Hormonal Regulation of Testicular Development in the Finless PorpoiseNeophocaena asiaeorientalis sunameri: Preliminary Evidence fromTesticular Histology and Immunohistochemistry

摘要

Sexhormones play a crucial role in regulating testicular development and maintainingspermatogenesis in the male reproductive system. Knowledge of hormonal regulation inodontocetes is limited to captive species. In this study, the characteristics of hormonalregulation during the testicular development were assessed by histological andimmunohistochemical methods in the East Asian finless porpoise ( ), native to the Chinese Yellow/Bohai Sea coast, China.The testes mass, seminiferous tubule cross section diameter, thickness of the tunicaalbuginea, and the level of testosterone (T) expression increased abruptly at the age of3-3.5 years (body length 140-145 cm). However, the estradiol (E ) expressionlevel decreased with age after 3 years. Therefore, we inferred that the male East Asianfinless porpoise (EAFP) > 3 years old (body length > 140 cm) could be classified as theage of puberty onset. Immuno-localization with T was only observed in the interstitialfluid of all animals at all ages. In contrast, a positive reaction for E and its receptorcould be observed in the Leydig, myoid, Sertoli, and germ cells at different developmentalstages. T is presumed to maintain the tubular microenvironment for spermatogenesis whileE may directly regulate spermatogenesis at the level of germ cells. Our findings provideuseful information for understanding reproductive status and hormonal regulation in themale EAFP.