Developmental changes in antioxidant enzymes and the effects of high O2 after birth on enzyme activity

Zhao, Yong (2002) Developmental changes in antioxidant enzymes and the effects of high O2 after birth on enzyme activity. Masters thesis, Memorial University of Newfoundland.

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Abstract

Antioxidant enzymes play a very important role in protecting newborn babies who have to cope with an increase in O₂ exposure after birth. Some researchers believe that the rise in antioxidant enzyme activity in the last stage of development of fetal life is an essential preparation for birth. However, there are contradictory reports. We have investigated the developmental changes in catalase (CAT), superoxide dismutase (both Mn-SOD and Cu/Zn-SOD) and glutathione peroxidase (GPx) activities in fetal rat livers at different stages of gestation and explored the effects of high O₂ after birth on antioxidant enzyme activities. Our results showed that CAT and GPx activities increased when enzyme activities were expressed per mg protein from 15 day of gestation to 22 day of gestation. But, when SOD activity is expressed per mg protein, total SOD activity decreased. High O₂ exposure induced an increase in AOE activities when newborn rats were exposed to 95% O₂ for 9 days. Both CAT and GPx activities increased continuously. However, the pattern of increasing SOD activity was different from that seen for both CAT and GPx. Total SOD activity rose by 20% at 3 days of exposure, by 34% at 6 days of exposure and by only 9% at 9 days of exposure when compared with corresponding newborn rats exposed to room air. Cu/Zn-SOD activity increased during the first 6 days of exposure and then decreased. There was no change in MnSOD activity during the first 3 days of exposure, but after 3 days of exposure, MnSOD activity began to increase. -- In conclusion: 1) both CAT and GPx activities increased during the last stage of development, 2) total SOD activity decreased before birth, 3) total SOD activity did not change concomitantly with both CAT and GPx activity during the last stage of development after birth, 4) all liver antioxidant enzyme activities increased significantly during exposure to high O₂, but total SOD enzyme activities decreased after having increased for 6 days.

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