Effect of estradiol on expression of cytoskeletal proteins during spermatogenesis in testis of sexually mature rats.
Earlier studies had shown that long term treatment with estradiol arrests spermatogenesis in adult male rats, at a dose of 0.1 mg/kg/day. The present study was therefore undertaken to ascertain the causes underlying the reduction in sperm counts by administering estradiol for a short term, at the dose of 0.1 mg/kg/day. Estradiol valerate was injected at a dose of 0.1 mg/kg/day, for a period of 10 days to one group of adult male rats, which were administered saline for 12 days prior to estradiol injection, and sacrificed after 22 days. The control group was administered saline for 22 days. The sera were analyzed for testosterone and FSH levels. One testis of each male was immersion fixed for histology, and for immunohistochemistry of two testicular cytoskeletal proteins, vimentin and vinculin. The contralateral testes were used for analysis of vimentin and vinculin gene expression by reverse transcriptase polymerase chain reaction (RTPCR) and western blotting. Another group exposed to estradiol for 10 days was injected with bromodeoxyuridine (BrdU), at a dose of 100 mg/kg/day, to ascertain the effect on germ cell proliferation, and sacrificed 12 days later, while estradiol treatment was continued till sacrifice. BrdU, at a dose of 100 mg/kg/day was injected i.p. to a group of control rats treated with saline for 10 days, and sacrificed 12 days later. The testes from both groups were immersion fixed for immunohistochemical detection of BrdU. Histology of estradiol treated testis showed predominance of tubules with round spermatids with accumulation of lipid droplets in Sertoli cell cytoplasm and decreased cell height, whereas controls showed elongating spermatids. BrdU immunolocalization in the testis, irrespective of treatment, indicated its incorporation in deoxyribonucleic acid (DNA) suggesting that estradiol sustained germ cell proliferation. Both vimentin and vinculin could be immunolocalized to the testis. The testicular levels of vimentin and vinculin, quantified after western blotting, were unaffected. The testicular expression of vimentin and vinculin seen by RTPCR was also unaffected. The study suggested that estradiol induced reduction in sperm counts was not due to adverse effects on proliferation. The observed predominance of seminiferous tubules showing round spermatids, accumulation of lipid droplets as compared to controls suggested that reduction in elongated spermatids occurred through reduced spermiation and phagocytosis. The study also suggested that reduction in Sertoli cell height after short-term estradiol treatment was not due to reduced expression of vimentin and vinculin, which could be maintained by estradiol. However, reduction in Sertoli cell height could have been due to suppression of FSH and testosterone, implicated in the polymerization of vimentin and organization of vinculin, two cytoskeletal proteins involved in inter-Sertoli or Sertoli-germ cell junctions. The study suggested that disorganization of Sertoli cell cytoskeleton and reduction in the volume of Sertoli cells could be an important factor for reduced efficiency of spermatogenesis after exposure to estrogenic molecules.