Changes in 5α- dihydrotestosterone binding to epididymal cytosol during sexual maturation in rabbits: Correlation with morphological changes in the testis and epididymis

Abstract

We previously demonstrated that the caput epididymis of intact sexually mature rabbits contains a specific high-affinity binding protein for 5α-dihydrotestosterone (5αDHT). The other anatomical segments (corpus and cauda) of the epididymes of these animals had no detectable 5αDHT-binding activity. We have further shown that this binding was due to an androgen-binding protein of testicular origin. In the present study we have investigated 5αDHT binding to epididymal cytosol from sexually immature rabbits (20−104 days old). Using sucrose gradient ultracentrifugation, we have detected a unique pattern of binding. The pattern correlated well with testicular and epididymal maturation, but there was little correlation with chronological age or body weight. In the most immature animals (Group I) the seminiferous tubules appsared as solid cords and the epithelium of the ductus epididymis consisted of a single row of columnar cells. Epididymes from this group had little or no detectable 5αDHT-binding activity. In the second group (Group II), there was 5αDHTbinding to all three segments. The seminiferous tubules of these rabbits exhibited spermatogenic activity and lumen formation. The height of the epididymal epithelium had increased uniformly throughout the duct. The third group (Group III) had 5αDHT-binding only in caput cytosol. Spermatogenesis had progressed to the formation of elongated spermatids in the most immature animals of this group to the release of spermatozoa in the most mature ones. The caput epithelium of this last group of rabbits was fully differentiated. Unilateral orchidectomy of Group II rabbits resulted in a decrease in [ 3H]5αDHT-binding activity on the operated side as compared to the contralateral non-operated control side, suggesting the testicular origin of the binding protein. The failure of cyproterone or cyproterone acetate to inhibit [ 3H5αDHT-binding to the protein, the lack of effect of N-ethylmaleimide on binding, and the rapid dissociation rate of the[ 3H5αDHT-binding protein complex suggested that the binding moiety was testicular androgen-binding protein (ABP).