Abstract 317 Poster Session II, Sunday, 5/2 (poster 61)

Uteroplacental insufficiency causes IUGR, and IUGR infants are at significant risk for perinatal hypoxic-ischemic neurological damage. A primary source of this hypoxic-ischemic damage is mitochondrial free radical production and subsequent lipid peroxidation (LP). We have previously reported that cerebral malondialdehyde levels (a measure of lipid peroxidation) and cerebral expression of Bax (a protein which promotes apoptosis)are unchanged in term IUGR rat pups who have suffered uteroplacental insufficiency. In contrast, cerebral gene expression of Bcl-2 is decreased in these animals(Lane et al-1998 Ped Res). Bcl-2 is an anti-apoptosis protein which protects cells from oxidative cell death. Decreased cerebral expression of Bcl-2 may cause the IUGR fetal brain to be more vulnerable to subsequent insults that cause cellular stress and initiate apoptosis. We therefore hypothesized that cerebral malondialdehyde levels would be increased in term fetal IUGR rat pups whose dams were placed in a hypoxic chamber prior to delivery; furthermore, this increase in lipid peroxidation would be associated with increased Bax gene expression and an increase in cerebral CPP32/Caspase-3 (Casp3) protease activity in hypoxic IUGR fetal rat brains. Casp3 activity is an early indicator of apoptosis and is necessary for DNA fragmentation. To test this hypothesis, we performed sham surgery(Con) and bilateral uterine artery ligation (IUGR) on day 19 of gestation (term-21d). 42 hours later, maternal rats (equally divided between Con and IUGR groups) were placed in 12% FiO2 for three hours or left in room air. A cesarean section was performed, and brain was harvested and prepared for malondialdehyde and Casp3 assays. Cerebral RNA was also extracted. RESULTS: Cerebral IUGR-hypoxic malondialdehyde levels were significantly increased to greater than 200% of control values (Con Hypoxic=134±34 µmol/mg protein; IUGR Hypoxic=306.4±69 µmol/mg protein*; *p <0.05) (n=8). The control hypoxic value is ≈ 2-3 times the values previously reported for normoxic Con and IUGR cerebral malondialdehyde values. mRNA levels of Bax were increased in IUGR hypoxic brains (Con Hypoxic=1.0; IUGR Hypoxic=3.9±0.2*;*p<0.05)(n=6). Similarly, Casp3 activity was increased in IUGR hypoxic brain to greater than 200% of control values (Con Hypoxic=1.0; IUGR Hypoxic=2.2±0.3*; *p<0.05)(n=4). In comparison, cerebral Casp3 activity was ≈60% of control hypoxic values in normoxic control and IUGR pups. We conclude that uteroplacental insufficiency and a subsequent decrease in maternal FiO2 results in increased cerebral lipid peroxidation, Bax mRNA levels, and Casp3 activities in IUGR term rat pups, when compared to pups who suffered from only a decrease in maternal FiO2. These findings contrast with our previous observations in normoxic con and IUGR pups, in which no significant difference in malondialdehyde and Bax mRNA levels exist. We speculate that the effects of uteroplacental insufficiency upon cerebral Bcl-2 expression cause the IUGR fetus to be less tolerant of subsequent insults, and result in increased lipid peroxidation and the initiation of apoptosis in response to hypoxia.