Baroreceptor reflex influence on peripheral circulations in salt-loading hypertension in dogs

To determine the importance of cardiovascular reflexes in the vasodilation found in skeletal muscle in the early stages of salt-loading hypertension in dogs, we gave for several days an intravenous infusion of isotonic sodium chloride, 190 ml/kg/day, to seven dogs with their renal mass reduced following extensive destruction of their arterial baroreceptor afferents. Mean arterial pressure, cardiac output (electromagnetic flowmeter), and regional blood flows (radioactive microspheres) were measured sequentially and the results compared with those obtained in five control dogs. The salt-loaded animals exhibited an increase in cardiac output and in arterial pressure on the first day of infusion. Blood flow to the splanchnic area, the skin, the bone, the skeletal muscle, the heart, the lungs and the brain increased significantly, but vascular conductance was unchanged in most territories, including skeletal muscle. After 5 to 7 days, cardiac output returned toward control values, but pressure remained elevated. Apart from the myocardium, the regional blood flows were normalized and the conductances were decreased. These results indicate that cardiovascular reflexes are responsible for the transient early vasodilation in skeletal muscle which characterizes salt-loading hypertension in intact animals.