Androgens stimulate gonadotropin-II beta-subunit in eel pituitary cells in vitro

Primary cultures of juvenile eel (Anguilla anguilla) pituitary cells were used to study the direct effects of sex steroids on gonadotropin (GtH-II) cell content and release (radioimmunoassay) as well as on mRNAs levels for alpha and GtH-II beta-subunits (dot-blot). Testosterone stimulated GtH-II production in a dose-and time-dependent manner by selectively increasing mRNAs for GtH-II beta-subunit but not alpha-subunit. This positive effect was also induced by non-aromatizable androgens (androstanediol and dihydrotestosterone) but not by estradiol, indicating an androgen-specific effect in the eel. The androgen-specific stimulation of eel GtH-II beta appears closer to the regulation of mammalian follice stimulating hormone-beta (FSH beta) than that of salmonid GtH-II beta or mammalian luteinizing hormone-beta (LH beta)-subunits. Comparison with previous in vivo experiments suggests multiple sites of action of sex steroids on the brain-pituitary gonadotropic axis for the positive feedback on GtH-II synthesis in this juvenile fish. (C) 1997 Elsevier Science Ireland Ltd.