Regulation of coronary blood flow by counteraction of coronary vascular alpha and beta adrenergic activation during experimental pliable coronary stenosis.

In order to evaluate the role of adrenergic receptor-mediated vasomotions of large epicardial coronary arteries in changing coronary blood flow (CBF), the effects of intracoronary norepinephrine (NE), 1.0 microgram/min, were examined in dogs with coronary stenosis which preserved stenosis vasomobility. In untreated dogs, NE caused no significant changes in CBF and stenosis resistance (SR). In dogs treated with propranolol, NE decreased CBF by 65 +/- 7.0% (mean +/- SE) and produced 12-fold intensification of SR followed by LV dP/dt reduction. Similar detrimental responses to NE were observed in dogs treated with atenolol. In dogs treated with phentolamine, NE increased CBF by 33 +/- 5.6% and decreased SR by 65 +/- 7.1%. When NE was administrated directly distal to the stenosis to exclude responses of the stenosed coronary segment, NE failed to affect CBF and SR. These results indicated that alpha receptor stimulation intensified stenosis severity, profoundly decreased CBF and evoked myocardial ischemia, whereas beta stimulation dilated coronary stenosis and increased CBF. The net effects of NE were due to balanced alpha and beta stimulation. Thus, disproportionate activation of alpha and beta (probably beta 1) adrenergic receptors in large coronary arteries with pliable stenosis could modulate their tone and plays an important role in the regulation of CBF.