation of insulin and somatostatin secretion.     

Bombesin stimulates the release of insulin and glucagon, but not pancreatic somatostatin, from the isolated perfused dog pancreas.

Synthetic bombesin, perfused in the isolated canine pancreas at a rate of 340-380 ng/min for 10 min, elicited a 4-fold rise in insulin to a peak at 2 min; a rapid decline followed discontinuation of bombesin. Glucagon rose by 50% to a peak at 6 min, but remained elevated after discontinuation of the bombesin. Somatostatin-like immunoreactivity was not significantly affected by perfusion with bombesin.     

Effects of salicylate on insulin and glucagon secretion by the isolated and perfused rat pancreas

The effects of sodium salicylate, a prostaglandin synthesis inhibitor, on glucose-induced secretion of insulin and glucagon by the isolated perfused rat pancreas have been studied. Sodium salicylate inhibited both basal (2.8 mM glucose) and stimulated (16.7 mM glucose) insulin release in a dose dependent manner (1, 5 and 10 mM). This inhibition is not interpretable in terms of a simple inhibition of cyclooxygenase by sodium salicylate. Basal glucagon release was not changed by 1 mM sodium salicylate but the latter partially blocked its inhibition by 16.7 mM glucose. Higher doses of sodium salicylate (5 and 10 mM) inhibited basal glucagon secretion without affecting its response to 16.7 mM glucose. These findings suggest a predominant stimulatory action of endogenous prostaglandins on glucagon release.     

Somatostatin, insulin and glucagon secretion by the perfused pancreas from the cysteamine-treated rat

In rats, administration of a single dose of cysteamine (300 mg/kg, intragastrically) induces a depletion of pancreatic somatostatin content (approximately 60%) without modifying pancreatic insulin or glucagon content. In perfused pancreases from cysteamine-treated rats, there was a lack of somatostatin response to glucose, arginine or tolbutamide. In the absence of stimulated somatostatin release, the secretory responses of insulin and glucagon to glucose, to arginine, and to tolbutamide were not significantly different from those observed in pancreases from control rats. Our data do not support the concept that pancreatic somatostatin plays a major role in the control of insulin and glucagon release.     

The effect of ventromedial hypothalamic nuclei destruction on somatostatin and insulin release from the isolated perfused rat pancreas

The effect of electrolytic lesions in the ventromedial hypothalamic nuclei (VMH) on somatostatin and insulin release was studied using the isolated perfused rat pancreas. Obesity gradually developed in the rats after placement of the VMH lesions, and fasting insulin levels determined immediately before the isolation of the pancreas were significantly higher than those in sham-operated controls. In the presence of 4.4 mM glucose, both perfusate somatostatin and insulin responses to arginine were significantly greater than in the controls, suggesting that VMH lesions cause not only hypersecretion of insulin but hypersecretion of somatostatin as well.     

Effect of leptin on insulin, glugacon and somatostatin secretion in the perfused rat pancreas.

We have investigated the effect of rat leptin as well as the 22-56 fragment of this molecule on pancreatic hormone secretion in the perfused rat pancreas. In pancreases from fed rats, leptin failed to alter the insulin secretion elicited by glucose, arginine or tolbutamide, but inhibited the insulin response to both CCK-8 and carbachol, secretagogues known to act on the B-cell by increasing phospholipid turnover. This insulinostatic effect was also observed with the 22-56 leptin fragment. In pancreases obtained from 24-hour fasted rats, no effect of leptin on carbachol-induced insulin output was found, perhaps as a consequence of depressed B-cell phospholipid metabolism. Leptin did not influence glucagon or somatostatin release. Our results do not support the concept of leptin as a major regulator of B-cell function. Leptin inhibition of carbachol-induced insulin output might reflect a restraining effect of this peptide on the cholinergic stimulation of insulin release.     

Effects of insulin, leptin, and glucagon on ghrelin secretion from isolated perfused rat stomach

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, was originally purified from the rat stomach. Although ghrelin has been recognized as an important regulator of energy metabolism, the regulation of the ghrelin secretion is largely unknown. Here, we examined the direct effects of insulin, leptin, and glucagon on the release of ghrelin from the isolated rat stomach. The isolated pancreas-spleen-duodenum deprived preparation of rat stomach was used. After a baseline control infusion into the left gastric artery, insulin, leptin, or glucagon were infused for 15 min at concentrations of 0.1, 1, and 10 nM. The levels of immunoreactive ghrelin in the venous effluents were measured with a radioimmunoassay. Insulin and leptin inhibited ghrelin secretion dose-dependently (total amount of ghrelin release: insulin at 1 nM, 73.5+/-7.3% of the control infusion; leptin at 1 nM, 81.8+/-2.5% of the control infusion; n=5, P<0.05), while glucagon increased it dose-dependently (total amount of ghrelin released at 10 nM was 143.9+/-19.3% of the control infusion; n=5, P<0.01). These results indicate that the ghrelin responses observed in vivo could be due to direct effects of multiple hormonal signals on the stomach.