The L-arginine-nitric oxide pathway

Endogenous nitric oxide in expired air: effects of acute exercise in humans

Nitric oxide (NO) is present in the exhaled breath of humans and experimental animals, but its physiologic role and cellular source(s) remain to be determined. Possible sites of origin are pulmonary endothelial cells and/or resident macrophages. Here we have tested the hypothesis that changes in cardiovascular status can alter the apparent pulmonary excretion of NO. Exercise on a stationary bicycle produced rapid and reversible increases in pulmonary NO excretion rate, and changes in NO excretion rate during exercise were well correlated with observed changes in heart rate. These results suggest that changes in expired NO during exercise are related to corresponding cardiovascular responses.

Nitric oxide synthase inhibitor, nitro-iminoethyl-L-ornithine, reduces ischemia-reperfusion injury in rabbit skeletal muscle

Nitric oxide (NO), originally identified as the mediator of endothelial-dependent relaxation of vascular smooth muscle, is now known to also have cytotoxic effects under certain conditions. Thus, we have investigated the effects of inhibition of NO synthesis on ischemia/reperfusion injury in the rabbit rectus femoris muscle. Three and a half hours of ischemia and 24 hours of reperfusion resulted in a 56% loss of viability. In muscles receiving an infusion of the nitric oxide synthase inhibitor, L-NIO (30 microM), the loss of viability was reduced to 15%. Post-ischemic blood flow was increased in muscles receiving a saline infusion, whereas there was a marked decrease in blood flow for at least the first 60 minutes of reperfusion in muscles treated with L-NIO (30 microM). The increase in myeloperoxidase levels (indicative of neutrophil accumulation) following 24 hours of reperfusion was attenuated with L-NIO infusion by approximately 50% and the reperfusion-induced edema was also attenuated in L-NIO treated muscle. These findings suggest that endogenous NO production during ischemia/reperfusion injury may be deleterious to muscle survival.

Impairment of endothelium-dependent relaxation in aorta from rats with arteriosclerosis induced by excess vitamin D and a high-cholesterol diet

The present investigation was undertaken to characterize the relaxing responsiveness in aortic strips from rats with arteriosclerosis, which was produced by excess vitamin D2 (VD) administration followed by treatment with or without a high-cholesterol diet for 6 weeks (VD + CHOL and VD group, respectively). This arteriosclerotic aorta was characterized by medial calcification and intimal cell proliferation. Helical strips of thoracic aorta were suspended in oxygenated Krebs-Henseleit solution. Under precontraction with noradrenaline, endothelium-dependent relaxations to acetylcholine were significantly attenuated in the VD and VD + CHOL as compared with the control. Relaxation to calcium ionophore A23187 was also significantly attenuated in the VD + CHOL. However, the relaxing responses to acetylcholine and A23187 in aortas from rats fed a high-cholesterol diet alone remained unaffected. Nitroglycerin caused an equal degree of relaxation in aortas from control and arteriosclerotic rats. There was a significant negative correlation between the relaxing response to acetylcholine and the calcium content in the aorta. These results indicate that in arteriosclerotic rat aortas, the endothelium-dependent relaxation to acetylcholine is impaired in proportion to the degree of calcification, and such impairment is facilitated by cholesterol feeding but can not be attributed to hypercholesterolemia or vascular cholesterol deposition.