Reactivity of isolated toad aortic rings to angiotension II: the role of nitric oxide

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 2009-05, Vol.179 (4), p.403-409
• Main Authors: Marañón, Rodrigo O, Joo Turoni, Claudio M, Coviello, Alfredo, de Bruno, María Peral
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Angiotensin II - metabolism; Angiotensin II - pharmacology; Animal Physiology; Animals; Anura - metabolism; Aorta - drug effects; Biochemistry; Biomedical and Life Sciences; Biomedicine; Blood pressure; Blood Pressure - drug effects; Catheters; Coronary vessels; Endothelium; Experiments; Human Physiology; Isometric Contraction - drug effects; Life Sciences; NG-Nitroarginine Methyl Ester - pharmacology; Nitric oxide; Nitric Oxide - metabolism; Nitrites - analysis; Norepinephrine - pharmacology; Original Paper; Reptiles & amphibians; Stainless steel; Toads; Zoology
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-008-0325-1

Little is known about the vascular actions of angiotensin II (Ang II) and nitric oxide (NO) in Amphibia. This study investigated (1) Ang II contractility, (2) NO concentrations, and (3) correlations between Ang II contractility, NO concentration and mean arterial pressure (MAP) in isolated Bufo arenarum toad aortic rings. Contractility was measured in isometric conditions, NO concentrations were determined by the Griess reaction, and MAP was determined by a direct method. In isolated toad aortic rings, Ang II produced a contractile response (292.7 ± 89.2 mg; n = 20). Furthermore, a contractile response to norepinephrine (NE) was also obtained. A significant correlation between both the Ang II and NE contractile responses was found (r = 0.89; n = 11; P < 0.01). Administration of Ang II increased MAP values (Basal 16.8 ± 1.7; n = 19 vs. Ang II 28.4 ± 1.8 mmHg; n = 19; P < 0.001), and the increase of MAP by Ang II was positively correlated with the Ang II contractile response (P < 0.01). Administration of L-NAME also increased MAP values, and this effect was higher in those toads that presented a lower pressure response to Ang II (Pearson r = -0.68; P < 0.05). NO was present in all aortic rings, and its concentrations were negatively related to the Ang II contractile response (P < 0.036) and pressure response (Pearson r = -7.08; P < 0.001). These findings suggest that, in the B. arenarum toad, the NO system contra-regulates both the contractile and pressure Ang II responses, although its action could be different in each specimen.