Characterization of an androgen receptor in salmonid lymphocytes: possible link to androgen-induced immunosuppression

Cytosol of rainbow trout (Oncorhynchus mykiss) leukocytes demonstrated specific and saturable binding of [3H]testosterone (Kd = 0.99 +/- 0.17 nM and Bmax = 30.4 +/- 4.9 fmol/mg protein; based on a total of 6 determinations from three different cytosolic pools). Specific binding of [3H]testosterone was high in leukocytes and other tissues with known androgen binding affinity (plasma, skin, and liver) and low in other tissues (heart, muscle, and red blood cells). Specific binding of [3H]testosterone was displaced by testosterone and dihydrotestosterone. Androstenedione displaced 50% of specifically bound [3H]testosterone between 10- and 100-fold excess, while 17-alpha-methltestosterone, 11-ketotestosterone, and progesterone displaced 50% of specifically bound [3H]testosterone between 100- and 500-fold excess. Cortisol, 17 beta-estradiol, 17 alpha,20 beta-dihydroxyprogesterone, the synthetic androgen mibolerone, and the synthetic estrogen ethenylestradiol did not displace [3H]testosterone binding, even at 500-fold excess. Treatment of cytosol with proteolytic enzyme significantly reduced the specific binding of [3H]testosterone. HPLC analysis determined that [3H]testosterone was not metabolized during assay incubation with cytosol. These data strongly suggest that androgen receptors exists in salmonid leukocytes and support the hypothesis that these receptors play a role in androgen induced immunosuppression.