Stimulation of corticotropin release by corticotropin-releasing factor (CRF) or by vasopressin following intrapituitary infusions in unanesthetized dogs: inhibition of the responses by dexamethasone.

Abstract

A new technique was developed for intrapituitary infusion of test substances into trained, unanesthetized. dogs. Blood from one adrenal was collected intermittently by a modification of the method of Hume and Nelson. Adrenal secretion rate of cortisol was variably increased by intrapituitary infusion of vehicle solutions at the rate of 40 μl/25 min. In contrast, infusions of crude ovine CRF at a rate of 170 μg in 40 μl/25 min into the pituitary provoked a rapid but submaximal increase in cortisol secretion rate. Similarly, lysine vasopressin infused into the pituitary of these unanesthetized dogs without pharmacological pretreatment had potent ACTH-releasing properties: at a dose of approximately 212 mU/25 min it also provoked rapid but submaximal increases in cortisol secretion rate in every case. The corticotropinreleasing properties of ovine CRF and of lysine vasopressin were completely suppressed by systemic dexamethasone (4 mg/og sc) if the dexamethasone was administered 2–8 hr before the ip injectio...