Heme oxygenase-1 gene expression increases vascular relaxation and decreases inducible nitric oxide synthase in diabetic rats.

Hyperglycemia represents the main cause of complication of diabetes mellitus and oxidative stress, resulting from increased generation of reactive oxygen species (ROS), and plays a crucial role in their pathogenesis. Impairment of vascular responses in diabetic rats, as a result of an increase in superoxide (O2-), formation is a major complication in diabetes. Since heme oxygenase (HO) expression regulates the level of ROS by increasing antioxidant, such as glutathione and bilirubin, we investigated whether upregulation of HO-1 modulates the levels of iNOS and eNOS and altered vascular responses to phenylephrine (PE) and acetylcholine (Ach) in aorta and femoral arteries of diabetic (streptozotocin (STZ)-induced) rats. Our results showed that iNOS expression was increased, but HO activity was reduced, in diabetic compared to nondiabetic rats (p<0.05). Upregulation of HO-1 expression by cobalt protoporphyrin (CoPP), an inducer of HO-1 protein and activity, conferred an increase in eNOS and differentially decreased iNOS protein levels (p<0.05). Isolated aortic and femoral arteries obtained from diabetic rats exhibited contraction to PE and relaxation to Ach, which were markedly increased and decreased, respectively. However, HO-1 induction in diabetic rats normalized relaxation compared to controls. Therefore, overexpression of HO-1 may mediate an increase in eNOS and a decrease in iNOS, potentially contributing to restoration of vascular responses in diabetic rats.

Vicinal nitrohydroxyeicosatrienoic acids: vasodilator lipids formed by reaction of nitrogen dioxide with arachidonic acid.

Nitric oxide (NO)-derived species could potentially react with arachidonic acid to generate novel vasoactive metabolites. We studied the reaction of arachidonic acid with nitrogen dioxide (NO2), a free radical that originates from NO oxidation. The reaction mixture contained lipid products that relaxed endothelium-removed bovine coronary arteries. Relaxation to the lipid mixture was inhibited approximately 20% by indomethacin and approximately 70% by a soluble guanylate cyclase (sGC) inhibitor (ODQ). Thus, novel lipid products, which activate sGC presumably through a mechanism involving NO, appeared to have contributed to the observed vasorelaxation. Lipids that eluted at 9 to 12 min during high-performance liquid chromatography fractionation accounted for about one-half of the vasodilator activity in the reaction mixture, which was inhibited by ODQ. Lipid products in fractions 9 to 12 were identified by electrospray tandem mass spectrometry to be eight isomers having molecular weight of 367 and a fragmentation pattern indicative of arachidonic acid derivatives containing nitro and hydroxy groups and consistent with the structures of vicinal nitrohydroxyeicosatrienoic acids. These lipids spontaneously released NO (183 +/- 12 nmol NO/15 min/micromol) as detected by head space/chemiluminescence analysis. Mild alkaline hydrolysis of total lipids extracted from bovine cardiac muscle followed by isotopic dilution gas chromatography/mass spectrometry analysis detected basal levels of nitrohydroxyeicosatrienoic acids (6.8 +/- 2.6 ng/g tissue; n = 4). Thus, the oxidation product of NO, NO2, reacts with arachidonic acid to generate biologically active vicinal nitrohydroxyeicosatrienoic acids, which may be important endogenous mediators of vascular relaxation and sGC activation.

Inhibition of growth of methane-producing bacteria of the ruminant forestomach by hydroxymethylglutaryl-SCoA reductase inhibitors.

Two hydroxymethylglutaryl-SCoA (HMG-CoA) reductase inhibitors, mevastatin and lovastatin, inhibited the in vitro growth and production of CH4 of strains of Methanobrevibacter isolated from the rumen. Mevastatin or lovastatin did not inhibit growth of species of rumen bacteria that are essential for fermenting cellulose, starch and other plant polysaccharides to acetate, propionate, and butyrate. Approximately 4 nmol of lovastatin per milliliter resulted in 50% growth inhibition of Methanobrevibacter strain ZA10 and concentrations > or =10 nmol per milliliter completely inhibited growth and CH4 formation. Results of in vitro growth studies suggest that supplementation of ruminant feeds with HMG-CoA inhibitors could decrease ruminant methane production and increase the efficiency of feed utilization by domestic ruminants.

Transplantation of IL-2-mobilized autologous peripheral blood progenitor cells for adults with acute myelogenous leukemia in first remission.

In order to improve leukemia-free survival we evaluated the feasibility and efficacy of autologous transplantation of interleukin-2 (IL-2)-mobilized peripheral blood progenitor cells for adult patients with acute myelogenous leukemia in first remission. Forty-nine consecutive patients (median age 49, range 21-70) with acute myelogenous leukemia in first remission were enrolled on a study of high-dose cytarabine/mitoxantrone consolidation chemotherapy with post-recovery IL-2 used as a method of in vivo purging for the purpose of autologous peripheral blood progenitor cell transplantation. A median of 2.08 x 10(6) CD34+ peripheral blood progenitor cells/kg were infused 1 day after preparative conditioning with 11.25 Gy total body irradiation and cyclophosphamide (120 mg/kg). Forty-one patients received myeloablative chemoradiotherapy followed by the infusion of IL-2-mobilized autologous peripheral blood progenitor cells. The median times to both neutrophil and platelet recovery were 16 days (range, 2-43) and 23 days (8-318+ days), respectively. Twenty-seven patients remain alive with 24 in continued first complete remission. Median remission duration for all eligible patients is 8 months, and actuarial leukemia-free survival is 49+/-15%. The actuarial risk of relapse is 43+/-16%. Toxicity of autologous peripheral blood progenitor cell transplant included treatment-related death in three patients and serious organ toxicity in 12. Advanced age was a negative prognostic factor for leukemia-free survival. Results were compared to an age-matched historical control treated with autologous transplantation of chemotherapy-mobilized progenitor cells; no significant difference in favor of IL-2 mobilization could be demonstrated. Our results demonstrate that autologous transplantation of IL-2-mobilized peripheral blood progenitor cells is feasible in an unselected population of adult patients with acute myelogenous leukemia in first remission with minimal toxicity but no clear evidence of benefit in leukemia-free survival.

New concepts in vascular nitric oxide signaling.

Low levels of nitric oxide (NO) control the activities of guanylate cyclase and mitochondrial respiration. Increasing NO levels interact with multiple signaling systems through the formation of peroxynitrite and other oxidation products. Signaling mechanisms linked to NO participate in the prevention of acute responses such as vasoconstriction, thrombosis and the recruitment of inflammatory cells. In contrast, processes related to vascular remodeling, and responses to injury that are associated with the progression and adaptation to disease processes, are not as well understood. Many of the opposing processes involved in these adaptations may originate from the diverse signaling mechanisms that NO and its oxidized products can regulate in a cell-specific manner in the vessel wall.

Thiol oxidation activates a novel redox-regulated coronary vasodilator mechanism involving inhibition of Ca2+ influx.

This study examines the mechanism of relaxation of isolated endothelium-removed bovine coronary arteries (BCAs) to the thiol oxidant diamide. BCAs precontracted with KCl or the thromboxane A(2) receptor agonist U46619 showed a concentration-dependent reversible relaxation on exposure to 10 micromol/L to 1 mmol/L diamide. This relaxation was enhanced by an inhibitor of glutathione reductase, and it was not altered by severe hypoxia, the presence of inhibitors of soluble guanylate cyclase, K(+) channels, tyrosine kinases, or probes that modulate levels of superoxide. The relaxation was almost eliminated when BCAs were precontracted with a phorbol ester that causes a contraction that is largely independent of extracellular Ca(2+). The initial transient contraction elicited by 5-hydroxytryptamine in Ca(2+)-free solution was not altered by the presence of 1 mmol/L diamide; however, a subsequent tonic contraction on addition of CaCl(2) was inhibited by diamide. Diamide also inhibited contractions caused by the addition of CaCl(2) to Ca(2+)-free Krebs' buffer containing Bay K8644 (an L-type Ca(2+) channel opener) or KCl. Relaxation to diamide was attenuated by L-type Ca(2+) channel blockers (nifedipine and diltiazem). Thus, thiol oxidation elicited by diamide appears to activate a novel redox-regulated vasodilator mechanism that seems to inhibit extracellular Ca(2+) influx.

Anaerobic bioconversion of cellulose by Ruminococcus albus, Methanobrevibacter smithii, and Methanosarcina barkeri.

A system is described that combines the fermentation of cellulose to acetate, CH4, and CO2 by Ruminococcus albus and Methanobrevibacter smithii with the fermentation of acetate to CH4 and CO2 by Methanosarcina barkeri to convert cellulose to CH4 and CO2. A cellulose-containing medium was pumped into a co-culture of the cellulolytic R. albus and the H2-using methanogen, Mb. smithii. The effluent was fed into a holding reservoir, adjusted to pH 4.5, and then pumped into a culture of Ms. barkeri maintained at constant volume by pumping out culture contents. Fermentation of 1% cellulose to CH4 and CO2 was accomplished during 132 days of operation with retention times (RTs) of the Ms. barkeri culture of 7.5-3.8 days. Rates of acetate utilization were 9.5-17.3 mmol l(-1) day(-1) and increased with decreasing RT. The Ks for acetate utilization was 6-8 mM. The two-stage system can be used as a model system for studying biological and physical parameters that influence the bioconversion process. Our results suggest that manipulating the different phases of cellulose fermentation separately can effectively balance the pH and ionic requirements of the acid-producing phase with the acid-using phase of the overall fermentation.

Depressed modulation of oxygen consumption by endogenous nitric oxide in cardiac muscle from diabetic dogs.

Our previous study indicated that nitric oxide (NO)-dependent coronary vasodilation was impaired in conscious dogs with diabetes. Our goal was to determine whether modulation of O(2) consumption by NO is depressed in canine cardiac muscle after diabetes. Diabetes was induced by injection of alloxan (40-60 mg/kg iv), dogs were killed after diabetes was induced (4-5 wk), and the cardiac muscle from the left ventricle was cut into 15- to 30-mg slices. O(2) uptake by the muscle slices was measured polarographically with a Clark-type O(2) electrode. S-nitroso-N-acetylpenicillamine decreased O(2) consumption in normal and diabetic tissues (10(-4) M, 61 +/- 7 vs. 61 +/- 8%, P > 0.05). Bradykinin (10(-4) M)- or carbachol (CCh, 10(-4) M)-induced inhibition of O(2) consumption was impaired in diabetic tissues (51 +/- 6 vs. 17 +/- 4% or 48 +/- 4 vs. 19 +/- 3%, respectively, both P < 0.05 compared with normal). The inhibition of O(2) consumption by kininogen or kallikrein was depressed in diabetic tissues as well. In coronary microvessels from diabetic dogs, bradykinin or ACh (10(-5) M) caused smaller increases in NO production than those from normal dogs. Our results indicate that the modulation of O(2) consumption by endogenous, but not exogenous, NO is depressed in cardiac muscle from diabetic dogs, most likely because of decreased release of NO from the vascular endothelium.

Interactions of oxidants with vascular signaling systems.

Individual reactive oxygen species (ROS) and oxidation products of NO interact with vascular signaling mechanisms in ways that appear to have fundamental roles in the control of vascular physiological and pathophysiological function. The activities of ROS-producing systems (including various NADPH and NADH oxidases, xanthine oxidase, and NO synthase) in endothelium and/or vascular smooth muscle are controlled by receptor activation, oxygen tension, metabolic processes, and physiological forces associated with blood pressure and flow. This review focuses on how the chemical properties and metabolic sensing interactions of individual ROS (including superoxide anion, hydrogen peroxide, and peroxynitrite) interact with cellular regulatory systems to produce vascular responses. These species appear to often function through producing selective alterations in individual heme or thiol redox-regulated systems (including guanylate cyclase, cyclooxygenase, mitochondrial electron transport, and tyrosine phosphatases) to initiate physiological responses through signaling pathways that control phospholipases, protein kinases, ion channels, contractile proteins, and gene expression.

Alterations in relaxation to lactate and H(2)O(2) in human placental vessels from gestational diabetic pregnancies.

We determined whether alterations in the mechanism of relaxation to H(2)O(2) potentially contribute to the enhanced prostaglandin-mediated contractile response to H(2)O(2) and posthypoxic reoxygenation seen in human placental vessels of pregnancies with gestational diabetes mellitus (GDM). Isolated placental arteries and veins from GDM and uncomplicated full-term pregnancies were precontracted with prostaglandin F(2alpha) (PO(2) 35-38 Torr) and then exposed to lactate (1-10 mM), arachidonic acid (0.01-10 microM), nitroglycerin (1 nM-1 microM), forskolin (0.01-10 microM), or H(2)O(2) (1 microM-1 mM + 10 microM indomethacin). The rates of tissue H(2)O(2) metabolism by catalase and nitrite production were measured. The relaxation to lactate was reduced in GDM placental arteries and veins by 54-85 and 66-80%, and the relaxation to H(2)O(2) was inhibited by 80-94% in GDM placental veins compared with vessels from uncomplicated full-term pregnancies. H(2)O(2) caused only minimal relaxation of placental arteries. Responses to other relaxing agents were not altered in the GDM placental vessels. Diabetic vessels showed rates of nitrite production that were increased by 113-195% and rates of H(2)O(2) metabolism by catalase that were decreased by 44-61%. The loss of relaxation to H(2)O(2) and lactate (mediated via H(2)O(2)), perhaps as a result of the inhibition of catalase by nitric oxide, may explain the previously reported enhancement of prostaglandin-mediated contractile responses to H(2)O(2) and posthypoxic reoxygenation seen in GDM placental vessels.

Low-dose daily subcutaneous interleukin-2 in combination with highly active antiretroviral therapy in HIV+ patients: a randomized controlled trial.

PURPOSE: Previous studies with intermittent interleukin-2 (IL-2) therapy using intermediate and high levels of IL-2 have demonstrated significant increases in the CD4 + T cell count in HIV-infected patients. Intermittent regimens are amenable to outpatient use, but severe adverse events are frequently experienced with intermediate- and high-dose levels of IL-2. Therefore in this study, the effect of daily, subcutaneous low-dose IL-2 therapy on safety and immunological endpoints was investigated to determine whether immunological benefit could be achieved without toxicity in HIV-infected patients also receiving highly active antiretroviral therapy (HAART). METHOD: A total of 115 patients were enrolled in the trial. Fifty-six asymptomatic HIV-infected patients who had CD4 + T cell counts less than 300 cells/microL at screening and a stable HIV viral load received low-dose IL-2 (1.2 million IU [MIU]/m 2 beginning dose) once daily in conjunction with HAART (IL-2 group). Fifty-nine patients received HAART alone (control group). RESULTS: A dramatic effect of IL-2 on the natural killer (NK) cell population was observed with mean increases of 156 cells/microL in the IL-2 group compared to 19.93 cells/microL in the control group (p <.001). Additionally, IL-2-treated patients experienced a statistically significant increase in the mean percentage of CD4 + T cells (3.52% increase) when compared to control patients (1.33% increase) (p <.001). The expanded CD4 + T cell population was primarily of the naive phenotype, with mean increases of 4.53% for the IL-2 group and 0.31% for the control group (p <.001 for between-group difference). In addition, a higher proportion of IL-2-treated patients (67%) compared to control patients (33%) achieved increases of greater than 50% in the CD4+ T cell count (p =.08). Adverse events of grade 3 or grade 4 toxicity were infrequent in the current study and were substantially lower by comparison to those in studies of intermittent dose IL-2 therapy. Also, negligible changes in the HIV viral load from baseline to final measurement were observed in both groups. A trend toward a reduced number of modifications of antiretroviral therapy was apparent in the IL-2 group when compared to control patients. CONCLUSION: Daily, low-dose subcutaneous IL-2 therapy in conjunction with HAART is safe and well tolerated and is effective in expanding lymphocyte cell types including NK cells and naive T cells in individuals who have <300 CD4+ T cells.

NADPH and heme redox modulate pulmonary artery relaxation and guanylate cyclase activation by NO.

The hemoprotein oxidant ferricyanide (FeCN) converts the iron of the heme on soluble guanylate cyclase (sGC) from Fe(2+) to Fe(3+), which prevents nitric oxide (NO) from binding the heme and stimulating sGC activity. This study uses FeCN to examine whether modulation of the redox status of the heme on sGC influences the relaxation of endothelium-removed bovine pulmonary arteries (BPA) to NO. Pretreatment of the homogenate of BPA with 50 microM FeCN resulted in a loss of stimulation of sGC activity by the NO donor 10 microM S-nitroso-N-acetylpenicillamine (SNAP). In the FeCN-treated homogenate reconcentrated to the enzyme levels in BPA, 100 microM NADPH restored NO stimulation of sGC, and this effect of NADPH was prevented by an inhibitor of flavoprotein electron transport, 1 microM diphenyliodonium (DPI). In BPA the relaxation to SNAP was not altered by FeCN, inhibitors of NADPH generation by the pentose phosphate pathway [250 microM 6-aminonicotinamide (6-AN) and 100 microM epiandrosterone (Epi)], or 1 microM DPI. However, the combination of FeCN with 6-AN, Epi, or DPI inhibited (P < 0.05) relaxation to SNAP without significantly altering the relaxation of BPA to forskolin. The inhibitory effects of 1 microM 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (a probe that appears to convert NO-heme of sGC to its Fe(3+)-heme form) on relaxation to SNAP were also enhanced by DPI. These observations suggest that a flavoprotein containing NADPH oxidoreductase may influence cGMP-mediated relaxation of BPA to NO by maintaining the heme of sGC in its Fe(2+) oxidation state.

A flavoprotein mechanism appears to prevent an oxygen-dependent inhibition of cGMP-associated nitric oxide-elicited relaxation of bovine coronary arteries.

The redox state of the heme of soluble guanylate cyclase (sGC) may regulate the sensitivity of vascular tissue to nitric oxide (NO). In this study, diphenyliodonium (DPI) is used as an inhibitor of flavoprotein oxidoreductases to examine their potential role in the expression of NO-elicited cGMP-associated arterial relaxation and sGC stimulation. The relaxation of endothelium-removed bovine coronary arteries (BCAs) precontracted with 30 mmol/L KCl to the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) or to NO is markedly suppressed by 10 micromol/L DPI under an atmosphere of 21% O(2) (5% CO(2)). In contrast, DPI has minimal effects on the relaxation to SNAP under 95% N(2) (5% CO(2)). If BCAs are treated with DPI under 21% O(2) and then exposed to the hemoprotein reductant sodium dithionite (1 mmol/L) under N(2), there is a partial reversal of the inhibitory effects of DPI compared with BCAs that were not treated with dithionite. DPI did not inhibit relaxation elicited by 8-bromo-cGMP or forskolin. Increases in tissue cGMP levels stimulated by SNAP were eliminated by pretreatment of BCAs with DPI under 21% O(2) but not under N(2). Activation of sGC by SNAP in BCA homogenate was also eliminated when vessels were pretreated with 10 micromol/L DPI under 21% O(2), but DPI did not have an inhibitory effect when directly added to the assay of sGC activity. These observations are consistent with a flavoprotein-dependent oxidoreductase functioning to prevent the expression of a novel O(2)-dependent process from oxidizing the heme on sGC and inhibiting NO-elicited cGMP-mediated BCA relaxation.

Nitric oxide modulates mitochondrial respiration in failing human heart.

Background-Our objective for this study was to investigate whether nitric oxide (NO) modulates tissue respiration in the failing human myocardium. Methods and Results-Left ventricular free wall and right ventricular tissue samples were taken from 14 failing explanted human hearts at the time of transplantation. Tissue oxygen consumption was measured with a Clark-type oxygen electrode in an airtight stirred bath containing Krebs solution buffered with HEPES at 37 degrees C (pH 7.4). Rate of decrease in oxygen concentration was expressed as a percentage of the baseline, and results of the highest dose are indicated. Bradykinin (10(-4) mol/L, -21+/-5%), amlodipine (10(-5) mol/L, -14+/-5%), the ACE inhibitor ramiprilat (10(-4) mol/L, -21+/-2%), and the neutral endopeptidase inhibitor thiorphan (10(-4) mol/L, -16+/-5%) all caused concentration-dependent decreases in tissue oxygen consumption. Responses to bradykinin (-2+/-6%), amlodipine (-2+/-4%), ramiprilat (-5+/-6%), and thiorphan (-4+/-7%) were significantly attenuated after NO synthase blockade with N-nitro-L-arginine methyl ester (10(-4) mol/L; all P<0.05). NO-releasing compounds S-nitroso-N-acetyl-penicillamine (10(-4) mol/L, -34+/-5%) and nitroglycerin (10(-4) mol/L, -21+/-5%), also decreased tissue oxygen consumption in a concentration-dependent manner. However, the reduction in tissue oxygen consumption in response to S-nitroso-N-acetyl-penicillamine (-35+/-7%) or nitroglycerin (-16+/-5%) was not significantly affected by N-nitro-L-arginine methyl ester. Conclusions-These results indicate that the modulation of oxygen consumption by both endogenous and exogenous NO is preserved in the failing human myocardium and that the inhibition of kinin degradation plays an important role in the regulation of mitochondrial respiration.

Inhibition of guanylate cyclase stimulation by NO and bovine arterial relaxation to peroxynitrite and H2O2.

The inhibitor of soluble guanylate cyclase (sGC) stimulation by nitric oxide (NO), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), was examined for its effects on the prolonged relaxation of endothelium-removed bovine coronary (BCA) and pulmonary (BPA) arteries to peroxynitrite (ONOO-) and on H2O2-elicited relaxation and sGC stimulation. Our previous studies suggest that ONOO- causes a prolonged relaxation of BPA by regenerating NO and that a 2-min exposure of BCA or BPA to 50 nM NO causes an ONOO--elicited relaxation. The relaxation of K+-precontracted BCA to 50 nM NO or 100 microM ONOO- was essentially eliminated by 10 microM ODQ. ODQ also eliminated relaxation to 0.1 nM-10 microM of NO donor S-nitroso-N-acetyl-penicillamine (SNAP), but it did not alter relaxation to 1-300 microM H2O2. Similar responses were also observed in BPA. ODQ did not increase lucigenin-detectable superoxide production in BCA, and it did not alter luminol-detectable endogenous ONOO- formation observed during a 2-min exposure of BCA to 50 nM NO. In addition, ODQ did not affect tissue release of NO after 2 min exposure of BCA to 50 nM NO. The activity of sGC in BPA homogenate that is stimulated by endogenous H2O2 was not altered by ODQ, whereas sGC activity in the presence of 10 microM SNAP (+fungal catalase) was reduced by ODQ. Thus relaxation of K+-precontracted BCA and BPA to ONOO- appears to be completely mediated by NO stimulation of sGC, whereas the actions of ODQ suggest that NO is not involved in H2O2-elicited relaxation and sGC stimulation. This study did not detect evidence for the participation of additional mechanisms potentially activated by ONOO- in the responses studied.

Changes of fermentation pathways of fecal microbial communities associated with a drug treatment that increases dietary starch in the human colon.

Acarbose inhibits starch digestion in the human small intestine. This increases the amount of starch available for microbial fermentation to acetate, propionate, and butyrate in the colon. Relatively large amounts of butyrate are produced from starch by colonic microbes. Colonic epithelial cells use butyrate as an energy source, and butyrate causes the differentiation of colon cancer cells. In this study we investigated whether colonic fermentation pathways changed during treatment with acarbose. We examined fermentations by fecal suspensions obtained from subjects who participated in an acarbose-placebo crossover trial. After incubation with [1-13C]glucose and 12CO2 or with unlabeled glucose and 13CO2, the distribution of 13C in product C atoms was determined by nuclear magnetic resonance spectrometry and gas chromatography-mass spectrometry. Regardless of the treatment, acetate, propionate, and butyrate were produced from pyruvate formed by the Embden-Meyerhof-Parnas pathway. Considerable amounts of acetate were also formed by the reduction of CO2. Butyrate formation from glucose increased and propionate formation decreased with acarbose treatment. Concomitantly, the amounts of CO2 reduced to acetate were 30% of the total acetate in untreated subjects and 17% of the total acetate in the treated subjects. The acetate, propionate, and butyrate concentrations were 57, 20, and 23% of the total final concentrations, respectively, for the untreated subjects and 57, 13, and 30% of the total final concentrations, respectively, for the treated subjects.

Roles for NAD(P)H oxidases and reactive oxygen species in vascular oxygen sensing mechanisms.

Observations that physiological levels of O2 control the rates of production of reactive O2 species by systems including NAD(P)H oxidases and that certain of these species have signalling mechanisms that regulate vascular tone has resulted in consideration of these systems in processes that mediate the sensing of changes in P(O2). Evidence exists for the participation of hydrogen peroxide-dependent regulation of prostaglandin production and soluble guanylate cyclase activity, resulting from the metabolism of peroxide by cyclooxygenase and catalase, respectively, in P(O2)-elicited signalling mechanisms that regulate vascular force generation. A microsomal NADH oxidase whose activity is controlled by the redox status of cytosolic NAD(H) appears to function as a P(O2) sensor in bovine pulmonary and coronary arteries where changes in O2 levels control the production of superoxide anion-derived hydrogen peroxide and a cGMP-mediated relaxation response. Interactions with nitric oxide and superoxide anion, and the activity of glutathione peroxidase appear to influence the function of these O2 sensing systems, and some of these interactions, along with the activation of other oxidases, may contribute to alterations in P(O2) sensing mechanisms under pathophysiological conditions that affect vascular function.

NO modulates myocardial O2 consumption in the nonhuman primate: an additional mechanism of action of amlodipine.

Recent evidence from our laboratory and others suggests that nitric oxide (NO) is a modulator of in vivo and in vitro oxygen consumption in the murine and canine heart. Therefore, the goal of our study was twofold: to determine whether NO modulates myocardial oxygen consumption in the nonhuman primate heart in vitro and to evaluate whether the seemingly cardioprotective actions of amlodipine may involve an NO-mediated mechanism. Using a Clark-type O2 electrode, we measured oxygen consumption in cynomologous monkey heart at baseline and after increasing doses of S-nitroso-N-acetylpenicillamine (SNAP; 10(-7)-10(-4) M), bradykinin (10(-7)-10(-4) M), ramiprilat (10(-7)-10(-4) M), and amlodipine (10(-7)-10(-5) M). SNAP (-38 +/- 5.8%), bradykinin (-19 +/- 3.9%), ramiprilat (-28 +/- 2.3%), and amlodipine (-23 +/- 4.5%) each caused significant (P < 0.05) reductions in myocardial oxygen consumption at their highest dose. Preincubation of tissue with nitro-L-arginine methyl ester (10(-4) M) blunted the effects of bradykinin (-5.4 +/- 3.2%), ramiprilat (-4.8 +/- 5.0%), and amlodipine (-5.3 +/- 5.0%) but had no effect on the tissue response to SNAP (-38 +/- 5.8%). Our results indicate that NO can reduce oxygen consumption in the primate myocardium in vitro, and they support a role for the calcium-channel blocker amlodipine as a modulator of myocardial oxygen consumption via a kinin-NO mediated mechanism.