In this study, we investigated the effects of testosterone and a nonaromatizable androgen, 11 beta-hydroxyandrosterone, on maturational gonadotropin (GtH-II) subunit gene expression in the goldfish pituitary. While testosterone treatment at physiological doses resulted in stimulation of GtH-II-alpha and -beta subunit mRNA production, time-course and dose-response studies performed on sexually immature goldfish of mixed sex, using a wider dose range exceeding physiological levels, demonstrated a biphasic response to in vivo androgen treatment. Time-related treatment with testosterone and 11 beta-hydroxyandrosterone (20 micrograms/fish) resulted in an initial inhibition of GtH-II subunit mRNA production (12-24 h) followed by stimulation at 72-96 h. In dose-response studies, treatment for 24 h with testosterone resulted in a significant stimulation at the low physiological doses of 0.2 and 2 micrograms/fish. At the supraphysiological level of 20 micrograms/fish, testosterone treatment resulted in no stimulation or in decreased GtH-II subunit mRNA levels compared to the control values. Similarly, treatment with 11 beta-hydroxyandrosterone resulted in a significant stimulation of GtH-II subunit mRNA levels at low physiological concentrations (0.2 microgram/ fish) and an inhibition, or no stimulation, at higher concentrations (2-20 micrograms/fish). In sexually mature goldfish of mixed sex, the biphasic effect of testosterone was not observed in vivo, and treatment with this steroid resulted in stimulation of GtH-II subunit mRNA production in a dose-related manner. To investigate the direct action of testosterone, studies were carried out using isolated goldfish pituitary fragments from goldfish of mixed sex in vitro. Treatment with testosterone at various concentrations was found to stimulate GtH-II subunit mRNA production in pituitary glands obtained from both sexually immature and sexually mature goldfish. Overall, the present study demonstrates a stimulatory effect of testosterone on GtH-II subunit mRNA levels in goldfish. The observed stimulation of basal GtH-II subunit mRNA production by testosterone occurs, in part, through a direct action at the level of the pituitary in both sexually immature and mature goldfish.

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.

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