α-Melanocyte-stimulating hormone and adrenocorticotropin in the regulation of glucocorticoid secretion during the perinatal period in sheep

Abstract

To determine the role of other ACTH-like peptides in the regulation of glucocorticoid secretion in fetal sheep, we examined the responses of the adrenal gland of fetal and newborn sheep to comparable single doses of MSH (75 μg) or ACTH (50 μg) during the last third of gestation and the first month of postnatal life. αMSH first increased the plasma glucocorticoid concentration at 121-130 days of gestation [from 16±1.5 to 36.9±9 (SE) ng/ml]; the response to αMSH persisted on days 131-140 of gestation and during the first month after birth. ACTH fust increased the plasma glucocorticoid concentration at 131-140 days of gestation and increased it further in the first month after birth (from 18.9±3.6 to 97.0±10 ng/ml). The observations that the adrenal glands of fetuses and newborn lambs responded to αMSH at a dose comparable to that of ACTH and that the response to aMSH in the fetus preceded the response to ACTH may indicate that adrenal receptors mature during fetal development. These data also suggest that the regulation of the adrenal during fetal life may involve more than one tropic hormone.