Aspects of steroid metabolism in the normal and neoplastic mammary gland of the bitch

Normal and neoplastic canine mammary tissues have been incubated with radio-labelled progesterone, testosterone and androstenedione and metabolites isolated. In both tissues the most active enzyme demonstrated was 5α-reductase. Testosterone was converted to the more active androgen 5α-dihydrotes-tosterone only in the tumours. A reversal of the 3β-hydroxysteroid Δ4−5 isomerase enzyme system was noted without the addition of cofactors. Epitestosterone was formed from both testosterone and andros-tenedione in the tumours only