PJ. Pulmonary vasodilator responses to sodium nitrite are mediated by an allopurinol-sensitive mechanism in the rat. Am J Physiol Heart Circ Physiol 296: H524 -H533, 2009. First published December 12, 2008 doi:10.1152/ajpheart.00543.2008.-Recent studies show that pulmonary vasodilator responses to nitrite are enhanced by hypoxia. However, the mechanism by which nitrite is converted to vasoactive nitric oxide (NO) is uncertain. In the present study, intravenous injections of sodium nitrite decreased pulmonary and systemic arterial pressures and increased cardiac output. The decreases in pulmonary arterial pressure were enhanced when tone in the pulmonary vascular bed was increased with U-46619. Under elevated tone conditions, decreases in pulmonary and systemic arterial pressures in response to nitrite were attenuated by allopurinol in a dose that did not alter responses to the NO donors, sodium nitroprusside and diethylamine/NO, suggesting that xanthine oxidoreductase is the major enzyme-reducing nitrite to NO. Ventilation with a 10% O 2 gas mixture increased pulmonary arterial pressure, and the response to hypoxia was enhanced by N G -nitro-L-arginine methyl ester and not altered by allopurinol. This suggests that NO formed by the endothelium and not from the reduction of plasma nitrite modulates the hypoxic pulmonary vasoconstrictor response. Although intravenous injections of sodium nitrite reversed pulmonary hypertensive responses to U-46619, hypoxia, and N G -nitro-L-arginine methyl ester, the pulmonary vasodilator response to nitrite was not altered by ventilation with 10% O2 when baseline pulmonary arterial pressure was increased to similar values in animals breathing room air or the hypoxic gas. These data provide evidence that xanthine oxidoreductase is the major enzyme-reducing nitrite to vasoactive NO, and that this mechanism is not modified by hypoxia. nitric oxide; xanthine oxidoreductase; pulmonary hypertension; nitric oxide synthase ENDOTHELIAL NITRIC OXIDE (NO) formation plays an important role in the regulation of the pulmonary and systemic vascular beds (15, 28). The importance of NO has been demonstrated in experimental animals and in human subjects by the use of NO synthase (NOS) inhibitors (2,15,28). Although NO synthesis is important in the regulation of baseline tone in most vascular beds, the role of NO in the regulation of tone in the pulmonary vascular bed of the rat has been questioned (15). NO once released from the endothelium into the blood reacts rapidly with red cell hemoglobin (14, 21a, 26). Furthermore, NO that escapes hemoglobin scavenging can be oxidized to nitrite (21a). NO formed from nitrite that escapes inactivation relaxes vascular smooth muscle by a cGMP-dependent mechanism (7, 26). It has been reported that plasma nitrite concentrations reflect constitutive NOS activity and correlate with endothelial function (21a). In addition, recent research speculates that nitrite anion represents a storage form of NO that can have important pharmacological actions (13,22). This is...

4-({(4-Carboxybutyl)[2-(5-fluoro-2-{[4'-(trifluoromethyl)biphenyl-4-yl]methoxy}phenyl)ethyl]amino}methyl)benzoic acid (BAY 60-2770) is a nitric oxide (NO)-independent activator of soluble guanylyl cyclase (sGC) that increases the catalytic activity of the heme-oxidized or heme-free form of the enzyme. In this study, responses to intravenous injections of the sGC activator BAY 60-2770 were investigated under baseline and elevated tone conditions induced by the thromboxane mimic U-46619 when NO synthesis was inhibited by N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME), when sGC activity was inhibited by 1H-[1,2,4]-oxadizaolo[4,3]quinoxaline-1-one (ODQ), an agent that oxidizes sGC, and in animals with monocrotaline-induced pulmonary hypertension. The intravenous injections of BAY 60-2770 under baseline conditions caused small decreases in pulmonary arterial pressure, larger decreases in systemic arterial pressure, and no change or small increases in cardiac output. Under elevated tone conditions during infusion of U-46619, intravenous injections of BAY 60-2770 caused larger decreases in pulmonary arterial pressure, smaller decreases in systemic arterial pressure, and increases in cardiac output. Pulmonary vasodilator responses to BAY 60-2770 were enhanced by L-NAME or by ODQ in a dose that attenuated responses to the NO donor sodium nitroprusside. ODQ had no significant effect on baseline pressures and attenuated pulmonary and systemic vasodilator responses to the sGC stimulator BAY 41-8543 2-{1-[2-(fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl}-5(4-morpholinyl)-4,6-pyrimidinediamine. BAY 60-2770 and sodium nitroprusside decreased pulmonary and systemic arterial pressures in monocrotaline-treated rats in a nonselective manner. The present data show that BAY 60-2770 has vasodilator activity in the pulmonary and systemic vascular beds that is enhanced by ODQ and NOS inhibition, suggesting that the heme-oxidized form of sGC can be activated in vivo in an NO-independent manner to promote vasodilation. These results show that BAY 60-2770 and sodium nitroprusside decreased pulmonary and systemic arterial pressures in monocrotaline-treated rats, suggesting that BAY 60-2770 does not have selective pulmonary vasodilator activity in animals with monocrotaline-induced pulmonary hypertension.

PJ. Mitochondrial aldehyde dehydrogenase mediates vasodilator responses of glyceryl trinitrate and sodium nitrite in the pulmonary vascular bed of the rat. Am J Physiol Heart Circ Physiol 299: H819 -H826, 2010. First published June 11, 2010; doi:10.1152/ajpheart.00959.2009.-It has been reported that mitochondrial aldehyde dehydrogenase (ALDH2) catalyzes the formation of glyceryl dinitrate and inorganic nitrite from glyceryl trinitrate (GTN), leading to an increase in cGMP and vasodilation in the coronary and systemic vascular beds. However, the role of nitric oxide (NO) formed from nitrite in mediating the response to GTN in the pulmonary vascular bed is uncertain. The purpose of the present study was to determine if nitrite plays a role in mediating vasodilator responses to GTN. In this study, intravenous injections of GTN and sodium nitrite decreased pulmonary and systemic arterial pressures and increased cardiac output. The decreases in pulmonary arterial pressure under baseline and elevated tone conditions and decreases in systemic arterial pressure in response to GTN and sodium nitrite were attenuated by cyanamide, an ALDH2 inhibitor, whereas responses to the NO donor, sodium nitroprusside (SNP), were not altered. The decreases in pulmonary and systemic arterial pressure in response to GTN and SNP were not altered by allopurinol, an inhibitor of xanthine oxidoreductase, whereas responses to sodium nitrite were attenuated. GTN was ϳ1,000-fold more potent than sodium nitrite in decreasing pulmonary and systemic arterial pressures. These results suggest that ALDH2 plays an important role in the bioactivation of GTN and nitrite in the pulmonary and systemic vascular beds and that the reduction of nitrite to vasoactive NO does not play an important role in mediating vasodilator responses to GTN in the intact chest rat. mitochondrial aldehyde dehydrogenase; xanthine oxidoreductase; nitric oxide; glyceryl trinitrate; sodium nitrite; sodium nitroprusside; allopurinol; cyanamide; U-46619; N G -nitro-L-arginine methyl ester GLYCERYL TRINITRATE (GTN) and, to a lesser extent, amyl nitrite have been used in the treatment of angina and heart failure for more than a century (4, 5, 38). However, the molecular mechanism by which GTN relaxes vascular smooth muscle is still the subject of current investigation and remains unknown. Although it is well established that nitric oxide (NO) activates soluble guanylyl cyclase, increases cGMP formation, and relaxes vascular smooth muscle, the role of NO release in mediating the vasorelaxant response to GTN is uncertain (11,17,21,26,30,37,39). Although studies in the literature provide evidence that NO is released from GTN, other studies show that NO is not released and suggest that the activation of guanylyl cyclase is mediated by a closely related but not currently identified chemical species with NO-guanylyl cyclase stimulating properties (2, 11, 16, 23, 25, 29 -31, 36, 39). There is substantial evidence in the literature that mitochondrial aldehyde dehydrogenase (ALDH2) plays an i...

Badejo AM Jr, Dhaliwal JS, Casey DB, Gallen TB, Greco AJ, Kadowitz PJ. Analysis of pulmonary vasodilator responses to the Rho-kinase inhibitor fasudil in the anesthetized rat. Am J Physiol Lung Cell Mol Physiol 295: L828 -L836, 2008. First published August 8, 2008 doi:10.1152/ajplung.00042.2008.-The small GTP-binding protein Rho and its downstream effector, Rho-kinase, are important regulators of vasoconstrictor tone. Rho-kinase is upregulated in experimental models of pulmonary hypertension, and Rho-kinase inhibitors decrease pulmonary arterial pressure in rodents with monocrotaline and chronic hypoxia-induced pulmonary hypertension. However, less is known about responses to fasudil when pulmonary vascular resistance is elevated on an acute basis by vasoconstrictor agents and ventilatory hypoxia. In the present study, intravenous injections of fasudil reversed pulmonary hypertensive responses to intravenous infusion of the thromboxane receptor agonist, U-46619 and ventilation with a 10% O2 gas mixture and inhibited pulmonary vasoconstrictor responses to intravenous injections of angiotensin II, BAY K 8644, and U-46619 without prior exposure to agonists, which can upregulate Rho-kinase activity. The calcium channel blocker isradipine and fasudil had similar effects and in small doses had additive effects in blunting vasoconstrictor responses, suggesting parallel and series mechanisms in the lung. When pulmonary vascular resistance was increased with U-46619, fasudil produced similar decreases in pulmonary and systemic arterial pressure, whereas isradipine produced greater decreases in systemic arterial pressure. The hypoxic pressor response was enhanced by 5-10 mg/kg iv nitro-Larginine methyl ester (L-NAME), and fasudil or isradipine reversed the pulmonary hypertensive response to hypoxia in control and in L-NAME-treated animals, suggesting that the response is mediated by Rho-kinase and L-type Ca 2ϩ channels. These results suggest that Rho-kinase is constitutively active in regulating baseline tone and vasoconstrictor responses in the lung under physiological conditions and that Rho-kinase inhibition attenuates pulmonary vasoconstrictor responses to agents that act by different mechanisms without prior exposure to the agonist.Rho-kinase pathway; Ca 2ϩ sensitization; pulmonary vascular bed; U-46619; isradipine; hypoxia; nitro-L-arginine methyl ester THE SMALL GTP-binding protein Rho and its downstream effector Rho-kinase play an important role in the regulation of vascular smooth muscle tone (3,4,6,18,20,28,34,36). It has been hypothesized that the Rho-kinase system is constitutively active in regulating vasoconstrictor tone and that upregulation of this pathway occurs in a variety of cardiovascular diseases (8,19,21,22,32,33,35). Rho-kinase has been shown to be a potential therapeutic target in a number of cardiovascular diseases including pulmonary hypertension (1,2,10,12,15,16,26,27,29,38). It has been reported that Rho-kinase is upregulated in monocrotaline and chronic hypoxia-induced pulmonary hypertensio...

Pulmonary hypertension (PH) is a rare disorder that without treatment is progressive and often fatal within 3 years. The treatment of PH involves the use of a diverse group of drugs and lung transplantation. Although nitrite was once thought to be an inactive metabolite of endothelial-derived nitric oxide (NO), there is increasing evidence that nitrite may be useful in the treatment of PH, but the mechanism by which nitrite exerts its beneficial effect remains uncertain. The purpose of this study was to investigate the effect of chronic sodium nitrite treatment in a PH model in the rat. Following induction of PH with a single injection of monocrotaline, 60 mg; daily ip injections of sodium nitrite (3 mg/kg) starting on day 14 and continuing for 21 days, resulted in a significantly lower pulmonary arterial pressure on day 35 when compared to values in untreated animals with monocrotaline-induced PH. In monocrotaline-treated rats, daily treatment with ip nitrite injections for 21 days decreased right ventricular mass and pathologic changes in small pulmonary arteries. Nitrite therapy did not change systemic arterial pressure or cardiac output when values were measured on day 35. The decreases in pulmonary arterial pressure in response to iv injections of sodium nitroprusside, sodium nitrite, and BAY 41-8543 were not different in rats with monocrotaline-induced pulmonary hypertension and rats with chronic nitrite therapy when compared to responses in animals in which pulmonary arterial pressure was increased with U46619. These findings are consistent with the hypothesis that the mechanisms that convert nitrite to vasoactive NO, activate soluble guanylyl cyclase and mediate the vasodilator response to NO or an NO derivative are not impaired. The present data are consistent with the results of a previous study in monocrotaline-induced PH in which systemic arterial pressure and cardiac output were not evaluated and are consistent with the hypothesis that nitrite is effective in the treatment of monocrotaline-induced PH in the rodent.