Expression and function of endothelial nitric oxide synthase messenger RNA and protein are higher in internal mammary than in radial arteries

Background: The internal mammary artery (IMA) has a better long-term patency rate than the radial artery (RA), but the underlying molecular mechanisms are unclear. We compared endothelial nitric oxide synthase (eNOS) and related NO release in these two arteries. Methods: Real-time polymerase chain reaction was used to quantify eNOS messenger RNA (mRNA) expression level in the endothelial cells of IMAs and RAs. eNOS protein localization was determined by immunohistochemistry. NO release from the endothelium of IMAs and RAs was directly measured by an electrochemical method using a membrane-type NO-sensitive electrode. Results: Endothelial nitric oxide synthase mRNA expression level was significantly higher in the endothelial cells of IMAs than in RAs (1.03 ± 0.19 vs 0.53 ± 0.09, n = 7, p < 0.05), but was similar in the whole vascular tissue. eNOS protein immunoreactivity was higher in the endothelial cells of IMAs than in RAs. NO release at both levels in IMAs was significantly greater than in RAs (basal: 17.5 ± 1.9 vs 10.2 ± 0.7 nM, n = 11 each, p = 0.003; stimulated with bradykinin -7 log M: 31.5 ± 3.6 vs 14.3 ± 5.3 nM, n = 6 each, p = 0.02). Conclusions: Endothelial cells in the IMA express higher levels of eNOS mRNA and protein than those in the RA, which is linked with higher release of NO. These findings may be related to the superior long-term patency rate of the IMA vs the RA. This study also provides some basic genetic information for grafting arteries.