Tomohiko Taminato

Characteristic features of insulin secretion in the streptozotocin-induced NIDDM rat model

Male Wistar neonatal rats at age 1.5 days (Streptozotocin [STZ] group 1) and 5 days (STZ group 2) received a subcutaneous injection of 90 mg/kg STZ. After 10 weeks, the rats were subjected to an oral glucose tolerance test (OGTT) (2 g/kg) in a conscious state. The pancreas perfusion experiments were conducted 2 weeks after the OGTT. There was no statistical difference in insulin response between the STZ group 1 and the control group. On the contrary, in the STZ group 2, the plasma glucose response to OGTT showed a typical diabetic pattern, and the plasma insulin response was markedly blunted. In the isolated perfused rat pancreas, the infusion of glucose evoked a biphasic insulin secretion, but the peak insulin levels induced by 16.7 mmol/L glucose in the STZ group 1 were significantly lower than in the controls. We further investigated characteristics of insulin secretion in response to different secretagogues in these animal models using isolated islets. The insulin content of the islets of the STZ group 1 were about one half that of the control group. Insulin secretion in the STZ group 1 was impaired in response to glucose stimulation, but remained normal in response to arginine and forskolin. These results suggest that insulin secretion of non-insulin-dependent diabetes mellitus (NIDDM) rat model is selectively impaired in response to glucose stimulation, possibly due to a disorder of signaling mechanism other than adenylate cyclase.

Effect of Antisomatostatin γ-Globulin on Gastrin Release in Rats

In order to determine the mechanism of endogenous gastric somatostatin in the regulation of gastrin release, antisomatostatin rabbit γ-globulin was administered in vivo and in vitro in the rat. First, in rats anesthetized by chloral hydrate, intravenous injection of 1 ml antisomatostatin rabbit γ-globulin had no significant effect on plasma gastrin levels. Second, basal gastrin release from the isolated perfused rat stomach was not affected by the administration of antisomatostatin rabbit γ-globulin (1:99 and 1:1 dilutions). Third, the addition of antisomatostatin rabbit γ-globulin (1:99) to incubated rat antral mucosa, however, significantly increased the basal gastrin release. From these results, it is concluded that antral somatostatin exerts its inhibitory effect on basal gastrin release mainly not through the circulation but via paracrine pathways.

Epidermal growth factor stimulates prostaglandin E release from isolated perfused rat stomach.

Summary Effect of epidermal growth factor, a potent stimulator of growth in many tissues, on immunoreactive-prostaglandin E secretion from isolated perfused rat stomach was investigated. Both mouse and human epidermal growth factor (10 −7 M) evoked a marked increase in immunoreactive prostaglandin E secretion from the rat stomach. Since prostaglandin E is a potent inhibitor of gastric acid secretion, the present study suggests that the increase in prostaglandin E secretion from the stomach may be responsible for the antisecretory effect of epidermal growth factor on gastric acid.

A functional study of a case of glucagonoma exhibiting typical glucagonoma syndrome.

A 46‐year‐old man had a 7‐year history of severe rash, which was then diagnosed as necrolytic migratory erythema. He had a weight loss of 6 kg, abnormal glucose tolerance test findings, anemia, glossitis, hair loss, and hypoproteinemia. Plasma amino acids levels were significantly decreased, and the fasting plasma glucagon (IRG) level was high at 5000 to 8000 pg/ml. Circulating IRG significantly increased after oral glucose loading, meal ingestion, and arginine infusion, and decreased with somatostatin infusion and insulin‐induced hypoglycemia. No other gut or pancreatic hormone levels in plasma were elevated. Plasma IRG was eluted by gel‐filtration, mainly in the position of true glucagon (MW 3500) by antiserum 30K. The rash was markedly improved after infusion of amino acids. Computerized tomography (CT) scan and celiac angiography revealed a large pancreatic tumor with multiple liver and lymph node metastases. The pancreatic tumor was totally resected, and was identified as glucagonoma by immunohistochemical technique. Since the plasma IRG levels remained high after surgery, the patient received dimethyltriazenoimidazole carboxamide therapy. After several courses of this treatment, plasma IRG levels decreased to 1000 to 2000 pg/ml, and the hepatic metastases were remarkably diminished in size.

Plasma immunoreactive somatostatin levels in rat hypophysial portal blood: Effect of glucagon administration

Abstract Plasma somatostatin levels of the hypophysial portal blood was examined in urethane-anesthetized rats. Portal blood was withdrawn at a rate of 4.7 μl/min via a cannula placed over the stump of the pituitary stalk, collected into the ice-cold tube at 20min intervals before and after the intraventricular injection of test materials. Immunoreactive somatostatin extracted from the plasma with acid acetone was measured by a specific radioimmunoassay. Basal plasma somatostatin concentrations, 778±52pg/ml (means±SE), did not significantly change after the administration of control solution (0.1N acetic acid in physiological saline), while intraventricular injection of glucagon (2, 10 and 50 μg) caused a significant and dose-related increase in plasma somatostatin during the first 20min. These results suggested that somatostatin release from the median eminence into the hypophysial portal vessel was stimulated by glucagon, although the physiologycal significance remains to be clarified.

Selective impairment of the cytoplasmic Ca2+ response to glucose in pancreatic β cells of streptozocin-induced non-insulin-dependent diabetic rats☆

Pancreatic islets from the streptozocin-induced non-insulin-dependent diabetes mellitus (NIDDM) rat model showed a diminished insulin response to 16.7 mmol/L glucose, but the insulin response to arginine remained intact. To evaluate the importance of intracellular calcium concentration ([Ca2+]i) in the diminished insulin response to glucose, the [Ca2+]i of pancreatic beta cells was investigated using fura-2. Glucose produced heterogeneous responses of [Ca2+]i, which were in beta-cell clusters of both the control and NIDDM groups. Many cells showed initial slight decreases of [Ca2+]i, which were followed by gradual and large increments of [Ca2+]i after glucose stimulation of beta cells in the control group. On the other hand, the increase of [Ca2+]i in response to glucose was markedly diminished in beta cells of the NIDDM group compared with controls. The average lag time to [Ca2+]i elevation of beta cells in the NIDDM group was significantly longer than that of the control group. Arginine produced marked increases of [Ca2+]i, in contrast to the effect of glucose stimulation in the NIDDM group. These results suggest that the diminished and delayed [Ca2+]i increases in beta cells of NIDDM rats in response to glucose stimulation are responsible for the selectively impaired insulin response to glucose in the rat model of NIDDM.

Effects of prostaglandin E2 and D2 on gastric somatostatin and gastrin secretion

The effects of PGE2 and PGD2 on gastric somatostatin and gastrin releases were investigated using the isolated perfused rat stomach. In the presence of 5.5 mM glucose, the infusion of PGE2 elicited a significant augmentation in somatostatin release, but suppressed gastrin secretion from the perfusate. On the other hand, PGD2 did not affect somatostatin release, although the gastrin secretion decreased significantly, the same as after PGE2 infusion. These results suggest that PGE2 and PGD2 may be important in the regulation of gastric endocrine function, but that PGD2 does not affect gastric somatostatin secretion.

Effect of the α2-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.

Effects of naloxone on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin from the isolated perfused rat stomach

The effects of naloxone, an opiate antagonist, on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin were examined using the isolated perfused rat stomach prepared with vagal innervation. Naloxone (10(-6) M) significantly inhibited basal somatostatin secretion in the presence and absence of atropine and of hexamethonium, whereas basal GRP and gastrin secretion was not affected by naloxone. Electrical stimulation (10 Hz, lms duration, 10V) of the distal end of the subdiaphragmatic vagal trunks elicited a significant increase in both GRP and gastrin but a decrease in somatostatin. Naloxone (10(-6) M) failed to affect these responses in the presence or absence of atropine. On the other hand, when hexamethonium was infused, naloxone significantly inhibited both the GRP and gastrin responses to electrical vagal stimulation. Somatostatin secretion was unchanged by vagal stimulation during the infusion of hexamethonium with or without naloxone. These findings suggest that basal somatostatin secretion is under the control of an opiate neuron and that opioid peptides might be involved in vagal regulation of GRP and gastrin secretion.

GROWTH HORMONE MODULATION OF ARGININE‐INDUCED GLUCAGON RELEASE: STUDIES OF ISOLATED GROWTH HORMONE DEFICIENCY AND ACROMEGALY

Plasma glucagon and insulin responses to l‐arginine were compared in normal controls and patients with isolated growth hormone deficiency and acromegaly. Patients with isolated growth hormone deficiency were characterized by high plasma glucagon response and low plasma insulin response, whereas acromegalic patients showed exaggerated plasma glucagon response and almost normal insulin response. These results suggest that growth hormone is probably required for optimum function of the islets, and since hyperglucagonaemia was observed in both growth hormone deficiency and acromegaly, metabolic disturbances stemming from the respective primary diseases may affect glucagon secretion.