It is widely assumed that oestrogen administration in the male mimics hypophysectomy by suppressing gonadotrophin secretion. Nevertheless, oestradiol treatment can increase germ-cell apoptosis mainly at stages IV–X of the spermatogenic cycle, rather than at stage VII when apoptotic germ-cell death is mainly triggered by gonadotrophin withdrawal caused by hypophysectomy. Since the roles of testicular oestrogens in spermatogenic regulation, if any, are unknown, we re-evaluated the germ-cell types that undergo apoptosis after oestradiol treatment. Adult male rats were injected daily with 50 μg oestradiol, oestradiol plus testosterone propionate (25 mg every 3 days) or oestradiol plus human menopausal gonadotrophin (equivalent to 25 iu FSH plus 25 iu LH) for 15 days. Apoptosis was assessed by in situ 3′-end labelling of internucleosomal DNA fragments in plastic semithin sections; the germ-cell types involved were identified by high-resolution light microscopy. The quantitative analysis of our results shows that the apoptosis pattern elicited by oestradiol treatment of the seminiferous epithelium differs from that reported to be caused by gonadotrophin or testosterone withdrawal, suggesting a possible role for oestradiol in the modulation of germ-cell death in the adult testis of the rat.
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