Regulation of plasma gonadotropin II secretion by sex steroids, aromatase inhibitors, and antiestrogens in the protandrous black porgy, Ancanthopagrus schlegeli Bleeker

Plasma gonadotropin II (GTH II) concentrations were significantly higher (a pprox. 15-20-fold) in estradiol-17 beta (E-2) treated (1.0 mug or 2.5 mug g (-1) body weight) female black porgy from days 4 to 12 compared with the co ntrol. E-2 (1 mug g-l wt.) had a stronger stimulation on plasma GTH II in e arly recrudescent phase (low GSI) males (11-fold) than in high GSI and late spermiating males (2.6-fold, P < 0.05). No effect of androgens (testostero ne, T; Soc-dihydrotestosterone, DHT) on plasma GTH II levels was observed e ither sex. The levels of plasma GTH II were stimulated in 1,4,6-androstatri ene-3,17-dione (ATD, 1 mug g(-1), 2 mug g(-1) body wt.) and fadrozole-treat ed (1 mug g(-1), 3 mug g(-1) body wt.) groups compared to control. Tamoxife n (1 mug g(-1), 3 mug g(-1) body wt.) but not enclomiphene could stimulate high GTH II levels in plasma. In another experiment of ATD in combination w ith T, T treatment further attenuated the ATD stimulation of plasma GTH II levels. We concluded that GTH II secretion is positively regulated by an es trogen-specific effect in female and male black porgy. Gonadal stage had si gnificant effects on the responsiveness of GTH II to E, stimulation in male s. A negative aromatase-dependent feedback control of plasma GTH II levels was also suggested in the protandrous black porgy, Acanthopagrus schlegeli. (C) 2001 Published by Elsevier Science Inc.