Vascular Effects of Commercially Available Preparations of Xanthine Oxidase

Abstract

Xanthine oxidase (XO) has been generally used with xanthine or hypoxanthine as a pharmacological probe to generate oxygen free radicals, which are known to affect the tension of the isolated vessels in vitro. However, it was reported that commercially available XO itself caused vasorelaxation. This study was undertaken to evaluate the vascular effects of four commercially available XO from Sigma [grade 1 (XO1) and 4 (XO2)], Biozyme Laboratories (XO3) and Boehringer Manheim (XO4). All XO preparations (0.01 U/ml) produced rapid and transient relaxation of endothelium intact rat aortic rings precontracted with phenylephrine in the presence of indomethacin (10 −5M). This relaxation was accompanied by an increase in tissue cyclic GMP level. Removal of the endothelium abolished the relaxation. XO-induced relaxation was inhibited markedly b pretreatment with NG-monomethyl-L-arginine (3 × 10 −4M), oxyhemoglobin (10−5M) and methylene blue (10−5M). Trypsin inhibitor (5 μg/ml) also abolished the relaxation induced b...