Concentrations Of Nitric Oxide Synthase Inhibitor Research Articles

Effect of nitrovasodilators and inhibitors of nitric oxide synthase on ischaemic and reperfusion function of rat isolated hearts.

1. The functional role of the nitric oxide (NO)/guanosine 3':5'-cyclic monophosphate (cyclic GMP) pathway in experimental myocardial ischaemia and reperfusion was studied in rat isolated hearts. 2. Rat isolated hearts were perfused at constant pressure with Krebs-Henseleit buffer for 25 min (baseline), then made ischaemic by reducing coronary flow to 0.2 ml min(-1) for 25 or 40 min, and reperfused at constant pressure for 25 min. Drugs inhibiting or stimulating the NO/cyclic GMP pathway were infused during the ischaemic phase only. Ischaemic contracture, myocardial cyclic GMP and cyclic AMP levels during ischaemia, and recovery of reperfusion mechanical function were monitored. 3. At baseline, heart rate was 287+/-12 beats min(-1), coronary flow was 12.8+/-0.6 ml min(-1), left ventricular developed pressure (LVDevP) was 105+/-4 mmHg and left ventricular end-diastolic pressure 4.6+/-0.2 mmHg in vehicle-treated hearts (control; n=12). Baseline values were similar in all treatment groups (P>0.05). 4. In normoxic perfused hearts, 1 microM N(G)-nitro-L-arginine (L-NOARG) significantly reduced coronary flow from 13.5+/-0.2 to 12.1+/-0.1 ml min(-1) (10%) and LVDevP from 97+/-1 to 92+/-1 mmHg (5%; P<0.05, n=5). 5. Ischaemic contracture was 46+/-2 mmHg, i.e. 44% of LVDevP in control hearts (n=12), unaffected by low concentrations of nitroprusside (1 and 10 microM) but reduced to approximately 30 mmHg (approximately 25%) at higher concentrations (100 or 1000 microM; P<0.05 vs control, n=6). Conversely, the NO synthase inhibitor L-NOARG reduced contracture at 1 microM to 26+/-3 mmHg (23%), but increased it to 63+/-4 mmHg (59%) at 1000 microM (n=6). Dobutamine (10 microM) exacerbated ischaemic contracture (81+/-3 mmHg; n = 7) and the cyclic GMP analogue Sp-8-(4-p-chlorophenylthio)-3',5'-monophosphorothioate (Sp-8-pCPT-cGMPS; 10 microM) blocked this effect (63+/-11 mmHg; P<0.05 vs dobutamine alone, n=5). 6. At the end of reperfusion, LVDevP was 58+/-5 mmHg, i.e. 55% of pre-ischaemic value in control hearts, significantly increased to approximately 80% by high concentrations of nitroprusside (100 or 1000 microM) or L-NOARG at 1 microM, while a high concentration of L-NOARG (1000 microM) reduced LVDevP to approximately 35% (P<0.05 vs control; n=6). 7. Ischaemia increased tissue cyclic GMP levels 1.8 fold in control hearts (P<0.05; n=12); nitroprusside at 1 microM had no sustained effect, but increased cyclic GMP approximately 6 fold at 1000 microM; L-NOARG (1 or 1000 microM) was without effect (n=6). Nitroprusside (1 or 1000 microM) marginally increased cyclic AMP levels whereas NO synthase inhibitors had no effect (n=6). 8. In conclusion, the cardioprotective effect of NO donors, but not of low concentrations of NO synthase inhibitors may be due to their ability to elevate cyclic GMP levels. Because myocardial cyclic GMP levels were not affected by low concentrations of NO synthase inhibitors, their beneficial effect on ischaemic and reperfusion function is probably not accompanied by reduced formation of NO and peroxynitrite in this model.

The effects of high dose N G-nitro- l-arginine-methyl ester on myocardial blood flow and left ventricular function in dogs

Purpose: Nitric oxide (NO) synthase inhibition has been reported to cause elevation in mean arterial pressure (MAP) and a decrease in cardiac index (Cl), the cause of which is not completely understood. It has been shown that increased concentrations of NO synthase inhibitors cause a further drop in cardiac output without a corresponding increase in arterial pressure, prompting the conclusion that NO inhibition results in direct myocardial depression. However, myocardial ischemia was not completely ruled out as a cause for myocardial dysfunction in these studies. The purpose of this study was to examine the effects of 30 mg/kg of the NO synthase inhibitor N G-nitro- l-arginine-methyl ester (L-NAME) to those of 300 mg/kg and assess the effects on coronary ischemia and myocardial function. Materials and Methods: Eight anesthetized dogs underwent median sternotomy and pericardiectomy. L-NAME 30 mg/kg was administered and the effects were recorded at 5, 15, and 30 minutes. Thereafter, 300 mg/kg was administered and the effects were observed for 5, 15, and 30 minutes. We measured MAP, heart rate (HR), Cl, left ventricle (LV) end systolic and diastolic pressures, the first derivative of LV pressure (dP/dt), left anterior descending artery blood flow, regional LV contraction, gas tensions, and lactates. A coronary sinus catheter allowed for measurements of coronary sinus pressure, lactate, and gas tensions. Stroke volume, percent myocardial shortening (dL/dt) myocardial oxygen consumption, and net lactate myocardial production were calculated. Results: Whereas 30 mg/kg had minimal effects on coronary blood flow and LV function, 300 mg/kg resulted in profound hypotension, drop in Cl, and acidocis. Conclusions: L-NAME at 30 mg/kg caused a rise in MAP and systemic vascular resistance; however, it had no effect on ventricular function. High dose NO synthase inhibition causes myocardial depression not related to increased afterload, coronary vasoconstriction, or myocardial ischemia.

Protection Against Ischemic Injury by Nonvasoactive Concentrations of Nitric Oxide Synthase Inhibitors in the Perfused Rabbit Heart

The functional and metabolic effects of inhibitors of nitric oxide (NO) synthase on ischemic hearts have not been investigated. This work was designed to perform such a study in isolated perfused rabbit hearts submitted to low-flow ischemia. After a 30-minute equilibration period, the hearts were submitted to low-flow ischemia for 60 minutes followed by reperfusion for 30 minutes. Functional and metabolic parameters were followed in hearts perfused with or without inhibitors of NO synthase or NO precursors, which were added 15 minutes before ischemia but were absent during reperfusion. Ischemic contracture was delayed and reduced in hearts perfused with 1 mumol/L L-N-monomethylarginine (L-NMMA) or 1 mumol/L L-N-arginine methylester, two inhibitors of NO synthase, but not with D-N-monomethylarginine, the inactive enantiomer of L-NMMA. The protection was suppressed by addition to the perfusate containing L-NMMA of 1 mmol/L L-arginine or 0.1 mmol/L sodium nitroprusside but not by addition of 10 mumol/L 8-bromo cGMP, a cGMP analogue. The functional protection by 1 mumol/L L-NMMA was related to a stimulation of glycolysis from exogenous glucose and a preservation of the glycogen stores. This resulted in a better maintenance of high-energy phosphates and a lower acidosis as measured by 31P nuclear magnetic resonance spectroscopy. During reperfusion, functional recovery was more than doubled, and enzyme release was halved in L-NMMA-treated hearts compared with controls. The functional and metabolic protection was maximal at 1 nmol/L to 1 mumol/L L-NMMA, ie, below the vasoactive concentrations of the inhibitor. Nonvasoactive concentrations of NO synthase inhibitors protect the heart against ischemic damage; this relates to a stimulation of glycolysis from exogenous glucose.