Changes in protein kinase activities in lamb adrenals at late gestation and early postnatal stages

Cytosols prepared from adrenal glands of ovine fetuses (110-144 days of gestation) and of newborn lambs (1-6 days post-partum) were analysed for their protein kinase activities. Two major peaks of casein kinase activities and two major peaks of histone kinase activities were observed in all cytosols of both fetal and neonatal adrenal glands. They were characterized as cAMP-independent casein kinases of type A and type G, and as cAMP-dependent histone kinase isoenzymes of type I and type II. The specific activity of each enzyme increased 2-fold between 118 days of gestation and 6 days post-partum. Casein kinase of the G type was 4-fold higher than casein kinase of the A type; in contrast, the mean ratio of type II to type I histone kinase activity varied between 5- and 12-fold. Infusion of ACTH1-24 (100 micrograms/day) for 5 days to 118- to 128-day-old ovine fetuses in utero increased their plasma corticosteroid levels and the responsiveness of their adrenal cells to stimulation by ACTH1-24 in vitro. In addition, such treatment doubled the specific activity of casein kinases A and G, but had no significant effect on cAMP-dependent histone kinase activities. In relation to current concepts of the role of protein kinases in adult adrenal cells, the present results suggest that casein kinase activities are involved in cell multiplication and differentiation in the fetal adrenal gland. In addition, they show that neither cytosolic histone kinase of type I nor that of type II is likely rate-limiting in the steroidogenic response to ACTH of ovine fetal adrenal cells.