Thirst and fluid regulatory responses to hypertonicity in older
adults.
Stachenfeld, Nina S., Gary W. Mack, Akira Takamata, Loretta Dipietro,
and Ethan R. Nadel.
The John B. Pierce Laboratory and Departments of Epidemiology &
Public Health, and Cellular & Molecular Physiology, Yale
University School of Medicine, 290 Congress Avenue, New Haven, CT
06519
APStracts 3:0117R, 1996.
To assess the fluid regulatory responses in aging adults, we measured
thirst perception and renal osmoregulation during and following
infusion of hypertonic (3% NaCl) saline in older (72 +/- 2 yrs, n=6)
and younger (26 +/- 2 yrs, n=6) subjects. Hypertonic saline was
infused at 0.1 ml x min-1 x kg-1 for 120 min. On a separate day, the
same subjects were infused identically with isotonic saline as a
control. After infusion and a 30 min equilibration period, the
subjects drank water ad libitum for 180 min. Hypertonic saline
infusion led to graded increases in plasma osmolality (Posm, 18 +/- 2
and 20 +/- 2 mosmol/kg H2O) and percent change (%_) in plasma volume
(16.2 +/- 1.9 and 18.0 +/- 1.2 %) that were similar in older and
younger subjects. Osmotically stimulated increases in thirst (94.8
+/- 18.9 and 88.3 +/- 25.6 mm) on a line rating scale and plasma
arginine vasopressin concentration (P[AVP], 6.08 +/- 1.50 and 4.51
+/- 1.37 pg/ml, for older and younger, respectively) were also
unaffected by age. Despite subsequent hypervolemia, both groups of
subjects drank sufficient water to restore pre-infusion levels of
Posm. Renal handling of free water and sodium was also unaffected by
age during recovery from hypertonic saline infusion, but was
significantly lower in older subjects during recovery from isotonic
saline infusion, resulting in net fluid retention and a significant
fall in Posm (6 mosmol/kg H2O). In contrast to earlier reports of a
blunted thirst response to dehydration and hypertonicity, we found
that osmotically stimulated thirst and renal osmoregulation were
intact in older adults following hypertonic saline infusion.
Received 6 December 1995; accepted in final form 22 March 1996.
APS Manuscript Number R768-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96