Tajima F, Sagawa S, Iwamoto J, Miki K, Claybaugh J R, Shiraki K
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Am J Physiol. 1988 Jun;254(6 Pt 2):R977-83. doi: 10.1152/ajpregu.1988.254.6.R977.
After overnight food and fluid restriction, seven healthy old (62-74 yr) and eight young (21-28 yr) men were examined before, during, and after 3-h head-out immersion (HOI) in thermoneutral water (34.5 +/- 0.5 degrees C). On separate days, all subjects remained seated in air for 5 h to obtain the time control data. Although HOI induced a reversible increase in urine flow in all subjects, the response was faster and greater in magnitude in the elderly than in the young. Na excretion and osmolal clearance also followed a response pattern identical to that of urine flow; thus the HOI-induced diuresis was entirely osmotic. Endogenous creatinine clearance increased in the elderly at 2 h of HOI, suggesting an age-related modification in kidney hemodynamics. Although there was virtually the same cephalad blood shift (measured by impedance cardiography), mean arterial pressure significantly increased (P less than 0.05) during HOI in the elderly, which also indicated a different response of peripheral circulation to HOI in the elderly. Control level of plasma atrial natriuretic factor (ANF) was nearly twofold greater in the elderly compared with the young. The HOI induced a nearly fourfold increase in ANF in the elderly, whereas that for the young was threefold. Both plasma aldosterone and ADH responses to HOI were attenuated in the elderly compared with the young, which had no correlation with urine flow or Na excretion. It is concluded that the elderly release more ANF at a given cephalad volume expansion compared with the young, but the vasodilative reaction to ANF was attenuated in the elderly.
在经过一夜的禁食禁水后，对7名健康的老年男性（62 - 74岁）和8名年轻男性（21 - 28岁）进行了研究。在34.5±0.5摄氏度的中性温度水中进行3小时的头低位浸浴（HOI）前、浸浴期间和浸浴后对他们进行了检查。在不同的日子里，所有受试者在空气中静坐5小时以获取时间对照数据。尽管HOI在所有受试者中均引起尿量可逆性增加，但老年人的反应更快且幅度更大。钠排泄和渗透清除率也呈现出与尿量相同的反应模式；因此，HOI诱导的利尿完全是渗透性的。HOI 2小时时，老年人的内生肌酐清除率增加，提示肾脏血流动力学存在与年龄相关的改变。尽管通过阻抗心动图测量的头向血液转移几乎相同，但老年人在HOI期间平均动脉压显著升高（P<0.05），这也表明老年人外周循环对HOI的反应不同。老年人血浆心房利钠因子（ANF）的对照水平几乎是年轻人的两倍。HOI使老年人的ANF增加近四倍，而年轻人增加三倍。与年轻人相比，老年人血浆醛固酮和抗利尿激素对HOI的反应均减弱，且与尿量或钠排泄无关。结论是，与年轻人相比，老年人在给定的头向容量扩张时释放更多的ANF，但老年人对ANF的血管舒张反应减弱。
