Role of purines and xanthine oxidase in reperfusion injury in perfused rat liver.

The purpose of this study was to evaluate the possible involvement of xanthine and xanthine oxidase in reperfusion injury in a low-flow, reflow model of liver perfusion. Livers were perfused at flow rates around 25% of normal for 90 min and then at normal flow rates (4 ml/g/min) for 30 min. When flow was restored to normal, malondialdehyde and lactic dehydrogenase (LDH) were released into the effluent perfusate. Malondialdehyde production rapidly reached values of 300 nmol/g/hr whereas LDH increased from basal levels of 100 to 600 U/l upon reperfusion. Trypan blue was taken up exclusively in cells in pericentral regions of the liver lobule under these conditions. Xanthine and hypoxanthine in the effluent perfusate increased steadily during the low-flow period reaching values around 5 and 10 microM, respectively, and decreased rapidly after the flow was restored to normal. Perfusion with nitrogen-saturated buffer for 3 min before restoration of normal flow rates or infusion of the radical scavenger catechin (400 microM) reduced cell damage by about 50%. Infusion of allopurinol (2-6 mM), an inhibitor of xanthine oxidase, prevented reperfusion injury in a dose-dependent manner. Taken together, these data indicate that a reperfusion injury occurs in liver upon reintroduction of oxygen which is initiated by oxidation of xanthine and hypoxanthine via xanthine oxidase and ultimately leads to production of lipid peroxides. Surprisingly, infusion of xanthine (4 mM), substrate for xanthine oxidase, reduced hepatocellular injury on reperfusion. LDH release was decreased from values around 700 to less than 200 U/l and trypan blue uptake in pericentral region was prevented totally by xanthine.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial reperfusion injury. Role of myocardial hypoxanthine and xanthine in free radical-mediated reperfusion injury.

The aim of this study was to differentiate myocardial reperfusion injury from that of ischemia. We assessed the role of the myocardial adenosine 5'-triphosphate (ATP) catabolites, hypoxanthine and xanthine, generated during ischemia and the early phase of reperfusion, in reperfusion injury by modulating adenosine transport and metabolism with specific metabolic inhibitors. This was followed by intracoronary infusion of exogenous hypoxanthine and xanthine. Twenty-four dogs instrumented with minor-axis piezoelectric crystals and intraventricular pressure transducers were subjected to 30 minutes of normothermic global myocardial ischemia and 60 minutes of reperfusion. In Group 1 (n = 7), normal saline was infused into the cardiopulmonary bypass reservior before ischemia and before reperfusion. Saline solution containing 25 microM p-nitrobenzylthioinosine (NBMPR) and 100 microM erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) was infused in Group 2 (n = 10) dogs. Group 3 (n = 7) dogs were treated exactly like those in Group 2 except, at the end of the ischemic period and immediately before releasing the cross-clamp, a solution of EHNA-NBMPR containing 100 microM hypoxanthine and 100 microM xanthine was infused into the aortic root. Left ventricular performance and myocardial adenine nucleotide pool intermediates were determined before and after ischemia. ATP was depleted by about 50% (p less than 0.05 vs. preischemia) in all groups after 30 minutes of ischemia. Inosine was the major ATP catabolite (9.29 +/- 1.2 nmol/mg protein) in Group 1, while adenosine (9.91 +/- 0.7 nmol/mg protein) was the major metabolite in EHNA-NBMPR-treated dogs (Groups 2 and 3). Hypoxanthine levels were fivefold more in Group 1 compared with Groups 2 and 3 (p less than 0.05). Left ventricular performance in Group 1 decreased from 76.8 +/- 7.6 to 42.9 +/- 9.8 and 52.3 +/- 8.4 dynes/cm2 x 10(3) (p less than 0.05), while myocardial ATP decreased from 30.9 +/- 2.2 to 17.2 +/- 1.0 and 16.5 +/- 1.0 nmol/mg protein during 30 and 60 minutes of reperfusion, respectively (p less than 0.05 vs. preischemia). Ventricular function in Group 2 dogs completely recovered within 30 minutes of reperfusion, and myocardial ATP recovered to the preischemic level at 60 minutes of reperfusion. In Group 3, left ventricular performance was depressed by 39% and 30% during 30 and 60 minutes of reperfusion (p less than 0.05), respectively, and myocardial ATP did not recover during reperfusion despite a significant intramyocardial adenosine accumulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Redox status and pulmonary vascular reactivity.

Oxygen radicals are produced during oxidative metabolism in proportion to the tissue oxygen tension. The studies reported here have shown that oxygen radicals or the sulfhydryl oxidant, diamide, caused pulmonary vasodilatation in the isolated perfused rat lung. Could oxygen radicals play a role in the physiologic control of pulmonary vascular smooth muscle tone?

Rat intestinal peroxidase: inhibition by endogenous xanthine and xanthine oxidase.

The high-speed supernatant from homogenates of rat small intestine contains a heat-stable, dialyzable factor which showed a time-dependent inhibition of peroxidase activity in salt extracts of the tissue. The inhibitor was purified by chromatography on Dowex 50W-X8 and identified as xanthine. The inhibition of peroxidase by xanthine was prevented by allopurinol, an inhibitor of xanthine oxidase, and hypoxanthine was also found to be inhibitory. H2O2, produced in the reaction catalyzed by xanthine oxidase, was shown to be directly responsible for the observed inhibition. The time-dependent loss of peroxidase activity in the presence of xanthine or hypoxanthine occurred more rapidly in NH4Cl than in CaCl2 extracts of small intestine and was due to the difference in the initial concentration of H2O2 in these two extracts. The possible relationship between peroxidase and xanthine oxidase in the rat small intestine is discussed.

Effect of caffeine on G2 repair and its reversion by adenosine.

Chromosome damage induced in root meristems of Allium cepa L. by an 18-h treatment with 5-aminouracil (AU) was enhanced by 2-h pulses with 5 mM caffeine, the most effective pulse being given from the 8th to the 10th h after AU. Chromosome damage was detected by the percentage of anaphases or telophases showing chromosomal aberrations. This caffeine effect was partially reversed by adenosine. We suggest that this caffeine anti-repair effect could be due to a competition between methylxanthine and an adenine-nucleotide derivative (ATP?) required for some step(s) of G2-prophase repair.

[Xanthine oxidase--xanthines as a system of endogenous regulation of phosphodiesterase activity]. / Ksantinoksidaza--ksantiny kak sistema éndogennoi reguliatsii aktivnosti fosfodiésterazy.

The paper is concerned with the data indicating close interaction between xanthinoxidase (Xase) and phosphodiesterase (PDE). PDE activity can be modified by affecting the activity of Xase. This effect is mediated by changes in the concentrations of endogenous xanthines. The action of PDE inhibitors, methylxanthines, is discussed from the point of view of the above effect. The data obtained hold promise for purposeful monitoring of tissue concentrations of the cyclic nucleotides in vivo and in vitro.