Journal of Applied Physiology, Vol 38, Issue 6 1038-1044, Copyright © 1975 by American Physiological Society
Suppression of ADH during water immersion in normal man
M. Epstein, D. S. Pins and M. Miller
Since previous studies from this laboratory have demonstrated that the
redistribution of blood volume and concomitant relative central
hypervolemia induced by water immersion to the neck causes a profound
natriuresis and a suppression of the renin-aldosterone system, it was of
interest to assess whether the diuresis induced by immersion was mediated
by an analogous inhibition of ADH. The effects of water immersion on renal
water handling and urinary ADH excretion were assessed in 10 normal male
subjects studied following 14 h of overnight dehydration on two occasions,
control and immersion. The conditions of seated posture and time of day
were identical. During control ADH persisted at or above prestudy values.
Immersion resulted in a progressive decrease in ADH excretion from 80.1
plus or minus 7 (SEM) to 37.3 plus or minus 6.3 muU/min (P smaller than
0.025). Cessation of immersion was associated with a marked increase in ADH
from 37.3 +/- 6.3 muU/min to 176.6 +/- 72.6 muU/min during the recovery
hour (P smaller than 0.05). Concomitant with these changes urine osmolality
decreased significantly beginning as early as the initial hour of immersion
from 1044 +/- 36 to 542 +/- 66 mosmol/kg H2O during the final hour of
immersion (P smaller than 0.001). Recovery was associated with a
significant mean increase in Uosm of 190 +/- 40 mosmol/kg H2O over the
final hour of immersion (P smaller than 0.001). The suppression of ADH
occurred without concomitant changes in plasma tonicity. These studies are
consistent with the suggestion that in hydrated subjects undergoing
immersion suppression of ADH release contributes to the enhanced free water
clearance, which has been previously documented.
