<

正

>

This study examines the effects of x-adrenergic stimulation on coronaryvasodilation induced by selective doses of intracoronary adenosine.In anesthetized open-chest dogs

the left anterior descending coronary artery（LAD）was perfused at a constant flow and its perfusionpressure was measured

pr ctolol（2.5 mg）was infused into the LAD to block β

1

-adrenergicreceptors in the myocardium.Intracoronary adenosine at increasing doses produced graded decreasesin coronary vascular resistance by 8.7%（2μg/min）

20.6%（10/μg/min）and 28%（50 μg/min）of the control.Identical doses（6μg）of intracoronary norepinephfine produced increases in coronaryvascular resistance by 17.4%（adenosine 2 μg/min）

23.2%（adenosine 10μg/min）and 34.1%（adenosine 50 μg/min）of the control when coronary vessels were dilated by increasing doses ofadenosine

respectively.It is suggested that the constrictive effect of x-adrenergic stimulalion can ex-ert a limiting effect on adenosine-induced coronary vasodilation.