On the Corticotrophin-Releasing Activity of Synthetic Neurohypophysial Hormones and Some Related Peptides

The corticotrophin-releasing (CR), pressor, antidiuretic and oxytocic activities of the mammalian neurohypophysial hormones and of some related synthetic analogues and homologues were investigated in pentobarbital-morphine blocked rats. The amount of a peptide which elicited a 100% increase of plasma corticosterone was considered equivalent to 1 CR unit, and the potency of the compounds was compared on this basis. The CR activity of the peptides was correlated with their pressor potency and an index of CR specificity was calculated. For the natural neurohypophysial hormones this value is remarkably uniform, whereas for the synthetic analogues it shows considerable variation. The results imply that the pressor and the CR activities of peptides related to the neurohypophysial hormones need not be strictly correlated.