Nuclear Androgen Receptors in Different Stages of the Seminiferous Epithelial Cycle and the Interstitial Tissue of Rat Testis*

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Abstract
Testicular androgen receptors were measured with a recently developed exchange assay using [3H]methyltrienolone from samples of interstitial tissue, whole seminiferous tubules and segments of tubules in different stages of the cycle of the seminiferous epithelium. The hexylene glycol method was used to isolate nuclei and pyridoxal 5''-phosphate for extraction of the androgen receptors. This method proved superior to other techniques. As a consequence, higher levels of androgen receptors were detected in seminiferous tubules than previously reported. Androgen receptors in seminiferous tubules and interstitial tissue had high affinity for methyltrienolone (Kd = .apprx. 3 nM) and steroid binding specificity similar to that of these receptors in other tissues. The concentration of nuclear androgen receptors in whole seminiferous tubules was 670 .+-. 100 fmol/mg DNA (mean .+-. SE), while that of the interstitial tissue was 1070 .+-. 295 fmol/mg DNA. Tubules in stages IX-XII and XIII-I of the epithelial cycle contained significantly significantly more nuclear androgen receptors (900 .+-. 170 and 805 .+-. 125 fmol/mg DNA, respectively) than those in stages II-VI and VII-VIII (485 .+-. 95 and 485 .+-. 65 fmol/mg DNA, respectively. Apparently, there are local differences in androgen receptor concentration along the length of the seminiferous tubule. A high concentration of nuclear androgen receptors was also present in interstitial tissue. Androgen receptors were measurable in cytosol prepared from interstitial tissue, but such measurements were obscured in cytosol from tubules, because of a high capacity binding protein for the 3H-labeled ligand. Evidently, nuclear androgen receptors can be measured in various testicular compartments, including different stages of the seminiferous tubules, using an exchange assay that maximizes recovery. The concentration of nuclear androgen receptors in the tubules varies with the cycle of the seminiferous epithelium.