Long-term trophic action of alpha-melanocyte-stimulating hormone on the zona glomerulosa of dexamethasone -or captopril-treated rats, with or without maintenance doses of ACTH or angiotensin. II: Stereology and plasma hormone concentrations.

The effects of a long-term (7 days) administration of alpha-melanocyte-stimulating hormone (alpha-MSH) on the zona glomerulosa were investigated in "normal" rats and in animals in which the hypothalamic-hypophyseal-adrenal axis and the renin-angiotensin system had been pharmacologically interrupted. alpha-MSH caused a notable hypertrophy of the zona glomerulosa and its parenchymal cells, as well as a significant increase in the plasma concentration of aldosterone, in rats infused with dexamethasone, dexamethasone plus ACTH or captopril plus angiotensin II, but not in animals treated with captopril alone. These findings indicate that alpha-MSH is directly involved in the stimulation of the growth and steroidogenic capacity of rat zona glomerulosa, and that this action of alpha-MSH requires a normal level of circulating angiotensin II.