[Xanthine oxidoreductase activity in rat brain tissue: the changes after decapitation]

Since only little xanthine oxidase (XO) activity in mammalian brain was detected in earlier reports, the major end product of AMP degradation in the brain has been believed to be hypoxanthine. Our recent experimental study however, has indicated the presence of uric acid in the rat brain subjected to focal ischemia or cold injury. Allopurinol, a xanthine oxidoreductase inhibitor, has been found to markedly suppress the uric acid production in the same experimental settings. These results suggested that uric acid is generated from hypoxanthine by enzymatic reaction in injured brain tissue. The aim of this experiment is to prove the existence of xanthine oxidoreductase activity in brain tissue. Xanthine oxidoreductase activity in rat cerebral tissue was measured immediately or at 24-hour after decapitation. Under pentobarbital anesthesia, twenty Sprague-Dawley rats were killed by decapitation following washout of the blood by trans-cardiac perfusion with cold physiological saline. Immediately or after 24 hours of decapitation ischemia, the forebrain was removed and homogenized in 6 ml ice cold 0.05 M potassium phosphate buffer (pH 7.8) containing 1 mM phenylmethylsulfonyl fluoride, 0.3 mM EGTA, and 10 mM dithiothreitol. The homogenate was centrifuged at 100,000 g for 60 min and then the supernatant was dialyzed overnight against 0.05 M potassium phosphate buffer (pH 7.8). Aliquot of each dialyzed supernatant (sample) and standard xanthine solution with NAD was reacted at 37 degrees C for 15 min to measure the combined activity of xanthine dehydrogenase (XDH) and XO. For the measurement of XO, standard xanthine solution without NAD was used.(ABSTRACT TRUNCATED AT 250 WORDS)