Site of Action of Vasopressin in Causing Corticotropin Release1

Abstract

The corticotropin-releasing properties of lysine vasopressin and that of a porcine pituitary extract were compared by means of injections into hypothalamic sites or into the adeno-hypophysis of dexamethasone-pretreated rats of both sexes. In all cases the doses used for central injections were below the minimal dose capable of causing an increase in adrenal secretion of cortico-sterone after intravenous injection, so that corticotropin (ACTH-like) effects or contamination by ACTH [adrenocorticotropic hormone] could be excluded as a cause of increased adrenal secretion of cortico-sterone after the central injections. Vasopressin provoked extensive release of ACTH when it was placed in the median eminence of the hypothalamus, as did the pituitary extract. When the 2 substances were tested by intra-adenohypophysial injection, the vasopressin caused much less ACTH release and the extract caused more ACTH release than observed after intrahypothalamic injections. Morphine abolished the ACTH release after vasopressin injections at either site, as well as after the injection of the extract into the median eminence. However, morphine failed to abolish or even diminish extensively the ACTH release observed after injection of the extract into the anterior pituitary. From these results it was concluded that the extract contained activity resembling that of a corticotropin-releasing factor, but that vasopressin did not have such activity at the doses used. The vasopressin apparently acted directly on the hypothalamus to cause release of endogenous corticotropin-releasing factor.