Polymorphonuclear leucocytes as potential source of free radicals in the ischaemic-reperfused myocardium

The feasibility of polymorphonuclear leucocytes as a potential source of free radicals during reperfusion of ischaemic myocardium was evaluated. Isolated rat heart was perfused in the presence of f-Met-Leu-Phe-activated and normal polymorphonuclear leucocytes for 30 min. To judge the degree of cellular injury which might result from activated polymorphonuclear leucocytes during perfusion, isolated hearts were also perfused with superoxide anions, hydroxyl radicals, and hypochlorous acid-generating systems in the absence or presence of their corresponding scavengers, superoxide dismutase plus catalase, dimethylthiourea, and allopurinol, respectively. Activated polymorphonuclear leucocytes stimulated the release of lactate dehydrogenase, a biological marker of cellular injury, and malondialdehyde, a presumptive marker for lipid peroxidation; increased tissue injury, as evidenced by morphologic examinations using light and electron microscopy; decreased dry/wet ratios of heart, signifying oedema formation; and reduced myocardial adenosine triphosphate and creatine phosphate content as well as coronary flow, indicating decreased myocardial performance. These biological, physiological, and morphologic parameters were reversed significantly, but not completely, by treating the heart with scavengers, superoxide dismutase plus catalase or allopurinol, but were reversed completely by simultaneous treatment with superoxide dismutase, catalase, and allopurinol. Comparable results were obtained when the hearts were treated with each of these free radical-generating systems and their corresponding scavengers. Generation of free radicals was confirmed either by cytochrome c reduction or by examining the chemiluminescence response using a luminometer. These results indicate that activated polymorphonuclear leucocytes can cause myocardial cellular injury equivalent to the damage caused by free radicals and oxidants which are present in an ischaemic-reperfused heart, suggesting that polymorphonuclear leucocytes may be a potential source of free radicals in the reperfused heart.

Enhanced prostaglandin production in the ischemic-reperfused myocardium by captopril linked with its free radical scavenging action

Captopril, an angiotensin converting enzyme inhibitor, has been shown to increase prostaglandin production by an as yet unknown mechanism, which this study was designed to explore. Isolated rat heart was perfused by the Langendorff technique for 15 minutes in the presence or absence of captopril. Ischemia was then induced for 60 minutes by terminating the coronary flow, followed by 60 minutes of reperfusion. Our results indicate that captopril stimulated prostaglandin and thromboxane production, but it inhibited malonaldehyde formation. Coronary flow and high energy phosphate compounds were increased, but lactate dehydrogenase and creatine kinase release decreased, demonstrating cardioprotective effects. Captopril also inhibited the production of hydroxyl radical in the heart during reperfusion, suggesting that stimulated prostaglandin production may be linked with the generation of free radicals via the eicosanoid system.

Direct scavenging of free radicals by captopril, an angiotensin converting enzyme inhibitor

Captopril, an angiotensin converting enzyme (ACE) inhibitor, was hypothesized to be a potential scavenger of free radicals because of the presence of a thiol group. The scavenging action of captopril was examined against superoxide anion (O2-), hydroxyl radical (OH.), hypohalite radical (HOCL) either generated biochemically, or derived from activated polymorphonuclear leukocytes (PMN). Our results indicate that captopril is an extremely potent free radical scavenger, scavenging power being as effective as superoxide dismutase (SOD) against O2-, or dimethylthiourea against OH., but better than allopurinol against OCL. plus HOCL. Free radical scavenging action of captopril against PMN-derived free radical is equivalent to the combined effects of SOD, catalase and allopurinol.