EFFECT OF TESTOSTERONE ON MATURATIONAL GONADOTROPIN SUBUNIT MESSENGER-RIBONUCLEIC-ACID LEVELS IN THE GOLDFISH PITUITARY

In this study, we investigated the effects of testosterone and a nonar omatizable androgen, 11 beta-hydroxyandrosterone, on maturational gona dotropin (GtH-II) subunit gene expression in the goldfish pituitary. W hile testosterone treatment at physiological doses resulted in stimula tion of GtH-II-alpha and -beta subunit mRNA production, time-course an d dose-response studies performed on sexually immature goldfish of mix ed sex, using a wider dose range exceeding physiological levels, demon strated a biphasic response to in vivo androgen treatment. Time-relate d treatment with testosterone and 11 beta-hydroxyandrosterone (20 mu g /fish) resulted in an initial inhibition of GtH-II subunit mRNA produc tion (12-24 h) followed by stimulation at 72-96 h. In dose-response st udies, treatment for 24 h with testosterone resulted in a significant stimulation at the low physiological doses of 0.2 and 2 mu g/fish. At the supraphysiological level of 20 mu g/fish, testosterone treatment r esulted in no stimulation or in decreased GtH-II subunit mRNA levels c ompared to the control values. Similarly, treatment with 11 beta-hydro xyandrosterone resulted in a significant stimulation of GtH-II subunit mRNA levels at low physiological concentrations (0.2 mu g/fish) and a n inhibition, or no stimulation, at higher concentrations (0.2 mu g/fi sh). 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-r elated manner. To investigate the direct action of testosterone, studi es were carried out using isolated goldfish pituitary fragments from g oldfish of mixed sex in vitro. Treatment with testosterone at various concentrations was found to stimulate GtH-II subunit mRNA production i n pituitary glands obtained from both sexually immature and sexually m ature 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 testos terone occurs, in part, through a direct action at the level of the pi tuitary in both sexually immature and mature goldfish.