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

The importance of extracellular sodium (Nao+) in the progesterone production in hen granulosa cells from the first (F1), second (F2), and third (F3) largest preovulatory follicles was investigated in short term incubations. Progesterone synthesis in the absence or presence of the gonadotropin increased with increasing Nao+ concentration. Luteinizing hormone (LH) caused an additional and significant increase in steroidogenesis at every Nao+ concentration tested. However, no significant difference in the ED50 of Nao+ among F1, F2, and F3 cells was observed whether in the absence or the presence of the gonadotropin. Furthermore, although LH provoked steroidogenesis dose dependently in F1, F2, and F3 granulosa cells, no significant change in the ED50 of LH was observed among F1, F2, and F3 cells. The Na+/H+ exchange inhibitor, amiloride, attenuated both basal and LH-stimulated steroidogenesis in a concentration-dependent manner in the presence of Nao+. Amiloride was ineffective in the absence of Nao+. The present studies indicate the importance of Nao+ 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 Nao+ 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.