Changes Of Ex Vivo Thoracic Aortic Reactivity Induced By Crushing Injury Of Rats

Objective: To observe the effects of crushing injury on thoracic aortic reactivity and investigate the potential role of nitric oxide in the vascular injury during crushing injury of hindlimbs in rats.Methods: Thirty adult Sprague-Dawley rats, either female or male, weighed between 150～200g, were used in this study. The rats were randomly divided into control group (C), crushing injury 8h group (C8h) and crushing injury 16h group (C16h). The crushing injury model of rat was estabolished as follows: The rats were anesthetized by 4% chloral hydrate. The hind limbs of rat were subjected to the standardized mechanical pressure of 12.5kg for 5 h, subsequently the rat was released and free for 8 h or16 h. Except for crushing injury of hind limbs, rats in C group was challenged in the same way as those in C8h or C16h group. The rats were killed and thoracic aortic rings (TARs) ex vivo were prepared. Some TARs ex vivo were selected to denude the endothelial cells. Using isolated vascular tension detective technique, the relaxation responses to acetylcholine (ACh), Calcium ionophore A23187, and contraction responses to phenylephrine(PE), angiotensinⅡ(AngⅡ) were tested in TARs with or without endothelium.In some experiments, TARs with or without endothelium were preincubated with nitric oxide synthase inhibitor N-nitro-L-arginine (L-NNA ) for 20 min, then contraction responses to PE, AngⅡwere also observed respectively.Results: (1) Changes of relaxation responses. Compared with C group, the endothelium -dependent relaxation responses to 10^-6mol/L ACh in C8h and C16h groups was significantly depressed (P<0.05⁰.01). The relaxation responses were worse in C16h group than in C8h group (P<0.01). Compared with C group, both the relaxation responses of TARs in C8h and C16h groups to 10^-810^-4 mol/L ACh and 10^-810^-5A23187 were significantly depressed in the dose-dependent manner (P<0.05⁰.01). The curve of cumulative dose responses to ACh and A23187 in C8h and C16h groups shifted downward obviously,in which the relaxation responses were worse in C16h group than in C8h group (P<0.05⁰.01). (2) Changes of contraction responses. Compared with C group, the contraction responses to 10^-6mol/L PE in C8h group showed tendency to depress(P>0.05) and in C16h groups was significantly depressed(P<0.01). Compared with C group, the contraction responses of TARs in C8h and C16h groups to 10^-710^-4mol/L PE or 10^-810^-5mol/L AngⅡwere significantly depressed in the dose-dependent manner(P<0.05⁰.01). The curve of cumulative dose responses to PE or AngⅡin C8h and C16h groups shifted downward obviously. The contraction responses to PE or AngⅡwere worse in C16h group than those in C8h group (P<0.05⁰.01). (3) The effect of NO. L-NNA preincubation led to elevate contraction responses to cumulative doses of AngⅡand PE in TARs among the three groups(P<0.05⁰.01). Compared with C group,the curve of cumulative dose responses to AngⅡand PE in C8h and C16h groups obviously elevated. (4) The effect of endothelium. The contraction responses of TARs without endothelium to cumulative doses of 10^-8～10^-5mol/ L AngⅡshowed the tendency to be elevated compared with those of TARs with endothelium, but there were significant differences in C8h and C16h groups(P<0.05⁰.01). In C group and C8h group, the contraction responses of TARs without endothelium to cumulative doses of 10^-8～10^-4mol/ L PE showed to be elevated compared with those of TARs with endothelium. However, the contraction responses of TARs without endothelium to cumulative doses of 10^-810^-4mol/ L PE tended to be depressed.Conclusions:The above-mentioned results revealed that crushing injury could cause constriction and relaxation dysfunctions of vascular system, in which vascular NO was involved.