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

1. 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. 2. Hearts were perfused under recirculating conditions (50 ml) with 5 x 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. 3. 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). 4. 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. 5. Neither L-arginine nor L-NMMA affected directly the A-23187-induced arachidonic acid (AA) metabolism in isolated PMNL alone. 6. 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. 7. 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.