Observations on the binding of androgens by rat testis seminiferous tubules and testis extracts

Abstract

Isolated seminiferous tubules from recently hypophysectomized adult rats rapidly bound 3H-testosterone (T). Analysis of Scatchard plots of the data indicated the existence of at least two androgen binding proteins (ABP), one of which had a high affinity for T and dihydrotestosterone (DHT). The binding capacity of the high affinity ABP was greatly decreased in tubules from regressed hypophysectomized rats, whereas that of the low affinity ABP was increased. Extracts were prepared from homogenates of seminiferous tubules or from whole testes of normal, cryptorchid and hypophysectomized rats, and endogenous androgens were removed from the high speed supernatant fractions by adsorption onto dextran-coated charcoal. Assays for the high affinity ABP ( K d of approximately 10 −9 M) indicated relatively high binding capacity in testis extracts from normal or cryptorchid testes, but very low capacities in testis extracts from regressed hypophysectomized rats. In vivo treatment of hypophysectomized animals with follicle stimulating hormone (FSH) increased ABP capacities in testis extracts within 24 h after hormone administration, whereas treatment with luteinizing hormone was less effective. The ABP was shown to be specific for T and DHT. After ligation of the efferent ducts from the testis, ABP of high binding capacity was observed in extracellular extracts. The data are discussed in relation to the hypothesis that Sertoli cells produce ABP and secrete this protein into tubular fluid under the regulation of FSH. A large portion of the high affinity ABP found in testicular extracts is derived from that present in tubular fluid. The remainder is from the cells of the seminiferous tubules, and little or none is in interstitial cell preparations.