Neuroprotective effect of phenytoin against in utero hypoxic brain injury in fetal guinea pigs

The present study tests the hypothesis that phenytoin, an antiepileptic agent known to block Na⁺ and Ca²⁺ channels, will prevent hypoxic brain injury in the fetus by preventing lipid peroxidation and preserving Na⁺, K⁺-ATPase activity. Studies were performed in 37 fetuses obtained from pregnant guinea pigs at 58-60 days gestation (term). The pregnant guinea pigs were divided into four groups: a normoxic group, a hypoxic group, a normoxic group treated with phenytoin, and a phenytoin treated hypoxic group. There were eight to ten fetal guinea pigs in each group. The treatment groups were given phenytoin 30 mg/kg (50 mg phenytoin/ml solvent) intraperitoneally. Hypoxia was induced by exposing the guinea pigs to 7% oxygen for 60 min. This level of hypoxia has been shown to decrease ATP and phosphocreatine levels by 90%. The fetal brains were harvested and the brain cell membranes were prepared from each group of fetuses. Na⁺, K⁺-ATPase activity and lipid peroxidation products, measured as relative fluorescent intensity, were determined. The mean Na⁺, K⁺-ATPase activity in the control, hypoxic, phenytoin-normoxic and phenytoin-hypoxic groups was 56.4 ± 9.7, 37.9 ± 10.6, 47.0 ± 8.4 and 52.0 ± 9.7 μmol inorganic phosphate/mg protein per h, respectively. The hypoxic group had significantly less Na⁺, K⁺-ATPase activity than both the normoxic group (P < 0.01), and the phenytoin treated hypoxic group (P < 0.05). There was no significant difference between the normoxic group and either of the phenytoin-treated groups (P = ns). The mean relative fluorescent intensity, measured in μg quinine sulfate/g brain, was higher in the hypoxic, 1.85 ± 0.36, than in the normoxic group, 1.25 ± 0.10 (P < 0.05). There was no significant difference between phenytoin-hypoxic group (1.53 ± 0.35) and the phenytoin-normoxic group (1.50 ± 0.45; P = ns). Exposure to hypoxia caused a decrease in Na⁺, K⁺-ATPase activity and an increase in lipid peroxidation of fetal brain cell membranes. Treatment with phenytoin before exposure to hypoxia prevented these changes, preserving brain cell membrane structure and function. These data suggest that administration of phenytoin prior to in utero hypoxia may be neuroprotective.