Pharmaceuticals are ubiquitous
pollutants in the aquatic environment where their potential effects on non-target species like fish has only recently become subject of systematic investigations. In the present study, experiments were undertaken to examine the effects of a synthetic
pharmaceutical endocrine disruptor, ethynylestradiol (EE2), given in water at 5 or 50 ng/L and sampled at days 0 (control), 3 and 7 after exposure, on hepatic phase I and II biotransformation and hormonal pathways of juvenile salmon using quantitative (real-time) polymerase chain reaction (qPCR), Vtg ELISA and
7-ethoxyresorufin O-deethylase (
EROD) catalytic activity. Our data show that EE2 produced time- and concentration-specific modulation of
estrogen receptor isoforms (
ERalpha,
ERbeta) and
androgen receptor-beta (ARbeta). EE2 produced a concentration-specific induction of
vitellogenin (Vtg) and
zona radiata
protein (Zr-
protein) at day 3 after exposure. At day 7, Vtg and Zr-
protein mRNA (and plasma Vtg
protein) expression were significantly decreased in the group given 5 ng EE2/L, compared to
dimethyl sulfoxide (
DMSO) control group. In the
xenobiotic biotransformation pathway, EE2 produced a significant increase of
aryl hydrocarbon receptor-alpha (AhRalpha) at day 3 in the group given 5 ng EE2/L and AhRbeta was decreased at the same concentration at day 7. While
CYP3A was not significantly affected by EE2 exposure, the
CYP1A1,
AhR nuclear translocator (Arnt) and AhR repressor (AhRR)
mRNA showed an apparent EE2 concentration and time-dependent decrease. The expression of
uridine diphosphoglucuronosyl
transferase (UGT) and
glutathione S-transferase class pi-like (GSTpi-like)
mRNA were decreased after exposure to 50ng EE2/L at both day 3 and 7 after exposure. The effect of EE2 on the
CYP1A1 gene expressions paralleled effect on
EROD and AhRR
mRNA, suggesting a direct role of EE2 in controlling cellular detoxification machinery. Interestingly, the carrier vehicle,
DMSO produced significant time-dependent induction of estrogenic (
ERalpha, Vtg and Zr-
protein) responses, compared with blank (i.e. without
DMSO) controls at day 7 post-exposure. The effect of
DMSO totally underscored the observed EE2 effect at day 7 after exposure. In general, these findings support previous reports on the endocrine effects of EE2, in addition to effects on hepatic biotransformation system. In view of the data presented here and our recent studies, the use of
DMSO as carrier vehicle in endocrine toxicological experimental studies should be re-evaluated.