ACTION OF PROSTAGLANDIN E2 AND OF LUTEINIZING HORMONE ON OVARIAN ADENYLATE CYCLASE, PROTEIN KINASE AND ORNITHINE DECARBOXYLASE ACTIVITY DURING POSTNATAL DEVELOPMENT AND MATURITY IN THE RAT

Abstract

SUMMARY The actions of luteinizing hormone (LH) and of prostaglandin E2 (PGE2) on the intact ovary or isolated components of the ovary from adult or prepubertal rats were studied in vitro with respect to (1) the rate of incorporation of [3H]adenine via ATP into cyclic adenosine-3′,5′-monophosphate (cAMP), or the level of cAMP measured by a competitive protein-binding assay; (2) protein kinase activity in the 27000 g supernatant, with calf thymus histone as the substrate; and (3) rate of oxidation of d-[6-14C]glucose. In addition, ornithine decarboxylase activity was assayed in the ovary in vitro after hormone treatment in vivo. When ovaries from adult or pubertal rats were incubated in Krebs—Ringer bicarbonate buffer, addition of PGE2 to the medium resulted within 1 min in a doubling of the rate of cAMP formation; the rate was about fourfold after 5 min. PGE2 was 25 times more potent in this respect than prostaglandin F2α. Both isolated Graafian follicles and corpora lutea responded to either PGE2 or LH with increased cAMP production. During the perinatal period and until the age of 10 days the ovaries were unresponsive to LH, but responded to PGE2 with increased cAMP formation. Follicles cultured with LH for 18 h and then washed were refractory to subsequent stimulation by LH, yet remained fully responsive to PGE2. A prostaglandin analogue, 7-oxa-13-prostynoic acid, did not inhibit LH-stimulated or PGE2-stimulated cAMP formation in vitro in whole ovaries. Indomethacin, a substance reported to inhibit prostaglandin synthesis in other tissues, likewise failed to inhibit this action of LH. Simultaneous addition of LH and PGE2 to the incubation medium augmented cAMP production to a significantly greater extent than did either agonist when added at maximally effective concentrations on their own, though this augmentation was short of a full additive effect. The latter finding provides presumptive evidence against the view that PGE2 is an obligatory mediator of LH action on the ovary, but this question remains open. PGE2 mimicked the action of LH in stimulating glucose oxidation by ovaries in vitro, and in causing a 15-fold increase in ovarian ornithine decarboxylase activity within 4 h of injection into prepubertal rats. Ovarian protein kinase activity in pubescent (28-day-old) rats was markedly enhanced by incubation of intact ovaries with LH or PGE2 or by exogenous cAMP added to the 27000 g supernatant. The stimulatory action of LH or PGE2 on the enzyme was attended by a significant decrease (to 10% of control value) in the binding of exogenous cyclic [3H]AMP to protein in the 2000 g supernatant fraction of the ovary, presumably reflecting saturation of the cAMP-binding regulatory subunit of protein kinase by enhanced endogenous generation of the cyclic nucleotide. Stimulation of ovarian protein kinase by exogenous cAMP was demonstrable in 12-day-old rats, but insignificant at the age of 7 days. It thus appears that the competence of ovarian protein kinase to respond to cAMP, and of ovarian adenylate cyclase to respond to LH, are both acquired during the 2nd week of postnatal development.