AGE-RELATED-CHANGES IN AORTIC SENSITIVITY TO NORADRENALINE AND ACETYLCHOLINE IN RATS

1. The purpose of the present study was to determine the relationship between plasma and tissue lipid levels and the effects of age on vascu lar responses to noradrenaline (NA) and acetylcholine (ACh), 2, Studie s were performed in young and aged rats and the response of endotheliu m-intact and -denuded aortic rings to NA and to ACh was measured. The plasma concentration of cholesterol (total, high-density lipoprotein ( HDL) and low-density lipoprotein (LDL)) and 17 beta-oestradiol was det ermined, as was the aortic tissue content of phospholipids, cGMP and c holesterol (total, free and esterified), 3, Levels of all types of cho lesterol in plasma and aorta increased with age; cholesterol levels in plasma correlated with those in the aorta; levels of phospholipid in the aorta did not increase with age but correlated with those of LDL c holesterol in plasma; levels of 17 beta-oestradiol did not change, but those of cGMP increased with age, 4, In endothelium-intact rings, the maximum tension developed by exposure to NA did not change, but the E C50 of NA increased with age and correlated with total cholesterol in the plasma and with the levels of all types of cholesterol in the aort a. In rings precontracted with NA, age decreased the maximum relaxatio n induced by ACh, The EC50 of ACh decreased with age and was inversely correlated with levels of cholesterol in the plasma and aorta. Treatm ent with NA increased cGMP levels in aged rats. Removal of the endothe lium abolished the response to ACh and heightened the sensitivity to N A in young and aged rats. 5, Aortic endothelial cells seem to inhibit amine-induced contraction, while age-related changes in the levels of cholesterol in aortic tissue affect the sensitivity of the tissue to N A and ACh.