Effects of 4-tert-octylphenol on initiation and maintenance of pregnancy following oral administration during early pregnancy in rats.

4-tert-Octylphenol (OP) is an alkylphenol that is an intermediate in the production of alkylphenol ethoxylates. OP has been reported to be the most potent estrogenic alkylphenol in vitro. In the present study, the effects of OP on initiation and maintenance of pregnancy were investigated in rats. Inseminated female rats were orally given OP at 0,15.6,31.3,62.5 and 125 mg/kg on day 0 through day 8 of pregnancy. Female rats were sacrificed on day 20 of pregnancy, and pregnancy outcome was determined. Decreases in body weight gain and food consumption on days 0-9 were found at 31.3 mg/kg and above, and at 15.6 mg/kg and above, respectively. The pregnancy rate was not adversely affected by OP administration during early pregnancy even at 125 mg/kg. The incidence of post-implantation loss per litter at 31.3 mg/kg and above was significantly higher than that in the control group. The body weights of live fetuses in the OP-treated groups were not significantly different from those in the control group. No increase in the incidence of fetuses with external malformations was found in any OP-treated group. We concluded that OP during early pregnancy caused post-implantation embryonic loss at doses that showed maternal toxicity.