Site of pulmonary vasodilation by inhaled nitric oxide in microembolic lung injury

The double free-muscle transfer technique has restored prehension in patients following complete avulsion of the brachial plexus. This achievement was almost inconceivable as recently as several years ago and has now given new hope for these patients to be able to use their otherwise useless limbs.     

Lack of nitric oxide contributes to vasospasm during ischemia/reperfusion injury

Vasospasm can be a complication after free tissue transfer and replant operations. Recent studies suggest that vasospasm may be due to endothelium dysfunction, resulting in impairment of nitric oxide production. The present experiment was designed to investigate acute responses of the microcirculation of skeletal muscle to local interarterial infusion of sodium nitroprusside (a direct donor of nitric oxide and thus an endothelium-independent vasodilator) or acetylcholine chloride (which stimulates endothelium release of endogenous nitric oxide) during reperfusion after 4 hours of warm ischemia. Male Sprague-Dawley rats, each weighing 100 to 120 gm, were anesthetized with sodium pentobarbitone and were surgically prepared with vascular isolated and denervated cremaster muscles that were subjected to 4 hours warm ischemia and 2 hours of reperfusion. Sodium nitroprusside (10(-3) M), acetylcholine chloride (10(-4) M), or normal saline (eight rats for each group) were administered by local infusion (0.1 ml/hour) through the femoral artery into the natural blood flow of the cremaster. The arterial tree in the cremaster was observed and arteriole diameters (A1-A4) were measured using intravital microscopy. The number of arteriole branches having temporary stoppage of flow were counted in each cremaster. The results from this study show that local infusion of sodium nitroprusside, but not acetylcholine chloride, prevents ischemia/reperfusion vasoconstriction in A3 and A4 arterioles and thus improves microvascular blood flow. Generalized vasoconstriction caused by topically applied norepinephrine (10(-6) M) to sham ischemia cremasters could be completely reversed by the local infusion of 10(-4) M acetylcholine chloride. These results indicate that vasospasm after ischemia/reperfusion may be related to temporary endothelial cell dysfunction, resulting in the inability to produce sufficient nitric oxide during early reperfusion. Vascular smooth muscle, however, is responsive to locally administered sodium nitroprusside infusion (which is thought to provide exogenous nitric oxide).     

Role of endothelins and nitric oxide in hepatic reperfusion injury in the rat

In epithelial cells, alpha-, beta-, and gamma-catenin are involved in linking the peripheral microfilament belt to the transmembrane protein E-cadherin. alpha-Catenin exhibits sequence homologies over three regions to vinculin, another adherens junction protein. While vinculin is found in cell-matrix and cell-cell contacts, alpha-catenin is restricted to the latter. To elucidate, whether vinculin is part of the cell-cell junctional complex, we investigated complex formation and intracellular targeting of vinculin and alpha-catenin. We show that alpha-catenin colocalizes at cell-cell contacts with endogenous vinculin and also with the transfected vinculin head domain forming immunoprecipitable complexes. In vitro, the vinculin NH2-terminal head binds to alpha-catenin, as seen by immunoprecipitation, dot overlay, cosedimentation, and surface plasmon resonance measurements. The Kd of the complex was determined to 2-4 x 10(-7) M. As seen by overlays and affinity mass spectrometry, the COOH-terminal region of alpha-catenin is involved in this interaction. Complex formation of vinculin and alpha-catenin was challenged in transfected cells. In PtK2 cells, intact alpha-catenin and alpha-catenin1-670, harboring the beta-catenin- binding site, were directed to cell-cell contacts. In contrast, alpha-catenin697-906 fragments were recruited to cell-cell contacts, focal adhesions, and stress fibers. Our results imply that in vivo alpha-catenin, like vinculin, is tightly regulated in its ligand binding activity.     

Inhibition of nitric oxide synthesis aggravates reperfusion injury after hepatic ischemia and endotoxemia

The potential role of nitric oxide (NO) was investigated in the pathophysiology of liver injury after priming with 20 min hepatic ischemia-reperfusion and administration of .5 mg/kg Salmonella enteritidis endotoxin. Liver injury during the early reperfusion phase of 4 h was characterized by severe vascular oxidant stress, lipid peroxidation (LPO), neutrophil infiltration, and a 33% reduction of the microvascular blood flow in the liver. Inhibition of NO synthesis with N omega-nitro-L-arginine methyl ester hydrochloride (L-NAME) aggravated liver injury by 90%, reduced LPO, and did not affect liver neutrophils but further impaired microvascular blood flow. Treatment with the NO-donor spermine-NONOate or L-arginine did not affect these parameters in postischemic animals, however, treatment did restore all values of L-NAME-treated animals back to disease control levels. These data suggest that endogenous NO formation is sufficient to limit ischemic liver injury during reperfusion but inhibition of NO synthesis will result in additional ischemic damage. NO may also be involved in scavenging of superoxide in the vasculature and in inducing LPO.     

Role of inducible nitric oxide synthase in endotoxin-induced acute lung injury

The role of nitric oxide (NO) in lung injury remains unclear. Both beneficial and detrimental roles have been proposed. In this study, we used mutant mice lacking the inducible nitric oxide synthase (iNOS) to assess the role of this isoform in sepsis-associated lung injury. Wild-type and iNOS knockout mice were injected with either saline or Escherichia coli endotoxin (LPS) 25 mg/kg and killed 6, 12, and 24 h later. Lung injury was evaluated by measuring lactate dehydrogenase activity in the bronchoalveolar lavage, pulmonary wet/dry ratio, and immunostaining for nitrotyrosine formation. In the wild-type mice, LPS injection elicited more than a 3-fold rise in lactate dehydrogenase activity, a significant rise in lung wet/dry ratio and extensive nitrotyrosine staining in large airway and alveolar epithelium, macrophages, and pulmonary vascular cells. This was accompanied by induction of iNOS protein and increased lung nitric oxide synthase activity. By comparison, LPS injection in iNOS knockout mice elicited no iNOS induction and no significant changes in lung NOS activity, lactate dehydrogenase activity, lung wet/dry ratio, or pulmonary nitrotyrosine staining. These results indicate that mice deficient in iNOS gene are more resistant to LPS-induced acute lung injury than are wild-type mice.     

L-arginine decreases alveolar macrophage proinflammatory monokine production during acute lung injury by a nitric oxide synthase-dependent mechanism

The hip abductor muscles are considered important for gait and biomechanics of the hip joint; however, their specific function has not been defined precisely. The intensity of magnetic resonance imaging signals in skeletal muscle has been reported to increase immediately after exercise. Making use of this phenomenon, we evaluated the hip abductor muscles. Magnetic resonance imaging was performed after isometric exercise of the hip abductor in three positions (20 degrees of abduction, neutral, and 20 degrees of adduction). The abduction force of the hip was measured with a dynamometer, and electromyographic measurements were made simultaneously for the same hip positions. Additionally, magnetic resonance imaging was performed after one-legged stance. As the hip was more adducted, the signal intensity increased on the scans. The values for muscle force, as evaluated with the dynamometer and integrated electromyography, also supported the results. The increase in signal intensity of the gluteus minimus at 20 degrees of abduction and after one-legged stance was significantly greater than that of the gluteus medius (p < 0.0001 and p < 0.0001, respectively). The results of this study indicate that the gluteus minimus muscle, along with the gluteus medius, plays an important role in hip abduction, gait, and stabilization of the pelvis.     

Attenuation of myocardial reperfusion injury by reducing intracellular calcium overloading with dihydropyridines

The effects of three different dihydropyridine (DHP) calcium channel antagonists, nisoldipine, nimodipine, and nifedipine, on myocardial ischemic and reperfusion injury were studied using isolated rat hearts subjected to ischemia and reperfusion. Hearts were perfused with Krebs-Henseleit bicarbonate buffer containing 0, 4, 16, 64 and 100 nM concentrations of the above dihydropyridines for 15 min. Global ischemia was then induced by terminating the aortic flow for 30 min at 37 degrees, followed by 30 min of reperfusion. Left ventricular (LV) functional (LV developed pressure, its first derivative and coronary flow) and biochemical parameters (creatine kinase release) were monitored prior to ischemia and during reperfusion. In separate group of hearts, intracellular free Ca2+ ([Ca2+]i) was monitored with an intracellular calcium analyzer using a fluorescent Ca2+ indicator (Fura-2 AM). Tissue Ca2+ was also measured by atomic absorption spectroscopy after perfusing the hearts with ion-free cold buffer to wash out extracellular Ca2+. Significant recovery of the coronary flow was observed in all hearts treated with a high concentration (100 nM) of DHPs compared with the control group (P < 0.05), while a lower dose of nisoldipine (16 nM) and nifedipine (64 nM) also improved the coronary flow effectively. Reduction of myocardial creatine kinase release and improvement of the recovery of LV developed pressure, dp/dtmax, were achieved by DHPs in a concentration-dependent manner. A higher concentration of DHPs also decreased the formation of myocardial thiobarbituric acid reactive substances, although these compounds did not possess direct free radical scavenging effects in vitro. Tissue Ca2+ content was reduced significantly in treated groups. The rise of [Ca2+]i during ischemia and reperfusion appeared to be attenuated by these DHPs. The concentration-response study of the three DHPs showed the effective concentrations for reducing [Ca2+]i to be 16, 64 and 100 nM nisoldipine, nifedipine and nimodipine, respectively, in this experimental setting. The above results indicate that pretreatment with DHPs can attenuate the myocardial reperfusion injury by modulating Ca2+ overloading and decreasing the susceptibility of the membrane to free radical attack.     

Protective effects of intravascular pressure and nitric oxide in ischemic lung injury

Cessation of blood flow during ischemia will decrease both distending and shear forces exerted on endothelium and may worsen ischemic lung injury by decreasing production of nitric oxide (NO), which influences vascular barrier function. We hypothesized that increased intravascular pressure (Piv) during ventilated ischemia might maintain NO production by increasing endothelial stretch or shear forces, thereby attenuating ischemic lung injury. Injury was assessed by measuring the filtration coefficient (Kf) and the osmotic reflection coefficient for albumin (sigmaalb) after 3 h of ventilated (95% O2-5% CO2; expiratory pressure 3 mmHg) ischemia. Lungs were flushed with physiological salt solution, and then Piv was adjusted to achieve High Piv (mean 6.7 +/- 0.4 mmHg, n = 15) or Low Piv (mean 0.83 +/- 0.4 mmHg, n = 10). NG-nitro-L-arginine methyl ester (L-NAME; 10(-5) M, n = 10), NG-nitro-D-arginine methyl ester (D-NAME; 10(-5) M, n = 11), or L-NAME (10(-5) M)+L-arginine (5 x 10(-4) M, n = 6) was added at the start of ischemia in three additional groups of lungs with High Piv. High Piv attenuated ischemic injury compared with Low Piv (sigmaalb 0.67 +/- 0.04 vs. 0. 35 +/- 0.04, P < 0.05). The protective effect of High Piv was abolished by L-NAME (sigmaalb 0.37 +/- 0.04, P < 0.05) but not by D-NAME (sigmaalb 0.63 +/- 0.07). The effects of L-NAME were overcome by an excess of L-arginine (sigmaalb 0.56 +/- 0.05, P < 0.05). Kf did not differ significantly among groups. These results suggest that Piv modulates ischemia-induced barrier dysfunction in the lung, and these effects may be mediated by NO.     

Interaction of nitric oxide and endothelin-1 in ischemia/reperfusion injury of rat heart

Although several studies have demonstrated that nitric oxide appears to be cardioprotective and endothelin-1 (ET-1) deleterious in myocardial ischemia/reperfusion injury, their interactions in the intact heart are unknown. Therefore, coronary effluent and interstitial fluid ("transudate") levels of ET-1 and cyclic GMP, an indirect measure of nitric oxide production, were determined simultaneously in normoxic and reperfused hearts and compared with myocardial and coronary function. Rat hearts were buffer-perfused at 9 ml/min/g heart wet weight for 45 min (baseline), followed either by another 45 min of perfusion (normoxia), or 15 min of total global ischemia and 30 min reperfusion. Hearts received, from 42-90 min, either vehicle, the inhibitor of nitric oxide formation NG-nitro-L-arginine (L-NNA; 200 micromol/l), the nitric oxide donor S-nitroso-N-acetyl-DL-penicillamine (SNAP; 200 micromol/l), or the ET receptor antagonist PD 142893 (200 nmol/l). Both mediators were released preferentially into the vascular lumen which resulted in similar luminal and interstitial concentrations of cyclic GMP, but three-fold higher levels of ET-1 in tissue because of the higher effluent than transudate flow rate. L-NNA increased the release of ET-1 and worsened coronary function, whereas SNAP had opposite effects. On reperfusion, considerable functional impairment was observed, although levels of cyclic GMP both in the vascular and tissue compartment were not reduced, but even increased. Reperfusion functional impairment was aggravated after inhibiting the synthesis of nitric oxide, whereas SNAP restored cardiac and coronary function close to pre-ischemic level. Deterioration of function corresponded with an increased level, and improvement with a decreased level of intersitial ET-1 at the onset of reperfusion. PD 142893 was similarly cardioprotective as SNAP both in normoxia and reperfusion. These results suggest that in reperfusion, cardiac function is depressed, despite increased rather than decreased endogenous nitric oxide production, largely due to the prevalence of the deleterious effects of ET-1 which are overcome by antagonism of ET receptors or exogenous nitric oxide supplied by SNAP.     

Photoactivation of the nitric oxide donor SIN-1

This study investigates whether nitric oxide (NO) release from linsidomine (SIN-1), the active metabolite of the antianginal drug molsidomine, is light sensitive. A 9-h irradiation with polychromatic visible light increased the formation of nitrite (NO index metabolite) from SIN-1 (1 mM) by 61% as compared to control samples incubated in the dark. Under the same conditions (9-h irradiation) the concentration of oxygen decreased to 2% of control. However, oxygen consumption was substantially reduced when light was excluded (35% recovery after 9 h). These results show that irradiation with visible light markedly enhances the oxygen-dependent NO release from SIN-1. Thus, sydnonimines appear to be suitable model compounds for the development of photoactivatable NO donors.     

SP/W-5186, A cysteine-containing nitric oxide donor, attenuates postischemic myocardial injury

The effects of SP/W-5186, a cysteine-containing nitric oxide (.NO) donor, on myocardial reperfusion injury were studied in a rabbit ischemia (45 min) and reperfusion (180 min) model. Five min before reperfusion, either low-dose (0.3 micromol/kg) or high-dose (1 micromol/kg) SP/W-5186 was given intravenously as a bolus. Administration of 0.3 micromol/kg SP/W-5186 did not change mean arterial blood pressure, heart rate or pressure-rate index. However, administration of low-dose SP/W-5186 exerted marked cardioprotective effects as evidenced by improved cardiac functional recovery (P <.05 vs. vehicle), decreased plasma creatine kinase concentration (P <. 01) and reduced infarct size (P <.01). Moreover, administration of SP/W-5186 significantly decreased platelet aggregation (P <.01 vs. vehicle), attenuated polymorphonuclear leukocyte (PMN) accumulation in myocardial tissue, inhibited PMN adhesion to endothelial cells and preserved endothelial function. Administration of high-dose SP/W-5186 resulted in a transient but significant decrease in mean arterial blood pressure and exerted more cardiac protection compared with low-dose treatment. However, the effects on platelet aggregation, PMN accumulation and PMN adhesion did not differ significantly between the two SP/W-5186 groups. Furthermore, administration of SP/W-6373, an analogue of SP/W-5186 that lacks the NO moiety, failed to exert any protective effects. These results demonstrate that NO released from SP/W-5186 significantly protected myocardial tissue from reperfusion injury. The primary mechanisms of the observed cardioprotection by SP/W-5186 involve inhibition of platelet aggregation, attenuation of PMN-endothelium interaction and preservation of endothelial function.     

Effect of inhaled nitric oxide on pulmonary hemodynamics after acute lung injury in dogs

Increased pulmonary vascular resistance (PVR) and mismatch in ventilation-to-perfusion ratio characterize acute lung injury (ALI). Pulmonary arterial pressure (Ppa) decreases when nitric oxide (NO) is inhaled during hypoxic pulmonary vasoconstriction (HPV); thus NO inhalation may reduce PVR and improve gas exchange in ALI. We studied the hemodynamic and gas exchange effects of NO inhalation during HPV and then ALI in eight anesthetized open-chest mechanically ventilated dogs. Right atrial pressure, Ppa, and left ventricular and arterial pressures were measured, and cardiac output was estimated by an aortic flow probe. Shunt and dead space were also estimated. The effect of 5-min exposures to 0, 17, 28, 47, and 0 ppm inhaled NO was recorded during hyperoxia, hypoxia, and oleic acid-induced ALI. During ALI, partial beta-adrenergic blockade (propranolol, 0.15 mg/kg i.v.) was induced and 74 ppm NO was inhaled. Nitrosylhemoglobin (NO-Hb) and methemoglobin (MetHb) levels were measured. During hyperoxia, NO inhalation had no measurable effects. Hypoxia increased Ppa (from 19.8 +/- 6.1 to 28.3 +/- 8.7 mmHg, P < 0.01) and calculated PVR (from 437 +/- 139 to 720 +/- 264 dyn.s.cm-5, P < 0.01), both of which decreased with 17 ppm NO. ALI decreased arterial PO2 and increased airway pressure, shunt, and dead space ventilation. Ppa (19.8 +/- 6.1 vs. 23.4 +/- 7.7 mmHg) and PVR (437 +/- 139 vs. 695 +/- 359 dyn.s.cm-5, P < 0.05) were greater during ALI than during hyperoxia. No inhalation had no measureable effect during ALI before or after beta-adrenergic blockade. MetHb remained low, and NO-Hb was unmeasurable. Bolus infusion of nitroglycerin (15 micrograms) induced an immediate decrease in Ppa and PVR during ALI.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of nitric oxide synthase inhibitor on reperfusion injury of the brain under hypothermic circulatory arrest

Selective ruminants, which prefer easily digestible plants, cannot digest fibrous forage as well as grass eaters. Low enzyme activity or short retention time of ingesta particles in fermentation chambers appeared to be responsible for reduced cellulose breakdown. Seasonal activity of cellulolytic enzymes, cellulose concentration and protozoa population in reticulorumen (RR) and caecocolon (CC) of roe deer as a typical concentrate selector were investigated. Cellulase activities were lowest in winter when cellulose concentration in RR contents were highest. Highest enzyme activities and lowest cellulose concentration were measured in early spring. Cellulolytic activities were significantly correlated with the number of protozoa in RR. Only one entodinomorphic genus was identified in the RR. The enzyme activities in CC were far lower compared with those in RR. Low cellulose digestion in the RR cannot be compensated for by cellulose breakdown in the CC. The reduced cellulose digestion of roe deer may be attributed to the short retention time of food particles in spring and summer, whereas decreased colonisation of microorganisms in the rumen may be the main reason for low cellulose breakdown in winter.     

Attenuation of cocaine kindling by 7-nitroindazole, an inhibitor of brain nitric oxide synthase

Recent studies suggest the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors and nitric oxide synthase (NOS) in the process of increased sensitivity to the convulsive effect of cocaine ("cocaine kindling"). The present study was undertaken to analyze the various behavioral stages in the development of cocaine kindling and to investigate the effect of 7-nitroindazole (7-NI), a relatively selective inhibitor of the neuronal NOS isoform, on the induction and expression of sensitization to the convulsive effect of cocaine. Also, the effect of 7-NI on responses produced by acute systemic administration of cocaine or N-methyl-D,L-aspartate (NMDLA) was investigated. Cocaine kindling was assessed on a five-stage scale following the administration of a sub-convulsant dose of the drug (35 mg/kg/day; i.p.) to Swiss Webster mice for 10 days. Stage 5 seizures developed following the 9th day of cocaine administration. Pre-treatment with 7-NI (25 mg/kg/day; i.p.) 15 min before cocaine for 10 days completely prevented the appearance of stage 4 and 5 seizures, and it significantly attenuated stage 3 behavior in response to a challenge cocaine dose (35 mg/kg) given either 24 hr or 10 days after 7-NI/cocaine administration was stopped. A single injection of 7-NI (25 mg/kg; i.p.) completely prevented the expression of cocaine kindled seizures. Whereas 7-NI had no effect on the responses elicited by acute cocaine administration (60 mg/kg; i.p.), this agent partially attenuated the effects induced by systemic administration of the NMDA receptor agonist NMDLA (250 mg/kg; i.p.). The present study indicates that 7-NI attenuates both the induction and expression of sensitization to the convulsive effect of cocaine. The findings that 7-NI attenuated cocaine kindling and partially blocked the effects produced by activation of the NMDA receptor, but not the effects induced by acute cocaine administration, support the role of the NMDA receptor and brain NOS in the development of cocaine kindling rather than in the acute effects of the drug.     

Factors influencing the tracheal fluctuation of inhaled nitric oxide in patients with acute lung injury

BACKGROUND: Inhaled nitric oxide (NO) improves arterial oxygenation in patients with acute lung injury (ALI) by selectively dilating pulmonary vessels perfusing ventilated lung areas. It can be hypothesized that NO uptake from the lung decreases with increasing ventilation perfusion mismatch. This study was undertaken to determine the factors influencing the fluctuation of tracheal NO concentration over the respiratory cycle as an index of NO pulmonary uptake in patients with ALI. METHODS: By using a prototype system (Opti-NO) delivering a constant flow of NO only during the inspiratory phase, 3 and 6 ppm of NO were administered during controlled mechanical ventilation into a lung model and to 11 patients with ALI. All patients had a thoracic computed tomography (CT) scan. Based on an analysis of tomographic densities, lungs were divided into three zones: normally aerated (-1.000 to -500 Hounsfield units [HU]), poorly aerated (-500 to -100 HU), and nonaerated (-100 to +100 HU), and the volume of each zone was computed. Concentrations of NO in the inspiratory limb and trachea were continuously measured by a fast-response chemiluminescence apparatus. RESULTS: In the lung model, tracheal NO concentration was stable with minor fluctuation. In contrast, in patients, tracheal NO concentration fluctuated widely during the respiratory cycle (55 +/- 10%). Because uptake of NO from the lungs was absent in the lung model but present in the patients, this fluctuation was considered as an index of pulmonary uptake of NO. This was further substantiated by (1) the coincidence of the peak and minimum tracheal NO concentration with the end-inspiratory and end-expiratory phases, respectively, and (2) continued decrease of tracheal NO concentration during prolonged expiratory phase. In patients with ALI, the fluctuation of tracheal NO concentration expressed as the difference between inspiratory and expiratory NO concentrations divided by inspiratory NO concentration was greater at 6 ppm than at 3 ppm (P < 0.01), was linearly correlated with normally aerated lung volume, inversely correlated with alveolar dead space and with poorly aerated lung volume. CONCLUSION: In patients with ALI, fluctuation of tracheal NO concentration over the respiratory cycle can be considered as an index of NO uptake from the lungs that depends on aerated lung volume and perfusion of ventilated lung areas. At bedside, it may be used to follow the evolution of ventilation-perfusion mismatch.     

Controlled reperfusion and pentoxifylline modulate reperfusion injury after single lung transplantation

OBJECTIVE: Rodent models have suggested that initial low-pressure reperfusion of transplanted lungs reduces injury after ischemia. We investigated this phenomenon and the use of pentoxifylline in a porcine model of left single lung transplantation. METHODS: Donor lungs were preserved with Euro-Collins solution for a mean ischemic time of 18.4 hours. Neutrophil trapping in the graft, pulmonary artery pressure, and gas exchange were assessed over a 12-hour period. Partial occlusion of the contralateral pulmonary artery allowed manipulation of the pulmonary artery pressure in the transplanted lung. Group A (n = 5) was perfused at a mean pulmonary artery pressure of 20 mm Hg, group B was reperfused at a mean pulmonary artery pressure of 45 mm Hg for 10 minutes before reducing the pressure to the same as group A, and group C was reperfused at a mean pressure of 20 mm Hg for 10 minutes, then increased to a mean of 45 mm Hg for the remainder of the experiment. Group D was reperfused as in group A with the addition of intravenous pentoxifylline. RESULTS: Leukocyte sequestration was observed in the first 10 minutes after reperfusion in groups A, B, and C, with maximal sequestration at 2 minutes. Significantly more sequestration was observed in the first 6 minutes in group B than in groups A and C, which were similar. Pentoxifylline significantly reduced leukocyte sequestration. Pulmonary venous oxygen tension in the allograft lung was worst in group B. Groups A and C were similar, but group D was superior to all other groups (p < 0.001). CONCLUSIONS: Low-pressure reperfusion, even when limited to the first 10 minutes, modulates reperfusion injury possibly through a leukocyte-dependent mechanism. The addition of pentoxifylline in the recipient confers significant additional benefit.     

Attenuation by creatine of myocardial metabolic stress in Brattleboro rats caused by chronic inhibition of nitric oxide synthase

1. The present experiment was undertaken to investigate: (a) the effect of nitric oxide synthase (NOS) inhibition, mediated by oral supplementation of the NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), on measures of myocardial energy metabolism and function: (b) the effect of oral creatine supplementation on these variables, in the absence and presence of L-NAME. 2. In one series of experiments, 4 weeks oral administration of L-NAME (0.05 mg ml-1 day-1 in the drinking water) to Brattleboro rats caused significant reductions in myocardial ATP, creatine, and total creatine concentrations and an accumulation of tissue lactate when compared with control animals. Administration of creatine (0.63 mg ml-1 day-1 in the drinking water) for 4 weeks elevated myocardial creatine and total creatine concentrations and reduced lactate accumulation, but did not significantly affect ATP or phosphocreatine (PCr). Concurrent treatment with creatine and L-NAME prevented the reduction in creatine and total creatine concentrations, and significantly attenuated the accumulation of lactate and the reduction in ATP seen with L-NAME alone. 3. In a second series of experiments, 4 weeks treatment with L-NAME and creatine plus L-NAME increased mean arterial blood pressure in conscious Brattleboro rats. Hearts isolated from these animals showed decreased coronary flow and left ventricular developed pressure (LVDP), and total mechanical performance. Treatment with creatine alone had no measurable effect on either mean arterial blood pressure or coronary flow in isolated hearts. However, there was an increase in LVDP, but not in total mechanical performance, because there was a bradycardia. 4. These results indicate that creatine supplementation can attenuate the metabolic stress associated with L-NAME administration and that this effect occurs as a consequence of the action of creatine on myocardial energy metabolism.