Adenosine, dipyridamole and isosorbide dinitrate are ineffective to prevent the sympathetic initiation of poststenotic myocardial ischemia

An activation of cardiac sympathetic nerves increases coronary vascular resistance distal to severe stenoses and induces ischemia of the dependent myocardium. The selective alpha 2-adrenoceptor antagonist rauwolscine and the calcium antagonist nifedipine prevent both poststenotic vasoconstriction and ischemia. To exclude the possibility that the beneficial action of nifedipine is based on unspecific coronary dilation rather than a functional antagonism against alpha 2-adrenoceptor mediated poststenotic vasoconstriction we now tested coronary dilatory drugs with a different underlying mechanism. The left ventrolateral cervical cardiac sympathetic nerve was stimulated in 12 anesthetized, vagotomized dogs. A severe stenosis of left circumflex coronary artery was defined by the absence of a postocclusive reactive hyperemia. Sympathetic stimulation increased end-diastolic poststenotic resistance from 0.45 +/- 0.10 to 0.83 +/- 0.18 mmHg X min X 100 g/ml and induced a net lactate production of the poststenotic myocardium. Adenosine (50 micrograms/kg X min i.c., n = 5), dipyridamole (0.2 mg/kg i.v., n = 3) and isosorbide-dinitrate (1 mg i.c., n = 4) did not prevent the increase in resistance and the net lactate production. Thus the effectiveness to prevent alpha 2-adrenergic poststenotic coronary constriction appears to be specific for alpha 2-antagonists and calcium antagonists.