Total 17β-hydroxyandrogen concentrations were determined using a competitive protein binding assay, for bovine reproductive fluids. Rete testis fluid and cauda epididymal plasma were separated from the spermcontaining fluids obtained through cannulae from conscious bulls. Al-through the concentration of total 17β-hydroxyandrogens in rete testis fluid was similar (P > 0.05) to that in cauda epididymal plasma (25 and 19 ng/ml), both fluids contained higher (P < 0.01) androgen concentrations than seminal plasma, accessory sex gland fluid or serum from peripheral blood (3–5 ng/ml). However, since the amount of cauda epididymal plasma recovered was much less than for rete testis fluid (0.25 vs 35 ml/day), cauda epididymal plasma contained less than 1 % of the total 17β-hydroxyandrogens which entered the epididymis in rete testis fluid (5 vs 883 ng/day).
Testosterone and/or dihydrotestosterone were isolated from the reproductive fluids by Sephadex LH-20 chromatography and quantified by a simple, specific and highly sensitive microassay. Dihydrotestosterone was found only in cauda epididymal plasma (14 ng/ml); identification of the isolated compound was confirmed by mass spectrometry. Dihydrotestosterone accounted for 52% of the 17β-hydroxyandrogens in cauda epididymal plasma while 23 % was testosterone. Testosterone represented 70 % of the 17β-hydroxyandrogens in rete testis fluid and 91 % of those in blood serum. Physiological implications of this shift in androgen balance are discussed.