Influence of follicular maturation on luteinizing hormone-, cyclic 3',5'-adenosine monophosphate-, forskolin- and cholesterol-stimulated progesterone production in hen granulosa cells.

Abstract

The influence of follicular maturation on progesterone production by collagenase-dispersed hen granulosa cells was measured in short-term incubations. Granulosa cells of the largest follicle (F1) produced up to ten times more progesterone than cells from smaller follicles (F3-F5), not only in response to luteinizing hormone (LH), but also when stimulated by exogenous cyclic AMP or forskolin, both of which raise intracellular cyclic AMP levels by nonreceptor-mediated mechanisms. Moreover, when granulosa cell progesterone synthesis was stimulated by incorporating 25-hydroxy-cholesterol into the incubation medium, an identical pattern was obtained. This could be attributed to a corresponding increase in the specific activity of the mitochondrial cholesterol side-chain cleavage enzyme (20,22 desmolase). An increase in the apparent Vmax was observed without a change in the apparent Km values. Pregnenolone substrate at concentrations which raised progesterone production to levels similar to those observed in response to LH stimulation was utilized equally by granulosa cells of mature and developing follicles. However, at high pregnenolone concentrations, granulosa cells of mature follicles converted significantly more of the precursor to progesterone. Assay of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) showed that the enzyme has two Kms: a low Km present in cells of both mature and developing follicles, and a high Km found only in granulosa cells of more mature follicles. It is concluded that LH-promoted progesterone synthesis in granulosa cells of developing chicken follicles is restricted not so much by the availability of receptors and the competence of the adenylate cyclase/cyclic AMP system, but by the activity of key enzymes, principally the cholesterol-20,22 desmolase.