Myocardial xanthine oxidase/dehydrogenase.

Area of Science:

• Biochemistry
• Cardiology
• Enzymology

Background:

• High-energy phosphates in heart muscle are rapidly catabolized into purine nucleosides and oxypurines during oxygen deprivation.
• Understanding the enzymes involved in this metabolic pathway is crucial for cardiac research.

Purpose of the Study:

• To investigate the role of xanthine oxidase/dehydrogenase in the breakdown of high-energy phosphates in the rat heart.
• To quantify xanthine oxidase activity in myocardial tissue.

Main Methods:

• Utilized novel high-pressure liquid chromatography techniques to analyze purine release from isolated perfused rat hearts.
• Administered allopurinol, a xanthine oxidase inhibitor, to assess its effect on purine release.
• Measured xanthine oxidase activity in rat heart homogenates before and after gel-filtration to remove inhibitors.

Main Results:

• Rat hearts released adenosine, inosine, hypoxanthine, xanthine, and urate under ischemic and anoxic conditions.
• Allopurinol significantly increased hypoxanthine release, indicating xanthine oxidase involvement.
• Calculated myocardial xanthine oxidase activity was approximately 18 mU/g wet weight.
• Measured activity in homogenates was 9 mU/g wet weight, increasing to 31 mU/g after inhibitor removal.
• Rat myocardial xanthine oxidase predominantly exists in the dehydrogenase form, converting to the oxidase form upon cold storage.

Conclusions:

• Xanthine oxidase/dehydrogenase is significantly involved in the purine breakdown pathway in oxygen-deprived heart muscle.
• Rat myocardial tissue possesses substantial xanthine oxidase activity, primarily in the dehydrogenase form.
• Further research into xanthine oxidase modulation may offer therapeutic targets for cardiac conditions involving ischemia.