Lack of Difference Between Retinoic Acid and Retinol in Stimulating Progesterone Production by Luteinizing Granulosa Cellsin Vitro

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Abstract
Receptors for retinoids in the immature rat ovary and the effects of retinol and retinoic acid on luteinizing granulosa cells were studied. Radioreceptor assay demonstrated the presence of specific cellular retinol-binding protein and cellular retinoic acid-binding protein in the ovaries of rats injected with PMSG alone or PMSG and hCG. In addition, when luteinizing granulosa cell from PMSG/hCG-ionjected immature rats were cultured with or without retinoic acid, the morphology, viability, number of cells in culture, and progesterone (P) accumulation were not affected by up to 10 .mu.M retinoic acid. Beyong 10 .mu.M, the cells began to round up, which was associated with a decrease in cell viability. Surprisingly, the deleterious concentrations of retinoic acid increased progesterone accumulation significantly higher than the medium control value. This increase in progesterone, however, was not accompanied by an increase in cAMP. When cells preincubated for 2 days with 1 .mu.M of either retinoic acid or retinol were subsequently incubated in retinoid-free medium containing various substrates for steroidogenesis, the following results were obtained. Basal progesterone and its accumulation in response to human low density lipoprotein were significantly higher in cells preincubated with retinoids than in the control cells. However, no difference was seen in the degree of stimulation between retinol and retinoic acid pretreatments. Both 25-hydroxycholesterol, a substrate for side-chain cleavage enzyme, and pregnenolone, a substrate for 3.beta.-hydroxysteroid dehydrogenase, significantly stimulated the accumulation of progesterone in cells preincubated with retinoids over the control value. Again, no appreciable difference was observed between retinol and retinoic acid pretreatments. Our results suggest that 1) receptors for retinoids are present in gonadotropin-primed immature rat ovaries, 2) retinoids increase luteal cell progesterone accumulation, and 3) no difference exists between retinol and retinoic acid in their ability to increase the accumulation of progesterone by these cells.