The Effects Of Taurine On The Reactivity Of Isolated Thoracic Aortic Rings At Different Preloads In Rats

OBJECTIVES: To observe the effects of taurine on the resting tension and the pre-contraction induced by potassium chloride or phenylephrine in the isolated thoracic aortic rings of rats at different preloads; To observe the effect on vascular relaxation of taurine and its synergistic effect with acetylcholine at different preloads. METHOD: Isolated rats thoracic aortic rings were suspended in organ chambers, bathed in Krebs-solution, maintained at 37 ℃and perfused with 95% O2 and 5% CO2 . The tone of thoracic aortic rings were recorded with Powerlab Computer System. RESULTS: 1. Tau(10,20,40mmol/L) augmented the resting tension of thoracic aortic rings in a dose-independent manner. The contraction amplitude of the rings enhanced with the increase of preloads (0.5-4.0g) (P<0.05) and the maximal change of tone were 24.32±2.81%,25.85±4.62%,28.8±3.36%,27.59 ±2.34%(they were calculated as percentage of the 40 mmol/L KCl-induced contraction) , respectively. 2. Tau(10, 20, 40 mmol/L) inhibited the contractions of the rings induced by KCl(20, 40, 60 mmol/L) or Phe(10-8, 10-7, 10-6mmol/L) significantly (P<0.05), and the effects decreased with the increasing of preloads(P<0.05); The maximal inhibits were produced at 0.5g preload, Tau(10mmol/L), KCl (20mmol/L) or Phe(10-8mmol/L), and the rates of inhibits were 47.60±2.44% or 38.17±3.14%. 3. Tau(10, 20, 40mmol/L) relaxed the pre-contraction induced by KCl(20, 40, 60mmol/L) in a dose-independent manner, and the effect decreased with the increasing of preloads(P<0.05); The maximal response was produced at 0.5g preload, KCl(20mmol/L) and Tau(10mmol/L), the rate of which was 38.17±3.14%. 4. The combination of Tau(10,20,40 mmol/L) and Ach(10-7mmol/L) could relax the pre-contraction induced by KCl, and the synergistic effect decreased with the increasing of preload(P<0.05); The maximal effect of relaxation was produced at the combination of Tau (10mmol/L) and Ach at 0.5g preload, the rate of which was 34.95±2.53%. CONCLUSIONS: 1. Data obtained from this experiment show that Tau could contract the isolated thoracic aortic rings in rats. The amplitude of contraction increased with the increasing of preloads, and the maximal response was produced at 2.0g preload. 2. The results suggest that Tau could decrease the contraction of aortic rings induced by KCl or Phe, and the effects decreased with the increasing of preloads. 3. The results indicate that Tau could relax the pre-contraction of aortic rings induced by KCl, the effect of relaxation decreased with the increasing of preloads. 4. The results also show the synergistic effect between Tau and Ach in aortic rings, which decreased with the increasing of preloads.