Androgen metabolism by and binding to mature rabbit epididymal tissue: the effects of castration.

Abstract

When minced epididymal tissue from intact sexually mature rabbits was incubated with 8.25 × 10 −9 M [ 3 H]-testosterone for 2 h at 0°C, followed by 1 h at 23°C, approx 10% of the unbound ether-soluble radioactivity in the cytosol was [ 3 H]-H17β-hydroxy-5α-androstan-3-one (5αDHT) and approx. 2% was [ 3 H]-5α-androstane-3α, 17β-diol (diols) and unidentified polar metabolites. Castration resulted in a decrease in 5αDHT formation. This decrease became significantly different ( P < 0.05) by 4 days postcastration. The same pattern of 5αDHT formation was observed when the incubation was conducted for 3 h at 0–4°C, except that the absolute amount and percentages of metabolites formed was reduced. Examination of binding to the slowly dissociating epididymal androgen cytoplasmic receptor indicated that the greatest amount of binding occurred 2–6 days after castration and returned to pre-castration levels by the 10th day after castration. Greater binding of androgens to the cytoplasmic receptor occurred upon incubation at 0°C than at 23°C. This was taken to indicate that nuclear translocation of the receptor-hormone complex had occurred during the 23°C incubation. Despite the post-castration induced decline in 5αDHT formation, the relative amount of 5αDHT bound to the cytoplasmic receptor remained virtually unchanged during the entire 14 day period after castration that was studied. Little radioactivity was bound to the KC1 extract of nuclei or was present in the post KCl extract nuclear debris when the minces were incubated at 0°C and most of the label present was testosterone. When the samples were incubated at 23°C, both testosterone and 5αDHT were present in the above nuclear fractions during the entire post-castration period. The time-course of maximal androgen binding to nuclei was similar to the time-course of maximal binding to the cytoplasmic receptor.