Vagal mediation of corticotropin-releasing-factor-induced increase in insulinemia in lean and genetically obese fa/fa rats.

The effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) on plasma glucose and insulin levels were investigated in lean Zucker (FA/FA) rats; i.c.v. CRF induced a rapid (within 1 min), marked, but transient increase in insulinemia that was not accompanied by any change in glycemia. At a time when insulinemia already returned toward basal values, glycemia started to increase. The effect of i.c.v. CRF in stimulating plasma insulin levels was dose-dependent and could be blocked by pretreatment of the animals with atropine methylnitrate. Similar results were obtained when studying the acute effects of i.c.v. CRF in genetically obese (fa/fa) rats. Although, in absolute values, the amount of insulin released in response to i.c.v. CRF was higher in obese than in lean animals, it was similar in both groups of rats, when expressed as fold increase over basal insulin levels. In summary, i.c.v. CRF elicits a rapid, vagally mediated stimulatory effect on insulin secretion both in lean and genetically obese fa/fa rats with no qualitative or quantitative difference between the two groups of animals. The site(s) of action of this CRF effect on insulinemia remains to be elucidated.