LACK OF CONVERSION OF XANTHINE DEHYDROGENASE TO XANTHINE-OXIDASE DURING WARM RENAL ISCHEMIA

Irreversible transformation of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) during ischemia was determined measuring XDH and total enzyme activity in kidneys before and after 60 min ofclamp ofthe renal pedicle. Tissue levels ofadenine nucleotides, xanthine and hypoxanthine were used as indicators of ischemia. After 60 min of clamping, ATP levels decreased by 72/. with respect to controls whereas xanthine and hypoxanthine progressively reached tissue concentrations of 732+49 and 979+ l5 nmol'g tissue 1, respectively. Both total and XDH activities in ischemic kidneys (30+ 15 and l9* I nmol'min I'g tissue-r) were significantly lower than in controls when expressed on a tissue weight basis. The fraction of enzyme in the XDH form was however unchanged indicating that the reduction of the nucleotide pool is not accompanied by induction ofthe type-O activity ofxanthine oxidase.