This study determined the changes in NO production from the coronary circulation of the conscious dog during exercise. The role of endogenous NO as it relates to coronary flow, myocardial work, and metabolism was also studied. Mongrel dogs were chronically instrumented for measurements of coronary blood flow (CBF), ventricular and aortic pressure, and ventricular diameter, with catheters in the aorta and coronary sinus. Acute exercise (5 minutes at 3.6, 5.9, and 9.1 mph) was performed, and hemodynamic measurements and blood samples were taken at each exercise level. Nitro-L-arginine (NLA, 35 mg/kg IV) was given to block NO synthesis, and the exercise was repeated. Blood samples were analyzed for oxygen, plasma nitrate/nitrite (an index of NO), lactate, glucose, and free fatty acid (FFA) levels. Acute exercise caused significant elevations in NO production by the coronary circulation (46 +/- 23, 129 +/- 44, and 63 +/- 32 nmol/min at each speed respectively, P < .05). After NLA, there was no measurable NO production at rest or during exercise. Blockade of NO synthesis resulted in elevations in myocardial oxygen consumption and reductions in myocardial FFA consumption for comparable levels of CBF and cardiac work. The metabolic changes after NLA occurred in the absence of alterations in myocardial lactate or glucose consumptions. NO production by the coronary circulation is increased with exercise and blocked by NLA. The absence of NO in the coronary circulation during exercise does not affect levels of CBF, because it shifts the relationship between cardiac work and myocardial oxygen consumption, suggesting that endogenous NO modulates myocardial metabolism.

Abstract-Our objective was to determine the precise role of endothelial nitric oxide synthase (eNOS) as a modulator of cardiac O 2 consumption and to further examine the role of nitric oxide (NO) consumption in tissues taken from iNOS (Ϫ/Ϫ) (Ϫ28Ϯ4%), wild-type eNOS (ϩ/ϩ) (Ϫ22Ϯ4%), and heterozygous eNOS(ϩ/Ϫ) (Ϫ22Ϯ5%) but not homozygous eNOS (Ϫ/Ϫ) (Ϫ3Ϯ4%) mice. Responses to bradykinin in iNOS (Ϫ/Ϫ) and both wild-type and heterozygous eNOS mice were attenuated after NOS blockade with N-nitro-L-arginine methyl ester (L-NAME) (Ϫ2Ϯ5%, Ϫ3Ϯ2%, and Ϫ6Ϯ5%, respectively, PϽ0.05). In contrast, S-nitroso-N-acetyl-penicillamine (SNAP, 10Ϫ4 mol/L), which releases NO spontaneously, induced decreases in myocardial O 2 consumption in all groups of mice, and such responses were not affected by L-NAME. In addition, pretreatment with bacterial endotoxin elicited a reduction in basal O 2 consumption in tissues taken from normal but not iNOS (Ϫ/Ϫ)-deficient mice. Our results indicate that the pivotal role of eNOS in the control of myocardial O 2 consumption and modulation of mitochondrial respiration by NO may have an important role in pathological conditions such as endotoxemia in which the production of NO is altered. . Their initial observations demonstrated that activated mouse peritoneal macrophages severely inhibited O 2 consumption in numerous tumor cell lines obtained from different tissues and animal species in cultures by an unknown mechanism. Evidence now suggests that the macrophage-induced cytotoxic effect on mitochondrial metabolism is NO related. 2,3 NO inhibits respiration by nitrosylating the iron-sulfur centers of aconitase, complexes I and II of the electron transport chain, and through a very potent reversible alteration in the activity of cytochrome c oxidase. 4 -6 Recently, we and others have provided direct evidence to suggest that under physiological conditions NO plays a modulatory role on mitochondrial respiration and tissue O 2 consumption. For instance, L-arginine analogues, which are nonspecific inhibitors of the 3 isoforms of nitric oxide synthase (NOS), 7 increase O 2 consumption in whole body, 8 heart, skeletal muscle, and kidney both in vivo 9 -12 and in vitro. [12][13][14] We have interpreted our previous studies to suggest that endothelial nitric oxide synthase (eNOS), the most highly expressed isoform of NOS in vascular tissue under physiological conditions, is responsible for the control of tissue O 2 consumption by NO. However, we have yet to determine which isoform of NOS regulates mitochondrial O 2 consumption, because almost all cells are capable of expressing all 3 different NOS isoforms. Studies of the effects of bacterial endotoxins have attributed a substantial role for inducible nitric oxide synthase (iNOS) in the development of shock and perhaps other pathological states. To address the role of NO in both physiological and pathophysiological states in the control of mitochondrial respiration, we used tissues from mice deficient in iNOS and eNOS and 3 additional groups, ie, control C57B...

These studies indicate that nitrate is a reliable measure of NO metabolism in vivo but that because of the long half-life, nitrate will accumulate in plasma once it is produced. Because of the large volume of distribution (21% of body weight versus the 4% of body weight usually attributed to plasma volume, the compartment in which nitrate is measured), simple measures of plasma nitrate underestimate by a factor of 4 to 6 the actual production of nitrate or NO by the body. In disease states, such as heart failure, in which renal function and extracellular volume are altered, caution should be exercised when increases in nitrate in plasma as an index of NO formation are evaluated.

Inhibition of NO synthesis has recently been shown to increase oxygen extraction in vivo, and NO has been proposed to play a significant role in the regulation of oxygen consumption by both skeletal and cardiac muscle in vivo and in vitro. It was our aim to determine whether NO also has such a role in the kidney, a tissue with a relatively low basal oxygen extraction. In chronically instrumented conscious dogs, administration of an inhibitor of NO synthase, nitro-L-arginine (NLA, 30 mg/kg i.v.), caused a maintained increase in mean arterial pressure and renal vascular resistance and a decrease in heart rate (all P<0.05). At 60 minutes, urine flow rate and glomerular flow rate decreased by 44+/-12% and 45+/-7%, respectively; moreover, the amount of sodium reabsorbed fell from 16+/-1.7 to 8.5+/-1.1 mmol/min (all P<0.05). At this time, oxygen uptake and extraction increased markedly by 115+/-37% and 102+/-34%, respectively (P<0.05). Oxygen consumption also significantly increased from 4.5+/-0.6 to 7.1+/-0.9 mL O2/min. Most important, the ratio of oxygen consumption to sodium reabsorbed increased dramatically from 0.33+/-0.07 to 0.75+/-0.11 mL O2/mmol Na+ (P<0.05), suggesting a reduction in renal efficiency for transporting sodium. In vitro, both a NO-donating agent and the NO synthase-stimulating agonist bradykinin significantly decreased both cortical and medullary renal oxygen consumption. In conclusion, NO plays a role in maintaining a balance between oxygen consumption and sodium reabsorption, the major ATP-consuming process in the kidney, in conscious dogs, and NO can inhibit mitochondrial oxygen consumption in canine renal slices in vitro.

Prediction of cardiovascular (CV) complications represents the Achilles' heel of end-stage renal disease. Surrogate markers of endothelial dysfunction have been advocated as predictors of CV risk in this cohort of patients. We have recently adapted a noninvasive laser Doppler flowmetry (LDF) functional testing of endothelium-dependent microvascular reactivity and demonstrated that end-stage renal disease patients are characterized by profound alterations in thermal hyperemic responsiveness. We hypothesized that such functional assessment of the cutaneous microcirculation may offer a valid, noninvasive test of the severity of endothelial dysfunction and CV risk. To test this hypothesis, we performed a cross-sectional study, in which we compared LDF measurements to conventional risk factors, and performed a pilot longitudinal study. LDF studies were performed in 70 patients and 33 controls. Framingham and Cardiorisk scores were near equivalent for low-risk patients, but more divergent as risk increased. C reactive protein (CRP) levels and LDF parameters (amplitude of thermal hyperemia (TH), area under the curve of TH) showed significant abnormality in high-risk vs low-risk patients calculated using either Framingham or Cardiorisk scores. Patients who had abnormal LDF parameters showed increased CV mortality, however, had similar risk assessments (Framingham, Cardiorisk, CRP, and homocysteine) to those with unimpaired LDF tracings. In conclusion, LDF parameters of microvascular reactivity offer a sensitive characterization of endothelial dysfunction, which may improve CV risk assessment through incorporation into the Framingham or Cardiorisk algorithm.

Adenosine is produced by renal tissue and has potent effects on renal blood flow and its distribution, glomerular filtration rate (GFR), and the secretion of renin. Intrarenal infusion of adenosine decreases GFR primarily by decreasing glomerular hydrostatic pressure through its effects in increasing afferent arteriolar resistance and possibly decreasing efferent arteriolar resistance. The fall in GFR due to adenosine is accompanied by little change or an increase in total organ blood flow. Regional renal blood flow during adenosine infusion is redistributed, with a greater percentage of total flow going to the juxtamedullary cortex. Intrarenal adenosine produces marked decreases in water and sodium excretion that are proportionally greater than its effect on GFR, suggesting a possible direct tubular action. Intrarenal adenosine also produces a rapid and pronounced inhibition of renin release that appears to be independent of its hemodynamic or tubular effects. A metabolic hypothesis for the control of glomerular filtration rate and renin release with adenosine acting as a mediator is considered, and criteria for establishing an intrarenal role for adenosine in the regulation of renal function are discussed.

Background and Purpose-Prenatal glucocorticoids prevent germinal matrix hemorrhage in premature infants. The underlying mechanism, however, is elusive. Germinal matrix is enriched with angiogenic vessels exhibiting paucity of pericytes and glial fibrillary acidic protein-positive astrocyte end feet. Therefore, we asked whether glucocorticoid treatment would suppress angiogenesis and enhance periendothelial coverage by pericytes and glial fibrillary acidic protein-positive end feet in the germinal matrix microvasculature. Methods-We treated pregnant rabbits with intramuscular betamethasone and delivered pups prematurely by cesarean section at E29 (termϭ32 days). Endothelial turnover, vascular density, pericyte coverage, glial fibrillary acidic protein-positive end feet, cell death, and growth factors orchestrating angiogenesis, including vascular endothelial growth factor, angiopoietins, transforming growth factor-␤, and platelet-derived growth factor-B, were compared between betamethasone-treated and untreated pups. Similar comparisons were done between autopsy materials from premature infants exposed and unexposed to prenatal glucocorticoids. Results-Antenatal glucocorticoid treatment reduced endothelial proliferation, vascular density, and vascular endothelial growth factor expression in the germinal matrix of both rabbits and humans. The pericyte coverage was greater in glucocorticoid-treated rabbit pups and human infants than in controls, but not the glial fibrillary acidic protein-positive end feet coverage. Transforming growth factor-␤, but not angiopoietins and platelet-derived growth factor-B, were elevated in glucocorticoid-treated rabbit pups compared with controls. Betamethasone treatment induced apoptosis, neuronal degeneration, and gliosis in rabbit pups. However, there was no evidence of increased cell death in glucocorticoid-exposed human infants. Conclusions-Prenatal glucocorticoid suppresses vascular endothelial growth factor and elevates transforming growth factor-␤ levels, which results in angiogenic inhibition, trimming of neovasculature, and enhanced pericyte coverage. These changes contribute to stabilizing the germinal matrix vasculature, thereby reducing its propensity to hemorrhage. Prenatal glucocorticoid exposure does not induce neural cell death in humans, unlike rabbits. (Stroke. 2010;41:1766-1773.)

Although the role of nitric oxide (NO) in the modulation of vascular tone has been studied and well understood, its potential role in the control of myocardial metabolism is only recently evident. Several lines of evidence indicate that NO regulates myocardial glucose metabolism; however, the details and mechanisms responsible are still unknown. The aim of this study was to further define the role of NO in the control of myocardial glucose metabolism and the nitric oxide synthase (NOS) isoform responsible using transgenic animals lacking endothelial NOS (ecNOS). In the present study, we examined the regulation of myocardial glucose uptake using isometrically contracting Langendorff-perfused hearts from normal mice (C57BL/6J), mice with defects in the expression of ecNOS [ecNOS (-/-)], and its heterozygote [ecNOS (+/-)], and wild-type mice [ecNOS (+/+)] (n=6, respectively). In hearts from normal mice, little myocardial glucose uptake was observed. This myocardial glucose uptake increased significantly in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME). Similarly, in the hearts from ecNOS (-/-), glucose uptake was much greater than in normal mice, whereas myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice was not different from normal mice. In addition, myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice increased significantly in the presence of L-NAME. At a workload of 800 g. beats/min, L-NAME increased glucose uptake from 0.1+/-0.1 to 3+/-0.4 microg/min x mg in ecNOS (+/-) mice and from 0.2+/-0.1 to 2.7+/-0.7 microg/min x mg in ecNOS (+/+) mice. Furthermore, in the hearts from ecNOS (-/-) mice, 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cGMP), a cGMP analog or S-nitroso-N-acetylpenicillamine (SNAP), a NO donor essentially shut off glucose uptake, and in hearts from ecNOS (+/-) mice, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), an inhibitor of cGMP, increased the glucose uptake significantly. These results indicate clearly that cardiac NO production regulates myocardial glucose uptake via a cGMP-dependent mechanism and strongly suggest that ecNOS plays a pivotal role in this regulation. These findings may be important in the understanding of the pathogenesis of the diseases such as ischemic heart disease, heart failure, diabetes mellitus, hypertension, and hypercholesterolemia, in which NO synthesis is altered and substrate utilization by the heart changes.