Regulation of Cyclic Adenosine 3′,5′-Mono-Phosphate Dependent Protein Kinase of Rat Ovarian Cells by Luteinizing Hormone and Human Chorionic Gonadotropin

Abstract

Regulation of cAMP dependent protein kinase activity from rat ovarian cells has been studied in response to luteinizing hormone and human chorionic gonadotropin. Treatment of cells with human chorionic gonadotropin in concentration range of 2.5ng-1000 ng/ml resulted in increased accumulation of cAMP, activation of protein kinase followed by the stimulation of progesterone synthesis. A sixfold increase in the activity ratio, defined as the ratio of protein kinase stimulated in situ to that maximally stimulated in vitro by exogenous cAMP, was observed with lug/ml of hCG. This concentration of hormone also produced a ten-fold increase in cAMP and a thirty-to forty-fold increase in progesterone synthesis. Protein kinase activation was specific for LH and hCG, as other polypeptide hormones were without any appreciable effect. The stimulation of protein kinase persisted even after the elevated cAMP level began to fall. It appears that the activation of protein kinase is an obligatory early event that mediates an increase in gonadotropin stimulated progesterone synthesis.