Inhibitory effect of peritoneal macrophages on progesterone release from cocultured rat granulosa cells is reversed by dexamethasone: evidence for an action independent of nitric oxide and distal to cyclic adenosine 3',5'-monophosphate generation.

We investigated the effects of cocultured macrophages on progesterone release from granulosa cells obtained at different stages of the rat estrous cycle and determined whether the immunosuppressive actions of the synthetic glucocorticoid can modulate the effects of cocultured macrophages. Basal and hCG-stimulated progesterone release from granulosa cell-only cultures varied according to the stage of the estrous cycle at which granulosa cells were obtained, but macrophages exerted profound inhibitory effects on both basal and hCG-stimulated steroidogenesis at all stages. These inhibitory effects were partially reversed by the addition of dexamethasone (5 x 10(-7) to 5 x 10(-5) M) to the culture medium. Measurement of nitrite accumulation in the media, as an index of nitric oxide production, showed that granulosa cells produce very low levels of this metabolite compared with macrophages, although granulosa/luteal cells from freshly ruptured follicles of estrous rats produced significantly higher concentrations of nitrite compared with granulosa cells obtained from diestrous and proestrous rats. Dexamethasone had only limited effects in suppressing the accumulation of nitrite, showing that the macrophages were synthesizing nitric oxide synthase and suggesting that the action of dexamethasone was independent of nitric oxide. Macrophages also inhibited the steroidogenic response of granulosa cells to forskolin (5 x 10(-6) M to 10(-4) M) and dibutyryl cAMP (1mM and 0.5 mM) and the potentiation of the response by the addition of hCG. However, this inhibition was reversed by the presence of 5 x 10(-6) M dexamethasone, and responses were comparable with those measured from granulosa cell-only cultures. Overall, the results suggest that macrophage inhibition of progesterone synthesis acts at a site distal to the generation of cAMP and that dexamethasone reverses this inhibition.