Role of beta 2-adrenergic receptors on coronary resistance during exercise.
The effects of regional alpha- and specific beta 2-adrenergic receptor blockade on measurements of late diastolic coronary resistance (LDCR) and mean coronary blood flow velocity (CBFV) during exercise were examined in 14 conscious adult mongrel dogs. Specific beta 2-adrenergic receptor blockade (ICI 118.551) significantly decreased CBFV and increased LDCR by blockade of beta 2-vasodilator tone independent of alpha-adrenergic receptor-mediated tone and independent of altering myocardial metabolism. alpha-Adrenergic receptor blockade (phentolamine, 1 mg) significantly increased CBFV and decreased LDCR by blocking sympathetically mediated vasoconstrictor tone. There was no significant difference in the magnitude of response between alpha- and beta 2-adrenergic receptor blockade. These results demonstrate that alpha- and beta 2-adrenergic receptors have a significant and evidently equal influence on CBFV and LDCR during exercise. Four weeks of daily exercise and left stellate ganglionectomy (LSGx) prevented phentolamine-induced vasodilation but not ICI 118.551-induced vasoconstriction. This suggests that daily exercise and LSGx significantly decreased the alpha-adrenergic receptor-mediated vasoconstrictor tone on the coronary circulation, resulting in an apparently greater role for the coronary vascular beta 2-adrenergic receptor on the control of CBFV and LDCR during exercise.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D003326:Coronary Circulation / Q000187:drug effects; D003971:Diastole; D004285:Dogs; D006339:Heart Rate; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D010101:Oxygen Consumption; D010646:Phentolamine / Q000494:pharmacology; D005082:Physical Exertion; D011412:Propanolamines / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects; D013233:Stellate Ganglion / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects
D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C026777:ICI 118551; D010646:Phentolamine