Effects Of Taurine On Vascular Tone Of Isolated Thoracic Aortic Rings In Rats

Aims: The effect of taurine has been shown to reduce the blood pressure in hypertensive patients as well as rats. However, the mechanism for this effect of taurine is still not fully understood. One of the most important reason decreasing the blood pressure is due to vasodilatation. The main purpose of this study was to investigate the effects of taurine on the reactivity of the thoracic aortic rings in male Wistar rats.Methods: The rats were sacrificed by luxation and the thoracic aorta was quickly removed from each animal and placed in physiological salt solution(PSS). The aorta was carefully cleaned of adherent fat and connective tissue. The vessel was then cut into rings of about 4mm length. Two stainless-steel wires were passed through the lumen of each ring. One stirrup was connected to an isometric force transducer to measure tension in the vessels. The rings were placed in a 10ml organ chamber containing PSS. The rings were stretched until they exerted an optimal basal tension of 2g, and then were allowed to equilibrate for 1 hour with the bath fluid being changed every 15 minutes. The solution was bubbled with 100% O2. Rings of the isolated rat thoracic aorta were mounted in organ baths and isometric contractile force was measured.Results: Taurine concentration-dependently contracted the thoracic aortic rings, Emax (Maximal effect of the contractile force, 0.56±0.13g ) was approximately equal to the 30% contraction induced by 60mmol/L KCl. Contractile response to phenylephrine (PE, 1.0μmol/L) and potassium chloride (KCl, 60mmol/L) were concentration-depedentedly attenuated by taurine, IC20 (20% inhibitory concentration) were 44.6±1.35mmol/L and 82.8±2.31mmol/L(P<0.05). Taurine augmented the contraction of endothelium-denuded aortic rings induced by 11.4mmol/L KCl, hardly affected the contraction induced by 17.4mmol/L KCl, and decreased the contraction induced by 35.4mmol/L KCl. Taurine reduced the constriction induced by the different concentration PE(1.0×10-8mol/L, 1.5×10-8mol/L, 2.0×10-8mol/L and 1.0×10-6mol/L). In free-Ca2+ PSS, the contratile force induced by Ca2+(3.0mmol/L) with and without incubation of taurine (80mmol/L) was 0.12±0.05g and 0.43±0.03g(P<0.05), and the contractile force induced by PE (1.0μmol/L) was 0.20±0.03g and 0.45±0.04g (P<0.05). Taurine(40mmol/L) attenuated the contration induced by PE (1.0μmol/L) with and without pretreated by NG-nitro-L-arginine methyl ester (L-NAME, 0.1mmol/L), and relaxant percentage were 18.6±3.4%and 17.1±2.2% (P>0.05). Taurine...