title: Alpha-receptor constriction induced by atrial fibrillation during maximal coronary dilatation.
abstract: The mechanism of coronary vasoconstriction induced by atrial fibrillation during maximal coronary dilatation was studied in 19 chloralose-urethane anesthetized dogs. Maximal coronary dilatation was achieved by carbochromene (5 mg/kg i.v.) or dipyridamole (0.2 mg/kg i.v.). Left circumflex coronary blood flow was measured with an electromagnetic flowmeter. Atrial fibrillation was compared with rhythmic atrial pacing at similar heart rates (207 +/- 12 vs. 204 +/- 12 beats/min). During maximal coronary dilatation, coronary resistance was 0.38 +/- 0.05 mm Hg X min X 100 g/ml (RU) at sinus rhythm, 0.41 +/- 0.06 RU at atrial pacing, and 0.52 +/- 0.07 RU at atrial fibrillation, that was significantly (p less than 0.005) higher than during sinus rhythm and atrial pacing. Accordingly, coronary oxygen extraction was 14 +/- 1% at sinus rhythm, 17 +/- 1% at atrial pacing (p less than 0.005 vs. sinus rhythm) and 27 +/- 2% at atrial fibrillation (p less than 0.001 vs sinus rhythm and atrial pacing). Beta-adrenoceptor blockade with propranolol (1 mg/kg i.v.) did not prevent this coronary vasoconstrictive effect. Following alpha-blockade with phenoxybenzamine (10 mg/kg i.v.), however, coronary resistance was 0.52 +/- 0.08 RU during sinus rhythm, 0.54 +/- 0.10 RU during atrial pacing and 0.57 +/- 0.09 RU during atrial fibrillation. The data suggest coronary vasoconstriction induced by atrial fibrillation mediated by an alpha-adrenoceptor mechanism.
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D002866:Chromonar / Q000494:pharmacology; D003326:Coronary Circulation / Q000187:drug effects; D003327:Coronary Disease / Q000503:physiopathology*; D004176:Dipyridamole / Q000494:pharmacology; D004285:Dogs; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010643:Phenoxybenzamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D013564:Sympathetic Nervous System / Q000503:physiopathology; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D010643:Phenoxybenzamine; D004176:Dipyridamole; D011433:Propranolol; D002866:Chromonar