Xanthine Oxidase Activation Modulates the Endothelial (Vascular) Dysfunction Related to HgCl₂ Exposure Plus Myocardial Infarction in Rats

Heavy metal exposure is associated with cardiovascular diseases such as myocardial infarction (MI). Vascular dysfunction is related to both the causes and the consequences of MI. We investigated whether chronic exposure to low doses of mercury chloride (HgCl₂) worsens MI-induced endothelial dysfunction 7 days after MI. Male Wistar rats were divided into four groups: Control (vehicle), HgCl₂ (4 weeks of exposure), surgically induced MI and combined HgCl₂-MI. Morphological and hemodynamic measurements were used to characterize the MI model 7 days after the insult. Vascular reactivity was evaluated in aortic rings. Chronic HgCl₂ exposure did not cause more heart injury than MI alone in terms of the morphological or hemodynamic parameters. Vascular reactivity increased in all groups, but the combination of HgCl₂-MI increased the vasorelaxation induced by ACh compared with the HgCl₂ and MI groups. Results showed reduced endothelial nitric oxide synthase (eNOS) protein expression in the MI group; increased iNOS activity in the HgCl₂-MI group, although without enough magnitude to reverse the reduction in NO bioavailability; and increased phenylephrine response in the HgCl₂-MI group due to an increase in ROS production, notably via xanthine oxidase (XO). Results suggest that the combination of 1 month pre-exposure of HgCl₂ before MI changed the endothelial generation of oxidative stress induced by mercury exposure from NADPH oxidase pathway to XO (xanthine oxidase)-dependent ROS production.