Estradiol-17 beta stimulates gonadotropin II expression and release in theprotandrous male black porgy Acanthopagrus schlegeli Bleeker: A possible role in sex change

The objective of the present study was to investigate the in vivo effects o f sex steroids (estradiol-17 beta, E-2; testosterone, T) and the nonaromati zable androgen 5 alpha -dihydrotestosterone (DHT) on the levels of gonadotr opin II (GTH II) in plasma and pituitary and on aromatase activity in 2-yea r-old male black porgy, Acanthopagrus schlegeli, during the prereproductive season. Black porgy GTH II and GTH II beta subunits were purified and anti -GTH II beta serum was induced. A specific radioimmunoassay for black porgy GTH II was developed. cDNA GTH II beta was also cloned from a black porgy pituitary cDNA library for use as a probe for Northern analysis. Male fish were divided into eight groups (n = 64): control; E-2 (3 doses, 2.4 ng, 72 ng, and 2.2 mug/g body weight); T (2 doses, 72 ng and 2.2 mug/g body weight ); and DHT (2 doses, 72 ng and 2.2 mug/g body weight). Fish were injected w ith the respective vehicle or different doses of material on days 0, 8, and 16. Plasma was collected at 4-day intervals from days 4 to 20. Plasma GTH II concentrations were significantly increased (up to 45-fold) in the E-2 g roup from days 4 to 20 in a dose-dependent manner. In a further experiment during the late reproductive season, plasma GTH II levels increased at 4 h and on days 1 and 2 following a single injection of 1.0 mug E-2/g body weig ht ton day 0). Androgens (T or DHT) had little or no effect on plasma GTH I I. Pituitary GTH II contents on day 20 were significantly lower in the 72-n g E-2 and 2.2-mug E-2 groups but not in the 2.4-ng E-2 group compared with the control group. Pituitary GTH II beta mRNA levels were significantly sti mulated in the 72-ng and 2.2-mug E-2 groups on day 20. Gonadal aromatase ac tivity was not significantly changed in any of the treated or control group s. It is concluded that GTH II secretion in black porgy is regulated by an estrogen-specific effect. Increased plasma GTH II levels or other factors i n addition to E-2 might be involved in the regulation of gonadal aromatase activity and sex change in protandrous black porgy. (C) 2001 Academic Press .