EFFECTS OF NITRATES ON THE RADIAL ARTERY AS AN EXAMPLE FOR A CONDUCTION VESSEL

Nitrates act, in part, by causing systemic venodilation. In addition, nitrates lead to dilation of arterial conductance vessels. The maximal dilation capacity and threshold of arterial conductance vessels have so far not been examined thoroughly. Therefore, we tested the radial a rtery diameter before and after i.v. nitroglycerin infusions at increa sing dosages (0.015, 0.05, 0.15, 0.5, and 1.5 mu g/kg/min), 7 min each dose in 28 patients with suspected coronary artery disease (mean age +/- SEM 58 +/- 2 years) using a high resolution ultrasound devise. The low doses of 0.05 and 0.15 mu g/kg/min, equal to a dose of 2.5 mg/12 hours and 7.5 mg/12 hours in a patient with 70 kg, led to substantial increases in the cross sectional luminal area of the radial artery of 14.8 +/- 1.5% and 29.3 +/- 2.2%, (*p < 0.05 vs baseline). The maximal increase (dilatory capacity) was 53.8 +/- 3.8% (mean diameter at base line: 2.7 +/- 0.1 mm, maximal 3.4 +/- 0.1 mm, p < 0.001). The nitrate sensitivity of the radial artery was estimated by calculation of the E D50 the dose that caused half-maximal dilation of the radial artery. T he ED50 of the radial artery was 0.13 +/- 0.003 mu g/kg/min. In conclu sion, nitroglycerin leads to a dose dependent dilatation of peripheral conductance vessels. Low doses of 0.05 and 0.15 mu g/kg/min lead to s ignificant arterial dilation. The maximal dilatory capacity of the rad ial artery is 53.8 +/- 3.5%.