Topical application of bradykinin or capsaicin to abdominal visceral organs produces adrenergically mediated, reflex increases in mean arterial pressure and cardiac work. To determine the effects on coronary blood flow, the left main coronary artery of anesthetized cats was perfused at constant pressure with a servo-controlled pump. Cardiovascular parameters were measured during reflex stimulation before and after beta-adrenoceptor blockade with propranolol. Before propranolol, reflex activation led to increases in the double product and myocardial oxygen consumption, usually accompanied by increases in coronary blood flow. However, in 32% of the observations, decreases in flow were observed. During beta-adrenoceptor blockade, reflex stimulation produced increases in cardiac work, whereas the increases in coronary blood flow were attenuated. Marked decreases in average coronary blood flow were observed more frequently (42%). In the presence of propranolol, contrary to the unblocked state, increases in oxygen consumption were achieved by increased oxygen extraction. Subsequent alpha-adrenoceptor blockade with phentolamine abolished all reflex changes. These data indicate that during stimulation of abdominal visceral chemoreceptors, the major coronary response is vasodilation, but in a sizable fraction of cases, abdominal visceral reflexes can produce sympathetically mediated coronary vasoconstriction.
Animals Blood Pressure