In Vivo Adrenocorticotropin-Releasing Activity of Neurohypophyseal Hormones and Their Analogs*

The ability of 21 neurohypophyseal hormones and related synthetic peptides to raise plasma ACTH or corticosterone concentrations was studied in female rats anesthetized with chlorpromazine, morphine, and pentobarbital. Corticotropin-releasing factor (CRF) activity was significantly correlated with pressor but not with antidiuretic or oxytocic activity. However, peptides with little or no pressor but very potent antidiuretic activity had weak CRF activity if given in a dose greater than 4 antidiuretic units/100 g BW; the dose-response slopes of these analogs were significantly flatter than that of arginine vasopressin. Pretreatment with antagonists with antipressor but not antiantidiuretic activity consistently reduced the CRF activity of the analogs with potent pressor activity. We conclude that the CRF activity of the neurohypophyseal hormones is primarily related to pressor activity.