MATURATION OF CEREBROVASCULAR RELAXANT MECHANISMS

心血管动态平衡在所有血管床的收缩和松弛影响之间微妙地平衡。在松弛机制中，一些最重要的机制与血管内皮及其释放血管活性因子的能力有关。尽管血管内皮细胞的功能重要性已被广泛接受，但内皮功能在出生后成熟过程中变化的机制尚未得到广泛研究，了解也很少，尽管越来越多的证据表明，未成熟血管床和成熟血管床之间的内皮功能差异很大。由于脑血管床中不成熟的内皮功能可能导致新生儿明显的发病率和死亡率，即使是轻微的脑血管损伤，本研究解决了出生后成熟以动脉特异的方式选择性地增强内皮依赖性脑血管扩张的普遍假设。这一主要假设有两个推论，每个推论都提出了内皮功能改变的机制：1)内皮细胞eNOS活性增强；2)血管鸟苷环化酶活性增强。为了评估这些想法，我们将进行实验，以确定：1)内皮细胞和血管平滑肌细胞之间的形态关系；2)在环氧合酶、eNOS和可溶性鸟苷环化酶抑制剂存在和不存在的情况下，血管内皮细胞介导的血管扩张能力；3)完整动脉和匀浆动脉标本中内皮细胞一氧化氮产生的能力和动力学；4)通过Western blotting和定量RT-PCR检测eNOS蛋白和mRNA的丰度；5)完整动脉和匀浆动脉标本中血管可溶性鸟苷末端环化酶合成能力和动力学；以及6)利用Western blotting和定量RT-PCR技术测定血管可溶性鸟苷末端环化酶蛋白和mRNA的丰度。为了解决围产期成熟对脑血管内皮细胞功能的影响，我们将在新生羔羊和未怀孕的成年羊身上进行这些实验。为了确定动脉大小和类型的重要性，所有实验都将在一系列动脉中进行，包括颈总动脉、基底动脉、后交通动脉和大脑中动脉。总之，这些实验的结果将使人们能够对成熟调节脑血管内皮细胞功能的细胞机制进行前所未有的评估。

Cardiovascular homeostasis is delicately balanced between contractile and relaxant influences in all vascular beds. Among relaxant mechanisms, some of the most important are related to the vascular endothelium and its ability to release vasoactive factors. Although the functional importance of the vascular endothelium is widely accepted, the mechanisms whereby endothelial function changes during postnatal maturation have not been widely studied and remain poorly understood, despite growing evidence that endothelial function varies dramatically between immature and mature vascular beds. Because immature endothelial function in the cerebrovascular bed could potentially contribute to the pronounced morbidity and mortality associated with even mild cerebrovascular insults in neonates, the present studies address the general hypothesis that postnatal maturation selectively enhances endothelium-dependent cerebral vasodilatation in an artery-specific manner. This main hypothesis has two corollaries, each of which proposes a mechanism whereby endothelial function is altered: 1) endothelial cell eNOS activity is enhanced; or 2) vascular guanylate cyclase activity is enhanced. To evaluate these ideas, we will conduct experiments designed to determine: 1) the morphological relations between endothelial and vascular smooth muscle cells; 2) the capacity for endothelium-mediated vasodilatation in whole arteries in the presence and absence of cyclooxygenase, eNOS, and soluble guanylate cyclase inhibitors; 3) the capacity and kinetics of endothelial nitric oxide production in both intact and homogenized artery preparations; 4) the abundances of eNOS protein and mRNA using Western blotting and quantitative RT-PCR; 5) vascular soluble guanylate cyclase synthetic capacity and kinetics in both intact and homogenized artery preparations; and 6) the abundances of vascular soluble guanylate cyclase protein and mRNA using Western blotting and quantitative RT-PCR. To address the effects of perinatal maturation on cerebrovascular endothelial function, we will conduct these experiments in both newborn lambs and non-pregnant adults. To define the importance of arterial size and type, all experiments will be conducted in a series of arteries including the common carotid, basilar, posterior communicating, and middle cerebral arteries. Together, the results of these experiments will enable an unprecedented assessment of the cellular mechanisms whereby maturation modulates cerebrovascular endothelial function.