Modulation and role of Ca2+ in LH and LHRH agonist action in rat Leydig cells.

The results of our recent studies on purified rat Leydig cells indicate that there are no major qualitative differences in the stimulating effects of LH and LHRH agonists on steroidogenesis via mechanisms that are dependent on calcium. This was demonstrated by using inhibitors of calmodulin and the lipoxygenase pathways of arachidonic acid metabolism. Using the fluorescent indicator quin-2, it was shown that LH and LHRH agonist increase intracellular calcium levels; LH was more potent than LHRH agonist (max increase in concentrations obtained were 500 nM and 60 nM respectively). This difference was probably the result of a direct effect of cyclic AMP (whose production is stimulated by LH but not by LHRH) because cyclic AMP analogues were as potent as LH in increasing calcium levels. These studies indicate a major role for calcium in the control of steroidogenesis in testis Leydig cells.