INFLUENCE OF ORGANOCHLORINE PESTICIDES ON MATURATION AND POSTFERTILIZATION DEVELOPMENT OF BOVINE OOCYTES IN-VITRO

The aim of this study was to perform a dose-response test to determine whether bovine oocytes exposed to dichlorodiphenyltrichloroethane (DD T), hexachlorocyclohexane (gamma HCH), or methoxychlor (MXC) in vitro would exhibit changes in maturation rates, cleavage rates at Day 2, or blastocyst rates at Day 7 to 8 after fertilization in vitro (IVF). Al l three pesticides affected maturation and degeneration rates in a dos e-dependent manner, but to different extents. Higher concentrations of pesticides were associated with higher rates of chromatin degeneratio n. Because the maturation of bovine oocytes was depressed in a dose-de pendent manner, the fertilizability and further embryonic development of in vitro matured oocytes was studied at the lowest previously teste d concentration (7.25 mu g/mL) only. No significant difference in fert ilization rates was seen between unexposed control and treated groups. The cleavage rates did not differ among groups 48 h after IVF, The nu mber of morulae and blastocysts on Day 7 to 8 after IVF, which is comm only used as a parameter for normal development, was significantly dif ferent between control and DDT- and gamma HCH-treated groups, but not between the control and MXC groups. The pesticides did not differ sign ificantly among themselves. These results show that the tested pestici des decrease the rate of normal oocyte maturation in vitro in a dose-d ependent manner. The effect of the lowest concentration of pesticides is seen only after Day 7 of embryo development. (C) 1998 Elsevier Scie nce Inc.