Immunoreactive ACTH and γ-MSH in rat plasma during early stages of adrenal regeneration

Recent evidence suggests that in addition to ACTH the pro-γ-melanotropins play a role in controlling both the steroidogenic activity and growth of the adrenal cortex. By using the regenerating gland as a model for rapid adrenal growth, studies were carried out to monitor plasma ACTH and pro-γ-melanotropins during the acute phase following adrenal enucleation. Adrenal enucleated rats (experimental group) were uninephroadrenalectomized; controls were uninephrectomized or uninephroadrenalectomized. At intervals up to 96 h after surgery, animals from each of the three groups were killed under quiescent conditions at the low and high points of their circadian rhythm. The plasma concentrations of both ACTH and 11 K γ-melanocyte-stimulating hormone (MSH) in the adrenal enucleated rats were markedly elevated as compared with either control group at each time point monitored. However, there were no significant differences in plasma ACTH or 11 K γ-MSH between the two control groups, and the levels of plasma 6 K γ-MSH remained unchanged in all three groups throughout the experiment. These data are consistent with a role for pro-γ-melanotropins in adrenal regeneration.