Nitric oxide modulates angiotensin II-induced endothelial vasoconstrictor prostanoid release

Nitric oxide and angiotensin II regulate cardiovascular homeostasis and the arterial baroreflex control of heart rate in conscious lambs

To investigate the potential role of angiotensin II (Ang II) type 1 receptors (AT1Rs) as well as endogenously produced nitric oxide (NO) in regulating cardiovascular homeostasis during ontogeny, experiments were carried out in conscious lambs aged approximately 1 week ( N = 9) and 6 weeks ( N = 11). The arterial baroreflex control of heart rate (HR) was assessed before and after intravenous (IV) infusion of the selective AT1R antagonist, ZD 7155, before and after IV administration of the L-arginine analogue, NG-nitro-L-arginine methyl ester (L-NAME). In both groups, after ZD 7155 alone, mean arterial pressure decreased then increased after L-NAME. At 1 but not 6 weeks, HR decreased after ZD 7155 as well as after L-NAME. At 1 but not 6 weeks, there was a decrease in the HR range after ZD 7155 and after ZD 7155 + L-NAME, as compared to control. There was also a decrease in minimum HR after ZD 7155 + L-NAME at 1 week. These data provide new evidence that, together, Ang II and NO regulate cardiovascular homeostasis as well as the arterial baroreflex of HR early in life which may help to explain the activation of these two systems early in life.

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

Endothelial dysfunction and improvement of the angiotensin II-reactivity in hypercholesterolemic rabbits: role of cyclooxygenase metabolites

The aim of this paper was to study the effect of high cholesterol diet on endothelial function and vascular reactivity to angiotensin II and to test the role of vasoconstrictor cyclooxygenase metabolites in this experimental condition. Rabbits were fed with either normal chow or a diet containing 1% cholesterol for 6-7-week. Isometric contractions were measured in rubbed or unrubbed aortic rings. Arteries were contracted with noradrenaline and then exposed to one cumulative dose-response curve to acetylcholine in absence (control) or in presence of indomethacin, (N-[2-cyvlohexyloxy)-4-nitrophenyl]-methanesulfonamide) (NS 398) or 4-hydroxy-2,2,6,6-tetraethylpiperidine-N-oxyl (tempol). After washing the arteries, one cumulative dose-response curve to angiotensin II was constructed in absence or presence of indomethacin, NS 398, [1S-[1 alpha,2 beta (5Z),3 beta,4 alpha]-7-[3-[[2-[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-5-heptenoic acid (SQ29548) or 17-octadecynoic acid (17-ODYA). In other group, resting potential was recorded in basal and angiotensin II-stimulated conditions. Indomethacin, NS 398 or 17-ODYA were added to the bath before angiotensin II-stimulation. Rabbits fed on a diet enriched with cholesterol showed higher plasma levels of total cholesterol and LDL. Hypercholesterolemic diet impaired acetylcholine relaxation. Indomethacin normalized endothelium-dependent relaxation whereas NS 398 and tempol had no effect on this phenomenon. Angiotensin II-reactivity was increased in endothelium intact hypercholesterolemic aortic rings and indomethacin, SQ29548 or 17-ODYA blocked this effect. The resting potential of unrubbed hypercholesterolemic arteries was significantly less negative to control after angiotensin II-stimulation. 17-ODYA but not indomethacin prevented angiotensin II-depolarization. High cholesterol diet caused endothelial dysfunction and increased the angiotensin II-reactivity. Both effects were cyclooxygenase1-dependent. Deficit in the NO-production might improve 20-hydroxyeicosatrienoic acid availability, which induces depolarization and angiotensin II-sensitization. In addition, 20-hydroxyeicosatrienoic acid would be metabolized by cyclooxygenase1 to 20-endoperoxides which act through thromboxane A(2)/prostaglandin H(2) receptors contributing to angiotensin II-reactivity increase.

TEMPOL, a membrane-permeable radical scavenger, attenuates peroxynitrite- and superoxide anion-enhanced carrageenan-induced paw edema and hyperalgesia: a key role for superoxide anion

Carrageenan produces both inflammation and pain when injected in rat paws via enhancement of the formation of reactive oxygen species. We have tested the effect of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL), a membrane-permeable superoxide dismutase (SOD) mimetic in carrageenan-induced rat paw edema. Treatment of rats with TEMPOL (15, 30, and 60 mg/kg, 15 min prior to carrageenan) inhibited the paw edema. Furthermore, treatment of rats with the SOD inhibitor diethylthiocarbamate (DETCA, 100 mg/kg, 1 h before carrageenan) enhanced the carrageenan-induced paw edema. Co-administration of peroxynitrite with carrageenan produced a similar fortification of the carrageenan-induced edema. Prior treatment of rats with TEMPOL (30 mg/kg) inhibited the enhancement produced by DETCA treatment (endogenous superoxide anion stress) as well as that produced by the peroxynitrite stress. The effect of TEMPOL as well as the influence of superoxide anion and peroxynitrite stresses was also tested in carrageenan-induced hyperalgesia model. Carrageenan (500 mug/paw) produced significant hyperalgesia presented as shortening of withdrawal latency times using hot plate (52 degrees C) starting 30 min after carrageenan and lasting for 3 h. TEMPOL (60 mg/kg, injected 15 min before carrageenan) ameliorated this hyperalgesia during the first 2 h. Concurrent administration of peroxynitrite promptly intensified the carrageenan hyperalgesia. TEMPOL (60 mg/kg, 15 min before peroxynitrite-carrageenan) inhibited the peroxynitrite enhancement of carrageenan hyperalgesia when tested at 60 min after injection of the cocktail. The present investigation gives the proof for the effectiveness of TEMPOL as anti-inflammation and analgesic agents in carrageenan-induced model of inflammation and hyperalgesia. It further indicated the importance of superoxide anion and peroxynitrite in acute inflammation and inflammatory pain. This raises the chances for considering pharmacologic interventions that interrupt superoxide anion and peroxynitrite stress for putative alternative agents as anti-inflammatory analgesic new medical strategies.