| Respiratory complications are the most common complications in spinal cord injury(SCI), which spinal cord injury(SCI) is very common in clinical treatment .Orthostatic hypotension(OH) often occurs in the chronic stage of patient who suffered from SCI above the sixth thoracic vertebrae(T6),but such stimulus as distension of bladder or clogging of intestinal tract often induces autonomic dysreflexia (AD) ,whose character is malignant hypertension .When AD occurs ,blood vessel all over the body contract with systolic pressure climbing up to 250~300mmHg and diastolic pressure up to 200~220mmHg.AD is one of the most serious complications of SCI because such high blood pressure can sometimes induce lung edema , intracranial hemorrhage ,and even death .Many therapeutic procedures can induce AD ,which brings great challenge for rehabilitation care of high level SCI patients .The peripheral mechanisms for autonomic dysreflexia that have been considered include upregulation of vascular catecholamine receptors and vascular hyperresponsiveness , enhanced vascular responsiveness were responsible for about half of the autonomic dysreflexia. The central mechanisms for autonomic dysreflexia include :the loss of the baroreceptor reflex and loss of tonic bulbospinal inhibitory input to spinal neurons. Only lacking of spinal input don't induce autonomic dysreflexia. The development of autonomic dysreflexia is time-dependent and progressive. After high level SCI, patients are always subjected to a low blood pressure, whether this can influence the structure and function of blood vessel ?And then contribute to the generation of autonomic dysreflexia ?The study have showed that smooth muscle of abdominal arota has confirmed role of vascular hyperresponsiveness under the injury level in chronically spinal cord injured rat .The latest study have reported that perivascular adipose tissue plays a role in relaxation of blood vessel .As the components of integrity blood vessel, whether perivascular adipose tissue and endothelium contribute to vascular hyper-responsiveness?Therefore, in this experiment, we will choose and make a rat model of high level(T4) spinal cord transaction, in order to investigate the remodeling of endothelium and adventitia related to abdominal aorta in chronically spinal cord injured rat.Objectives: 1. The aim of this research is to explore structural remodeling of endomembrane and adventitia related to abdominal aorta in chronically spinal cord injured rat through the examination of histopathology and electron microscope.2. To assess influence of noradrenaline and acetylcholine, then to explain the functional remodeling of endomembrane and perivascular adipose tissue.Methods:1. Experiments were performed on male SD rats, which were randomly divided into two groups: SCT group and SHAM group.T4 spinal cord was transected in SCT group, while spinal cord was exposed but not transsected in SHAM group.2. Two weeks and eight weeks after transection of the forth thoracic spinal cord, the rats were respectively killed, then abdominal aorta (distal to the renal artery and proximal to the bifurcation of the iliac arteries) was adopted to make four different rings,each 2~3 mm long in axial length. Abdominal aortic rings were prepared with both perivascular adipose tissue and endothelium intact, with either perivascular adipose tissue or endothelium removed or with both removed for functional studies. Then to assay sensitivity to noradrenaline and acetylcholine by isolated organ perfusion.Results:1. Compare SCT group with SHAM group, the change of outer and inner diameter, wall thickness, the ratio between wall thickness and inner diameter are not obvious, have no significant statistics (P>0.05). And so were the relative area of collagen fiber ,smooth muscle fiber, elastic fibers and the ratio between smooth muscle cell nucleus every visual fields. Under the examination of transmission electron microscope, we observed that endothelial exfoliation partly,the injury of basilar membrane,the proliferationand migration of smooth muscle cells,and injury of endothelial cell in abdominal aortic artery . Injury of endothelial cell included: mitochondria swelling and distension, mitochondrial crista widening,a lot of watery structure like lysosomes in cytoplasm.2. Compare SCT group with SHAM group,reactivity of all abdominal aortic rings to KCl(60mmol/L), phenylephrine (10-5mol/L),noradrenaline were significantly higher(p<0.01). Compare SCT( eight weeks) group and SCT(two weeks)group, reactivity of all abdominal aortic rings to KCl (60mmol/L) phenylephrine (10-5 mol / L ),noradrenaline were significantly higher(p<0.01). And the reactivity of all rings were dose dependant when reactd to noradrenaline. Within SCT(eight weeks)group, compare perivascular adipose tissue intact with or without endothelium with perivascular adipose tissue removed with or without endothelium, the reactivity to noradrenaline were lower(p<0.01). Within SCT(eight weeks)group, compare perivascular adipose tissue removed with endothelium and perivascular adipose tissue removed without endothelium, the reactivity to noradrenaline were lower, but have no significant statistics(p>0.05).Compare SCT group with SHAM group , reactivity of all abdominal aortic rings to acetylcholine were lower(p<0.01),except the ring without perivascular adipose tissue and endothelium which hardly had reactivity. Compare SCT( eight weeks) group and SCT(two weeks)group, reactivity of all abdominal aortic rings to acetylcholine was lower(p<0.01). Within SCT(eight weeks)group, compare perivascular adipose tissue intact with endothelium with perivascular adipose tissue intact without endothelium, reactivity to acetylcholine was higher(p<0.01),and so is perivascular adipose tissue intact with endothelium and perivascular adipose tissue removed or endothelium removed.Conclusion:1. In chronically spinal cord injured rat ,the pathological changes of abdominal arota was not significant ,but under electron microscope,we observed that abdominal arota have present with apoptosis and the injury of endothelial cells were in disorder ,this indicatedthat abdominal arota in chronically spinal cord injured rat have functional remodeling.2. In chronically spinal cord injured rat ,the reactivity of abdominal aortic rings to KCl(60mmol), phenylephrine(10-5mol/L), noradrenaline were higher and the reactivity of abdominal aortic rings to acetylcholine were lower. Perivascular adipose tissue can contribute to regulation,its functional mechanism was partly related with endothelium. The formation of autonomic dysreflexia may related with the functional remodeling of perivascular adipose twassue and endothelium.
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