Coronary interactions between nifedipine and adenosine in the intact dog heart.
Coronary vascular interactions between adenosine and the calcium entry blocker, nifedipine were studied in the open-chest, blood-perfused dog heart. Adenosine was administered either as a constant intra-coronary infusion or released endogenously during brief occlusions of the left anterior descending (LAD) coronary artery. Nifedipine was administered in therapeutic concentrations as a single i.v. bolus via the femoral vein. Prior to nifedipine treatment, adenosine (1.2 mumol/kg per min) produced a significant (P less than 0.05) 2-3 fold increase in LAD flow. This response was reduced markedly (P less than 0.05) in a dose-dependent manner by nifedipine (6-20 microgram/kg). Following administration of an average dose of 11 microgram/kg nifedipine, adenosine (1.2 mumol/kg per min) failed to elevate LAD flow significantly. Further, reactive hyperemia, produced by releasing a 30-s occlusion of the LAD, was significantly attenuated by these same nifedipine concentrations. The nifedipine-mediated attenuation could be partially overcome by prolonging the period of occlusion (60 s), or by increasing the rate of adenosine infusion. These results could not be accounted for by a nifedipine-mediated alteration of hemodynamics and suggest the possibility of pharmacological competition between adenosine and nifedipine at a vascular smooth muscle receptor.
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects; D003331:Coronary Vessels / Q000502:physiology; D004285:Dogs; D004347:Drug Interactions; D006321:Heart / Q000187:drug effects*; D006439:Hemodynamics / Q000187:drug effects; D006940:Hyperemia / Q000503:physiopathology; D009543:Nifedipine / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology*
D011725:Pyridines; D009543:Nifedipine; D000241:Adenosine