膵ホルモン分泌・合成に関する研究 : 特にtris(hydroxymethyl)aminomethaneの膵Langerhans島insulin, glucagon, somatostatin分泌並びにinsulin合成に及ぼす影響
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The Golgi apparatus and Golgi-endoplamic reticulum-lysosomal (GERL) system have known to be important subcellular organelles in endocrine cells. In pancreatic B cells these organelles have been considered to be the site for the conversion of proimsulin to insulin largely by autoradiographic studies. The Golgi membrane and the GERL system in various cells have recentry been found to be affected by tris(hydroxymethyl)aminomethane (Tris). To my knowledge no reports have been encountered to clarify the relationships of the Golgi area and insulin biosynthesis biochemically using agents to selectively affect the area. Therefore, the present study was carried out to evaluate the effect of Tris on insulin biosynthesis and release of insulin and the morphology of islets. Besides, glucagon and somatostatin release were studied. Rat islets were isolated by collagenase method and preincubated in Krebs-Henseleit bicarbonate buffer (KHBB, pH 7.4) containing 3.3 mM glucose and 0.5% bovine serum albumin (BSA) at 37℃ for 20 min under a gas phase of 95% O_2-5% CO_2. Thereafter, islets were incubated for 60 min in KHBB containing 0.5% BSA and glucose (3.3, 8.3 or 16.7 mM) or 3.3 mM glucose plus 20 mM arginine with and without Tris (1 or 10 mM) under the same conditions as in preincubation. Insulin, glucagon and somatostatin release in the medium were radioimmunoassayed. Some islets after incubation were subjected to measurement of immunoreactive proinsulin and insulin contents. For studies on insulin biosynthesis islets were incubated in KHBB containing 3^H-Ieucine and 16.7 mM glucose with and without 10 mM Tris for 120 min. Insulin in the islets was extracted with 75% acid ethanol. The extracts were fractionated into proinsulin and insulin on Bio-gel P-30 with 3 N acetic acid as eluate and the radioactivity of both fractions was counted. Tris suppressed glucose-induced insulin release, whereas it did not affect the glucagon or somatostatin release. Arginine-induced insulin release was suppressed by 1 and 10 mM Tris, whereas the glucagon and somatostatin release were not by 1 mM Tris. However, it was suppressed by 10 mM Tris. Islets preincubated by 10 mM Tris for 20 min showed the suppression of insulin release by 8.3 mM glucose and 20 mM arginine. Immunoreactive proinsulin and insulin contents in 10 mM Tris-treated islets were significantly higher than those in islets without Tris treatment. 3^H-Ieucine incorporation into the insulin fraction was suppressed by Tris, but the sum of the radioactivity of both proinsulin and insulin fractions were not influenced. The radioactivity ratio of proinsulin and insulin fraction increased in Tris-treated islets. Electron-microscopically, the Golgi apparatus and the GERL system of B cells were affected, but those of A cells were not. These observations indicate that Tris seems to destroy selectively the Golgi apparatus and the GERL system in the islet B cells and the area may play a role in insulin biosynthesis and secretion in pancreatic B cells, and that Tris may become an useful agent to investigate the mechanism of processing of proinsulin to insulin. And Tris also may make an experimental diabetic model for hyperproinsulinemia which is observed in the early stage of type II diabetes.
- 神戸大学の論文
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関連論文
- 膵ホルモン分泌・合成に関する研究 : 特にtris(hydroxymethyl)aminomethaneの膵Langerhans島insulin, glucagon, somatostatin分泌並びにinsulin合成に及ぼす影響
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