[The importance of oxygen free radicals in the neonatal period]

Redox, acid-base and clinical analysis of preterm and term neonatal lambs

During pregnancy, fetal lambs are exposed to low oxygen tension. Thus, an effective antioxidant mechanism is partially developed which sensitizes fetus to oxidative stress. Consequently, term and preterm neonates are susceptible to molecular and cellular injury caused by oxygen species (ROS). This study aimed to evaluate the development of antioxidant enzymes and oxidative profile of preterm (135 days of pregnancy) and term (145 days of pregnancy) neonatal lambs, correlating with clinical analysis. Preterm lambs had significantly (P ≤ 0.05) lower score of vitality (4.00 ± 1.10), bradycardia (99 ± 34 bpm) and bradypnea (13 ± 10 mpm). However, both groups were normothermic and euglycemic. Preterm group had low blood pH (7.07 ± 0.10) and both groups had hypercapnia, more severe in preterm group (85.52 ± 18.65 mmHg). In addition, premature newborns had lower pO² (10.67 ± 5.65 mmHg) and SO² (6.17 ± 5.85%) values. No significant difference (P ≥ 0.05) on antioxidant enzymes and oxidative stress were verified among experimental groups, although glutathione peroxidase negatively correlated with Apgar score, heart rate, SO² and pO². Our data show that preterm neonates are less adapted to the odds of labor and to overcome the immediate changes of extra-uterine life. Furthermore, we verified an influence of glutathione peroxidase in controlling oxidative stress, which highlights mature enzymatic mechanisms of cell redox, even in premature lambs.

Roles of reactive oxygen species in female reproduction

Reactive oxygen species (ROS) are highly reactive oxidizing agents. Cells, under aerobic conditions, have a defence system against ROS, and in normal circumstances, there is an appropriate balance between pro-oxidants and antioxidants. When an overproduction of ROS develops or the body fails to eliminate ROS in excess, oxidative stress arises, during which ROS accumulate and damage cells and tissues. Besides their noxious effects, accumulating data have shown that controlled and adequate ROS concentrations exert physiologic functions. Different studies have confirmed the presence of ROS and the transcripts of the various antioxidant enzymes in the female reproductive tract. When ROS production overwhelms antioxidant defences, oxidative stress occurs, which may deeply threaten the anatomical and functional integrity of the genital tract. This review addresses the main physiological and pathological roles exerted by ROS and their scavenging systems in several processes involved in the main physiological functions of the female reproductive tract of both women and domestic animals. Particularly, the involvement of the oxidant system in several reproductive processes is investigated, such as follicular development, ovarian steroidogenesis, ovulation, corpus luteum formation and function, luteolysis, germ cell function, maintenance of pregnancy and beginning of parturition.