Microvessel O2 Responses in Salt-Sensitive Hypertension

描述（由申请人提供）：局部血流控制机制的改变可能在高血压的容积扩张型中从心输出量升高到血管阻力维持升高的转变中起主要作用。在许多形式的高血压中已经证明了对增加的O2可用性的反应是小动脉的增强收缩，但是关于介导O2诱导的微血管收缩的机制知之甚少。 细胞色素P450（CYP 450）4A ω-羟化酶催化20-HETE（花生四烯酸的血管收缩代谢物）的形成，可以在微循环中充当O2传感器。本研究探讨了CYP 450 4A ω-羟化酶和20-HETE在Dahl S大鼠（盐敏感性高血压的遗传模型）和SS. BN 13 consomic大鼠（其中血压正常的Brown Norway大鼠的13号染色体被替换为Dahl S遗传背景）微循环中介导O2诱导的小动脉收缩中的作用。SS.BN13 consomic大鼠与Dahl S大鼠在遗传上有98%相同，但在高盐饮食下没有表现出血压升高。待检验的总体假设是，Dahl S高血压大鼠中小动脉对升高的PO 2的反应增强是由于以下3个因素中的一个或组合：20-HETE产生增加、小动脉对20-HETE的血管收缩作用的敏感性增加和/或CYP 450 4A ω-羟化酶表达改变。将在高盐（HS）和低盐（LS）饮食的Dahl S和SS. BN 13大鼠的原位提睾肌中测定20-HETE抑制对PO 2升高的小动脉反应的影响。将通过RT-PCR和蛋白质印迹法评估Dahl S大鼠和SS. BN 13大鼠在高盐和低盐饮食下的小动脉和实质细胞中的细胞色素P450-4A ω-羟化酶亚型，并将在小动脉和实质细胞中测量响应于升高的PO 2的20-HETE产生的变化。还将在Dahl S大鼠和SS. BN 13大鼠的原位微循环中比较高盐和低盐饮食不同时间段的响应于外源性20-HETE的小动脉收缩。这些研究应该提供更多的理解，在O2可用性变化期间调节血管张力的机制如何在高血压期间和饮食盐摄入增加期间改变

DESCRIPTION (provided by applicant): Alterations in local blood flow control mechanisms may play a major role in the transition from an elevated cardiac output to a maintained elevation in vascular resistance in volume-expanded forms of hypertension. An enhanced constriction of arterioles, in response to increased O2, availability has been demonstrated in many forms of hypertension, but little is known regarding the mechanisms that mediate O2-induced constriction of microvessels. Cytochrome P450 (CYP450) 4A omega-hydroxylase, which catalyzes the formation of 20-HETE (a vasoconstrictor metabolite of arachidonic acid), may act as an 02 sensor in the microcirculation. This study investigates the role of CYP450 4A omega-hydroxylase and 20-HETE in mediating O2-induced constriction of arterioles in the microcirculation of the Dahl S rat, a genetic model of salt sensitive hypertension, and in SS.BN13 consomic rats, in which chromosome 13 of the normotensive Brown Norway rat is substituted into the Dahl S genetic background. The SS.BN13 consomic rats are 98% identical to the Dahl S rat genetically, but do not exhibit elevated blood pressure in response to high salt diet. The overall hypothesis to be tested is that the enhanced response of arterioles to elevated PO2 in Dahl S hypertensive rats is due to one or a combination of 3 factors: increased 20-HETE production, increased sensitivity of arterioles to the vasoconstrictor effects of 20-HETE, and/or altered expression of CYP450 4A omega-hydroxylase. The effect of 20-HETE inhibition, on arteriolar responses to elevated PO2 will be determined in the in situ cremaster muscle of Dahl S and SS.BN13 rats on high salt (HS) and low salt (LS) diets. Cytochrome P450-4A omega-hydroxylase isoforms in arterioles and parenchymal cells of Dahl S rats and SS.BN13 rats on high and low salt diets will be assessed by RT-PCR and Western blotting, and changes in 20-HETE production in response to elevated PO2 will be measured in arterioles and parenchymal cells. Arteriolar constriction in response to exogenous 20-HETE will also be compared in the in situ microcirculation of Dahl S rats and SS.BN13 rats on high salt and low salt diets for various periods of time. These studies should provide an increased understanding of how the mechanisms that regulate vascular tone during changes in 02 availability, are altered during hypertension and during increases in dietary salt intake