Previous studies have suggested that (1) nitroglycerin causes vasodilatation by interacting with sulfhydryl groups in vascular smooth muscle, thereby activating guanylate cyclase and increasing the intracellular concentration of cyclic GMP, and (2) N-acetylcysteine, a source of sulfhydryl groups, potentiates the peripheral vasodilatory effect of nitroglycerin. This study was performed to explore the influence of N-acetylcysteine on nitroglycerin-induced coronary dilatation. In 18 patients (13 men and five women, 30 to 76 years old), coronary sinus blood flow (by thermodilution) was measured before and during intracoronary administration of nitroglycerin, 25 micrograms, both before and 5 min after a 15 min intravenous infusion of (1) 5% dextrose in water (n = 8, control) or (2) 100 mg/kg N-acetylcysteine (n = 10). Nitroglycerin caused no change in heart rate or systemic arterial pressure. In the control patients, coronary sinus blood flow behaved similarly during the two injections: it was 134 +/- 36 ml/mi...
Calcium channel antagonists have been shown to blunt maximal coronary flow after brief coronary occlusion and during pharmacologic coronary dilation in animals. This property, if present in humans, would result in a reduction in coronary flow reserve in the absence of intrinsic abnormalities of the coronary circulation. A reduction of maximal vasodilator capacity by calcium channel antagonists could also constitute an important anti-ischemic mechanism of action of these agents. To evaluate the effect of calcium channel antagonists on coronary flow reserve in awake humans, we measured coronary flow reserve using the coronary Doppler catheter and intracoronary papaverine at baseline and after diltiazem administered by intravenous (125 or 250 micrograms/kg bolus, 5 micrograms/kg/min infusion, n = 8) or intracoronary (150-600 micrograms bolus, n = 10) routes. Intravenous diltiazem reduced heart rate from 77 +/- 18 to 72 +/- 17 beats/min (mean +/- SD, p less than 0.005) and reduced mean arterial pressure from ...
Intravenous dipyridamole is widely used to produce coronary vasodilation during cardiac imaging procedures. However, the routinely used dose of dipyridamole (0.56 mg/kg IV over 4 min) does not always result in maximal coronary dilation. The addition of isometric handgrip during dipyridamole coronary dilation has been reported to substantially increase coronary blood flow over dipyridamole alone. We compared the coronary vasodilation resulting from infusion of the standard dose of dipyridamole with that resulting from a maximally dilating dose of intracoronary papaverine in 12 patients with angiographically normal coronary arteries. We also assessed the effect on coronary blood flow velocity of the addition of isometric handgrip during dipyridamole coronary dilation. Changes in coronary blood flow velocity were measured with a 3F coronary Doppler catheter. The coronary flow reserve (peak/resting coronary flow velocity ratio) after dipyridamole (3.7 +/- 1.2 [mean +/- SD] was less than that seen after papave...
