Endothelium-derived vasoactive peptide and cerebral vasospasm

蛛网膜下腔出血(SAH)后发生脑血管痉挛。严重血管收缩的机制尚不清楚。近年来，从血管内皮细胞的培养液中分离出内皮素，发现它是一种有效的血管收缩多肽。我们研究了内皮素在脑血管痉挛发病机制中的可能作用。在狗的离体脑动脉中，内皮素-1和内皮素-2均引起持续收缩。内皮素引起的收缩不能通过反复洗涤而逆转，这表明内皮素的作用是不可逆转的。内皮素-3和大内皮素是较弱的血管收缩药。因此，ET-型内皮素受体在脑动脉中占主导地位。采用双抗体夹心酶联免疫测定法测定血浆和脑脊液中内皮素的含量。蛛网膜下腔出血患者脑脊液内皮素含量在出血后第7天和第14天升高。进一步观察实验性蛛网膜下腔出血犬血浆内皮素含量变化的时程。正常犬脑脊液中未检测到内皮素。SAH后第2天和第4天，血浆内皮素水平显著升高。免疫组织化学研究显示，对照组犬的基底动脉内仅有少量内皮素阳性的内皮细胞。出血后2天和4天，可见大量内皮素阳性细胞。这些结果表明SAH后脑动脉内皮素的产生增加。用抑制内皮素基因表达的放线菌素D治疗犬，可防止SAH后脑血管痉挛的发生。提示内皮素在脑血管痉挛的发病机制中起重要作用。

Cerebral vasospasm develops following subarachnoid hemorrhage (SAH). The mechanism of the severe vasoconstriction is still not known. Recently, endothelin was isolated from the culture medium of vascular endothelial cells and found to be a potent vasoconstrictor peptide. We examined a possible contribution of endothelin in the pathogenesis of cerebral vasospasm. In isolated cerebral arteries of dogs, both endothelin-1 and endothelin-2 elicited sustained contractions. The contraction induced by endothelin was not reversed by repeated washings, indicating the irreversible nature of the endothelin action. Endothelin-3 and big endothelin were weak vasoconstrictors. Thus, ET-Atype endothelin receptors are dominant in cerebral arteries. Next, we determined the endothelin contents in plasma and cerebrospinal fluid (CSF) by a sandwich enzymatic immunoassay. Endothelin content in CSF of patients with SAH increased at 7th and 14th day of hemorrhage. The time course of the change of endothelin content was further examined in dogs with experimental SAH. In the CSF of normal dogs, endothelin was undetectable. However, 2 and 4 days following SAH, the endothelin levels increased significantly. Immunohistochemical studies revealed the presence of few endothelin-positive endothelial cells in the basilar artery of control dogs. Two and 4 days after the hemorrhage, many endothelin-positive cells appeared. These indicate that the production of endothelin increased in cerebral arteries following SAH. Treatment of the dogs with actinomycin D, which inhibits the production of mRNA for endothelin, prevented the generation of cerebral vasospasm after SAH. These results suggest that endothelin plays a critical role in the pathogenesis of cerebral vasospasm.