Effect of sodium on progesterone production in granulosa cells of rapidly growing chicken ovarian follicles

Abstract

The importance of extracellular sodium ( Na o + ) in the progesterone production in hen granulosa cells from the first (F 1), second (F 2), and third (F 3) largest preovulatory follicles was investigated in short term incubations. Progesterone synthesis in the absence or presence of the gonadotropin increased with increasing Na o + concentration. Luteinizing hormone (LH) caused an additional and significant increase in steroidogenesis at every Na o + concentration tested. However, no significant difference in the ED 50 of Na o + among F 1, F 2, and F 3 cells was observed whether in the absence or the presence of the gonadotropin. Furthermore, although LH provoked steroidogenesis dose dependently in F 1, F 2, and F 3 granulosa cells, no significant change in the ED 50 of LH was observed among F 1, F 2, and F 3 cells. The Na + H + exchange inhibitor, amiloride, attenuated both basal and LH-stimulated steroidogenesis in a concentration-dependent manner in the presence of Na o + . Amiloride was ineffective in the absence of Na o + . The present studies indicate the importance of Na o + in the modulation of steroidogenesis in hen granulosa cells. Since steroidogenesis was suppressed by amiloride only in the presence of sodium, it is suggested that Na o + is important for the maintenance/regulation of intracellular pH by an exchange with intracellular H +. Our studies also suggest that the sodium modulatory mechanism may not be a determinant in the differential progesterone production observed among the three largest preovulatory follicles.