Studies on the Circadian Rhythm of Pituitary Adrenocorticotropic Release in Man

Abstract

A study was made of the effect of a single intravenous injection of a synthetic analog of vasopressin (CRA-41) on corticotropin release during various times of the circadian rhythm of the circulating plasma 17-hydroxycorticosteroids. The material was administered at 8:00 am, 5:00 pm and 12:00 midnight, and the plasma 17-hydroxycorticosteroids were determined at intervals within 1 hr of administration. Corticotropin release, as indicated by an increase in 17-hydroxycorticosteroid levels, was greater at 5:00 pm and 12:00 midnight than at 8:00 am, and the data suggest that the amount of ACTH released at 12:00 midnight was in excess of that released during the other 2 test periods. It is proposed that release of corticotropin in response to stress varies inversely with the levels of plasma cortisol and that this may be related to variations in pituitary ACTH content. The data further indicate that there was no difference between the corticotropin-releasing activity of equipressor doses of CRA-41 and synthetic lysine-vasopressin at 5:00 pm.