The renin-angiotensin system and coronary vasomotion.

0.5 Coronary vasomotion, which controls myocardial perfusion, is closely regulated by myocardial metabolic demand and has been assessed by changes of coronary vascular resistance. Only two decades ago evidence of neural and hormonal control overriding the metabolic control of coronary arterioles, which represent the "resistance vessels" was reported (fig 1). Numerous groups reported persistence of a coronary vasodilator reserve or progressive vasoconstriction despite ischaemia.1-11 Studies showed that a adrenergic receptor mediated coronary constriction may restrict metabolic dilatation to avoid wasting blood flow to the heart muscle.'2 Infusion of a receptor stimulating or blocking drugs, and activation of the sympathetic nervous system during ,B blockade, defined the potential of such influences on coronary blood flow.'314 a Receptor coronary constriction may be one component of the constrictor tone during ischaemia.'4-18 In the meantime, numerous mediators have been identified which may constrict or dilate coronary vessels. Thus receptors are abundant in coronary vas-