Androgen-binding protein in efferent duct fluid of rat testis.

Testicular fluid obtained from the rete testis and vasa efferentia has been reported to contain testosterone in concentrations approaching the amount in spermatic venous blood (Voglmayr, Waites & Setchell, 1966; White & Hudson, 1968). Flow rates, which have been established in several mammalian species (Setchell, 1970; Tuck, Setchell, Waites & Young, 1970) would indicate that the exocrine secretion may deliver a substantial quantity of androgen to the caput epididymidis. Testosterone and possibly other androgens in rete testis fluid might also exert a direct influence on spermatozoa as they are transported in this fluid. In the present report, a specific androgen-binding protein with high affinity for dihydrotestosterone (DHT) and testosterone (T) is demonstrated in rete testis and efferent duct fluid from the rat testis. Fluid was collected after ligation of the vasa efferentia for 18 to 20 hr or for 3 days. The 18to 20-hr ligations were made as close to the capsule of the testis as possible and rete testis fluid was collected from anaesthetized rats as described by Setchell& Waites (1971). The 3-day ligations were placed mid-way between testis and caput epididymidis. Animals were decapitated and the efferent ducts were dissected free of blood vessels before collection of fluid by opening the distended ducts. Spermatozoa were removed by centrifugation and the fluid was stored at -20° C. Both methods yielded 0-2 to 0-4 ml fluid/testis. Total protein concentrations were measured by the method of Lowry, Rosebrough, Farr & Randall (1951), using a bovine serum albumin standard. Values of the means and individual standard deviations were 2-4 + 0-6 mg/ml in several samples of rete testis fluid collected 18 to 20 hr after ligation and 8-4+0-4 mg/ml in efferent duct fluid collected 3 days after ligation. Testicular fluid was diluted in 0-01 M-tris-HCl buffer, pH 7-5, containing 0-0015 M-EDTA, 0-002 M-2-mercaptoethanol, 10% glycerol and 0-5% bovine albumin (TEMGA-buffer). Aliquots of diluted fluid were equilibrated at 0° C for 2 hr with tritium-labelled steroids. Proteins were fractionated by polyacrylamide gel electrophoresis (PAGE) and the radioactivity measured in 2-4-mm slices as described by Ritzen, Nayfeh, French & Dobbins (1971). Text-figure 1 shows the single peak of bound [l,2-3H]dihydrotestosterone