EFFECT OF TESTOSTERONE ON GROWTH-HORMONE GENE-EXPRESSION IN THE GOLDFISH PITUITARY

This study investigated the effects of testosterone and a nonaromatiza ble androgen, 11 beta-hydroxyandrosterone, on growth hormone gene expr ession in the goldfish pituitary. In the sexually immature goldfish, t reatment with physiological doses of both testosterone and 11 beta-hyd roxyandrosterone significantly increased the growth hormone mRNA produ ction above basal levels. However, at supraphysiological doses, treatm ent with these androgens resulted in a lower level of stimulation or a n inhibition of growth hormone mRNA levels. In sexually mature goldfis h, testosterone treatment stimulated growth hormone mRNA levels in a d ose-related fashion, with a lower level of sensitivity compared with s exually immature fish. To investigate the direct action of testosteron e at the level of the pituitary, studies were performed in vitro, usin g isolated pituitaries obtained from both sexually immature and mature goldfish. A dose-dependent stimulation of the pituitary growth hormon e mRNA level was observed in both sexually immature and mature goldfis h. Overall, the present results indicate that physiological concentrat ions of androgens stimulate pituitary growth hormone synthesis in both sexually immature and mature goldfish. The observed stimulatory effec t of testosterone occurs directly at the level of the pituitary, altho ugh it is possible that testosterone may also exert indirect effects t hrough other neuroendocrine factors.