Effect of opioid receptor antagonists on vasodilator nerve actions in the perfused rat mesentery

Nicotine effect on cardiovascular system and ion channels

Smoking is a leading cause of cardiovascular disease, hypertension, myocardial infarction, and stroke. Nicotine is one of the components of cigarette smoke. Nicotine effects on the cardiovascular system reflect the activity of the nicotine receptors centrally and on peripheral autonomic ganglia. It has been found that cigarette smoke extract-induced contraction of porcine coronary arteries is related to superoxide anion-mediated degradation of nitric oxide. Treatment of rabbit aortas with an oxygen free radicals scavenger attenuated cigarette smoke impairment of arterial relaxation. Treatment of smokers with vitamin C, an antioxidant, improved impaired endothelium-dependent reactivity of large peripheral arteries. Thus it appears that chronic smoking and acute exposure to cigarette smoke extract may alter endothelium-dependent reactivity via the production of oxygen derived free radicals. This review discusses the effects of nicotine on resistance arterioles, compliance arteries, smooth muscle cells, and ion channels in the cardiovascular system. We discuss studies performed on humans, nicotine-exposed animals, and cell cultures yielding varying and inconsistent results that may be due to differences in experimental design, species, and the dose of exposure. Nicotine exposure appears to induce a combination of free radical production, vascular wall adhesion, and a reduction of fibrinolytic activity in the plasma.

Nitric oxide modulates responses to sensory nerve activation of the perfused rat mesentery

The modulatory actions of nitric oxide on sensory nerves were investigated on dilator responses of the perfused rat mesentery to transmural nerve stimulation. N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis, caused a significant augmentation of vasodilator responses to transmural nerve stimulation, an effect which was abolished by L-arginine. L-NAME had no effect on vasodilator responses to exogenous calcitonin gene-related peptide. In preparations without endothelium L-NAME still caused potentiation of vasodilator responses to transmural nerve stimulation. Methylene blue, an inhibitor of guanylate cyclase, also significantly enhanced vasodilator responses to transmural nerve stimulation. After pretreatment with diethyldithiocarbamate to inhibit superoxide dismutase, vasodilator responses to transmural nerve stimulation were also potentiated. This response was abolished by exogenous superoxide dismutase. These findings suggest that endogenous nitric oxide modulates, in an inhibitory fashion, the actions of sensory nerves in the rat mesentery. The results also suggest that endogenous superoxide dismutase may participate in the regulation of the actions of sensory nerves via control of cellular superoxide anion level.