Toxic Effects of In Vitro Exposure to p-tert-Octylphenol on Bovine Oocyte Maturation and Developmental Competence

Alkylphenolic compounds are a widespread family of xenoestrogens. High concentrations of these substances are present in sewage sludge that is spread on arable land and pasture as fertilizer. Because of their known endocrine system-disrupting activity, alkylphenols represent a potential risk for the reproductive health of farm animals. In this study, the impact of p-tert-octylphenol (OP) on the developmental competence of bovine oocytes was evaluated. Endocrine activity of OP was investigated for its effect on estrogen receptors (alpha) and (beta) (ER(alpha) and ER(beta)) and progesterone receptor (PR) mRNA levels. Cumulus-oocyte complexes (COCs) were exposed during in vitro maturation to serial concentrations of OP (1–0.0001 (mu)g/ml) and were compared with vehicle-treated controls and a group of COCs treated with 17(beta)-estradiol (E2). A dose-related decrease in the percentage of oocytes that completed maturation after 24 h and in oocyte fertilization competence was observed at doses of OP as low as 0.01 (mu)g/ml. Groups treated with >=0.001 (mu)g/ml OP showed impaired embryo development. No adverse effects of E2 were observed. In the E2-treated COCs, ER(alpha) mRNA was decreased but PR mRNA was upregulated compared with controls. Treatment with 0.001 and 0.0001 (mu)g/ml OP induced a decrease in ER(alpha) mRNA, but ER(beta) and PR mRNA were not affected. Treatment with 0.01 (mu)g/ml OP did not produce changes in the expression of any of the mRNAs studied. OP impairs meiotic progression and developmental competence of bovine oocytes without demonstrating clear estrogen-mimic activity.