Regulation of insulin secretion studied with pieces of rabbit pancreas incubated in vitro

Publisher Website
Google Scholar
Abstract
The effect of various factors on the rate of release of insulin from pieces of rabbit pancreas incubated in vitro has been studied by estimating the insulin concentration in the medium after incubation by immunological assay with insulin-antibody precipitate, and the conditions necessary for eliciting consistent responses have been defined. Insulin release was accelerated by D-glucose at concentrations above 0.35-0.7 mg/ml and by D-mannose (3 or 6 mg/ml), but not by D-galac-tose, 3-O-methyo-D-glucose, D-fructose, D-ribose or sodium D-gluconate (3 mg/ml), D-2-deoxyglucose (3 or 6 mg/ml), N-acetyl-D-glucosamine (15 mg/ml) or D-mannoheptulose (3 mg/ml). The stimulating effect of glucose (3 mg/ml) on insulin release was abolished by mannoheptulose but not by 2-deoxyglucose, 3-O-methylglucose, ribose or N-acetylglucosamine. Insulin release at a low glucose concentration (0.6 mg/ml) was accelerated by tolbutamide (200 [mu]g/ml) but not by anoxia, 2,4-dinitrophenol, salicylate, p-phenylenediamine or phenazine methosulphate. The rate of insulin release at a high glucose concentration (3 mg/ml) was markedly diminished by anoxia, 2,4-dinitrophenol (250 [mu]M), salicylate (5 mM), p-phenylenediamine (1 mM) and phenazine methosulphate (100 [mu]M), but not by malonate (10 mM). The stimulating effect of tolbutamide (unlike that of glucose) was not influenced by mannoheptulose. The stimulating effect of glucose (3 mg/ml) on insulin release was augmented by the presence in the medium of glutamate, fumarate and pyruvate. At a low glucose concentration (0.6 mg/ml) neither these acids nor octanoate, acetoacetate or [beta] -hydroxybutyrate influenced the rate of insulin release. The stimulating effect of glucose (3 mg/ml) on insulin release was abolished by epinephrine (200 [mu]mg/ ml), and the effect of norepinephrine was suppressed by ergotamine tartrate (2.8 [mu]g/ml). Evidence is presented that the release of insulin by rabbit pancreas in vitro provides a suitable model for the behavior of [beta] -cells in vivo and for studying the influence of various factors on insulin secretion. The possible roles of glucose phosphorylation and of pathways of metabolism of glucose 6-phosphate in [beta] -cells in the stimulation of insulin release induced by glucose are discussed.