Convertino V A, Polet J L, Engelke K A, Hoffler G W, Lane L D, Blomqvist C G
Biomedical Operations and Research Office, National Aeronautics and Space Administration, Kennedy Space Center, Florida 32899, USA.
Am J Physiol. 1997 Jul;273(1 Pt 2):R93-9. doi: 10.1152/ajpregu.1997.273.1.R93.
We studied hemodynamic responses to alpha- and beta-receptor agonists in eight healthy men before and after 14 days of 6 degrees head-down tilt (HDT) to test the hypothesis that increased adrenoreceptor responsiveness is induced by prolonged exposure to simulated microgravity. Steady-state infusions of isoproterenol (Iso) at rates of 0.005, 0.01, and 0.02 microgram.kg-1.min-1 were used to assess beta 1- and beta 2-adrenoreceptor responsiveness. Infusions of phenylephrine (PE) at rates of 0.25, 0.50, and 1.00 microgram.kg-1.min-1 were used to assess responsiveness of alpha 1-vascular adrenoreceptors. Slopes calculated from linear regressions between Iso and PE doses and changes in beat-to-beat heart rate, blood pressure, and leg vascular resistance (occlusion plethysmography) for each subject were used as an index of alpha- and beta-adrenoreceptor responsiveness. HDT increased the slopes of heart rate (1,056 +/- 107 to 1,553 +/- 83 beats micrograms-1.kg-1.min-1; P = 0.014) and vasodilation (-469 +/- 111 to -1,446 +/- 309 peripheral resistance units.microgram-1.kg-1.min-1; P = 0.0224) to Iso infusion. There was no alteration in blood pressure or vascular resistance responses to PE infusion after HDT. Our results provide evidence that simulated microgravity causes selective increases in beta 1- and beta 2-adrenoreceptor responsiveness without affecting alpha 1-vascular adrenoreceptor responses.
我们研究了8名健康男性在14天6°头低位倾斜（HDT）前后对α和β受体激动剂的血流动力学反应，以检验长期暴露于模拟微重力环境会导致肾上腺素能受体反应性增加这一假设。分别以0.005、0.01和0.02微克·千克⁻¹·分钟⁻¹的速率持续输注异丙肾上腺素（Iso），以评估β1和β2肾上腺素能受体的反应性。分别以0.25、0.50和1.00微克·千克⁻¹·分钟⁻¹的速率输注去氧肾上腺素（PE），以评估α1血管肾上腺素能受体的反应性。将每个受试者Iso和PE剂量与逐搏心率、血压和腿部血管阻力（闭塞体积描记法）变化之间的线性回归计算出的斜率用作α和β肾上腺素能受体反应性的指标。HDT增加了对Iso输注的心率斜率（从1,056±107至1,553±83次·微克⁻¹·千克⁻¹·分钟⁻¹；P = 0.014）和血管舒张斜率（从-469±111至-1,446±309外周阻力单位·微克⁻¹·千克⁻¹·分钟⁻¹；P = 0.0224）。HDT后对PE输注的血压或血管阻力反应没有改变。我们的结果提供了证据，表明模拟微重力会导致β1和β2肾上腺素能受体反应性选择性增加，而不影响α1血管肾上腺素能受体反应。
