Nitric oxide modulation of transcellular biosynthesis of cys‐leukotrienes in rabbit leukocyte‐perfused heart

Abstract

We have studied the role of nitric oxide (NO) in the regulation of the transcellular biosynthesis of sulphidopeptide leukotrienes (cys‐LT) generated upon neutrophil‐vascular wall interactions and their functional consequences, in the spontaneously beating, cell‐perfused, heart of the rabbit. Hearts were perfused under recirculating conditions (50 ml) with 5×10⁶ purified human neutrophils (PMNL), and challenged with 0.5 μm A‐23187 for 30 min. Coronary perfusion pressure (CPP) and left‐ventricular end‐diastolic pressure (LVEDP) were monitored. Cys‐LT formation was measured by reversed phase high performance liquid chromatography (h.p.l.c.) and u.v. spectral analysis. Myeloperoxidase (MPO) enzyme activity, assayed in aliquots of the recirculating buffer, was used as a marker of PMNL adhesion to the coronary endothelium. Basal CPP and LVEDP values averaged 45±1.4 mmHg and 5±0.1 mmHg, respectively; A‐23187 triggered an increase in CPP (134±9 mmHg, at 30 min) which was significantly attenuated by pretreatment with l‐arginine, 100 μm (90±3 mmHg, at 30 min). Pretreatment with N^G‐monomethyl‐l‐arginine, 10 μm (l‐NMMA), induced a marked increase in CPP (290±40 mmHg, at 20 min) and in LVEDP (47±16 mmHg), so pronounced that it caused cardiac arrest in systole in 5 out of 6 hearts and these were prevented by l‐arginine, 100 μm (CPP 115±10 mmHg, LVEDP 6±1.1 mmHg, at 30 min). The increase in CPP was accompanied by the release of cys‐LT in the circulating buffer, which was reduced significantly by l‐arginine. Pretreatment with l‐NMMA, caused a marked rise in cys‐LT concentrations which was prevented by l‐arginine. Neither l‐arginine nor l‐NMMA affected directly the A‐23187‐induced arachidonic acid (AA) metabolism in isolated PMNL alone. Pretreatment with l‐NMMA caused a prompt drop in myeloperoxidase (MPO) activity, suggesting rapid adhesion of PMNL to the coronary wall; this effect was significantly blunted by l‐arginine. This study suggests that NO provides cardioprotection in an organ model of transcellular metabolism of cys‐LT by preventing PMNL adhesion to the coronary intima. British Journal of Pharmacology (1997) 120, 1128–1134; doi:10.1038/sj.bjp.0700994