Some acute effects of intracerebroventricular neuropeptide Y on insulin secretion and glucose metabolism in the rat.

Acute administration of neuropeptide Y(NPY) into the hypothalamus and cerebral ventricles can stimulate insulin secretion in the absence of available food. However, the relationship of this effect to blood glucose and other hormones which regulate glucose metabolism remains unclear. The purpose of this study was to compare the effects of NPY injected into the third ventricle (ICV) on serum insulin, glucose, glucagon, corticosterone and non-esterified fatty acids. Studies were performed on conscious, unrestrained female rats, not given access to food. ICV NPY, 2 and 5 micrograms produced an increase in serum insulin and glucagon, while the 5 micrograms dose only increased plasma glucose transiently and increased non-esterified fatty acids for a longer period. Corticosterone was not affected by ICV NPY. The insulinaemic response to i.v. glucose, 0.5 g/kg was doubled by ICV NPY, 4 micrograms. The maximal insulin levels were 113 +/- 18 for ICV NPY versus 67 +/- 8 microU/ml for ICV saline-treated animals. The glycaemic response was not altered. The hypoglycaemic response to i.v. insulin, 0.15 U/kg was significantly attenuated by ICV NPY, 5 micrograms. We concluded that ICV NPY promotes insulin secretion in the absence of available food and may potentiate the insulinaemic response to hyperglycaemia. Furthermore, possibly through its effects on glucagon and non-esterified fatty acids, ICV NPY may decrease the ability of insulin to control glucose metabolism.