IN-VITRO AND IN-VIVO STUDIES OF THE EFFECTS OF ARGININE-VASOPRESSIN ON THE SECRETION AND GROWTH OF RAT ADRENAL-CORTEX

Arginine-vasopressin (AVP) markedly increased basal aldosterone (ALDO) secretion by dispersed zona-glomerulosa (ZG) cells, and its effect wa s selectively reversed by V1-receptor antagonists (AVP-A1). Corticoste rone (B) production by dispersed zona fasciculata (ZF) cells was not a ffected. The bolus intraperitoneal (i.p.) administration of AVP acutel y raised the plasma concentrations of both ALDO and B in normal rats, but only that of ALDO in bilaterally adrenalectomized animals bearing regenerated adrenocortical autotransplants, which are deprived of medu llary chromaffin cells. Accordingly, AVP raised ALDO and B secretions by adrenal slices (including both cortical and medullary tissues), and only ALDO production by autotransplant quarters. The B response of ad renal slices to AVP was blocked by alpha-helical-CRH and corticotropin -inhibiting peptide (two competitive inhibitors of CRH and ACTH, respe ctively), but not by 1-alprenolol (a beta-adrenoreceptor antagonist); ALDO response was not affected by any of these antagonists. A 7-day i. p. infusion with AVP increased the volume of ZG cells and ZG-like cell s of autotransplants, as well as their basal and maximally angiotensin -II-stimulated ALDO secretory capacity; it also raised the volume, and basal and maximally ACTH-stimulated B secretory capacity of ZF cells, but it did not affect ZF-like cells of autotransplants. The simultane ous administration of AVP-A1 annulled all these effects of AVP. When i nfused alone, AVP-A1 caused a marked atrophy of ZG cells, coupled with a net drop in their steroidogenic capacity; however, AVP-A1 infusion did not change the morphology and function of either ZF cells or ZG-li ke and ZF-like cells of autotransplants. Taken together, our findings allow us to draw the following conclusions: (i) AVP plays an important physiological role in the maintenance and stimulation of ZG growth an d mineralocorticoid secretory activity in rats, the source of endogeno us AVP exerting adrenoglomerulotropic action probably being adrenal ch romaffin cells; and (ii) AVP indirectly stimulates the growth and gluc ocorticoid secretory activity of rat ZF cells, by activating intramedu llary CRH/ACTH system; however, the physiological relevance of this ef fect of AVP appears to be doubtful.