Effects of nifedipine on coronary vasculature in canine models of dynamic and fixed coronary stenoses.
The effects of nifedipine were examined in dogs with flow-limiting dynamic and fixed coronary stenoses. During dynamic coronary stenosis, produced by an intraluminal microballoon occluder which preserved active vasomotion in a stenosed segment of a proximal left circumflex coronary artery, intracoronary infusion of nifedipine (0.01 and 0.1 microgram/kg/min) increased coronary blood flow (CBF) by 15 +/- 5.0% (P less than .05) and 50 +/- 11.6% (P less than .01), respectively (mean +/- S.E.) and reduced stenosis resistance (SR) resulting in the alleviation of myocardial ischemia due to preferential vasodilation of large coronary arteries. In contrast, nifedipine (1.0 microgram/kg/min) did not increase CBF and reduced distal coronary pressure associated with intensified SR mainly due to arteriolar vasodilation. During fixed coronary stenosis created by external application of an occluder device, all doses of nifedipine failed to affect CBF and SR. Intravenous nifedipine (3 micrograms/kg) caused a biphasic response during dynamic coronary stenosis; an initial transient decrease and a late sustained increase in CBF concomitant with a transient augmentation and a subsequent prominent reduction of SR. These results suggest that nifedipine is capable of preferentially dilating large epicardial coronary arteries and reducing stenosis severity resulting in the relief of myocardial ischemia during pliable coronary stenosis, and this mechanism may contribute to the beneficial effects of nifedipine in clinical ischemic syndrome.
D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects; D003327:Coronary Disease / Q000503:physiopathology*; D003331:Coronary Vessels / Q000187:drug effects*; D004195:Disease Models, Animal; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D007275:Injections, Intravenous; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*
D009543:Nifedipine