ABNORMAL RENAL VASCULAR REACTIVITY TO ACETYLCHOLINE AND NITROPRUSSIDEIN AGING RATS

1. The actions of acetylcholine (ACh), CaCl2 and nitroprusside (NP) we re studied in aortic strips and in the perfused kidneys from adult (4- 6 months old) and aging (23-24 months old) rats. 2. ACh and CaCl2 prod uced a dose-related relaxation in aortic strips from adult and old rat s; maximal responses to both vasodilators were significantly reduced ( ACh: adult=66.4+/-6.1%, Old=27.1+/-5.7%, P<0.001; CaCl2: adult=75.6+/- 3.9%, Old=54.1+/-4.1%, P<0.01) in aortas from old rats. NP-evoked rela xation was not significantly different between the two groups. 3. In k idneys from adult rats, ACh produced dose related decreases in renal p erfusion pressure (RPP), whereas, in kidneys from old rats, ACh produc ed a dose-related decrease at low doses, and biphasic responses (vasod ilatation followed by vasoconstriction) at medium to high doses, with a reduced vasodilator component. Vasodilator response to ACh to the hi ghest dose; ACh; adult=78.7+/-2.8%, Old=40.6+/-2.6%, P<0.001). In kidn eys from adult rats, NP produced a dose related decrease in RPP. Howev er, in kidneys from old rats, NP produced vasoconstriction at low dose s, biphasic responses at medium doses (vasoconstriction followed by va sodilation), and vasodilation at the highest dose. 4. The results of t he present study demonstrated that: (a) The isolated perfused kidney f rom aging rats had a dual response (with an important vasoconstrictor component) to ACh and NP, which may be due to the release of a nonpros tanoid vasoconstrictor or to abnormalities in the renal vascular smoot h muscle, In contrast, in aortic strips from old and adult rats, these agents only caused relaxation; (b) aging is accompanied by reduced en dothelium dependent relaxation both in large arteries and in resistanc e vessels; and (c) large arteries from aging rats require a higher con centration of extracellular calcium to stabilize the membrane of smoot h muscle cells. Copyright (C) 1997 Elsevier Science Inc.