Adventitia-dependent Influences On Vascular Remodeling And Dysfunction

Background and objective: Blood vessel wall is composed of three layers: intima, media and adventitia. Before 1980, studies focused primarily on the media. The endothelium was largely considered a haemostatic barrier and the adventitia a support structure of the vessel wall. It was not until 1980 that Furchgott first discovered the phenomenon that endothelium had a dependent vasorelaxation. In the past two decades, numerous studies have showed that endothelial dysfunction also contributed to the pathogenesis of cardiovascular diseases. However, the role of adventitia continued to receive only minor attention as a potential contributor to vascular function, but recent evidence demonstrated that the pathogenesis of hypertension and arteriosclerosis are closely related to the adventitia. In view of these evidence, the question is : does adventitia influence vascular remodeling and function and how?MethodsIn vivo studies: Establishing rabbit models of adventitia removal combined with hypertension or hyperlipidemia. Adventitia of carotid artery was removed by surgical scraping and collagenase type Ⅱ soaking. Infusing norepinephrine using osmotic minipump induced hypertension and hyperlipidemia was induced by feding with 2% cholesterol-containing diet for 1 week and 2 weeks. Intravascular blood pressure was measured by telemetry-radio technique. Carotid arteries were isolated for histopathologic and morphometric examination. Vasotension were measured by polygraph. In situ hybridization and RT-PCR were used to determine the mRNA expressions of NADPH Oxidase p22phox, MCP-1, Rho-A, Rho-kinase. In vitro studies: Establishing co-culture system of carotid artery adventitia and VSMC. Lipopolysaccharide (LPS) induced the intracellular Ca2+ increase of VSMC was measured using Fura-2/AM ratio fluoresces analysis. Concentration of NO (NO2－) and antiperoxidant activities were observed by chromatometry. The proliferation of VSMC was performed by 3H-Thymidine (TdR) and 3H-Leucine (Leu) incorporations. Western blotting detected the expression of Heme oxygenase-1.Results1. Adventitia removal without intima and media damage was confirmed histologically by optical microscope and electron microscope, also evidenced functionally by analyzing the response of carotid artery to vasoconstrictor and vasodilator stimulation. 2. The levels of blood lipids and blood pressure were significantly increased at one week and two weeks through infusion NE and feding high lipid diet, which indicated that hypertensive and hyperlipidemia models were established successfully.3. Removal of the adventitia caused a remarkable proliferation of the vascular media and the neointima formation. Hyperlipidemia and hypertension promoted the proliferation degree of neointima in the absence of adventitia.4. Compared with the control ring , norepinephrine(NE)-induced vasocontraction in adventitia-denuded carotid artery was significantly increased at 2 weeks after the operation in three groups (P<0.05), which was more prominent in the hypertensive rabbit. Acetylcholine(ACh)-induced vasodilatation in adventitia- denuded carotid artery was significantly decreased at 2 weeks after the operation in rabbit with hyperlipidemia.5. Adventitia removal up-regulated p22phox and Rho-kinase mRNA expression of carotid artery compared with intact carotid artery. 6. LPS significantly increased the 3H－TdR incorporation of VSMC. Adventitia- derived NO production induced by LPS decreased the 3H－TdR incorporation of VSMC.7. [Ca2+]i mediated by Bayk 8644 and AngⅡwas markedly elevated in VSMC plus LPS. Adventitia significantly inhibited Bayk 8644-mediated [Ca2+]i increase (P<0. 01), but had no effect on AngⅡ-mediated [Ca2+］i increase.8. Inflammation induced by LPS enhanced HO-1 protein expression of VSMC in presence of adventitia compare with control(P<0. 01)Conclusions1. Surgical scraping combined with enzymatic soaking can completely remove the adventitia layer of carotid artery without the damage of vascular media and intima.2.