Effect of testosterone on growth hormone gene expression in the goldfish pituitary

This study investigated the effects of testosterone and a nonaromatizable androgen, 11 beta-hydroxyandrosterone, on growth hormone gene expression in the goldfish pituitary. In the sexually immature goldfish, treatment with physiological doses of both testosterone and 11 beta-hydroxyandrosterone significantly increased the growth hormone mRNA production above basal levels. However, at supraphysiological doses, treatment with these androgens resulted in a lower level of stimulation or an inhibition of growth hormone mRNA levels. In sexually mature goldfish, testosterone treatment stimulated growth hormone mRNA levels in a dose-related fashion, with a lower level of sensitivity compared with sexually immature fish. To investigate the direct action of testosterone at the level of the pituitary, studies were performed in vitro, using isolated pituitaries obtained from both sexually immature and mature goldfish. A dose-dependent stimulation of the pituitary growth hormone mRNA level was observed in both sexually immature and mature goldfish. Overall, the present results indicate that physiological concentrations of androgens stimulate pituitary growth hormone synthesis in both sexually immature and mature goldfish. The observed stimulatory effect of testosterone occurs directly at the level of the pituitary, although it is possible that testosterone may also exert indirect effects through other neuroendocrine factors.