Steroid Secretion by Sexually Immature Rat and Rabbit Testes Perfused in Vitro*

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Abstract
Puberty in the mammal signals a dramatic change in testicular function. Previous studies of steroid production by pubertal rat and rabbit testes have been incomplete and the results have not been comparable because of the variety of techniques used. The purpose of the present experiments was to quantify and compare the in vitro testicular steroid secretion profiles of rats and rabbits at the same pubertal stage as defined by spermatogenic development: near the completion of meiosis. The secretion rates of testosterone, its 5α-reduced metabolites (dihydrotestosterone, 3α-androstanediol, 3β-androstanediol), and testosterone biosynthetic intermediates (pregnenolone, 17α-hydroxypregnenolone, dehydroepiandrosterone, androstenediol, progesterone, 17α-hydroxyprogesterone, androstenedione) were measured in order to elucidate testicular steroidogenic capacity. Steroids in the venous effluent of testes perfused in vitro were extracted, isolated by thin layer and Celite-column chromatography, and subsequently quantified using gas chromatography. The results provide the first data on steroid secretion by pubertal rat testes perfused in vitro and the first comprehensive understanding of the steroidogenic capabilities of sexually immature rat and rabbit testes. The 30-day-old rat testis produces a radically different steroid secretion profile from that of the mature rat: 3α-androstanediol secretion is elevated and 17α-hydroxypregnenolone, 17α-hydroxyprogesterone, and testosterone secretion is depressed. In contrast, 11-week-old and sexually mature rabbit testes exhibit similar steroid secretion profiles. These observations suggest that the rabbit testicular steroidogenic capacity matures before sexual maturation, whereas maturation of the rat testicular steroidogenic capacity is delayed until after sexual maturation. These striking ontological differences may indicate different steroidal requirements of immature rats and rabbits.