Disproportionate elevation of N-terminal pro-brain natriuretic peptide in scleroderma-related pulmonary hypertension.

N-terminal pro-brain natriuretic peptide (NT-proBNP) is a marker of neurohormonal activation that is useful in the diagnosis and prognosis of various forms of pulmonary arterial hypertension (PAH). We sought to characterise and compare NT-proBNP in a cohort of PAH related to systemic sclerosis (PAH-SSc) and idiopathic PAH (IPAH) patients. NT-proBNP levels, collected from PAH-SSc and IPAH patients followed prospectively, were compared and correlated with haemodynamic variables. Cox proportional hazard models were created to assess the predictive value of NT-proBNP. 98 patients (55 PAH-SSc, 43 IPAH) were included. Haemodynamics were similar, except for lower mean pulmonary arterial pressure in PAH-SSc. NT-proBNP levels were significantly higher in PAH-SSc (3,419+/-3,784 versus 1,393+/-1,633 pg x mL(-1); p<0.01) and were more closely related to haemodynamics in PAH-SSc than IPAH. 28 patients died. NT-proBNP predicted survival (hazard ratio (HR) 3.18; p<0.01) in the overall cohort; however, when stratified by group, predicted survival only in PAH-SSc (HR 3.07, p<0.01 versus 2.02, p = 0.29 in IPAH). This is the first description showing NT-proBNP levels are 1) significantly higher in PAH-SSc than IPAH despite less severe haemodynamic perturbations, and 2) stronger predictors of survival in PAH-SSc, suggesting that neurohormonal regulation may differ between PAH-SSc and IPAH. Future studies to define pertinent mechanisms are warranted.

Assessment of pulmonary vasculature and right heart by invasive haemodynamics and echocardiography.

Understanding the haemodynamical profile of the right ventricle and pulmonary circulation is critical to not only the initial evaluation of, but also the continued management of pulmonary hypertension. Despite advances in non-invasive imaging techniques, right heart catheterisation (RHC) remains the gold standard for diagnosis of pulmonary hypertension and its various causes. Even so, integration of invasive haemodynamical data with the echo-Doppler exam provides the most comprehensive assessment of the pathophysiology of pulmonary hypertension in the individual patient. Here, we review technical aspects of basic RHC as well as specialised procedures including exercise and fluid challenge in the evaluation of pulmonary hypertension. Interpretation of data in the context of pulmonary vascular disease is discussed. Echocardiographical assessment of the right ventricular structure and function in pulmonary vascular disease are discussed along with the integration of haemodynamical and echocardiographical data in the clinical context.

Role of nitric oxide in the control of mitochondrial function.

In summary, NO is capable of decreasing mitochondrial respiration in a variety of mammalian tissues. This effect is mediated primarily via binding of NO to the O2 binding site of cytochrome oxidase. This highly sensitive interaction presumably reflects a remnant homology between cytochrome oxidase and bacterial nitrate reductase. This effect has been demonstrated at physiologic levels of NO, highlighting the role for NO in the tonic control of cellular respiration. As this inhibition is dependent upon the levels figure: see text[ of NO and O2 in the tissue, various states of NO production and oxygen supply dictate the ultimate respiratory rate of the mitochondria. Furthermore, deviation from a physiologic NO: O2 may lead to an exacerbation of pathologic states, such as congestive heart failure and septic shock. Thus, NO may play a crucial role in the control of cellular respiration, providing an additional mechanism of action for this biologically diverse molecule that is distinct yet inseparable from its dilator effect on blood vessels.

Simvastatin acts synergistically with ACE inhibitors or amlodipine to decrease oxygen consumption in rat hearts.

Statin drugs, which are cholesterol-lowering agents, can upregulate endothelial nitric oxide synthase (eNOS) in isolated endothelial cells independent of lipid lowering. We investigated the effect of short-term simvastatin administration on NO-mediated regulation of myocardial oxygen consumption (MV(O2)) in tissue from rat hearts. Male Wistar rats were divided into (a) control group (n = 14), and (b) simvastatin group (n = 10, 20 mg/kg/day by oral gavage). After 2 weeks, left ventricular myocardium was isolated to measure MV(O2) using a Clark-type oxygen electrode, and aortic plasma nitrates and nitrites (NOx) were measured. Baseline plasma NOx levels (19+/-2.6 in control vs. 20+/-2.5 microM/L in simvastatin) and baseline MV(O2) (288+/-23 in control vs. 252+/-11 nmol/g/min; p = 0.09) were not significantly different between the two groups. NO-dependent regulation of MV(O2) in response to bradykinin, ramipril, or amlodipine was augmented in simvastatin rats compared with controls (p < 0.05). Decrease of MV(O2) from baseline in response to highest doses in control versus simvastatin groups was as follows-bradykinin, -28+/-5% vs. -44+/-6%; ramipril, -35+/-5% vs. -50+/-8%; and amlodipine, -32+/-9% vs. -42+/-3%. Response to highest dose of NO donor S-nitroso N-acetyl penicillamine (SNAP) was not significantly different in the two groups (-55+/-5% vs. -52+/-7%). Treatment with Nw-nitro-L-arginine methyl ester, inhibitor of NO synthesis, attenuated the effect of bradykinin, ramipril, and amlodipine on MV(O2) (p < 0.05). In conclusion, short-term administration of simvastatin in rats potentiates the ability of angiotensin-converting enzyme (ACE) inhibitors and amlodipine to cause NO-mediated regulation of MV(O2).

Bovine polymerized hemoglobin increases cardiac oxygen consumption and alters myocardial substrate metabolism in conscious dogs: role of nitric oxide.

We investigated the effect of bovine polymerized hemoglobin-based oxygen carrying (HBOC) solution on myocardial oxygen consumption (MVO2) and substrate use. At 15 min after the end of HBOC infusion (20% blood volume, i.v.) in nine permanently instrumented conscious dogs, mean arterial pressure and coronary blood flow were both increased by 41+/-5% and 93+/-20% (p<0.01) without affecting late diastolic coronary resistance and left ventricular dP/dtmax. Administration of HBOC did not affect arterial PO2 or O2 content, but significantly decreased coronary sinus PO2 and O2 content by 21+/-3% and 36+/-3%, respectively. MVO2 was increased from 7.2+/-0.8 to 15+/-1.8 ml O2/min (p<0.01). Despite an increase in triple product from 44+/-2 to 56+/-3 (p<0.01) 15 min after HBOC, the ratio of MVO2 and triple product was markedly elevated by 62+/-19%. Myocardial free fatty acid consumption was decreased from 14+/-1 to 4.5+/-2.2 microEq/min, whereas consumption of lactate increased from 19+/-6 to 69+/-10 micromol/ min and that of glucose increased from 1.0+/-0.5 to 10+/-3 mg/min (all p values, <0.05). These metabolic changes were not observed in dogs that received angiotensin II at a dose used (20-40 ng/kg/min, i.v.) to match those hemodynamic effects of HBOC. These results suggest that administration of HBOC increases coronary blood flow and MVO2 and shifts cardiac metabolism from using free fatty acid to using lactate and glucose in conscious dogs at rest. These metabolic changes are independent of the HBOC-induced change in hemodynamics.

Pharmacodynamics of plasma nitrate/nitrite as an indication of nitric oxide formation in conscious dogs.

BACKGROUND: The present investigation was undertaken to better understand the production of nitric oxide (NO) in vivo as measured by alterations in plasma nitrite or nitrate in blood samples from studies in experimental animals or clinical studies in humans. METHODS AND RESULTS: Plasma samples were taken from the aorta, the coronary sinus, a peripheral vein in the leg (skeletal muscle), or the right ventricle (mixed venous) in chronically instrumented conscious dogs. Plasma nitrite was converted to NO gas in an argon environment by use of hydrochloric acid, and plasma nitrate was converted first to nitrite with nitrate reductase and then to NO gas with acid. Standard curves were constructed, and the amount of nitrite and nitrate in plasma was determined. The primary metabolite was nitrate, whereas nitrate was approximately 10% of the total and remained constant. In the resting dog, the only vascular bed with a positive arterial-venous nitrate difference, evidence for production of NO, was the heart. Nitrate infusion into quietly resting dogs resulted in increases in plasma nitrate up to 38 +/- 3.4 mmol/L, increases in systemic arterial pressure, and a marked diuresis. The plasma half-life was calculated as 3.8 hours. The volume of distribution was calculated as 0.215 L/kg, or equivalent to the extracellular volume. CONCLUSIONS: 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.

Relationship between plasma NOx and cardiac and vascular dysfunction after LPS injection in anesthetized dogs.

The relationship between plasma nitrite, nitrate, and nitric oxide (NOx), cytokines, and cardiac and vascular dysfunction after lipopolysaccharide (LPS) was studied in chronically instrumented anesthetized dogs. LPS was administered (1 mg/kg i.v.), and hemodynamics were recorded at baseline, every 15 min for 1 h, and every hour for an additional 14 h. Dramatic reductions in mean arterial pressure (-48 +/- 6%), cardiac output (-40 +/- 8%), stroke volume (-42 +/- 9%), and first derivative of left ventricular pressure (LV dP/dt, -38 +/- 7%) were seen within 1 h after injection of endotoxin. Cardiac output was not different from control by 9 h, whereas mean arterial pressure (-19 +/- 7%), stroke volume (-32 +/- 8%), and LV dP/dt (-21 +/- 10%) remained significantly depressed from control. Total peripheral resistance was not significantly different from control. Therefore, the hypotension appears to be due to a reduction in cardiac function and not to vasodilation. Levels of plasma NOx were not different from control until 4 h after LPS reached levels 597 +/- 126% higher than control at 15 h. In vitro production of nitrite by coronary microvessels was also elevated, supporting our in vivo findings. In contrast, production of tumor necrosis factor-alpha and interleukin-6 occurred shortly after endotoxin injection, reaching peak levels at 45 and 150 min, respectively. Our data suggest that inducible nitric oxide synthase induction occurred after LPS injection. It is unlikely that nitric oxide contributed significantly to the hypotension and cardiac dysfunction early in our study, whereas cardiodepressive cytokines, particularly tumor necrosis factor-alpha, may be important. In contrast, the hemodynamic effects seen late after injection of endotoxin may be the result of an overproduction of nitric oxide, since there was a sixfold increase in plasma NOx levels at this time and a marked production of nitric oxide in isolated coronary microvessels in vitro.

Role of nitric oxide in the control of renal oxygen consumption and the regulation of chemical work in the kidney.

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.

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.