Nitric oxide contributes to the regulation of vasomotor tone but does not modulate O2-consumption in exercising swine

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Objective: The role of nitric oxide (NO) in the regulation of vasomotor tone and tissue O2-consumption is incompletely understood. We therefore determined the contribution of endogenous NO to regulation of systemic, pulmonary and coronary vasomotor tone and myocardial (MVo2) and whole body (BVo2) O2-consumption in exercising swine. Methods and results: Exercise (1-5 km/h) up to 85% of maximum heart rate in 11 swine produced a 4-fold increase in BVo2, which was accommodated for by 2-fold increases in both cardiac output (CO) and body O2-extraction. The NO synthase inhibitor N(ω)- nitro-L-arginine (NLA, 20 mg/kg, i.v.) increased mean aortic pressure by 30 mmHg both at rest and during exercise, due to a decrease in systemic vascular conductance from 37 ± 2 to 22 ± 1 ml/min mmHg-1 at rest and from 88 ± 3 to 60 ± 3 ml/min mmHg-1 at 5 km/h (all P ≤ 0.05 versus control). NLA produced vasoconstriction at rest and at 5 km/h in virtually all regional beds but did not affect the exercise-induced redistribution of CO. NLA increased mean pulmonary artery pressure from 15 ± 1 to 21 ± 1 mmHg at rest and from 30 ± 2 to 40 ± 2 mmHg at 5 km/h, due to a decrease in pulmonary vascular conductance (all P ≤ 0.05). BVo2 remained unchanged and consequently the decrease in CO resulted in a compensatory increase in O2- extraction. NLA in a dose of 40 mg/kg produced similar responses. NLA had no significant effect on myocardial O2-demand or MVo2 either at rest or during exercise, but decreased coronary vascular conductance which resulted in a decrease in coronary venous Po2 from 24.5 ± 1.1 to 21.9 ± 0.8 mmHg at rest and from 23.5 ± 0.5 to 21.0 ± 0.6 mmHg at 5 km/h (all P ≤ 0.05). Conclusions: Endogenous NO dilates the systemic, pulmonary and coronary vascular bed, but does not modify MVo2 or BVo2 in swine at rest and during exercise. (C) 2000 Elsevier Science B.V.




Duncker, D. J., Stubenitsky, R., Tonino, P. A. L., & Verdouw, P. D. (2000). Nitric oxide contributes to the regulation of vasomotor tone but does not modulate O2-consumption in exercising swine. Cardiovascular Research, 47(4), 738–748.

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