Eicosanoid-Dependent and Endothelium-lndependent Oscillations of Rat Aorta

Abstract

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 (less than 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.

Role of Endothelium in Oscillatory Contractile Responses to Various Receptor Agonists in Isolated Small Mesenteric and Epicardial Coronary Arteries

“…The inability of SNP to generate the oscillations in the NE-preconstricted endotheliumdenuded strips is inconsistent with the previous studies in aorta and mesenteric artery in which SNP or 8-bromo cyclic GMP induced the oscillations in PE-or NE-preconstricted endothelium-denuded preparations (7,33). Furthermore, although the PE-or NE-induced oscillations were completely eliminated after removal of the endothelium in the previous and present studies (7,33), removal of the endothelium did not significantly affect the NE-induced oscillations in rat aorta (10) or it did reduce but failed to completely eliminate the PE-induced oscillations in rabbit ear artery (12). These considerable differences among the previous and present studies suggest heterogeneity in the mechanisms underlying the oscillatory contractile activity; they might be due to a species or regional difference or due to possible differences in in vitro experimental conditions.…”

“…The oscillatory contractile activity observed in resistance and coronary arteries have been suggested to be specifically related to hypertension (2,3,8,9) and coro-nary vasospasm (22 -24), respectively. However, the oscillatory contractions or blood flow oscillations have also been documented in a number of intact (normal strains) animals including healthy human volunteers (6, 7, 10-12, 20, 21), suggesting that the oscillatory activity is a general characteristic of normal blood vessels rather than a specific characteristic of blood vessels in a certain pathological state (10,15,25). The functional importance of the oscillatory contractile activity of blood vessels, often referred to as vasomotion, appears to be still a matter of discussion; however, the suggested physiological roles of vasomotion particularly in small arteries or arterioles are as follows: 1) regulation of vascular resistance in such a way that local tissue can receive blood flow at least intermittently, thereby preventing the tissue from becoming continuously hypoxic; 2) minimization of fluid filtration into the extravascular space by reducing hydrostatic pressure; and 3) enhancement of lymphatic drainage through the pumping action of closely adjacent arterioles The cellular mechanisms behind generation of the oscillatory contractile responses have not been fully clarified.…”

Vasomotion: cellular background for the oscillator and for the synchronization of smooth muscle cells

“…This is the case in hamster aorta (Jackson, 1988), hamster cheek pouch (Jackson, 1993), rat mesenteric arteries (Gustafsson, 1993;Huang & Cheung, 1997;Mauban et al, 2001;Peng et al, 2001;Okazaki et al, 2003), rabbit mesenteric Akata et al, 1995) and coronary arteries (Akata et al, 1995) and the human cutaneous circulation (Kvandal et al, 2003). Vasomotion is promoted when the endothelium is removed (or the NO synthase inhibited) in the rabbit ear artery (Griffith & Edwards, 1993), rat aorta (Marchenko & Sage, 1994), hamster cheek pouch (Bertuglia et al, 1995) and rat mesenteric arteries (Sell et al, 2002), while in some situations the presence or absence of the endothelium is reported to be without effect on vasomotion rat aorta (Chemtob et al, 1992;Freeman et al, 1995), rabbit mesenteric arteries and pig coronary arteries (der Weid & Beny, 1993). Such a variability of results even within the same artery might suggest that one or more factors from the endothelium influence one or more of the key control variables that are important for vasomotion.…”

Augmentation of diabetes-associated renal hyperfiltration and nitric oxide production by pregnancy in rats

“…Thoracic aortas were isolated and placed in oxygenated (95% O 2 and 5% CO 2 ) Krebs buffer (pH 7·4) of the following composition (mM): NaCl 117, KCl 4·7, CaCl 2 2·5, MgSO 4 1·18, KH 2 PO 4 1·2, NaHCO 3 25, dextrose 11 and EDTA 0·03 (Chemtob et al 1992). The buffer was gassed with a mixture of 95% O 2 and 5% CO 2 .…”