Effect of Nitric Oxide Synthase Inhibitors in Vivo Tumor Necrosis Factor-induced

目前的研究已经进行，以确定，在体内，如果一氧化氮是负责细胞因子诱导心肌抑制。根据体外实验数据，细胞因子对心脏的负离子化作用被认为是由一氧化氮介导的。在离体仓鼠心脏乳头肌中，细胞因子的这种负离子化作用可被一氧化氮合酶抑制剂N-G单甲基- l-精氨酸（NMA）阻断。由于体外实验数据表明，一氧化氮合酶抑制剂可以阻止肿瘤坏死因子（TNF）诱导的心肌抑制的快速发作和逆转，因此我们在犬中研究了低剂量重组人TNF的攻击。这种TNF挑战产生显著的、早期的和短暂的心肌抑制（24小时消退）。令人惊讶的是，我们发现NMA并不能阻止TNF对心功能的早期（长达6小时）有害影响。事实上，在这段时间内，TNF和NMA对所有心脏和血流动力学参数的影响是可加性的（即NMA不阻断TNF的作用）。然而，在TNF输注24 h后，NMA确实改善了TNF对某些参数的影响，如酸碱失调，平均动脉压和全身血管阻力降低。这些数据表明，tnf诱导的心脏和血管异常的早期阶段可能与一氧化氮的产生无关。然而，TNF的一些后期效应可能与一氧化氮的产生有关。鉴于NMA在TNF输注后24小时的有益作用的提示性发现，我们评估了在高剂量TNF引起更持久心肌抑制的情况下一氧化氮抑制的作用。先前在犬中使用TNF挑战的实验表明，这是一个合理的假设，即心脏损伤可能有两个阶段。在犬中，心肌抑制存在早期（小于8小时）、剂量无关的机制和晚期（大于24小时）、剂量依赖的机制。据推测，当心肌抑制是剂量依赖性时，抑制一氧化氮合成可能不是早期有利的。因此，我们研究了预防性治疗（预处理）或NMA治疗（肿瘤坏死因子激发后的治疗，检查早期和晚期时间点）。NMA治疗降低了早期和晚期一氧化氮产生的测量值。在早期时间点，无论是治疗性还是预防性给予NMA都不能预防TNF的不良影响。然而，在24小时后，用l-精氨酸（一氧化氮生成的天然底物）逆转NMA后，预防性NMA改善了TNF挑战引起的心功能下降。这些数据表明TNF对心功能有双重作用。早期效应似乎与一氧化氮无关，而后期效应似乎与一氧化氮相关。在未来的研究中，我们计划在实际的细菌感染引起的心肌抑制模型中证实这些发现。NMA正在与细胞因子疗法一起用于癌症患者，以抑制其心血管毒性，并计划在艾滋病患者中进行同样的研究。这些研究将有助于确定这种方法的可取性。

The present investigation has been undertaken to determine, in vivo, if nitric oxide is responsible for cytokine-induced myocardial depression. The negative ionotropic effects of cytokines on the heart are believed to be mediated by nitric oxide, based on in vitro data. In isolated hamster cardiac papillary muscle, this negative ionotropic effect of cytokines can be blocked by N-G monomethyl-L-arginine (NMA), a nitric oxide synthase inhibitor. Because the in vitro data demonstrates that nitric oxide synthase inhibitors prevented tumor necrosis factor (TNF)-induced myocardial depression of rapid onset and reversal, we studied a low dose of recombinant human TNF challenge in canines. This TNF challenge produces significant, early, and short-lived myocardial depression (resolved by 24 h). Surprisingly, we found that NMA did not prevent the early (up to 6h) deleterious effects of TNF on cardiac function. In fact, during this time period, TNF and NMA effects on all cardiac and hemodynamic parameters were additive (i.e., NMA did not block TNF effects). However, 24 h after TNF infusion, NMA did ameliorate the effects of TNF on some parameters such as acid-base derangements and decreases in mean arterial pressure and systemic vascular resistance. These data suggest that the early phase of TNF-induced cardiac and vascular abnormalities may not be related to nitric oxide production. However, some of the later effects of TNF may be related to the production of nitric oxide. Given the suggestive finding of a beneficial effect of NMA 24 h post TNF infusion, we evaluated the effects of nitric oxide inhibition in the setting of higher doses of TNF causing longer-lasting myocardial depression. Previous experiments using TNF challenges in canines suggest that this is a reasonable hypothesis, i.e., there may be two phases of cardiac injury. In canines, there is an early (less than 8 h), dose-independent mechanism of myocardial depression and a late (greater than 24 h), dose-dependent mechanism of myocardial depression. It was hypothesized that the inhibition of nitric oxide synthesis might not be advantageous early when myocardial depression is dose dependent. Therefore, we studied both prophylactic treatment (pretreatment) or therapeutic treatment with NMA (post-treatment after TNF challenge examining both early- and late-time points). Treatment with NMA lowered measures of nitric oxide production in both early and late-time points. At early-time points, NMA given either therapeutically or prophylactically did not prevent the adverse affects of TNF. However at 24 hour, after reversal of the NMA with l-arginine, the natural substrate for nitric oxide production, prophylactic NMA ameliorated the decline in cardiac function seen with TNF challenge. These data suggest a dual effect of TNF on cardiac function. The early effect appears to be nitric oxide independent, while the later effect appears to be nitric oxide dependent. In future studies, we plan to confirm these findings in actual bacterial infection-induced myocardial depression models. NMA is being used with cytokine therapy for cancer patients to inhibit their cardiovascular toxicity and studies are planned in AIDS patients to do the same. These studies will help determine the advisability of this approach.