We tested the hypothesis that nitric oxide (NO) is responsible for blunting sympathetic α-adrenergic vasoconstriction in the active muscles of humans (functional sympatholysis). We measured forearm blood flow (Doppler ultrasound) and calculated the reductions in forearm vascular conductance (FVC) in response to α-adrenergic receptor stimulation during rhythmic handgrip exercise and during a control non-exercise vasodilator condition (intra-arterial adenosine), before and after local NO synthase (NOS) inhibition in healthy men. The forearm vasoconstrictor responses to endogenous noradrenaline release (intra-arterial tyramine) were significantly blunted during moderate exercise compared with adenosine, and these vasoconstrictor responses were not restored by NOS inhibition with NG-monomethyl-l-arginine (l-NMMA; n = 6) or NG-nitro-l-arginine methyl ester (l-NAME; n = 8). Similarly, l-NAME did not restore the vasoconstrictor responses to tyramine in contracting muscle during heavy rhythmic handgrip exercise (n = 4). In four additional subjects, we also found that the vasoconstrictor responses evoked by tyramine during exercise or adenosine were repeatable in the absence of NOS inhibition (i.e. time control). Finally, in five subjects the forearm vasoconstrictor responses to direct α1-adrenergic (phenylephrine) and α2-adrenergic (clonidine) receptor stimulation were blunted during moderate exercise compared with adenosine; these responses were also unaffected by l-NAME. Taken together, our results demonstrate that NO is not obligatory for functional sympatholysis in contracting skeletal muscles of healthy men.
展开▼
机译:我们测试了一氧化氮(NO)导致人类活动肌肉中交感性α-肾上腺素血管收缩(功能性交感神经)的假说。我们测量了前臂节律性锻炼期间和控制性非运动性血管舒张剂状况(动脉内腺苷)前后,前臂血流(多普勒超声)并计算了对α-肾上腺素能受体刺激反应的前臂血管传导(FVC)的减少。健康男性中局部NO合酶(NOS)抑制后的结果。与腺苷相比,适度运动期间前臂对内源性去甲肾上腺素释放(动脉内酪胺)的血管收缩反应明显减弱,并且这些NGN-单甲基-1-精氨酸对NOS的抑制作用不能恢复这些血管收缩反应(1-NMMA; n = 6 )或NG-硝基-1-精氨酸甲酯(1-NAME; n = 8)。同样,在重度有节奏的手握练习中,l-NAME不能恢复收缩肌肉对酪胺的血管收缩反应(n = 4)。在另外四名受试者中,我们还发现,在没有NOS抑制的情况下(时间控制),运动或酪氨酸引起的酪胺引起的血管收缩反应是可重复的。最后,与腺苷相比,在适度运动中,有五名受试者在中度运动期间对直接α1-肾上腺素(去氧肾上腺素)和α2-肾上腺素(可乐定)受体刺激的前臂血管收缩反应减弱。这些响应也不受l-NAME的影响。两者合计,我们的结果表明,在健康男性的骨骼肌收缩中,NO并不是功能性交感神经交感性所必需的。
展开▼