Editorial Focus Does arterial myogenic tone determine blood flow distribution in vivo?

BLOOD FLOW DISTRIBUTION at rest and during exercise is intri-cately controlled by centrally driven neuroeffector mechanisms and circulating hormones (particularly epinephrine), local au-tacoids, and metabolites, all superimposed on the inherent or “myogenic ” reactivity of the arterial smooth muscle. During exercise, the cardiac output of a trained athlete can increase 5-fold, and these mechanisms serve to coordinate a huge (20-fold) increase in the amount of blood routed to the exercising muscle (3). The dramatic nature of this increase is illustrated by the fact that the proportion of the cardiac output diverted to skeletal muscle can change from 20 % to 80%! Importantly, and to the benefit of the individual, despite this enormous increase in the flow of blood to muscle, brain blood flow is not compromised (3). But to what extent do the inherent characteristics of the arteries of the brain and musculatur