EFFECT OF TESTOSTERONE ON THE RELEASE AND SYNTHESIS OF GONADOTROPIN HYPOTHALAMUS PITUITARY COMPLEX IN VITRO IN THE JAPANESE EEL (ANGUILLA JAPONICA)

摘要

The effects of testosterone (T) on the synthesis and release of gonadotropin (GtH) in the hypothalamus pituitary complex or pituitary alone of Japanese eel (Anguilla japonic ) were investigated in vitro . The intact hypothalamus pituitary complex (HPC), the separate hypothalamus plus pituitary (H+P) or the pituitary (P) of male eel were incubated with TC 199 medium without (control) or with different concentrations of testosterone (0.1, 1.0, or 10.0 μmol/L) for 8 h. In the control group, the GtH content of HPC group was the highest both in medium or pituitaries while the P group was the lowest. It indicated that the gonadotropin releasing hormone (GnRH) reaches pituitary directly. Incubation of pituitary alone with different concentrations of T increased the GtH content in a dose dependent manner either in medium or pituitary. We suggested that T acted directly as a positive feedback on the synthesis and release of GtH in eel pituitary. Low dosages of T (0.1 and 1.0 μmol/L) stimulated the synthesis and release of GtH in both HPC group and H+P group after 8 h incubation, indicating that there was a positive feedback effect of T on either hypothalamus or pituitary in eel; whereas a negative feedback effect of T were observed when HPC or H+P incubated with high dosage of T (10.0 μmol/L). In the highest dosage group, the inhibitory effect of GtH release was more significant than the GtH synthesis. These results demonstrated that the synthesis and release of pituitary GtH was regulated by hypothalamus via GnRH. Testosterone in male fish had feedback effects on either hypothalamus or pituitary in Japanese eel.