Urantide对心肌缺血性损伤的保护作用

研究UT受体拮抗剂——urantide对心肌缺血性损伤的保护作用及其机制。小鼠心肌缺血采用皮下注射(sc)异丙肾上腺素(Iso)法，观察心电图ST段的变化，测定小鼠血清中乳酸脱氢酶(LDH)、一氧化氮合酶(NOS)的活性以及丙二醛(MDA)、一氧化氮(NO)的含量， HE染色观察心肌组织病理损伤情况。建立乳鼠原代心肌细胞缺氧再给氧模型，采用ELISA法观察urantide对细胞培养上清液中肌钙蛋白I(cTnI)的影响，比色法测LDH活性；MTT法观察细胞存活率及激光共聚焦检测细胞内钙离子浓度的变化。实验揭示urantide (3～30 μg·kg^-1)可明显抑制小鼠心电图ST段的抬高； urantide (10及30 μg·kg^-1)可显著降低小鼠血清中LDH活性和MDA含量，明显升高NOS活性和NO含量，同时减轻异丙肾上腺素诱导的心肌病理损伤。在乳鼠原代心肌细胞缺氧再给氧模型中， urantide (1×10^-6和1×10^-7 mol·L^-1)能明显增加细胞存活率，降低培养上清液中LDH的活性； urantide (1×10^-6～1×10^-9 mol·L^-1)能显著降低细胞培养上清液中cTnI的增高和细胞内钙离子浓度的上升。上述结果表明， urantide对心肌缺血及缺氧再给氧所致心肌细胞的损伤具有一定的保护作用，其作用机制可能与增加NOS活性、促进NO合成及抑制钙超载有关。

Protective effect of urantide against myocardial ischemia injury

This study is to investigate the protective effect of urantide against myocardial ischemia injury in mice and its mechanism. The ischemic model was made by using subcutaneous injection of isoproterenol (Iso) in mice, the change of ST segment of electrocardiogram (ECG) was observed, and the activitise of lactate dehydrogenase (LDH) and nitric oxide synthetase (NOS), the contents of malonaldehyde (MDA) and nitric oxide (NO) in serum were measured. The histopathological changes of myocardium were observed by using HE staining. The anoxia/reoxygenation (A/R) model of myocardial cells on neonatal Sprague-Dawley rats was established. Methyl thiazolyl tetrazolium (MTT) assay and confocal microscopy were respectively used to measure the viability and intracellular Ca2+ concentration in myocardial cells exposed to A/R. LDH activity and cTnI content in the cell culture medium were assayed for the evaluation of myocardial cells injury. The results revealed that urantide in the range of 3 - 30 microg kg(-1) iv markedly inhibited Iso-induced raise of the ST segment of ECG; 10 and 30 microg kg(-1) significantly reduced the increases of MDA content and LDH activity in mice serum, remarkably raised the activity of NOS and the content of NO. Urantide (10 and 30 microg kg(-1)) also significantly ameliorated myocardial ischemic injury. On the A/R model of myocardial cells, urantide (1 x 10(-6) - 1 x 10(-9) mol L(-1)) could evidently inhibit the increases of cTnI content, reduce the rise of intracellular Ca2+ concentration. Urantide (1 x 10(-6) - 1 x 10(-7)) mol L(-1) increased the viability of myocardial cells injured by A/R and cut down LDH activity in the cell culture medium. Therefore urantide has significant protective effect against myocardial ischemia or A/R injury via the inhibition of Ca2+ overload and the augmentation of NO synthesis.