NG-methyl-L-arginine restores arterial pressure in hemorrhaged rats.

NG-methyl-L-arginine (NMA) has been shown to inhibit nitric oxide production in vascular endothelium in vitro, and to cause vascular constriction and pressor responses in vivo. This study evaluated the ability of NMA to restore arterial pressure in hemorrhaged rats in order to determine the role of nitric oxide in modulating vascular tone following hemorrhage. Rats were anesthetized with pentobarbital, and hemorrhaged (0.5 ml/min/100 g body weight for 2 min) to a pressure of 41 +/- 4 mm Hg (control 111 +/- 5 mm Hg). Five minutes after ending the hemorrhage, administration of NMA (30 mg/kg, i.v.) caused rapid and complete restoration of arterial pressure, due primarily to increased systemic vascular resistance. Administration of L-arginine before NMA greatly attenuated the pressor response to NMA. NMA caused similar pressor responses in nonhemorrhaged rats, which were also partially blocked by L-arginine. Cardiac output was transiently increased by NMA in hemorrhaged, but not in nonhemorrhaged, animals. These results support the hypothesis that endothelial nitric oxide production has a significant modulatory effect on vascular tone during hemorrhage, and that inhibition of nitric oxide production permits greater expression of vasoconstrictor influences.

Efficacy and safety of deferoxamine conjugated to hydroxyethyl starch.

The efficacy and safety of deferoxamine conjugated to hydroxyethyl starch (HES-DFO) was evaluated in an in vitro rat cardiac membrane lipid peroxidation (CMLP) assay and in a swine model of regional myocardial ischemia/reperfusion injury in comparison to DFO. The rat CMLP results demonstrate that HES-DFO is at least as potent as DFO (IC50 = 10 and 13 microM, respectively). HES-DFO given intravenously (i.v.) at the equivalence of 25 mg/kg and 100 mg/kg DFO in a swine model of regional myocardial ischemia [20-min left anterior descending coronary artery (LAD) occlusion followed by 60-min reperfusion] showed no significant changes in hemodynamics as compared with DFO at 25 mg/kg i.v. In addition, HES-DFO was at least as potent as DFO with regard to recovery of regional segment shortening function (%SS). Furthermore, both HES-DFO and DFO significantly reduced tissue water content (edema) in the area at risk (AAR). We conclude that conjugation of DFO to HES improves the safety without any interference in the efficacy of DFO.

NG-monomethyl-l-arginine (NMA) restores arterial blood pressure but reduces cardiac output in a canine model of endotoxic shock.

Previous studies have suggested that NMA or similar inhibitors of nitric oxide synthesis from L-arginine reverses or prevents the hypotension associated with endotoxin administration. We wanted to determine if vascular and cardiac responses to NMA support the idea that inhibitors of nitric oxide synthesis might be useful in the treatment of septic shock. Pentobarbital-anesthetized beagle dogs were administered endotoxin for 2 hours at a dose of 250 ng/kg/min. This resulted in reductions in systemic vascular resistance (34% decrease) and mean arterial pressure (25% decrease). Administration of NMA (30 mg/kg, IV) caused large and sustained increases in mean arterial pressure and systemic vascular resistance, and a large decrease in cardiac output and femoral arterial blood flow. Although NMA restored arterial pressure, the large and sustained fall in cardiac output suggests that the cardiovascular action of NMA is detrimental to dogs treated with endotoxin.

Cardiovascular actions of inhibitors of endothelium-derived relaxing factor (nitric oxide) formation/release in anesthetized dogs.

NG-monomethyl-L-arginine (NMA) and NG-nitro-L-arginine (NNA), both of which are inhibitors of nitric oxide (endothelium-derived relaxing factor, EDRF) production from L-arginine, have been shown to be pressor agents in vivo. This study compared the cardiac and vascular responses to intraaortic administration of NMA and NNA in anesthetized dogs. NMA at doses of 3, 10, 30 and 100 mg kg-1 i.a. increased systemic vascular resistance and decreased cardiac output; mean arterial pressure increased by 10 mm Hg (at 100 mg kg-1 dose). Heart rate did not change. NNA, administered at doses of 1, 3, 10 and 30 mg kg-1 i.a. produced similar cardiovascular actions and was equipotent to NMA. Pretreatment with indomethacin abolished the pressor response to NMA; however, systemic vasoconstriction and cardiac depression still occurred. Increasing mean arterial pressure by phenylephrine infusion to levels much greater than produced by NMA and NNA caused only small reductions in cardiac output. NMA did not reduce coronary blood flow, but instead caused a transient flow increase. Therefore, systemic administration of NMA and NNA result in pronounced systemic vasoconstriction and cardiac depression with only a small pressor response in anesthetized dogs. The cardiac depression did not result from elevated arterial pressure nor was it due to coronary vasoconstriction and reduced myocardial oxygen supply/demand ratio.

Myocardial cytoprotective efficacy of azapropazone in a swine model of regional myocardial ischemia/reperfusion injury.

The purpose of the present study is to determine the myocardial cytoprotective efficacy of azapropazone (AZA) on regional myocardial function in anesthetized swine model of regional myocardial ischemia/reperfusion injury. AZA was administered (100 mg/kg, i.v.) 15 minutes prior to reflow. The left anterior descending (LAD) coronary artery occlusion was maintained for a total of 30 minutes and then reperfused for 120 minutes. The effects of AZA on regional segmental shortening (% SS) as well as on neutrophil migration were examined in the (proximal) central and border (distal) zones within the area at risk (AAR). AZA reduced the incidence of myocardial fibrillation which occurred in some animals during the LAD occlusion/reperfusion periods. AZA produced a significant recovery of left ventricular segmental shortening (% SS) in the border, but not in the central zones within the AAR. No significant differences in the hemodynamic parameters were observed between the AZA (n = 14) and the saline-treated (n = 17) groups. AZA produced a significant inhibition of neutrophil migration (as evident from the decrease in myeloperoxidase activity) into epi- and endocardium central and border zones within the AAR. It is concluded that AZA may elicit its cardioprotection in moderately but not in severely injured myocardium by inhibiting the neutrophil migration.