A morphometric study of the effects of melatonin on the rat adrenal zona glomerulosa.

The effects of a long-term administration of melatonin on the zona glomerulosa were investigated both in "normal" rats and in animals in which the hypothalamo-hypophyseal-adrenal axis and the renin-angiotensin system had been pharmacologically interrupted. Melatonin caused a notable hypertrophy of zona glomerulosa cells and a significant rise in the plasma concentration of aldosterone in both groups of rats. These findings indicate that melatonin exerts in vivo a strong direct stimulatory action on the growth and steroidogenic capacity of the rat zona glomerulosa.