LAUSR

Hormone assays The concentrations of testosterone were determined using a direct radioimmunoassay (RIA) method derived from Garnier et al. (1978) and Hochereau-De Reviers et al. (1990). For each sample, 50μl of plasma was assayed in duplicate. To each tube, buffer containing 7.5 nCi-labelled testosterone with 0.5 μg rabbit γ-globulins and buffer with a specific antiserum from rabbit (diluted at 1/45 000) were added. After 1 h at 37°C, 50μl of anti-rabbit γ-globulin sheep serum (diluted at 1/10) were added. After an overnight incubation at 4°C, 2ml of a solution with polyethylene glycol at 80 g/l was added. After centrifugation and elimination of the supernatant a second washing with 2ml of a solution of polyetylene glycol at 60 g/l was performed, the remaining precipitate was dissolved with 100 μl of ethanol and 2ml of scintillation liquid were then added. The level of radioactivity was measured with a beta counter. The antiserum crossreacted with dihydrotestosterone (43%), androstenediol (4.5%), androstenedione (4.5%) androstanediol (3.5%) and less with other steroids (0.1%). The minimum level of quantification was 0.06 ng/ml. All samples were assayed in the same assay. The intra-assay coefficients of variation were 20.3%, 7.1% and 12.1% for samples containing 0.6, 2.3 and 4.2 ng/ml of testosterone, respectively.