1-1-diethyl-2-hydroxy-2-nitrosohydrazine and Hypertension

Experiments were performed to determine whether or not acute exposure to elevated pressure would disrupt endothelium-dependent dilatation by increasing local angiotensin II (ANG II) signaling. Vasomotor responses of mouse-isolated carotid arteries were analyzed in a pressure myograph at a control transmural pressure (PTM) of 80 mmHg. Acetylcholine-induced dilatation was reduced by endothelial denudation or by inhibition of nitric oxide synthase (NG-nitro-L-arginine methyl ester, 100 μM). Transient exposure to elevated PTM (150 mmHg, 180 min) inhibited dilatation to acetylcholine but did not affect responses to the nitric oxide donor diethylamine NONOate. Elevated PTM also increased endothelial reactive oxygen species, and the pressure-induced endothelial dysfunction was prevented by the direct antioxidant and NADPH oxidase inhibitor apocynin (100 μM). The increase in endothelial reactive oxygen species in response to elevated PTM was reduced by the ANG II type 1 receptor (AT1R) antagonists losartan (3 μM) or valsartan (1 μM). Indeed, elevated PTM caused marked expression of angiotensinogen, the precursor of ANG II. Inhibition of ANG II signaling, by blocking angiotensin-converting enzyme (1 μM perindoprilat or 10 μM captopril) or blocking AT1Rs prevented the impaired response to acetylcholine in arteries exposed to 150 mmHg but did not affect dilatation to the muscarinic agonist in arteries maintained at 80 mmHg. After the inhibition of ANG II, elevated pressure no longer impaired endothelial dilatation. In arteries treated with perindoprilat to inhibit endogenous formation of the peptide, exogenous ANG II (0.3 μM, 180 min) inhibited dilatation to acetylcholine. Therefore, elevated pressure rapidly impairs endothelium-dependent dilatation by causing ANG expression and enabling ANG II-dependent activation of AT1Rs. These processes may contribute to the pathogenesis of hypertension-induced vascular dysfunction and organ injury.

Topics: Acetylcholine; Angiotensin II; Angiotensin II Type 1 Receptor Blockers; Angiotensin-Converting Enzyme Inhibitors; Animals; Blood Pressure; Captopril; Carotid Arteries; Endothelium, Vascular; Hydrazines; Hypertension; Indoles; Losartan; Male; Mice; Mice, Inbred C57BL; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase Type III; Reactive Oxygen Species; Signal Transduction; Tetrazoles; Valine; Valsartan; Vasodilation

Nitrite has become a topic of interest in the field of medical research because of its potential therapeutic role as an alternative source of nitric oxide (NO). While the bioconversion of nitrite to NO occurs via either nonenzymatic or enzymatic reduction under acidic or hypoxic conditions, little is known about its conversion to NO under normoxic conditions. Because of a recent report of aldehyde dehydrogenase 2 (ALDH2)-catalyzed glyceryl trinitrate (GTN) vasorelaxation by denitration of GTN to 1,2-glyceryl dinitrate (1,2-GDN) and nitrite, we therefore investigated a catalytic activity of ALDH2 for nitrite reduction and subsequent effect on N(ω)-nitro-l-arginine methyl ester (l-NAME)-induced hypertension in normoxic rat. Male Sprague-Dawley rats treated with l-NAME in drinking water for 3 weeks developed hypertension with significantly reduced plasma levels of nitrite and nitrate. The intravenous injection of sodium nitrite lowered the arterial pressure in a dose-dependent manner (17, 50 and 150 μmol/kg). Pretreatment with ALDH2 inhibitors (cyanamide and chloral hydrate) partially inhibited the hypotensive responses to sodium nitrite. In addition, cyanamide significantly delayed the nitrite clearance from plasma and most of the organs examined during the experimental period. These results suggest that ALDH2 may be at least in part involved in nitrite-mediated hypotensive effects and nitrite catalysis in many organs of normoxic rats.

Topics: Aldehyde Dehydrogenase; Aldehyde Dehydrogenase, Mitochondrial; Animals; Antihypertensive Agents; Blood Pressure; Disease Models, Animal; Dose-Response Relationship, Drug; Hydrazines; Hypertension; Male; Mitochondrial Proteins; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitroglycerin; Rats; Rats, Sprague-Dawley; Sodium Nitrite; Time Factors

Chronic-ouabain administration to rats induces hypertension and increases the endothelial modulation of vasoconstrictor responses. The aim of this study was to analyze whether ouabain-treatment affects the mechanisms involved in endothelium-dependent relaxation of coronary arteries.. Coronary arteries from control and ouabain-treated rats (approximately 8.0 microg/day, 5 weeks) were used. Vascular reactivity was analyzed by isometric tension recording and membrane currents were measured using the whole-cell configuration of the patch-clamp technique.. In 5-hydroxytryptamine (5-HT) precontracted arteries, acetylcholine (ACh, 1 nmol/l-10 micromol/l) induced a similar relaxant response in coronary arteries from both groups that was abolished by the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (100 micromol/l). However, when arteries were contracted with high KCl (60 mmol/l) or preincubated with the large-conductance Ca2+-activated K+ (BKCa) channels-blocker iberiotoxin (0.1 micromol/l), the relaxation elicited by ACh was more reduced in ouabain-treated than control rats. After iberiotoxin preincubation, the relaxant response of the nitric-oxide donor, DEA-NO (10 nmol/l-100 micromol/l) was significantly inhibited in ouabain-treated coronary arteries but not in control vessels. The soluble guanylyl cyclase activator BAY 41-2272 (10 nmol/l-30 micromol/l) induced relaxant responses that were inhibited by iberiotoxin. In coronary-artery myocytes isolated from ouabain-treated rats DEA-NO (1 micromol/l) markedly increased the amplitude of the iberiotoxin-sensitive current in the whole range of test potentials, compared with nontreated rats.. Our results indicate that chronic ouabain treatment increases activation of BKCa currents by nitric oxide and this effect might contribute to preserve the endothelial function in coronary arteries in this hypertension model.

Topics: Animals; Coronary Vessels; Endothelium, Vascular; Hydrazines; Hypertension; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Male; Nitric Oxide; Ouabain; Potassium Channels; Pyrazoles; Pyridines; Rats; Rats, Wistar; Vasodilation

Soluble guanylyl cyclase activity and its stimulation by diethylamineNONOate was measured in aortae from hypertensive TGR(mREN2)27 rats (TGR) and Sprague-Dawley controls. Superoxide dismutase was added in vitro to evaluate the contribution of oxidative breakdown of nitric oxide (NO) by superoxide anions. Expression of soluble guanylyl cyclase was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). Basal and stimulated soluble guanylyl cyclase activity was significantly reduced in TGR rats, addition of superoxide dismutase had no effect. Expression of soluble guanylyl cyclase subunits was not different between strains. The independent contribution of hypertension and the overactive renin-angiotensin system to soluble guanylyl cyclase subsensitivity was assessed after normalization of TGR's blood pressure by the Ca(2+)-channel blocker amlodipine or the angiotensin converting enzyme-inhibitor enalapril. Soluble guanylyl cyclase activity in TGR was slightly increased by amlodipine and almost completely restored by enalapril. In conclusion, TGR showed desensitized vascular soluble guanylyl cyclase, depending on their overactive renin-angiotensin system.

Topics: Aging; Amlodipine; Analysis of Variance; Animals; Animals, Genetically Modified; Aorta, Thoracic; Blood Pressure; Calcium Channel Blockers; Cyclic GMP; Dose-Response Relationship, Drug; Enalapril; Guanylate Cyclase; Hydrazines; Hypertension; Male; Nitrogen Oxides; Rats; Rats, Sprague-Dawley; Renin-Angiotensin System; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Solubility