Steroidogenesis in Avian Granulosa Cells: Early and Late Kinetics of oLH-and Dibutyryl Cyclic AMP-Promoted Progesterone Production

Abstract

Progesterone production was studied in granulosa cells isolated from the two largest preovulatory follicles of regularly laying White Leghorn hens. oLH (0.1 µg/ml) and dibutyryl cyclic AMP (BU₂ cAMP; 2 mM) stimulated progesterone release after a lag period of 10 and 40 min, respectively. While this "induction" period appeared to be related to the intensity of the stimulus, the rate of increase in the intracellular content of progesterone was different for the two agonists. Moreover, dose-response curves during the early phase of steroidogenesis (40 min) were markedly different from those obtained after 3 h incubation. Under the latter conditions, 50 ng/ml oLH provoked maximal steroidogenic responses while higher concentrations of the hormone were less effective. During the early phase, however, maximal stimulation was not observed even at 2 µg/ml concentrations. When we compared the relative potencies of the two agonists, we found BU₂ cAMP to be more effective than oLH during this early phase but less so after more prolonged incubation (3h). By employing cycloheximide we demonstrated that continuous protein synthesis is required for full steroidogenic responses to both oLH and BU₂ cAMP. On the other hand actinomycin D was inhibitory only when present during the first hour. Later addition of this inhibitor actually potentiated the steroidogenic effect of LH. These results are consistent with current concepts of the mode of action of LH in ovarian cells of mammals.