Coronary arteriolar vasoconstriction in myocardial ischaemia: reflexes, sympathetic nervous system, catecholamines

The sympathetic nervous system exerts important control over the coronary circulation. Studies from our laboratory have demonstrated that reflex input from skeletal muscle during static contraction causes coronary vasoconstriction. Similarly, stimulation of abdominal visceral chemosensitive afferents can, on occasions, elicit coronary vasoconstriction or limit the extent of vasodilation so that the myocardium needs to extract additional oxygen from arterial blood. Recently, we have examined the innervation of the coronary collateral circulation and found that these vessels contain catecholamines which demonstrate a pattern of fluorescence similar to that of catecholamines in the native circulation. Furthermore, stimulation of alpha 2- but not alpha 1-adrenoceptors can cause an increase in collateral vascular resistance. Thus, reflex input into the coronary circulation, perhaps during static exercise or post-prandially, can cause coronary vasoconstriction. Such constriction occurs in native coronary vessels and has the potential to be present in the coronary collateral circulation.