IN VITRO BIOSYNTHESIS OF ANDROGENS IN CANINE TESTES

ABSTRACT In the cell-free homogenates (supernatant fluid at 800× g) of canine testes, the following Δ5-pathway was suggested as the major biosynthetic route of testosterone in vitro: Pregnenolone → 17α-hydroxypregnenolone → dehydroepiandrosterone → 5-androstenediol → testosterone. This pathway was found to be partly dependent on a predominant cofactor present in the medium. In addition to the androgen formation, 17α,20α-dihydroxy-4-pregnen-3-one and 11 -deoxycortisol were produced in significant yields from 17α-hydroxyprogesterone by the cell-free homogenates. The activities of 17α-hydroxylase, 21-hydroxylase, C17—C20 lyase and 17β-hydroxysteroid dehydrogenase were concentrated in the microsomal fraction (10 000-105 000× g precipitate) of the testicular homogenates. By a time-course study on the metabolism of 17α-hydroxypregnenolone and dehydroepiandrosterone with the testicular microsomal fraction in the presence of NAD and NADPH, testosterone was formed from 17α-hydroxypregnenolone via dehydroepiandrosterone and subsequently 5-androstenediol or androstenedione. The biosynthetic pathways of androgens among vertebrates are discussed from the comparative endocrinological point of view.