Role of calcium in luteinizing hormone-induced progesterone and cyclic AMP production in granulosa cells of the hen (Gallus domesticus).

The effects of calcium on steroidogenesis and cyclic AMP production in chicken granulosa cells were examined. For the expression of full steroidogenic effects by LH, forskolin, and 8-bromo cyclic AMP the presence of calcium in the incubation medium was essential, the optimal concentration being 1 mM. Moreover, calcium antagonists (verapamil, TMB-8) significantly suppressed steroidogenesis in response to all three agonists. The metabolism of 25-hydroxycholesterol and the conversion of pregnenolone to progesterone, however, were not affected by the lack of calcium or by coincubation with calcium antagonists. LH-stimulated cyclic AMP production was also suppressed in calcium-deficient medium and in the presence of the putative calcium channel blocker, verapamil. However, TMB-8 did not affect LH-induced cyclic AMP production. Moreover, neither forskolin- nor IBMX-induced cyclic AMP accumulation was significantly affected by lack of calcium or verapamil. These results are interpreted to indicate that the continuous presence of extracellular calcium is essential for hormonal regulation of steroidogenesis and is important for events both proximal and distal to cyclic AMP generation up to pregnenolone synthesis.