L-Arginine Ameliorates the Abnormal Sympathetic Response of the Dysfunctional Human Coronary Microvasculature

Abstract

A nitric oxide (NO)-related defect may contribute to abnormal coronary sympathetic responses that can cause ischemia in patients with endothelial dysfunction. Because L-arginine, the NO synthase (NOS) precursor, augments NO bioactivity, we hypothesized that L-arginine would improve dysfunctional coronary sympathetic responses. Eleven patients with atherosclerosis or its risk factors were challenged with the cold pressor test, a specific provocative test of cardiac sympathetic activity, after 3 separate and sequential intracoronary infusions, as follows: 1) Normal saline; 2) L-NMMA, a competitive inhibitor of NOS; and 3) L-arginine. Study patients exhibited abnormal microvascular responses with coronary vascular resistance (CVR) increasing by 22.3 ±9.7% (mean ± 1 SEM), p<0.01. In addition, the change in coronary blood flow (CBF) did not correlate with the change in rate pressure product (RPP), r = -0.29, p = NS, suggesting an uncoupling of CBF from cardiac work. In the presence of L-NMMA, the CVR response, 10.3 ±9.8%, did not differ from the baseline response, and there was no relationship between the changes in CBF and RPP, r=0.13, p = NS. In contrast, L-arginine ameliorated the CVR response, -3.2 ±3.1%, p<0.05 vs baseline response, and restored the normal correlation between the changes in CBF and RPP, r = 0.74, p<0.01. L-arginine not only improved abnormal microvascular responses to sympathetic activation, but it also restored the coupling that normally exists between coronary blood flow and cardiac work. L-arginine warrants further investigation as a therapy for coronary artery disease.