The coronary hemodynamic effects of propranolol (0.1mg/kg, i.v.) were examined in anesthetized dogs with flow-limiting dynamic and fixed coronary stenosis of the left circumflex coronary artery. During fixed coronary stenosis created by external application of an occluder device, propranolol significantly decreased coronary blood flow (CBF) by 6.8±2.7% (mean±SEM, p<0.05) and increased mean distal coronary pressure (DCP) by 7±2.1mmHg (p<0.05). This resulted in a decrease in stenosis resistance (SR) by 26±3.1% (p<0.01) due to oxygen demand reduction. By contrast, during dynamic coronary stenosis produced by an intraluminal microballoon occluder, propranolol decreased CBF by 68±3.4% (p<0.01) and mean DCP by 36±4.2mmHg (p<0.01), resulting in an increase in SR by 694±109% (p<0.01). This increase in SR was attenuated by pretreatment with an alpha-adrenergic receptor antagonist phentolamine (0.5mg/kg, i.v.), or by holding heart rate constant at the pretreatment level.
These results suggest that propranolol ameliorated the severity of stenosis during fixed coronary stenosis and exacerbated the severity during dynamic coronary stenosis. This increase in SR appears to be related to vasoconstriction of the large stenosed coronary artery, mediated both by alpha-adrenergic receptors in the coronary artery and by myocardial oxygen demand reduction.
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