Opposed effects of chronic prolactin administration on the zona fasciculata and zona reticularis of the rat adrenal cortex: an ultrastructural stereological study.

The effects of a prolonged treatment with prolactin on the morphology and hormone secretion of rat adrenal zona fasciculata and zona reticularis, were investigated by coupled morphometric and radio-immunological techniques. Chronic prolactin administration provoked a notable atrophy of zona fasciculata cells and a small but significant increase in the corticosterone plasma level, which can be the result of the prolactin-induced inhibition of the intra-adrenal 5 alpha-reductase. Therefore, the atrophy of the zona fasciculata may be reasonably supposed to be not a direct effect of prolactin, but indirectly caused by a negative feed-back mechanism blocking ACTH release. On the contrary, prolonged prolactin treatment induced a conspicuous hypertrophy of zona reticularis cells, as well as a notable rise in the plasma concentration of testosterone, which cannot be due to gonad stimulation by prolactin since orchiectomized rats were employed. As the zona reticularis, like zona fasciculata, is ACTH-dependent, it must be concluded that prolactin exerts a direct stimulating effect on the growth of the zona reticularis, whose functional counterpart conceivably is an enhanced production of androgen hormones.