RESUMEN
Objective To investigate the mechanism involved in the brain protection afforded by prenatal hypoxic adaptation by determining the quantitative variation in bcl-2 and bax mRNA expression.Methods Twenty-four Wistar pregnant (22d pregnant) rat were randomly divided into two groups: group I (hypoxia group) and group *** ( control group) . In group Ⅰ the pregnant rats were placed in an airtight cabin specially designed for hypoxic adaptation. When O2 % in the cabin decreased to 15%, the animals were taken out breathing fresh air for 5min and then placed back in the cabin and underwent another episode of hypoxia. In group Ⅱ the animals were placed in the cabin which was not tightly closed and underwent no hypoxia. 7 fetal or newborn rats were taken at 1st, 3rd, 24th, 48th, 72nd, 120th, and 168th h after prenatal hypoxic adaptation from each group and their brains removed for determination of bcl-2 mRNA and bax mRNA. Results In control group the expression of bcl-2 and bax were observed in the brain tissue of normal fetal or newborn rats from the 22nd day in the uterus to the 7th day postpartum during which there were no significant changes in bcl-2 gene expression while bax gene expression gradually decreased with time ( the decrease was of no statistical significance) . In hypoxia group bax gene expression decreased at 8th h after hypoxic adaptation and reached the bottom at 24th h which persisted until 120th h; while bcl-2 gene expression started increasing at 24th h after hypoxic adaptation and persisted until 72nd h. The bcl-2/bax ratio also started increasing at 8th h after hypoxic adaptation and peaked at 24th h and persisted until 72nd h. Conclusions In the brain tissue of fetal and newborn rats which have undergone prenatal hypoxic adaptation, bcl-2 gene expression is elevated, bax gene expression decreases and bcl-2/bax ratio increases. These changes are time -dependent.