Glycerol hyperhydration: hormonal, renal and vascular fluid
responses .
Freund, Beau J., Scott J. Montain, Andrew J. Young, Michael N. Sawka,
Jane P. Deluca, Kent B. Pandolf, C. Robert Valeri.
U.S. Army Research Institute of Environmental Medicine, Natick,
Massachusetts 01760-5007, and Naval Blood Research Laboratory, Boston
University Medical Center, Boston, Massachusetts 02118
APStracts 2:0341A, 1995.
Glycerol ingestion has been shown to mediate hyperhydration, however,
the mechanism(s) responsible for this improved fluid retention are
not well understood. This study examined the hormonal, renal and
vascular fluid responses to glycerol hyperhydration in 11 resting
male volunteers who ingested one of two experimental solutions
followed by the ingestion of a water bolus. The volume of fluid
ingested was determined from the subjects' measured total body water
(TBW) (total volume = 37 ml_l TBW-1, =1765 +/- 162 ml). Experimental
solutions (5.0 ml_l TBW-1) were matched for color and taste and
differed only in that one contained 1.5 g glycerol_l TBW-1 (total
osmolar load = 777 +/- 24 mOsmols). Nine of the 11 subjects also
completed a control trial during which no fluid was ingested.
Glycerol ingestion (GI) resulted in greater fluid retention compared
to the ingestion of water alone (WI), (60 vs 32% 3-h post
hyperhydration, p<0.01). This improved fluid retention with GI
resulted from lower urine flow rates (peak 6.2 vs 10.5 ml_min-1,
p<0.01) associated with lower free water clearance rates (peak =
1.2 vs. 8.2 ml_min-1, p<0.01). Hyperhydration had no effect on
plasma atrial natriuretic peptide concentrations. Changes in plasma
aldosterone were unrelated to differences in fluid retention.
Antidiuretic hormone concentrations (ADH) were significantly reduced
from pre-hyperhydration levels during both hyperhydration trials, but
tended (p=0.07) to rise during GI compared to WI at the very time
urine flow and free water clearance differences were also evident.
This suggests ADH may, in part, be responsible for glycerol's
effectiveness although, differences in ADH concentrations were small
and near the assay's sensitivity limits. Alternatively, glycerol's
effectiveness may result from it directly increasing the kidneys'
medullary concentration gradient and hence, water reabsorption.
Received 29 November 1994; accepted in final form 30 June 1995.
APS Manuscript Number A1210-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 August 1995.