INHIBITION OF NITROVASODILATORS BY PYOCYANIN AND METHYLENE-BLUE IS DISSOCIATED FROM NITRIC-OXIDE FORMATION

The phenazine pigment pyocyanin (Pyo), like methylene blue (MB), inhib its vascular relaxation induced by organic nitrates. These nitrovasodi lators are pro-drugs that have in common the ability to generate nitri c oxide (NO). In this study, we characterized responses of rabbit isol ated aortic ring to 3-morpholinosydnonimine (SIN-1), S-nitroso-N-acety lpenicillamine (SNAP), sodium nitroprusside, glyceryl trinitrate (GTN) , and isosorbide dinitrate in the presence and absence of 10 mu M Pyo. We also examined the effect of Pyo (1 and 10 mu M) and MB (1 and 10 m u M) on vasorelaxation induced by authentic NO, and finally we tested the effects of Pyo and MB on the tissue-independent formation of NO fr om SIN-1, SNAP, and sodium nitroprusside, using the chemiluminescence - headspace gas method. Pyo (10 mu M) surmountably inhibited aortic re sponses to GTN, isosorbide dinitrate, SIN-1, and SNAP with a character istic rightward shift of the dose-response curve; the apparent EC(50) of these drugs for relaxation of phenylephrine-contracted aorta was in creased 18-, 4-, 13-, and 15-fold, respectively. Pyo (1 and 10 mu M) a nd MB (10 mu M) inhibited NO-induced vasorelaxation at the EC(50) of N O by 35, 72, and 56%. In contrast, Pyo did not inhibit sodium nitropru sside induced vasodilation. For a 10-min incubation, 10 mu M Pyo or MB increased NO production from SNAP 1.8- and 2.9-fold, respectively, an d increased NO production from SIN-1 by 3.8-and 7.1-fold, respectively . Neither Pyo nor MB enhanced NO formation from sodium nitroprusside. These data indicate that Pyo and MB inhibit nitrovasodilator-induced r elaxation of aortic ring by interfering with the action of NO, subsequ ent to its formation.