25-Hydroxycholesterol-supported and 8-bromo-adenosine 3',5'-monophosphate-stimulated testosterone production by primary cultures of two populations of rat Leydig cells.

Previous studies from this laboratory have demonstrated the presence of two populations of rat Leydig cells (I and II), which differ in their capacity for hCG- or cAMP-stimulated testosterone production. In the present study, we examined the metabolism of 25-hydroxycholesterol in primary cultures of both populations of Leydig cells. 25-Hydroxycholesterol bypasses the cAMP-dependent transport mechanism to the mitochondrial cytochrome P-450 side-chain cleavage enzyme (P-450scc) required by cholesterol and thus provides an index of the relative activity of P-450scc. Incubation of Leydig cells with increasing concentrations of 25-hydroxycholesterol resulted in a concentration-dependent increase in the amount of testosterone produced, with maximal amounts in both populations being reached at 25-hydroxycholesterol concentrations of 5 microM or greater. Population II produced more than twice as much testosterone as population I Leydig cells, whether incubated with 25-hydroxycholesterol or with 8-bromo-cAMP. Each population of Leydig cells produced 2.5-fold greater amounts of testosterone when incubated with 25-hydroxycholesterol than when incubated with 8-bromo-cAMP. In both populations of Leydig cells, cAMP-stimulated testosterone production was not different in cells cultured for 24 h from that in freshly isolated Leydig cells. These data suggest that cholesterol transport to P-450scc limits maximal testosterone production, and that the difference in hCG- or cAMP-stimulated testosterone production between the two populations of Leydig cells is primarily due to differences in P-450scc activity between the two populations and is not a result of population I consisting mostly of damaged Leydig cells.