Changes in regional vascular resistance in canine aortic coarctation

Aortic coarctation was created experimentally in dogs and regional blood flows were measured at various times thereafter with radioactive microspheres in the conscious state. Mean arterial pressure increased moderately proximal to the stenosis, whereas distally it was reduced below control immediately, returning progressively toward control over 28 days. Blood flows were compared in tissues that are found both proximally and distally (skeletal muscles, skin and bones). In several groups of muscles located in the anterior part of the body, vascular conductance increased during the first hours after coarctation, then decreased below control. A similar pattern was observed in muscles of the hind leg. In the skin and in the bones of the front leg and of the hind leg, vascular conductance also increased in the early stages and decreased during the late stages. It therefore appears that aortic coarctation in dogs is characterized by a late generalized decrease in vascular conductance that extends to tissues which are never exposed to increased arterial pressure. These findings suggest that a systemic vasoconstrictor influence (possibly the measured increase in plasma renin activity) overrides local mechanisms in the control of regional circulations.