The biosynthesis of some androst-16-enes from C21 and C19 steroids in boar testicular and adrenal tissue

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Abstract
1. The formation of androst-16-enes from [4−14C]progesterone has been investigated with long-term incubations and short-term kinetic studies. After 4hr., 1·7 and 10·3% respectively of 3α- and 3β-hydroxy-5α-androst-16-enes were formed in boar testis minces, but much smaller yields were obtained in boar adrenal. Both tissues formed small quantities of androsta-4,16-dien-3-one. 2. The amounts of androst-4-ene-3,17-dione and testosterone isolated were small, suggesting that androst-16-ene formation may occur preferentially in the boar testis. 3. In the absence of tissue no radioactive androst-16-enes were formed. 4. Incubation of both [4−14C]pregnenolone and [7α−3H]progesterone resulted in 3α- and 3β-hydroxy-5α-androst-16-enes containing 3H/14C ratios of near unity and confirmed that both C21 steroids were precursors. A similar incubation with 17α-hydroxy[4−14C]-progesterone and [7α−3H]progesterone gave the same Δ16-alcohols, but they contained only 3H, indicating that side-chain cleavage of pregnenolone and progesterone occurred before 17α-hydroxylation. 5. Dehydroepiandrosterone, testosterone, testosterone acetate and 16-dehydroprogesterone were not found to be precursors of Δ16-steroids. 6. A pathway is proposed for the biosynthesis of 3α- and 3β-hydroxy-5α-androst-16-enes from pregnenolone and progesterone; this may involve androsta-4,16-dien-3-one as an intermediate, but excludes 17α-hydroxyprogesterone, testosterone and dehydroepiandrosterone.