15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and 1-1-diethyl-2-hydroxy-2-nitrosohydrazine

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% O(2) 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.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Allopurinol; Animals; Blood Pressure; Cardiac Output; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hydrazines; Hypoxia; Injections, Intravenous; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroprusside; Oxypurinol; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Sodium Nitrite; Time Factors; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents; Xanthine Oxidase

The present study was designed to evaluate endothelium-dependent relaxation to the calcium ionophore A-23187 in isolated canine saphenous veins. Isometric force recordings and cGMP measurements using isolated veins with and without valves were performed. During contractions to U-46619 (3 x 10(-7) M), endothelium-dependent relaxations to A-23187 (10(-9)-10(-6) M) were significantly reduced in rings with valves compared with rings without valves. Endothelial removal abolished A-23187-induced relaxation. Relaxations to forskolin (FK; 10(-8)-10(-5) M) and diethylaminodiazen-1-ium-1,2-dionate; DEA-NONOate, 10(-9)-10(-5) M) were identical in rings with and without valves. In rings without valves, a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-4) M), and a cyclooxygenase inhibitor, indomethacin (10(-5) M), partially reduced A-23187-induced relaxation. However, in rings with valves, L-NAME had no effect, whereas indomethacin abolished the relaxation to A-23187. A selective soluble guanylate cyclase inhibitor, 1H-[1,2,4]-oxadiazolo [4,3-a]quinoxalin-1-one (ODQ; 3x10(-6) M), had no effect on the relaxation to A-23187 in either group. In contrast, ODQ abolished the A-23187-induced increase in cGMP levels, suggesting that relaxation to nitric oxide released by A-23187 is independent of increases in cGMP. These results demonstrate that endothelium-dependent relaxation to A-23187 is reduced in regions of veins with valves compared with relaxation in the nonvalvular venous wall. Lower production of nitric oxide in endothelial cells of valvular segments appears to be a mechanism responsible for reduced reactivity to A-23187.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Calcimycin; Calcium; Colforsin; Cyclic GMP; Cyclooxygenase Inhibitors; Dogs; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Hydrazines; In Vitro Techniques; Indomethacin; Ionophores; NG-Nitroarginine Methyl Ester; Nitric Oxide Donors; Nitrogen Oxides; Oxadiazoles; Potassium Chloride; Quinoxalines; Saphenous Vein; Vasoconstrictor Agents; Vasodilation

The 4-amino analogue of tetrahydrobiopterin (4-ABH(4)) is a potent pterin-site inhibitor of nitric oxide synthases (NOS). Although 4-ABH(4) does not exhibit selectivity between purified NOS isoforms, a pronounced selectivity of the drug towards inducible NOS (iNOS) is apparent in intact cells. This work was carried out to investigate the potential iNOS selectivity of 4-ABH(4) in isolated pig pulmonary and coronary arteries. Endothelium-dependent relaxations of pig pulmonary and coronary artery strips to bradykinin or calcium ionophore A23187 were inhibited by 4-ABH(4) in a concentration-dependent manner. Half-maximal inhibition was observed at 60 - 65 microM (pulmonary artery) and 200 - 250 microM 4-ABH(4) (coronary artery). Pig coronary artery strips precontracted with 0.1 microM 9, 11-dideoxy-9, 11-methanoepoxy-prosta-glandin F(2alpha) (U46619) showed a time-dependent relaxation (monitored for up to 18 h) upon incubation with 1 microg ml(-1) lipopolysaccharide (LPS). Addition of 10 microM 4-ABH(4) 1 h after LPS led to a pronounced inhibition of the LPS-triggered relaxation, whereas the pterin antagonist had no effect when given> or =4 h after LPS. Incubation of pulmonary and coronary artery strips with 1 microg ml(-1) LPS attenuated contractile responses to norepinephrine (1 microM) and U46619 (0.1 microM). This hyporeactivity of the blood vessels to vasoconstrictor agents was inhibited by 4-ABH(4) in a concentration-dependent manner [IC(50)=17.5+/-5.9 microM (pulmonary artery) and 20.7+/-3 microM (coronary artery)]. The effect of 0.1 mM 4-ABH(4) was antagonized by coincubation with 0.1 mM sepiapterin, which is known to supply intracellular BH(4) via a salvage pathway. These results demonstrate that 4-ABH(4) is a fairly selective inhibitor of iNOS in an in vitro model of endotoxaemia, suggesting that this drug and/or related pterin-site NOS inhibitors may be useful to increase blood pressure in severe infections associated with a loss of vascular responsiveness to constrictor agents caused by endotoxin-triggered iNOS induction in the vasculature.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Biopterins; Bradykinin; Calcimycin; Coronary Vessels; Dose-Response Relationship, Drug; Endothelium, Vascular; Endotoxins; Enzyme Inhibitors; Hydrazines; In Vitro Techniques; Lipopolysaccharides; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Nitrogen Oxides; Norepinephrine; Pteridines; Pterins; Pulmonary Artery; Swine; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

Sodium 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NO; Et2N-[N(O)NO]Na) is a compound that spontaneously generates nitric oxide (NO). Because of its short half-life (2.1 min), we hypothesized that inhaling DEA/NO aerosol would selectively dilate the pulmonary circulation without decreasing systemic arterial pressure. We compared the pulmonary selectivity of this new NO donor with two other reference drugs: inhaled NO and inhaled sodium nitroprusside (SNP). In seven awake sheep with pulmonary hypertension induced by the infusion of U-46619, we compared the hemodynamic effects of DEA/NO with those of incremental doses of inhaled NO gas. In seven additional awake sheep, we examined the hemodynamic effects of incremental doses of inhaled nitroprusside (i.e., SNP). Inhaled NO gas selectively dilated the pulmonary vasculature. Inhaled DEA/NO produced nonselective vasodilation; both systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were reduced. Inhaled SNP selectively dilated the pulmonary circulation at low concentrations (< or = 10(-2)M), inducing a decrease of PVR of up to 42% without any significant decrease of SVR(-5%), but nonselectively dilated the systemic circulation at larger doses (> 10(-2)M). In conclusion, despite its short half-life, DEA/NO is not a selective pulmonary vasodilator compared with inhaled NO. Inhaled SNP appears to be selective to the pulmonary circulation at low doses but not at higher levels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acute Disease; Administration, Inhalation; Aerosols; Animals; Hemodynamics; Hydrazines; Hypertension, Pulmonary; Nitric Oxide; Nitrogen Oxides; Nitroprusside; Prodrugs; Pulmonary Circulation; Sheep; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

The effects of tetraethylammonium (TEA), a K+ channel antagonist, on vasodilator responses were investigated in the hindquarters vascular bed of the cat under constant-flow conditions. After administration of TEA in a total dose of 60 mg/kg into the hindquarters perfusion circuit, vasodilator responses to acetylcholine, bradykinin, and substance P were reduced, whereas vasodilator responses to the NO donors, diethylamine-NO complex, S-nitroso-N-acetylpenicillamine, and sodium nitroprusside, and to prostaglandin E1, albuterol, vasoactive intestinal polypeptide, isradipine, and levcromakalim were not altered. The inhibitory effect of TEA on responses to the endothelium-dependent vasodilators was reversible with time, and vasoconstrictor responses to norepinephrine, U-46619, angiotensin II, and BAY K 8644 were enhanced by the K+ channel antagonist. Although TEA had no sustained effect on baseline systemic arterial and hindquarters perfusion pressures, the NO synthase inhibitor, N omega-nitro-L-arginine methyl ester, increased these pressures in the presence of TEA. The results of the present investigation suggest that TEA attenuates vasodilator responses to acetylcholine, bradykinin, and substance P by inhibiting the release of endothelium-derived relaxing factor. These data suggest that the acetylcholine-, bradykinin-, and substance P-stimulated release of endothelium-derived relaxing factor may involve the opening of a TEA-sensitive K+ channel in the endothelium in the hindlimb vascular bed of the cat, but that a TEA-sensitive mechanism is not involved in the maintenance of baseline tone in this vascular bed.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Acetylcholine; Albuterol; Alprostadil; Analysis of Variance; Angiotensin II; Animals; Benzopyrans; Blood Pressure; Bradykinin; Cats; Cromakalim; Endothelium, Vascular; Female; Glyburide; Heart Rate; Hindlimb; Hydrazines; Isradipine; Male; Muscle, Smooth, Vascular; NG-Nitroarginine Methyl Ester; Nitrogen Oxides; Nitroprusside; Norepinephrine; Penicillamine; Prostaglandin Endoperoxides, Synthetic; Pyrroles; S-Nitroso-N-Acetylpenicillamine; Substance P; Tetraethylammonium; Tetraethylammonium Compounds; Thromboxane A2; Vasoactive Intestinal Peptide; Vasodilation; Vasodilator Agents