Progesterone attenuates the inhibitory effects of cardiotonic digitalis on pregnenolone production in rat luteal cells

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Abstract
Previous studies have shown that digoxin decreases testosterone secretion in testicular interstitial cells. However, the effect of digoxin on progesterone secretion in luteal cells is unclear. Progesterone is known as an endogenous digoxin‐like hormone (EDLH). This study investigates how digitalis affected progesterone production and whether progesterone antagonized the effects of digitalis. Digoxin or digitoxin, but not ouabain, decreased the basal and human chorionic gonadotropin (hCG)‐stimulated progesterone secretion as well as the activity of cytochrome P450 side chain cleavage enzyme (P450scc) in luteal cells. 8‐Br‐cAMP and forskolin did not affect the reduction. Neither the amount of P450scc, the amount of steroidogenic acute regulatory (StAR) protein, nor the activity of 3β‐hydroxysteroid dehydrogenase (3β‐HSD) was affected by digoxin or digitoxin. Moreover, in testicular interstitial and luteal cells, progesterone partially attenuated the reduction of pregnenolone by digoxin or digitoxin and the progesterone antagonist, RU486, blocked this attenuation. These new findings indicated that (1) digoxin or digitoxin inhibited pregnenolone production by decreasing the activity of P450scc enzyme, but not Na+–K+‐ATPase, resulting in a decrease on progesterone secretion in rat luteal cells, and (2) the inhibitory effect on pregnenolone production by digoxin or digitoxin was reversed partially by progesterone. In conclusion, digoxin or digitoxin decreased progesterone production via the inhibition of pregnenolone by decreasing P450scc activity. Progesterone, an EDLH, could antagonize the effects of digoxin or digitoxin in luteal cells. J. Cell. Biochem. 86: 107–117, 2002.

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