Acute intravenous corticotropin-releasing factor administration: effects on insulin secretion in lean and genetically obese fa/fa rats.

The effect of an i.v. administration of different doses (250, 500, and 1000 pmol) of ovine CRF (oCRF) on plasma glucose and insulin levels in lean and genetically obese fa/fa rats was investigated. In both phenotypes, i.v. CRF promoted a rapid (peak at 1 min) transient doubling of basal insulin levels without a concomitant change in glycemia. The dose-dependency of this early insulin response was bell-shaped in both lean and obese animals, with a maximal response at 500 pmol oCRF. After this early rise in insulinemia, glycemia increased in a dose-dependent manner in both lean and obese rats. It was accompanied by a bell-shaped insulin response in lean rats, while such a response was linear in obese rats. The early transient stimulatory effect of CRF on plasma insulin levels could not be prevented by the prior administration of an anti-CRF serum or the alpha-helical CRF-(9-41) antagonist, although administration of either one of these compounds was effective in preventing the CRF-induced changes in the pituitary-adrenal axis. The effect of CRF on the early insulin response was, however, completely suppressed by an acute cholinergic blockade (i.v. injection of atropine). It is suggested that i.v. CRF administration mimics the reflex, cephalic phase insulin secretion. Such cephalic phase insulin output is known to play a role in oral glucose tolerance and may be of physiopathological importance in the Zucker rat strain.