1 Digoxin (10 77 ± 10 75 M) or digitoxin (10 77 ± 10 75 M) decreased the basal and human chorionic gonadotropin (hCG)-stimulated release of progesterone from rat granulosa cells. 2 Digoxin (10 75 M) or digitoxin (10 75 M) attenuated the stimulatory eects of forskolin and 8-bromo-cyclic 3' : 5'-adenosine monophosphate (8-Br-cAMP) on progesterone release from rat granulosa cells. 3 Digoxin (10 75 M) or digitoxin (10 75 M) inhibited cytochrome P450 side chain cleavage enzyme (cytochrome P450 scc ) activity (conversion of 25-hydroxyl cholesterol to pregnenolone) in rat granulosa cells but did not in¯uence the activity of 3b-hydroxysteroid dehydrogenase (3b-HSD). 4 Neither progesterone production nor P450scc activity in rat granulosa cells was altered by the administration of ouabain. 5 Digoxin (10 75 M) or digitoxin (10 75 M), but not ouabain, decreased the expression of P450scc and steroidogenic acute regulatory (StAR) protein in rat granulosa cells. 6 The present results suggest that digoxin and digitoxin decrease the progesterone release by granulosa cells via a Na + ,K + -ATPase-independent mechanism involving the inhibition of post-cyclic AMP pathway, cytochrome P450scc and StAR protein functions.

1 The present study was to investigate the direct effect and action mechanism of propylthiouracil (PTU), an antithyroid drug, on the production of progesterone in rat granulosa cells. 2 PTU (3 -12 mm) decreased the basal and human chorionic gonadotropin (hCG)-stimulated release of progesterone from rat granulosa cells. 3 PTU (3 -12 mm) attenuated the stimulatory effects of forskolin and 8-bromo-cyclic 3 0 :5 0 -adenosine monophosphate on progesterone release from rat granulosa cells. 4 PTU (12 mm) inhibited the activities of both the cytochrome P450 side-chain cleavage enzyme (P450scc, conversion of 25-hydroxyl cholesterol to pregnenolone) and the 3b-hydroxysteroid dehydrogenase (conversion of pregnenolone to progesterone) in rat granulosa cells. PTU decreased the V max but increased the K m of P450scc. 5 PTU (12 mm) decreased the hCG-increased amount of steroidogenic acute regulatory (StAR) protein in rat granulosa cells. 6 The present results suggest that PTU decreases the progesterone release by granulosa cells via a thyroid-independent mechanism involving the inhibition of post-cAMP pathway, and the activities of intracellular calcium, steroidogenic enzyme, and StAR protein functions.

Ionomycin, a calcium ionophore, facilitates the sustained entry of extracellular calcium; however, in myometrial tissue it stimulates phasic contractions. This study sought to define further this unanticipated effect of ionomycin and to begin to explore the possible mechanism(s) involved. Utilizing rat uterine strips, in vitro isometric contraction studies were performed to determine the effects of ionomycin with and without membrane-permeant inhibitors of cytosolic calcium oscillations. To determine the effects of ionomycin on phospholipase C, qualitative inositol phosphate production studies were performed. The in vitro contraction studies confirmed that ionomycin-stimulated phasic myometrial contractions were potentially dependent on stimulation of phospholipase C, calcium-induced calcium release, and additional calcium influx through dihydropyridine-sensitive membrane calcium channels. The inositol phosphate production studies confirmed that ionomycin stimulated phospholipase C in a dose-related fashion to levels comparable to oxytocin. In summary, these observations have confirmed the ability of ionomycin to generate dose-related phasic myometrial contractions through mechanisms potentially involving the phosphatidylinositol-signaling pathway.