NO EVIDENCE FOR A GENERAL CHANGE IN CONTRACTILE RESPONSIVENESS OF THEMESENTERIC-ARTERY WITH AGING

Rings of hurtles mesenteric artery (1-3 mm diameter) suspended in Kreb s solution,were contracted (maximal contraction relative to KCl 80 mM = 100%) by the thromboxane mimetic U46619 (190 +/- 10%), noradrenaline (162 +/- 9%), angiotensin II (107 +/- 11%), and 5-hydroxytryptamine ( 5-HT) (96 +/- 10%). Reducing extracellular Ca2+ strongly inhibited the maximal contraction to angiotensin II and 5-HT and moderately inhibit ed tire maximal contraction to noradrenaline, but had less effect oil the maximal contraction to U46619 (contraction in Ca2+ 1.3 mu M was re duced to 24 +/- 5, 20 +/- 3, 38 +/- 4 and 52 +/- 4% respectively of th e contraction in 2.5 mM Ca2+). Reducing extracellular Ca2+ lowered sen sitivity to 5HT, angiotensin II, and U46619, bat did not alter sensiti vity to noradrenaline The EC(50) and maximal contraction for each of t he 4 agonists did not change with patient age at 2.5 mM Ca2+ or ill re duced extracellular Ca2+. It is concluded that aging does not affect t he responsiveness of mesenteric arterial smooth mascle to physiologica l vasoconstrictors.