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Objective and Design: To investigate the effect of nitric oxide (NO) donors on inflammatory mouse paw edema (MPE)., Materials and Methods: Mice previously treated with sodium nitroprusside (SNP; 1.5, 5 and 10 micromol/kg) or S-nitroso-N-acetyl-DL-penicillamine (SNAP; 7, 14 and 28 micromol/kg) were injected with inflammatory mediators in the paw. Paw edema, myeloperoxidase activity and vascular dye leakage were measured., Results: Pre-treatment with SNP and SNAP (4 h or 12 h) reduced (approximately 50%) MPE induced by carrageenan, dextran sulfate, bradykinin and histamine but not by serotonin. Pre-treatment with SNP also inhibited carrageenan-induced increases in myeloperoxidase activity and vascular dye leakage. Methylene blue blocked the SNP-induced reduction in MPE when injected 30 min before or 2 h after SNP, but not 4 or 6 h after the NO donor. Tetraethylammonium blocked the SNP-induced reduction in MPE if injected 30 min before or 2, 4 or 6 h after SNP., Conclusions: NO donors have a long-lasting anti-inflammatory effect in MPE, which involves guanylate cyclase and tetraethylammonium-sensitive potassium channels.

Excessive nitric oxide (NO) production by inducible NO synthase has been implicated in the hyporesponsiveness to vasoconstrictors present in septic shock. Here we show that a brief incubation (30 min) of rat aorta rings with NO donors renders the vessels hyporesponsive to phenylephrine for several hours. Contraction of rings without endothelium by phenylephrine (0.1 nM to 100 microM) was decreased by 50-60% after incubation (30 min) with sodium nitroprusside (3-300 microM) or S-nitroso-acetyl-D,L-penicillamine (SNAP; 70-200 microM). This decrease was characterized by reductions in maximal response and rightwards shifts of phenylephrine concentration/response curves, present even 130 min after NO donor removal. Soluble guanylate cyclase inhibitors methylene blue ( 10 microM) and 1H-(1,2,4)-oxadiazol-(4,3-a)quinoxalin-1-one (ODQ, 1 microM) or the potassium channel blockers TEA (tetraethylammonium; 10 mM) and charybdotoxin (100 nM) inhibited the hyporesponsiveness to phenylephrine induced by the NO donors. In contrast, 4-aminopyridine (1 mM) and glibenclamide (10 microM) had no effect. Our results show that incubation with NO donors reproduces the hyporesponsiveness to phenylephrine and that NO alone accounts for most, if not all, the refractoriness to vasoconstrictors present in septic shock. In addition, soluble guanylate cyclase activation and opening of potassium channels, more specifically the calcium-activated subtype, play a predominant role in this NO-induced hyporesponsiveness to phenylephrine in the rat aorta.

The article discusses an ex vivo animal study which investigates whether a reduced activity in the Rho-A/Rho-kinase pathway could be involved in the impaired vascular reactivity noticed in septic shock. The study focused on male Wistar rats receiving an intraperitoneal injection of lipopolysaccharide (LPS). It revealed that changes in mechanisms involved in calcium sensitization play a crucial role in cardiovascular changes found in septic shock.