Krishna G G, Danovitch G M
Am J Physiol. 1983 Apr;244(4):R481-6. doi: 10.1152/ajpregu.1983.244.4.R481.
The renal response to central volume expansion induced by head-out water immersion was examined in 10 normal, salt-replete subjects studied during the day (0900-1300) and during the night (0000-0400). Sodium excretion in the hour preceding the study was 155 +/- 21 mueq/min and 120 +/- 14 mueq/min, respectively. During the day, immersion was followed by a natriuresis, which reached a mean peak level of 293 +/- 46 mueq/min during the 2nd h of immersion and which was maintained for the remainder of the immersion. During the night, there was no significant increase in sodium excretion from prestudy values during the first 3 h of immersion. Values rose significantly in the 4th h and reached a mean peak level of 211 +/- 20 mueq/min. Potassium excretion rose during the day (from 61 +/- 12 mueq/min to 126 +/- 16 mueq/min) but was unaltered at night. Neither glomerular filtration rate nor plasma levels of aldosterone differed between day and night. To exclude the possibility that the blunted nocturnal natriuresis could be explained by a lesser degree of central fluid translocation induced by immersion at night six normal salt-replete subjects received a 2-liter infusion of normal saline administered over 4 h during the day and during the night. The blunting of the nocturnal natriuresis was again observed. We conclude that, in addition to well-described diurnal variations in electrolyte excretion, there are diurnal variations in the responsivity of volume regulatory mechanisms.
在10名正常、盐储备充足的受试者中，研究了白天（09:00 - 13:00）和夜间（00:00 - 04:00）头低位水浸引起的中心血容量扩张时的肾脏反应。研究前一小时的钠排泄量分别为155±21微当量/分钟和120±14微当量/分钟。白天，水浸后出现利钠作用，在水浸第2小时达到平均峰值水平293±46微当量/分钟，并在水浸剩余时间维持该水平。夜间，水浸前3小时钠排泄量与研究前值相比无显著增加。在第4小时显著升高，达到平均峰值水平211±20微当量/分钟。钾排泄量白天升高（从61±12微当量/分钟升至126±16微当量/分钟），但夜间无变化。昼夜的肾小球滤过率和醛固酮血浆水平均无差异。为排除夜间利钠作用减弱可能是由于夜间水浸引起的中心液体转移程度较小所致，6名正常盐储备充足的受试者在白天和夜间接受了4小时内输注2升生理盐水的实验。再次观察到夜间利钠作用减弱。我们得出结论，除了电解质排泄中已充分描述的昼夜变化外，容量调节机制的反应性也存在昼夜变化。
