TONIC TONE IN ARTERIES EXPOSED CONTINUOUSLY TO ANGIOTENSIN-II IN-VITRO

We evaluated long-term actions of angiotensin II (ATII) on arterial sm ooth muscle. In isolated sympathectomized renal artery segments that h ad been denuded of endothelium, isometric force was recorded during 3 days of incubation in nutrient medium with and without 1 muM ATII. The peptide induced, after an acute transient contraction and a latency o f at least 12 hr, a slowly developing tonic increase in wall tension. This chronic effect was not influenced by indomethacin but could be re versed by sodium-nitroprusside. In vessels that had been chronically e xposed to ATII, acute contractile responses to high potassium, seroton in and ATII were not altered. Also effects on agonist-induced tone of removal and readministration of extracellular potassium were not modif ied. Relaxing responses after exposure to NH4Cl were attenuated. Durin g continuous exposure of isolated arteries to ATII, release of a stabl e contractile factor could not be detected, nuclear incorporation of t he thymidine analog 5-bromo-2'-deoxyuridine was not stimulated, but th e media cross-sectional area was significantly increased. These observ ations indicate that ATII induces in arterial smooth muscle, besides i ts well known acute contractile effect and its trophic action, a long- term tonic increase in tone. The mechanism largely remains to be estab lished, but may involve altered cellular handling of hydrogen ions.