EFFECT OF DIETARY SALT LOADING AND HIGH-CALCIUM DIET ON VASCULAR SMOOTH-MUSCLE RESPONSES AND ENDOTHELIUM FUNCTION IN RATS

1. The present study examined the effects of concurrent manipulation o f dietary calcium and salt on contractile responses of vascular smooth muscle (VSM) and endothelial function of aortic rings from Sprague-Da wley rats. 2. Salt loading enhanced the contractile response of the ao rtic rings to noradrenaline (NA), an effect that was blunted by a high calcium intake. 3. Removal of the endothelium and incubation of aorti c rings in physiological salt solution containing methylene blue incre ased the sensitivity of the rings to NA. 4. The increase in the sensit ivity of aortic rings induced by endothelium removal was more pronounc ed in aortic rings from salt-loaded rats. 5. Acetylcholine caused simi lar degrees of relaxation in all experimental groups, but the relaxati on to histamine was smaller (P<0.05) in salt-loaded rats than in other groups of rats; however, after removal of the endothelium, the contra ctile response to histamine was higher in salt-loaded rats. 6. The res ults indicate that the hypersensitivity of isolated aortic rings to ag onists, as observed in salt-loaded rats, is due to altered responses o f the VSM and not as a result of changes in the endothelium. In additi on, salt loading tends to increase the synthesis of endothelium-depend ent relaxing factor, The ability of salt loading to enhance the contra ctile responses of VSM to agonists can be prevented by supplementing t he diet with high calcium.