A review of in vitro testicular steroidogenesis in rodents, monkeys and humans.

Abstract

Abstract This review covers pertinent literature regarding the synthesis of androgens by the testis of the rodent, the subhuman primate and man. By increasing the activity of the cholesterol side-chain cleavage mitochondrial enzyme complex, LH is rate-limiting for the synthesis of testicular androgens by regulating the conversion of cholesterol to pregnenolone. In the rat, available information suggests that pregnenolone is converted to testosterone primarily through the 4-ene pathway. Testosterone is the major metabolite of pregnenolone and progesterone in the newborn and adult rat, while in the immature rat 5α-reduced androgens are predominant. In subhuman primates, the 4-ene pathway also appears to be predominant for testosterone synthesis in more primitive species, such as the marmoset and the baboon. However, in higher primates, such as the orang-utan, both the 4-ene and the 5-ene pathways appear to be utilized for testosterone synthesis. In man, the 5-ene pathway is the major pathway for the metabolism of pregnenolone to testosterone, and this pathway may involve the conversion of sulfated intermediates to testosterone. There is apparently little 5α-reductase activity in the prepubertal human testis, but the activity of this enzyme increases with age after puberty. The reduction in 20α-hydroxysteroid dehydrogenase activity prior to puberty may invoke the onset of puberty in man.