AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 4 481-R486, Copyright © 1983 by American Physiological Society
Renal response to central volume expansion in humans is attenuated at night
G. G. Krishna and G. M. Danovitch
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.
