Antioxidant enzymatic activity in embryos and placenta of rats chronically exposed to hypoxia and hyperoxia

Embryos exhibit lower enzymatic antioxidant activity (EAOA) than adults, in accordance with the low in utero oxygen concentration. We asked whether external oxygen stress can modulate embryonic EAOA and what the placenta role is as a mediator between embryos and external milieu. Pregnant rats were exposed to hyperoxia (90% O-2) or hypoxia (10% O-2) during 8 days in the second or third trimester. Activities of catalase (CAT), superoxide dismutase and glutathione peroxidase (GPx) were measured in the term embryonic brain, lung and heart and liver; 2-week-old whole embryonic sac and placenta. In term ''hyperoxic'' embryos, only CAT increased by 30% in heart and lungs and liver. In the placenta, GPx increased by 31%. In term ''hypoxic'' embryos, only CAT activity decreased by 64%, 25% and 29% in brain, liver and placenta. In 2-week-old ''hyperoxic'' embryos CAT activity increased by 85% and GPx by 45% in the embryonic sac. In the placenta, GPx increased by 55%. The limited embryonic EAOA response is possible due to maternal physiological buffering of oxygen supply. Placental EAOA is similar to other embryonic organs. It may protect the placenta proper, thus ensuring normal embryonic development. (C) 1997 Elsevier Science Inc.