DEVELOPMENTAL REGULATION OF PROTEIN KINASE-A AND KINASE-C ACTIVITIES IN THE BABOON FETAL ADRENAL

We have previously demonstrated that the estrogen-regulated change in transuteroplacental metabolism of cortisol (F) and cortisone (E) from preferential reduction (E to F) at midgestation to oxidation (F to E) near term results in activation of the hypothalamic-pituitary-adrenal axis of the baboon and the ontogenesis of rate-limiting steroidogenic enzymes, culminating in de novo F secretion. It is well established that transcription of messages activated by peptide-mediated binding to membrane receptors can occur via cAMP-dependent protein kinase-A (PKA) and/or phospholipid/calcium-dependent protein kinase-C (PKC). The present study was designed to determine whether basal levels of PKA and PKC in the fetal adrenal are developmentally regulated during baboon gestation and, thus, could provide the mechanism(s) by which activation of the fetal adrenal near term is mediated. Fetal adrenal glands were obtained on day 100 (n = 8) and day 165 (n = 6) of gestation (term = day 184) from untreated baboons and on day 100 after treatment of the mother with estradiol benzoate, injected sc between days 70-100 to increase estrogen production. PKA activity (picomoles of P-32 incorporated into kemptide per min/mg protein) was determined by incubation of adrenal cytosol (12,000 x g; 0.3-30 mug protein) in reaction mixtures containing 0.25 mM ATP, 1 x 10(6) dpm [lambda-P-32]ATP, and 3 mug kemptide in the presence or absence of 0.02 mM cAMP. PKC activity (picomoles of P-32 incorporated into histone IIIS per min/mg protein) was determined in cytosol (105,000 x g) and detergent-solubilized membrane fractions after incubation with 0.02 mm ATP, 50 mug histone IIIS, and 1 x 10(6) dpm [lambda-P-32]ATP in the presence or absence of calcium and phospholipids. Mean (+/-SE) maternal serum estradiol concentrations (nanograms per ml) were 3-fold greater (P < 0.05) at term (1.9 +/- 0.3) than at midgestation and increased (P < 0.05) after treatment with estradiol. PKA activity was greater at term (3965 +/- 546) than at midgestation (2130 +/- 240) and increased (P < 0.05) 2-fold after treatment with estrogen (3525 +/- 416) at midgestation. PKC activity was always 3- to 4-fold lower than that of PKA and was similar in the cytosol and membrane fractions of the cell. In contrast to PKA, cytosolic PKC activity was similar at mid (265 +/- 98)- and late (353 +/- 99) gestation and was not altered by treatment with estradiol (223 +/- 27). Similar results were observed for membrane-bound PKC. We conclude that activation of fetal adrenal enzymes catalyzing the ontogenesis of de novo F production near term and at midgestation after an experimental increase in estrogen is due in part to an increase in the cAMP-dependent second messenger system involving PKA.