Responsiveness to Cardiac Sympathetic Nerve Stimulation During Maximal Coronary Dilation Produced by

SUMMARY. This study examined effects of adrenergic constrictor stimuli on total and transmural myocardial blood flow during maximal coronary dilation produced by adenosine. Our goal was to determine (1) if coronary vessels maximally dilated with adenosine respond to constrictor stimuli and (2) if the constrictor effect is uniform transmurally. In anesthetized dogs, the circumflex coronary artery was perfused at constant pressure. Total circumflex flow was measured with an electromag-netic flowmeter; transmural flow was measured with 9-/im radiolabeled spheres injected into the perfusion tubing. Propranolol (2 mg/kg, iv) was administered to block myocardial and coronary /?-receptors. Coronary responses to cardiac sympathetic nerve stimulation (CSNS) at 10 Hz and intracoronary administration of angiotensin (0.125 and 0.50 /ig/min), phenylephrine (0.50 and 2.00 /ig/min), norepinephrine (0.25 and 1.0 jug/min) and tyramine (200;tg/min) were obtained during intracoronary infusion of adenosine (4.7 jum/min). This dose of adenosine abolished reactive hyperemia; moreover, a higher dose of adenosine did not produce further increases in flow. Control flow during adenosine averaged 382 ± 50 (SE) for endocardium and 524 ± 44 ml/min per 100 g for epicardium. During adenosine, CSNS at 10 Hz decreased epicardial flow to 308 ± 44 ml/min per 100 g; P < 0.05), but did not decrease endocardial flow (378 ± 58 ml/min per 100 g; NS). In contrast