EICOSANOID-DEPENDENT AND ENDOTHELIUM-INDEPENDENT OSCILLATIONS OF RAT AORTA

We studied the role of endothelium and eicosanoids in rhythmic contractions of rat thoracic aorta. Spontaneous oscillations were observed in 35% of 385 endothelium-intact and in 46 % of 22 endothelium-denuded aortic strips from normotensive Sprague-Dawley male rats. Vasoactive agents (norepinephrine, epinephrine, phenylephrine, isoproterenol, arachidonic acid, PGF2-alpha, serotonin, potassium, endothelin, atrial natriuretic factor and angiotensin II) induced rhythmic contractions in the majority of tissues. Rhythmic activity was also observed in aortic strips from adult female, pregnant and old male rats. Aortic oscillations were partially inhibited by indomethacin, ibuprofen and nordihydroguaiaretic acid (NDGA), and completely inhibited by indomethacin plus NDGA, nifedipine, low external calcium (<1 mM) and pretreatment with dexamethasone. Indomethacin, NDGA and arachidonic acid did not affect oscillations of the portal vein. Rhythmic contractions were observed in thoracic aortic strips from neonatal but not from adult rabbits. However, oscillations could be induced in strips of the mesenteric artery and terminal abdominal aorta of adult rabbits. Also, adult rabbit thoracic aortic strips exhibited oscillations when set up in close proximity of rat aorta. It is suggested that rhythmic contractions are physiological characteristics of many and perhaps all blood vessels and may play a role in blood flow and turbulence; the likely cause of these oscillations is the cyclic release of one or more eicosanoids.