Preferential Effect of Nitroglycerin on Large Microvessels

Abstract

In Response: We appreciate the valuable comments of Drs. Wang and Shernan. Because the purpose of our study [1] was to investigate the effect of mild hypothermia on nitroglycerin-induced vasodilation, their comment does not affect our results. However, we believe that this letter raises an important point. In our study, using an in vivo technique, topically applied nitroglycerin produced a dose-dependent dilation of both large and small pial (cerebral) arterioles in normothermic conditions. Similar results of in vivo techniques have been reported by several authors [2]. Unfortunately, there have been no reports investigating the influence of vessel size on the sensitivity of cerebral microvessels to nitroglycerin using an in vitro technique. In contrast, in vitro studies by Wang et al. [3] demonstrated that nitroglycerin caused preferential dilation of large porcine coronary arterioles and produced only minimal relaxation of small arterioles. These findings were confirmed by in vivo studies, which showed that nitroglycerin caused dilation of large coronary vessels without significantly affecting coronary blood flow [4]. Because most factors including in vivo or in vitro study, species, and different vascular beds are different, it is difficult to compare them simply. Further study is required regarding the influence of vessel size on the sensitivity of cerebral microvessels to nitroglycerin. Masahiko Kawaguchi, MD Hitoshi Furuya, MD Department of Anesthesiology; Nara Medical University; Nara 634-8522, Japan