Involvement of sex steroid hormones in the early stages of spermatogenesisin Japanese huchen (Hucho perryi)

In higher vertebrates, considerable progress has been made in understanding the endocrine regulation of puberty; however, in teleosts, the regulatory mechanisms of spermatogenesis during the first annual cycle remain unclear. The present study was conducted to understand the regulatory mechanisms of spermatogenesis throughout the different stages of the first spermatogenic cycle and to check the ability of various steroids and hormones to induce in vitro spermatogonial proliferation in Japanese huchen (Hucho perryi). Th e results indicate that the serum level of 11-ketotestosterone (11-KT) was positively associated with germ cell type; the level first began to rise wi th the appearance of late-type B spermatogonia and continued to increase gr adually throughout the active spermatogenic stages and spermiogenesis, reac hing a peak value 2 wk before spawning, and then declined. During the sperm atogenic stages, the serum concentration of 17 alpha ,20 beta -dihydroxy-4- pregnen-3-one (17 alpha ,20 beta -DP) was undetectable. Only a small peak w as detected with the appearance of spermatocytes and spermatids, and at the time of spawning, the level increased dramatically, reaching its maximum v alue with the onset of milt production. Despite the high variation in serum levels of 17 beta -estradiol (E-2) both between months and among the indiv iduals, E-2 was found during the whole reproductive cycle. From these resul ts, we concluded that 1) 11-KT is necessary for the initiation of spermatog enesis and sperm production, and it probably plays a role in spermiation, 2 ) 17 alpha ,20 beta -DP is essential for the final maturation stage, could play a significant role in the mitosis phase and meiosis process, and proba bly participates in the regulation of spawning behavior, and 3) estrogen is an indispensable male hormone that plays a physiological role in some aspe cts of testicular functions, especially during the mitotic phase. The three steroids were also able to induce DNA synthesis, spermatogonial renewal, a nd/or spermatogonial proliferation in vitro.