Role of Calcium in the Action of LHRH on Ovarian Progesterone Production

Abstract

In fura-2AM-loaded rat granulosa cells, [Ca⁺⁺]i rapidly increased after addition of LHRH (10^-6M). The effect of LHRH on [Ca⁺⁺]i changes could be completely blocked by an LHRH antagonist. In a 5-h incubation, combined treatment of granulosa cells with LHRH and EDTA caused a 45% decrease in P production induced by LHRH. Concomitant treatment with EDTA plus TPA caused a 30% reduction in P accumulation when compared with TPA treatment alone. In a 24-h incubation, concomitant treatment with FSH plus LHRH markedly decreased P accumulation induced by FSH. Addition of EDTA to the cells partially reversed the inhibitory effect of LHRH upon FSH-induced P formation, by ca. 25%. Likewise, the inhibitory effect of TPA on P production could be partially reversed by the concomitant presence of 1 mM EDTA. Further, the reversal effect of EDTA could be completely abolished by the simultaneous addition of 1 mM Ca⁺⁺, and P production went down to the same levels as those induced by TPA alone. These data further support the hypothesis that the action of LHRH on ovarian steroidogenesis is mediated, at least in part, by a Ca⁺⁺-dependent protein kinase C.