Comparison of coronary microvascular response to nipradilol and nitroglycerin

Nitrovasodilators and beta-adrenoceptor antagonists are effective in the treatment of angina pectoris and hypertension, but each has side effects that may prevent their long-term use. In the present study responses of coronary arteries and arterioles to nipradilol, a beta-adrenoceptor antagonist with nitrovasodilator action, were compared to nitroglycerin in normal myocardium of the beating left ventricle in anesthetized dogs. Coronary arteries and arterioles were visualized using stroboscopic illumination of epicardial surface of the heart and intravital microscopy with fluorescence angiography. Diameters were measured under control conditions and during topical suffusion of nipradilol (10(-8)-10(-4) M) or nitroglycerin (10(-8)-10(-4) M). Nipradilol produced dose-dependent dilation of all size arteries and arterioles however, dilation was inversely related to vessel size. Arterioles less than 100 microns in diameter dilated more than arteries greater than 200 microns in diameter. In contrast, dilation to nitroglycerin was directly related to vessel size. Arteries larger than 200 microns dilated more than arterioles less than 100 microns. In conclusion, although nipradilol and nitroglycerin are both nitrovasodilators the microvascular response to these agents is different.