Biosynthesis of 3β‐hydroxy‐5,7‐pregnadien‐20‐one by the horse fetal gonad

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Abstract
The production of equilin and the other ring B-unsaturated estrogens by the pregnant mare is anomalous in that they are biosynthesised by a cholesterol-independent pathway. Fetal horse gonads were incubated with tritiated sodium acetate and radiochemically pure 3β-hydroxy-5,7-pregnadien-20-one and 3β-hydroxy-5,7-androstadien-17-one were isolated. A fetal gonad-placental system is proposed for equilin production, 3β-hydroxy-5,7-pregnadien-20-one being a precursor for 3β-hydroxy-5,7-androstadien-17-one in the fetal gonad and the latter being the precursor of equilin in the placenta. The nature of the possible precursor of 3β-hydroxy-5,7-pregnadien-20-one is discussed.