Kregel K C
Department of Exercise Science, University of Iowa, Iowa City 52242, USA.
J Appl Physiol (1985). 1996 Feb;80(2):540-6. doi: 10.1152/jappl.1996.80.2.540.
The experimental objective was to determine whether sympathetic nervous system activity and cardiovascular adjustments to hypoxia are altered with advancing age. Norepinephrine (NE) synthesis was blocked with alpha-methyl-DL-p-tyrosine, and NE turnover rates were determined in the left ventricle of the heart, kidney, liver, and adrenal gland in groups of conscious unrestrained mature (12-mo-old) and senescent (24-mo-old) Fischer 344 rats in conditions of normoxia and acute hypocapnic hypoxia (10% O2-90% N2). Calculated NE turnover rates were similar in all four tissues sampled for both age groups in the normoxic condition. Thirty minutes of hypoxia produced elevations in NE turnover rates in the kidney, liver, and adrenal gland, but not in the heart, for both the mature and senescent groups. However, NE turnover rates were attenuated in the kidney (92 vs. 195%) and liver (119 vs. 190%) of senescent compared with mature rats. Hypoxia produced no change in mean arterial pressure from normoxic levels in the mature rats, whereas older rats had a progressive decline in mean arterial pressure (-24 +/- 3 mmHg from baseline) over the course of the hypoxic exposure. In contrast, heart rate responses were similar in the normoxic and hypoxic conditions for both age groups. These findings indicate that sympathetic nerve activity, as estimated from NE turnover rates, increases in a tissue-specific manner with moderate hypoxia, but this increase is markedly attenuated in the kidney and liver with advancing age. In addition, the ability to maintain MAP during a hypoxic challenge is impaired with aging, perhaps due, in part, to a reduced sympathetic vasoconstriction to selected internal organs.
实验目的是确定交感神经系统活动以及心血管系统对缺氧的调节是否会随着年龄增长而改变。用α-甲基-DL-对酪氨酸阻断去甲肾上腺素（NE）的合成，并在常氧和急性低碳酸血症性缺氧（10% O₂ - 90% N₂）条件下，测定清醒不受约束的成年（12月龄）和衰老（24月龄）Fischer 344大鼠心脏、肾脏、肝脏和肾上腺左心室中的NE周转率。在常氧条件下，两个年龄组的所有四个采样组织中计算出的NE周转率相似。对于成年组和衰老组，30分钟的缺氧均使肾脏、肝脏和肾上腺中的NE周转率升高，但心脏中的NE周转率未升高。然而，与成年大鼠相比，衰老大鼠肾脏（92%对195%）和肝脏（119%对190%）中的NE周转率有所降低。成年大鼠缺氧时平均动脉压与常氧水平相比无变化，而老年大鼠在缺氧暴露过程中平均动脉压逐渐下降（比基线降低-24±3 mmHg）。相比之下，两个年龄组在常氧和缺氧条件下的心率反应相似。这些发现表明，根据NE周转率估计，交感神经活动在中度缺氧时以组织特异性方式增加，但随着年龄增长，这种增加在肾脏和肝脏中明显减弱。此外，衰老会损害在缺氧挑战期间维持平均动脉压的能力，这可能部分归因于对选定内脏器官的交感缩血管作用减弱。
