Effects of the Neurohypophysial Hormones on Insulin Secretion

Publisher Website
Google Scholar
Abstract
Single doses of synthetic oxytocin or vasopressin were rapidly injected into the jugular vein to study their effects on insulin secretion in anesthetized dogs. Oxytocin at a dose of 100 mU/kg resulted in a prompt, striking and short-lived elevation in the immunoreactive insulin level in pancreatic effuent plasma, prior to appearance of hyperglycemia. With a similar dosage of either arginine- or lysine-vasopres-sin, a delayed, gradual and less marked increase in the pancreatic venous plasma level of immunoreactive insulin was induced, unaccompanied by hyperglycemia. The rate of pancreatic venous blood flow did not change following injection of oxytocin, whereas an abrupt, significant depression occurred after vasopressin, but to a much lesser extent than the rise in the pancreatic plasma level of immunoreactive insulin. A significant enhancement of the immunoreactive insulin level in femoral arterial plasma was also observed in 3 groups, with peaks a few minutes later than in the pancreatic venous plasma. With a dosage of less than 5 mU/kg, oxytocin produced negligible or no increase in plasma insulin levels. Section of the dorsal vagus nerve failed to abolish the hyperinsulinemia and hyperglycemia evoked by oxytocin. From these results it was concluded that both oxytocin and vasopressin are able to increase insulin secretion, that the rise in insulin release may apparently be initiated by unidentified factors other than the hyperglycemia itself produced by the hormones; and that the effect of these 2 hormones on insulin secretion is mediated by different mechanisms.