Effects of Melanotropic Peptides

A B S T R A C T Adrenal glands from early, mid, and late fetuses of rabbit, guinea pig, and rat, and from newborn animals of each species, were incubated for 1-4 h with and without 0.1 nM-1 ,uM ACTH, aor ,B-melanocyte-stimulating hormone (aMSH or ,3MSH). The effects of the peptides were measured on production of glucocorticoids, and on incorporation of labeled thymidine or leucine into DNA or protein, respectively. The findings were similar in all three species. ACTH stimulated synthesis of glucocorticoids throughout fetal life. Potency increased progressively, as reflected by declining minimal effective dose and rising maximal response. In early and mid fetus aMSH and fMSH caused a modest glucocorticoid steroidogenic effect. ACTH and aMSH stimulated DNA and protein synthesis in the early and mid fetal gland. aMSH was more potent than ACTH in these respects, minimal effective dose being generally 10 times less and maximal response 25-200% greater. The effects diminished or disappeared in the late fetal and newborn gland. These data indicate that aand 8MSH possess steroidogenic or growth-promoting properties, or both, for the fetal adrenal gland.