DOSE-DEPENDENT EFFECT OF ALLOPURINOL ON FREE RADICAL PRODUCTION DURING CEREBRAL HYPOXIA IN NEWBORN PIGLETS. ▴ 413

Abstract

Previous studies have shown that allopurinol, a xanthine oxidase inhibitor and free radical scavenger, has a neuroprotective effect during hypoxia-ischemia. The present study tests the hypothesis that allopurinol has a dose-dependent effect on the hypoxia-induced generation of free radicals in the cerebral cortex of newborn piglets. Studies were performed on 15 piglets divided into 6 groups. Group 1 (control n=5) pretreated with saline and Groups 2-6 (n=2 each) pretreated with allopurinol at doses of 10, 20, 50, 100 and 200 mg/kg IV respectively. Hypoxia was induced by lowering the FiO2 to 5-7% for 1 hr to achieve a PaO2 of 18-20 mmHg. Cortical biopsies were obtained via cranial windows and tissue homogenized in 100 mMα-phenyl-N-tert-butyl-nitrone (PBN). PBN spin adducts were extracted in a 2:1 mixture of chloroform:methanol and electron spin resonance spectroscopy performed. Signal height (intensity) of spectrum divided by tissue weight was expressed as mm/g tissue. Brain tissue ATP and phosphocreatine (PCr) concentrations were used to determine cellular energy metabolism. Tissue levels of allopurinol were measured by HPLC and increased linearly with drug dose. Free radical intensity in Group 1 was 387±16 mm/g tissue(mean±S.E.). Groups 2-6 showed a linear decrease in free radical intensity with values approaching zero in the groups receiving 100 and 200 mg/kg of allopurinol (p<0.01). ATP concentrations (μmole/g tissue) increased linearly from 1.09±0.55 in Group 1 to 5.02±0.45 in the 200 mg/kg group (p<0.01). PCr concentrations (μmol/g brain) increased linearly from 0.19±0.03 in Group 1 to 1.10±0.29 in the 200 mg/kg group (p<0.01). The data show that administration of allopurinol decreases free radical production and preserves high energy phosphate compounds during hypoxia in a dose-dependent menner. We speculate that allopurinol reduces free radical production by inhibiting xanthine oxidase and scavenging free radicals and may play a direct neuromodulatory role in reducing excitotoxicity during hypoxia. (NIH-HD-20337, MOD-#6-FY94-0135).