Raffetto Joseph D, Ross Reagan L, Khalil Raouf A
VA Boston Healthcare System, West Roxbury, MA, USA.
J Vasc Surg. 2007 Feb;45(2):373-80. doi: 10.1016/j.jvs.2006.10.041.
Varicose veins are a common disorder of extensive venous dilation and remodeling with an as-yet unclear mechanism. Studies have shown increased plasma and tissue levels of matrix metalloproteinases (MMPs) in human varicose veins and animal models of venous hypertension. Although the effects of MMPs are generally attributed to extracellular matrix degradation, their effects on the mechanisms of venous contraction/relaxation are unclear. Our preliminary experiments have demonstrated that MMP-2 causes inhibition of phenylephrine-induced venous contraction. The purpose of this study was to determine whether MMP-induced inhibition of venous contraction involves an endothelium-dependent and/or -independent pathway.
Circular segments of the inferior vena cava (IVC) were isolated from male Sprague-Dawley rats and suspended between two wire hooks in a tissue bath, and the effects of MMP-2 on phenylephrine- and KCl-induced contraction were measured. To study the role of endothelium-derived vasodilators, experiments were performed in the presence and absence of endothelium; N(G)-l-nitro-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis; indomethacin, an inhibitor of prostacyclin synthesis; cromakalim, an activator of adenosine triphosphate-sensitive K+ channels (K(ATP)); and iberiotoxin, a blocker of large-conductance Ca2+-dependent K+ channels (BK(Ca)) and smooth muscle hyperpolarization.
In endothelium-intact IVC segments, phenylephrine (10(-5) mol/L) caused significant contraction that slowly declined to 82.0% in 30 minutes. The addition of MMP-2 (1 microg/mL) caused a gradual decrease of phenylephrine contraction to 39.5% at 30 minutes. In endothelium-denuded IVC, MMP-2 induced a greater reduction of phenylephrine contraction, to 7.6%. In the presence of L-NAME (10(-4) mol/L), MMP-2 caused a marked decrease in phenylephrine contraction, to 4.4%. Large MMP-2-induced inhibition of phenylephrine contraction was also observed in IVC treated with L-NAME plus indomethacin. MMP-2 caused relaxation of phenylephrine contraction in IVC pretreated with cromakalim (10(-7) mol/L), an activator of K(ATP) channels. MMP-2-induced inhibition of phenylephrine contraction was abrogated in the presence of iberiotoxin (10(-8) mol/L), a blocker of BK(Ca). MMP-2 did not inhibit venous contraction during membrane depolarization by 96 mmol/L KCl, a condition that prevents outward K+ conductance and cell hyperpolarization.
MMP-2 causes significant IVC relaxation that is potentiated in the absence of endothelium or during blockade of endothelium-mediated nitric oxide and prostacyclin synthesis. The lack of effects of MMP-2 on KCl contraction and in iberiotoxin-treated veins suggests MMP-2-induced smooth muscle hyperpolarization and activation of BK(Ca) channels--a novel effect of MMP that may play a role in the early stages of venous dilation and varicose vein formation.
静脉曲张是一种常见的广泛性静脉扩张和重塑疾病，其发病机制尚不清楚。研究表明，在人类静脉曲张和静脉高压动物模型中，血浆和组织中的基质金属蛋白酶（MMPs）水平升高。尽管MMPs的作用通常归因于细胞外基质降解，但其对静脉收缩/舒张机制的影响尚不清楚。我们的初步实验表明，MMP-2可抑制去氧肾上腺素诱导的静脉收缩。本研究的目的是确定MMP诱导的静脉收缩抑制是否涉及内皮依赖性和/或非依赖性途径。
从雄性Sprague-Dawley大鼠分离下腔静脉（IVC）的环形节段，悬挂于组织浴中的两个金属丝钩之间，测量MMP-2对去氧肾上腺素和氯化钾诱导的收缩的影响。为研究内皮源性血管舒张剂的作用，在内皮完整和缺失的情况下进行实验；N(G)-L-硝基精氨酸甲酯（L-NAME），一氧化氮合成抑制剂；吲哚美辛，前列环素合成抑制剂；克罗卡林，三磷酸腺苷敏感性钾通道（K(ATP)）激活剂；iberiotoxin，大电导钙依赖性钾通道（BK(Ca)）阻滞剂和平滑肌超极化剂。
在内皮完整的IVC节段中，去氧肾上腺素（10(-5) mol/L）引起显著收缩，30分钟内缓慢降至82.0%。加入MMP-2（1 μg/mL）导致去氧肾上腺素收缩在30分钟时逐渐降至39.5%。在内皮剥脱的IVC中，MMP-2诱导去氧肾上腺素收缩的更大降低，降至7.6%。在L-NAME（10(-4) mol/L）存在下，MMP-2导致去氧肾上腺素收缩显著降低，降至4.4%。在用L-NAME加吲哚美辛处理的IVC中也观察到MMP-2对去氧肾上腺素收缩的显著抑制。MMP-2导致用克罗卡林（10(-7) mol/L）预处理的IVC中去氧肾上腺素收缩舒张，克罗卡林是K(ATP)通道激活剂。在iberiotoxin（10(-8) mol/L）存在下，MMP-2诱导的去氧肾上腺素收缩抑制被消除，iberiotoxin是BK(Ca)阻滞剂。在96 mmol/L氯化钾使膜去极化期间，MMP-2不抑制静脉收缩，这种情况可阻止外向钾电导和细胞超极化。
MMP-2导致显著的IVC舒张，在内皮缺失或内皮介导的一氧化氮和前列环素合成被阻断时增强。MMP-2对氯化钾收缩和iberiotoxin处理的静脉无影响，提示MMP-2诱导平滑肌超极化和BK(Ca)通道激活——这是MMP的一种新作用，可能在静脉扩张和静脉曲张形成的早期阶段起作用。
