Two distinct corticotrophin releasing activities of vasopressin

The effect of various corticotrophin releasing factors (CRFs) on the secretion of corticotrophin (ACTH) by segments of rat anterior pituitary tissue has been studied in vitro. ACTH release was stimulated by CRF-41 (5.0 X 10(-9) - 2.0 X 10(-7) M), hypothalamic extracts (0.2 - 1.6 HE ml-1) and arginine vasopressin (AVP, 5.0 X 10(-9) - 8.0 X 10(-7) M). The slopes of the dose-response lines of CRF-41 were greater than those of AVP, less than those of hypothalamic extracts from control animals and resembled those of hypothalamic extracts from Brattleboro rats. Simultaneous addition of AVP (10(-10) M) to the incubation medium enhanced the response to CRF-41 and increased the slope of its dose-response lines. The adrenocorticotrophic response to CRF-41 was enhanced similarly by pretreatment of the tissue with AVP (1.25 X 10(-11) - 2.0 X 10(-10) M) as also was the response to hypothalamic extracts. In contrast, pretreatment of the tissue with CRF-41 (2.3 X 10(-11) - 2.3 X 10(-8) M) depressed the subsequent response to CRF-41 and to hypothalamic extracts. The marked difference between the concentrations of vasopressin required to facilitate maximally the response to CRF-41 and those necessary to evoke ACTH release suggests that the two effects may be mediated by different types of vasopressin receptor.