| OBJECTIVE:To observe and compare the differences of contractions to thromboxane A2 analog(U46619),potassium chloride(KCl)and relaxations to acetylcholine(ACh), taurine(TAU)in middle cerebral and coronary arterial rings isolated from adult(4-5 months)and old(24-36 months)rats.METHODS:The male Wistar rats were sacrificed by luxation.Whole brains and hearts were quickly removed and stored in 4℃physiologic salt solution(PSS)that contained following components in mmol/L:NaCl 144,KCl 5.8,MgCl2 1.2,CaCl2 2.5,Glucose 11.1, HEPES 5,pH 7.40.Segments of the middle cerebral(near to internal carotid artery)and coronary(near to aorta)arteries were carefully dissected free from connective tissue and cut into rings(2mm in length),then mounted on two 40μm tungsten wires in the jaws of chambers of Multi Myograph System-610M(Danish Myo Technology A/S,DMT).PSS in the chambers were persistently bubbled with pure 100%O2.Temperature of the chambers was kept at 37℃.The tensions signal collected from DMT were recorded with Powerlab computer system.RESULTS:1.Contractions induced by U46619,60 mmol/L KCl in middle cerebral and coronary arterial rings isolated from adult and old rats.①U46619 10-8～10-6mol/L concentration dependently contracted the rings of middle cerebral artery of adult and old rats,the maximal effect of the contraction were 1.95±0.32 mN and 1.58±0.21 mN respectively(P＜0.05).U46619 10-7～3×10-6mol/L concentration dependently contracted the rings of coronary artery of adult and old rats,the maximal effect of the contraction were 4.53±0.64 mN and 2.36±0.59 mN respectively(P＜0.05).②KCl 20～120 mmol/L concentration dependently contracted the rings of middle cerebral and coronary artery of adult and old rats.In middle cerebral arterial rings of adult and old rats, the maximal effect of the contraction were 2.69±0.49 mN and 2.52±0.63 mN respectively; in coronary arterial rings of adult and old rats,the maximal effect of the contraction were 7.21±1.17 mN and 7.83±1.34 mN respectively.There were no significant differences between adult and old rats in KCl-induced vasoconstrictions in isolated middle cerebral and coronary arterial rings(P＞0.05).2.Responses of middle cerebral and coronary arterial rings isolated from adult and old rats to A Ch.①ACh 10-8～10-5mol/L slightly relaxed 60 mmol/L KCl-induced contractions in middle cerebral arterial rings of adult rats,the maximal relaxation(tension decline)percentage over the contraction was 6.33±2.87%;whereas in old rats,ACh weakly increased 60 mmol/L KCL-induced contractions,with the maximal contraction increased by 0.79±2.72%.These effects of ACh were concentration independent.In other hand,coronary arterial and middle cerebral arterial rings were opposite.ACh increased 60 mmol/L KCl-induced contractions in coronary arterial rings of adult rats,with a tension increase of 11.76±5.07%over the contraction;whereas in old rats,ACh slightly relaxed 60 mmol/L KCl-induced contractions, with a tension decline of 4.60±3.68%.These effects of ACh were also concentration independent.②ACh 10-8～10-5mol/L concentration dependently relaxed 10-6mol/L U46619-induced contractions in middle cerebral arterial rings of adult and old rats,and the maximal relaxation were 47.62±5.20%and 25.96±4.57%over the contraction,respectively. The vasodilatator responses to ACh were significantly pronounced in adult rats in comparison with old rats(P＜0.05).3.The effects of TAU on KCl precontractions in middle cerebral and coronary arterial rings isolated from adult and old rats.①TAU 20～120 mmol/L concentration dependently relaxed 60 mmol/L KCl-induced contractions in middle cerebral arterial rings of adult and old rats,relaxation responses to TAU were significantly greater in adult rats than in old rats(40.99±5.62%vs 32.90±5.30%, P＜0.05).②In coronary arterial rings of adult rats,20～60 mmol/L TAU relaxed 60 mmol/L KCl-induced contractions,the maximal tension decline over the contration was 22.08±5.48%, but 80～120mmol/L TAU potentiated KCl-induced contractions,with a tension rise of 5.12±2.11%.Whereas in old rats,20～120 mmol/L TAU sometimes slightly relaxed (3.16±1.24%),and sometimes enhanced(6.90±3.12%)60 mmol/L KCl-induced contractions.CONCLUSION:1.Vasoconstrictor responses to U46619 were significantly decreased in old rats in comparison with adult rats.2.There were no significant differences between adult and old rats in KCl-induced vasoconstrictions in middle cerebral and coronary arterial rings.3.The effects of ACh on KCl-induced contractions in middle cerebral and coronary arterial rings of adult and old rats were diverse.4.Relaxations to ACh on U46619-induced contractions in middle cerebral arterial rings were significantly decreased in old rats in comparison with adult rats.5.In comparison with old rats,TAU pronoucedly relaxed the rings of middle cerebral artery of adult rats.TAU mainly relaxed the rings of coronary artery of adult rats, but TAU might sometimes enhance KCl-induced contractions in coronary arterial rings of old rats. |
PDF Full Text Request