Key result
Local L-NMMA infusion decreases pulmonary flow velocity by ~33%, demonstrating basal nitric oxide regulation.
Why the study?
Endothelium-derived nitric oxide may be an important mediator of pulmonary vascular resistance, but its role in basal resistance and receptor-mediated vasodilation in conscious adults was unclear.
Does local endothelial nitric oxide production regulate basal pulmonary vascular resistance and mediate acetylcholine-induced vasodilation in conscious adults?
Does local endothelial nitric oxide production regulate basal pulmonary vascular resistance and mediate acetylcholine-induced vasodilation in conscious adults?
In conscious adults, basal pulmonary vascular resistance is maintained in part by continuous local production of nitric oxide, which also mediates further vasodilation in response to receptor stimulation.
BackgroundEndothelium-derived nitric oxide (NO) may be an important mediator of vascular resistance in the pulmonary circulation. We tested the hypotheses that in conscious adults the endothelium, through NO production, is important in maintaining basal pulmonary vascular resistance and that it can increase NO production further in response to receptor-mediated stimulation, leading to further vasodilation.Methods and ResultsPulmonary arterial resistance vessel function was studied within the distribution of a segmental lower lobe pulmonary artery in eight conscious adults 37 to 76 years old who were undergoing cardiac catheterization. Segmental blood flow was determined with use of a Doppler-tip guide wire and quantitative angiography. Drugs were administered locally within the segmental artery through an infusion catheter.NG-Monomethyl-l-arginine (L-NMMA) was used as a specific inhibitor of NO production, whereas acetylcholine (ACh) was used to test receptor-mediated vasodilation. To demonstrate that vasodilation to ACh was NO dependent, ACh response was tested alone, in the presence of L-NMMA, and in the presence of a control constrictor phenylephrine. Basal pulmonary vascular resistance was NO dependent because L-NMMA infusion resulted in a dose-dependent decrease in local flow velocity (P<.005), with flow decreasing 33% at the highest dose of L-NMMA. ACh infusion resulted in a dose-dependent increase in flow velocity (P=.001). The ACh response was at least in part NO dependent because it was diminished by the presence of L-NMMA (P<.05). The effect of L-NMMA on the ACh response was not due to nonspecific preconstriction because L-NMMA diminished the ACh response significantly more than did the endothelium-independent constrictor phenylephrine (P<.05) despite comparable preconstriction.ConclusionsIn healthy conscious adults, (1) normal basal pulmonary resistance is maintained in part by continuous local production of NO and (2) the local NO production is responsive to receptor-mediated stimulation, leading to further vasodilation, and can be tested with ACh.
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Landzberg et al. (1996) studied Patients undergoing cardiac catheterization (n=8). Local infusion of L-NMMA and Acetylcholine vs. Baseline / Phenylephrine was evaluated on Change in local flow velocity (p=<.005). Local infusion of L-NMMA decreased pulmonary flow velocity by 33% at the highest dose (P<0.005), demonstrating that basal pulmonary vascular resistance is partially maintained by continuous NO production.
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