Response of the Anterior Pituitary-Adrenocortical Axis to Purified CRF11

Abstract

Purified corticotropin releasing factor (CRF) was given via an internal carotid artery as an infusion during a 10-min. period to rats with median eminence lesions (MEL). The secretory rate of corticosterone (B) showed an obvious increase with 5 to 10 min. after beginning the infusion of CRF. Ten to 15 min. after the infusion was stopped, B was maximal and was 4- to 5-fold greater than the preinfusion rate. Thereafter, B fell steadily for 30 min. before attaining a constant level. The infusion of 0. 1 M ammonium acetate solution or a solution of brain cortex had no effect on B. The effect of CRF on B is considered a secondary effect follow-ing changes in secretion of ACTH. The effect was not due to exogenous corticotropin (ACTH) since the solution of CRF had no effect on B in MEL rats that were hypophysectomized 2 hr. before use. Local blood flow in the right lobe of the pituitary of rats with MEL of 2 days" duration was not significantly different from flow in rats without MEL. CRF had no noticeable effect on local blood flow of the pars distalis of rats with MEL. It is concluded that the inability of the animals with MEL to respond to stressful stimuli by increasing the secretion of ACTH, as evidenced by, B, is due to inability to secrete CRF and is not due to deficiencies in pituitary blood flow, that the activity of the pituitary-adrenocortical system varies directly with CRF output, and that CRF is involved in the minute-to-minute regula-tion of ACTH secretion.