Effects of cholesterol,hydroxycholesterols and calcium in pregnenolone production rates in mitochondrial fractions from rat testes

The in vitro regulationof the mitochondrial conversion of cholesterol to pregnenolone in rat testis tissue has been further investigated. Pregnenolone production rates by isolated mitochondrial fractions could be stimulated by the addition of cholesterol. The stimulation was always highest in mitochondria isolated from lutropin-treated testes relative to control and cycloheximide-treated testes.Additionof 20- ro 25-hydroxycholesterol resulted in a greater stimulation of pregnenolone production rates and these rates were unaffected by prior treatmetn with cycloheximide. When both cholesterol and 20- or 25-hydroxy-cholesterol were present in the incubation medium, prepgnenolone production rates were mainly influenced by the hydroxycholesterol, even in the presence of a ten-fold excess of cholesterol.Ca²⁺ in vitro stimulated pregnenolone production rates from endogenous cholesterol as well as from added choleterol. However, pregnenolone production rates in the presence of hydroxycholesterol were not influenced by the addition of Ca²⁺ in vitro.