Ns. Stachenfeld et al., THIRST AND FLUID REGULATORY RESPONSES TO HYPERTONICITY IN OLDER ADULTS, American journal of physiology. Regulatory, integrative and comparative physiology, 40(3), 1996, pp. 757-765
To assess the fluid regulatory responses in aging adults, we measured
thirst perception and renal osmoregulation during and after infusion o
f hypertonic (3% NaCl) saline in older (72 +/- 2 yr, n = 6) and younge
r (26 +/- 2 yr, n = 6) subjects. Hypertonic saline was infused at 0.1
ml . min(-1). kg(-1) for 120 min. On a separate day, the same subjects
were infused identically with isotonic saline as a control. After inf
usion and a 30-min equilibration period, the subjects drank water ad l
ibitum for 180 min. Hypertonic saline infusion Zed to graded increases
in plasma osmolality (P-osm; 18 +/- 2 and 20 +/- 2 mosmol/kgH(2)O) an
d percent changes in plasma volume (16.2 +/- 1.9 and 18.0 +/- 1.2%) th
at were similar in older and younger subjects. Osmotically stimulated
increases in thirst (94.8 +/- 18.9 and 88.3 +/- 25.6 mm), assessed on
a line rating scale, and plasma arginine vasopressin concentration (6.
08 +/- 1.50 and 4.51 +/- 1.37 pg/ml, for older and younger, respective
ly) were also unaffected by age. Despite subsequent hypervolemia, both
groups of subjects drank sufficient water to restore preinfusion leve
ls of P-osm. Renal handling of free water and sodium was also unaffect
ed by age during recovery from hypertonic saline infusion, but was sig
nificantly lower in older subjects during recovery from isotonic salin
e infusion, resulting in net fluid retention and a significant fall in
P-osm (6 mosmol/kgH(2)O). In contrast to earlier reports of a blunted
thirst response to dehydration and hypertonicity, we found that osmot
ically stimulated thirst and renal osmoregulation were intact in older
adults after hypertonic saline infusion.