Felodipine prevents the poststenotic myocardial ischemia induced by alpha 2-adrenergic coronary constriction

Prevention of alpha-adrenergic coronary constriction by calcium-antagonists

This manuscript reviews the experimental evidence for a functional antagonism of Ca-antagonists against alpha-adrenoceptor-mediated increases in coronary vasomotor tone. In studies on anesthetized dogs, intravenous nifedipine effectively prevented the alpha 1-adrenoceptor-mediated increase in epicardial coronary resistance, as well as the increase in end-diastolic resistance mediated by both alpha 1- and alpha 2-adrenoceptors during cardiac sympathetic nerve stimulation. Both intracoronary and intravenous administration of nifedipine also prevented the alpha 2-adrenoceptor-mediated increase in coronary resistance distal to severe stenoses, as well as the resulting ischemic dysfunction and net lactate production during cardiac sympathetic nerve stimulation. Felodipine was equally effective as nifedipine in preventing an alpha 2-adrenoceptor-mediated increase in coronary resistance and the resulting contractile dysfunction distal to severe coronary stenoses. alpha 1- and alpha 2-Adrenergic coronary constriction also contribute to the severity of myocardial ischemia in conscious dogs during treadmill exercise. Again, nifedipine improved regional myocardial blood flow and attenuated regional contractile dysfunction during exercise-induced ischemia in conscious dogs with a chronic coronary stenosis. This beneficial effect of nifedipine was attributed to a recruitment of coronary dilator reserve and not to a reduction in heart rate or afterload. In conclusion, there is solid experimental evidence for a functional antagonism of Ca-antagonists against alpha-adrenergic coronary constriction and its contribution to myocardial ischemia.

Minimal alpha 1- and alpha 2-adrenoceptor-mediated coronary vasoconstriction in the anaesthetized swine

alpha-Adrenoceptor-mediated coronary vasoconstriction contributes to the initiation and aggravation of experimental and clinical myocardial ischaemia. However, the extent of alpha 1- and alpha 2-adrenoceptor-mediated constriction has not been characterized in the porcine coronary circulation despite the frequent use of this experimental model. Fifteen swine were anaesthetized with either alpha-chloralose, enflurane or isoflurane to determine the amount of alpha-adrenoceptor-mediated coronary constriction elicited by either the selective alpha 1-adrenoceptor agonist methoxamine or the selective alpha 2-adrenoceptor agonist azepexole. The left anterior descending coronary artery was cannulated and perfused by an external pump delivering constant blood flow from the carotid artery. Following bilateral cervical vagotomy and beta-adrenoceptor blockade with propranolol (2 mg kg-1), graded dosages of either one of the alpha-adrenoceptor agonists (9-45 micrograms kg-1 min-1) were infused into the coronary perfusion line while coronary arterial pressure (CAP) was measured through a distal side arm of the cannula to detect changes in coronary vascular resistance. Infusion of the alpha-adrenoceptor agonists was terminated when systemic arterial pressure increased. Sonomicrometers were used to measure anterior left ventricular wall thickening for the assessment of regional contractile function. During methoxamine infusion, no increase in vascular resistance was observed during alpha-chloralose, enflurane or isoflurane anaesthesia, whereas the infusion of azepexole increased CAP from 103 +/- 31 mmHg to 120 +/- 35 mmHg (alpha-chloralose), from 101 +/- 16 mmHg to 122 +/- 11 mmHg (enflurane) and from 84 +/- 20 mmHg to 94 +/- 19 mmHg (isoflurane), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)