In order to investigate the influence of estrogen and androgen on reproductive activities of male teleosts, male red sea bream were implanted with silicone capsules containing estradiol-17β (E2), testosterone (T) or 11-ketotestosterone (11-KT) in immature and early spermatogenic stages. One month after implantation of either E2 or T, the gonadosomatic index decreased in accordance with testicular regression in both stages. Implantation of E2 decreased circulating 11-KT levels but did not affect gonadotropin (GTH) subunits, follicle stimulating hormone-β (FSHβ), luteinizing hormone-β (LHβ), α glycoprotein subunit (αGSU) gene expression, and serum LH levels in both stages. Alternatively, T decreased serum 11-KT and LH levels, and FSHβ and LHβ mRNA levels in the early spermatogenic stage but not in the immature stage. These results suggest E2 may directly inhibit testicular development through the suppression of 11-KT production. Meanwhile, T may decrease serum 11-KT levels through the suppression of FSH and LH secretion, resulting to inhibition of testicular development in the early spermatogenic stage. Treatment with 11-KT did not affect the testis in either stage, whereas 11-KT increased LHβ and αGSU mRNA levels in immature, and decreased FSHβ mRNA levels in the early spermatogenic stage. These results suggest that 11-KT may have different effects on GTH subunit gene expression in each reproductive stage.
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