Effects of hypophysectomy on the testis of the European eel (Anguilla anguilla L.)

The pituitary control of testis activity in the freshwater silver European eel (Anguilla anguilla L.) was investigated by study of some variations of gonad structure and particularly changes in plasma levels of testosterone and 11-oxotestosterone (radioimmunoassay) following hypophysectomy. Germ cells comprised only spermatogonia, which were associated with Sertoli cells to form cysts. No mitotic activity of spermatogonia was observed. Gonadosomatic index (GSI) was low. Plasma levels of the main androgens (testosterone, 11-oxotestosterone) were under 1 ng ml-1. The male gonad appeared immature. After hypophysectomy, GSI decreased rapidly and cysts of germ cells were rapidly dissociated. Plasma level of testosterone decreased significantly, whereas that of 11-oxotestosterone increased significantly. These changes were not observed in sham-operated eels. Thus pituitary control appears essential for the maintenance of structural organization and secretory activity of the immature testis.