Myocardial xanthine oxidoreductase activity in hypertensive and hypercholesterolemic rats

In several species, xanthine oxidoreductase activity seems to be a major source of free radicals in myocardial tissue. Its activity changes during development and aging, at least in the rat heart. Hardly any data are available about its activity in two important diseases, hypertension and hypercholesterolemia, in which the production of free radicals induced by xanthine oxidoreductase activity could play a role. Therefore we measured the activity of xanthine oxidase and dehydrogenase in myocardial tissue of spontaneously hypertensive, Wistar (control hypertensive), Yoshida (hypercholesterolemic) and Brown Norway (control hypercholesterolemic) rats of various ages. Cytosolic fractions were incubated at 30°C, pH 8.3, with 60 μM xanthine, and the formation of urate was measured with high performance liquid chromatography. In the Wistar group, xanthine oxidoreductase activity was relatively constant during aging (about 1.8 U/g protein). In the hypertensive group, the activity increased gradually from 1.7 to 2.3 U/g at 18 months (p <0.05 compared with Wistar at 18 months). Xanthine oxidase was about twice as high in both groups at 18 months (p <0.001 compared with 2 and 6 months). The ratio of xanthine dehydrogenase to xanthine oxidase had decreased 42% at this age (p <0.001). In the Yoshida and Brown Norway groups, xanthine oxidoreductase activity was similar, with a peak at 6 months. These data suggest that the hypercholesterolemic state does not influence xanthine oxidoreductase activity. In contrast, in hypertrophied myocardium, xanthine oxidoreductase activity was higher than in the control, suggesting a different potential for free-radical generation. The combined effect of aging and hypertrophy could make these hearts more susceptible to damage from ischemia and reperfusion, especially in the light of the decrease in detoxifying systems with age.