Calcium-dependent regulation of progesterone production by isolated rat granulosa cells: effects of the calcium ionophore A23187, prostaglandin E2, dl-isoproterenol and cholera toxin.
The role of calcium in the regulation of ovarian steroidogenesis was investigated in granulosa cells from estradiol-treated immature rats. Incubation of granulosa cells with various calcium channel blockers (verapamil, cobalt or manganese) and a calcium chelator (EGTA) resulted in marked decreases in progesterone production in response to follicle-stimulating hormone (FSH), cholera toxin, prostaglandin E2, dl-isoproterenol and dibutyryl cyclic AMP (Bt2cAMP). Cyclic AMP production, however, was unaffected by treatment with EGTA and verapamil at concentrations which attenuated steroidogenesis (0.1-1.0 mM and 125 microM, respectively). Two inhibitors of the calcium-dependent regulatory protein, calmodulin [trifluoperazine, 40 microM and 1[bis-(p-chlorophenyl)methyl] 3-[2,4-dichloro-beta-(2,4- dichlorobenzyloxy )-phenethyl]imidazolium chloride, ( R24571 ) 20 microM] significantly inhibited both cyclic AMP and progesterone production elicited by these stimulatory agents. Over the concentration range of 62.5 ng/ml-1.0 micrograms/ml, the calcium ionophore A23187 increased basal progesterone production in a dose-dependent manner, with half-maximal stimulation at approximately 0.14 microgram/ml. Maximal steroidogenic response to the calcium ionophore (1 microgram/ml) however, was only 50% of that evoked by FSH (0.33 microgram/ml). A23187 (0.5 microgram/ml) significantly enhanced progesterone production stimulated by a low concentration of FSH (0.025 microgram/ml) but failed to potentiate the maximally stimulatory action of the gonadotropin (0.33 microgram/ml). These findings support our earlier suggestion that the calcium-calmodulin system plays a central role in the gonadotropic regulation of ovarian steroidogenesis and suggest that a transmembrane flux of extracellular calcium may be an important and common step in the mechanism of stimulation of granulosa cell progesterone production.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D015232:Dinoprostone; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D011374:Progesterone / Q000096:biosynthesis*; D011458:Prostaglandins E / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D002121:Calcium Channel Blockers; D002147:Calmodulin; D011458:Prostaglandins E; D000001:Calcimycin; D011374:Progesterone; D004533:Egtazic Acid; D005640:Follicle Stimulating Hormone; D002772:Cholera Toxin; D000242:Cyclic AMP; D015232:Dinoprostone; D007545:Isoproterenol; D002118:Calcium