AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 5 972-R978, Copyright © 1987 by American Physiological Society
Extracellular fluid and plasma volumes during water immersion in nephrectomized dogs
K. Miki, G. Hajduczok, S. K. Hong and J. A. Krasney
Extracellular fluid volume (ECF, [125I]iothalamate space), blood volume
(BV, 51Cr-labeled erythrocyte space), and hematocrit were measured
continuously to study the kinetics of fluid movements between
intracellular, interstitial, and plasma compartments during water immersion
(WI) at 38 degrees C in seven splenectomized and acutely nephrectomized
dogs. ECF and plasma volume (PV) increased linearly during WI by 10 +/- 2
ml/kg (4% of initial ECF volume, P less than 0.05) and 12 +/- 2 ml/kg (33%
of initial PV, P less than 0.05), respectively, above the control level by
120 min of WI. We estimate that 83% of the fluid entering the intravascular
compartment is derived from the intracellular space at 120 min of WI. The
results of this study indicate that WI leads to a sustained fluid movement
of intracellular fluid toward the intravascular compartment. The increase
in interstitial hydrostatic pressure (wick method) by 28.5 mmHg from the
control level at 5 min of WI in response to the external water pressure
exceeds the increase in mean capillary pressure by 10-11 mmHg relative to
the control level. We postulate that this negative hydrostatic pressure
gradient across the capillary wall leads to an increase in PV during WI.
