Differences in the control of sterol metabolism between mouse and rat Leydig cells

The metabolism of hydroxysterols, which bypass the cAMP-dependent, cycloheximide-inhibitable transport to cytochrome P-450 side-chain cleavage enzyme complex (P-450scc) required by cholesterol, and whose metabolism exceeds that of cholesterol in luteal cells, has been investigated in primary cultures of Leydig cells purified from the mouse and the rat. An unexpected finding was that metabolism of 25-hydroxycholesterol by mouse Leydig cells was far lower than cAMP-stimulated cholesterol metabolism. The metabolism of 20 alpha-hydroxycholesterol and 22R-hydroxycholesterol was equivalent to and greater than, respectively, maximal cholesterol metabolism by mouse Leydig cells. As expected, metabolism of 25-hydroxycholesterol by rat Leydig cells was much greater than cholesterol metabolism, as was metabolism of 20 alpha-hydroxycholesterol and 22R-hydroxycholesterol. Hydroxysterol metabolism was not increased by cAMP. Cycloheximide abolished the cAMP-stimulated increase in testosterone production by Leydig cells of both species but had no effect on metabolism of any of the hydroxysterols by Leydig cells of either species. In addition, it was shown that the relatively low rate of 25-hydroxycholesterol supported testosterone production in mouse Leydig cells was not due to inhibition of the conversion of pregnenolone to testosterone. It is concluded that a species-specific difference in the control of mitochondrial sterol metabolism exists between the rat and the mouse. The data suggest that either the P-450scc differs between mice and rats or that an effector of P-450scc, which greatly facilitates the binding and metabolism of cholesterol, is of particular importance in the control of sterol metabolism in the mouse Leydig cell.