Abstract: Objective To investigate the androgen effects of synthetic progesterone (Medroxyproges-terone acetate, MPA) exposure on the female mosquitofish (Gambusia affinis). Methods The mature female mosquito fish were randomly divided into four groups, with one control group and three experimental groups exposed with 40 ng/L, 200 ng/L and 1 000 ng/L MPA respectively. Parallel experimental groups were also established. After 28-day-long exposure, five indexes including the body length (BL), body weight (BW), health index (CF), the section number (FJ) of the 3rd anal fin, the length (FL) change of the 4rd, 5rd, 6rd anal fin, and the morphological changes in the 14, 15 and 16 vertebral ribs in mosquito fish were observed and measured. The mRNA expression levels of vitellogenin gene (VTG〈), cytochrome P450 gene (CYP19〈) in livers, and androgen receptor gene (AR〈) in anal were also determined after 7, 14, 21 and 28 days exposure. Results The BL, BW and CF of experimental groups exposed in concentrations of 200 ng/L and 1000 ng/L MPA for 28 d were not changed significantly (respectively, P>0.05) when compared with those of the control group. The 3rd anal fin of FJ and the 6rd anal fin of FL were not changed significantly (P>0.05), however, the 4rd, 5rd of FL in experimental groups had been increased in varying degrees (P<0.01). When exposed in 200 ng/L and 1000 ng/L MPA, the L, D values of the 14th vertebral ribs, the P, P:D value of the 15th vertebral ribs, and the P, L:D, P:D value of the 16th vertebral ribs in female G. affinis were appeared very significantly different (P<0.05 or P<0.01), respectively. Centrum haemal spine elongation and with the spine nearly vertical were displayed significant changes in morphological masculinization. Compared with the control group, low concentration groups (40 ng/L MPA) VTG〈, CYP19〈 genes expression were increased significantly (P<0.01), while AR〈 expression was inhibited (P<0.05); medium concentration groups (200 ng/L MPA) VTG〈, CYP19〈, AR〈 genes expression were increased significantly (P<0.01); high concentration groups (1 000 ng/L MPA) CYP19〈, AR〈?genes expression were increased significantly (P<0.01), however the expression of VTG〈 was inhibition (P<0.05). Conclusion MPA exposure induced skeletal development morphological masculinizing effects in female mosquitofish, and the results of target gene expression level changes showed that the effects of androgen induced by MPA in mosquitofish, indicating that the MPA was a kind of androgen effect of progesterone.

Key words: Medroxyprogesterone(MPA), Gambusia affinis, Masculinization, Cytochrome P450 gene (CYP19α), Vitellogenin gene (VTGα), Androgen receptor gene (ARα), mRNA expression, Skeleton morphology