STEROIDOGENESIS IN EQUINE TESTIS

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Abstract
When the cell-free homogenates (supernatant fluid at 800 × g) and the supernatant fluid at 10 000 × g of equine testis were incubated with 4-14C-labelled progesterone and 17α-hydroxyprogesterone, radioactive androstenedione and testosterone were isolated as the metabolites. Oestrone was also produced by the same equine testicular preparation from the above mentioned C-21 steroids, androstenedione and dehydroepiandrosterone, while 17β-oestradiol was obtained from the testosterone which had been incubated as the substrate. In addition to the androgens and the oestrogens which were obtained as the metabolites, 19-hydroxyandrostenedione, 20α-dihydroprogesterone and androst-5-ene-3β,17β-diol were identified as the metabolites by thin layer chromatography, chemical derivation procedures, and isotope dilution methods in the course of recrystallization. The testicular 19-hydroxylase and aromatizing enzyme system were found to be concentrated intracellularly in the microsomal fraction (10 000-105 000 × g precipitate), while the 20α-hydroxysteroid dehydrogenase which preferably converted progesterone into 20α-dihydroprogesterone were exclusively found in the soluble fraction or the supernatant fluid at 105 000 × g. The role and mechanism of aromatization by equine testicular preparations are discussed in relation to those of the placental microsomal aromatase.

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