THE ROLE OF SEROTONIN IN CARBOHYDRATE METABOLISM. VII. IN VITRO OBSERVATIONS SUGGESTING ENHANCED RELEASE OF INSULIN IN RESPONSE TO SEROTONIN TREATMENT

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Abstract
The glycogen level of rat diaphragm incubated in serum of the serotonin-treated rat was higher than that in control serum. Either cysteine-treatment of the serum or induction of alloxan-diabetes in serum donor rats completely abolished this effect. Thus it was concluded that subcutaneous administration of serotonin resulted in an enhanced secretion of endogenous insulin. In the diaphragm obtained from serotonin-treated rat, the in vitro effect of insulin or epinephrine disappeared in phosphate-buffered saline but not in Krebs-Ringer bicarbonate solution. Diaphragms excised from alloxan-diabetic rats treated with serotonin were found to exhibit the ordinary response to insulin and epinephrine in either incubation medium. Since preincubation of diaphragm with insulin abolished the effect of added insulin in further incubation in phosphate-buffered saline, but not in Krebs-Ringer bicarbonate solution, serotonin-treated tissue was assumed to be bound with endogenous insulin as a result of accelerated pancreatic secretion. A possibility was suggested that serotonin is a physiological accelerator of insulin secretion in organism.