Mechanism of attenuated thirst in aging: role of central volume
receptors.
Stachenfeld, Nina S., Loretta Dipietro, Ethan R. Nadel, and Gary W.
Mack.
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 3:0255R, 1996.
To test the hypothesis that the inhibitory action of central blood
volume expansion on thirst and renal fluid regulation is attenuated
with aging, we monitored the drinking and renal responses of
dehydrated older (70 +/- 2 yr, n=6) and younger (24 +/- 1 yr, n=6)
subjects during 195 min of head-out water immersion (HOI), which
shifts blood centrally and increases plasma volume (PV). Subjects
dehydrated by exercising for 2 hr at 36 degrees C in the evening and
refraining from fluids overnight prior to HOI in 34 degrees C water
or a seated control in water perfusion suit (time control, TC) the
next morning. Ad libitum water intake was allowed after 15 min of
HOI. Dehydration decreased PV by 10.6+/-1 and 7.3+/-1.8% (p <
0.05) and increased plasma osmolality by 6+/-2 and 7+/-1 mosmol x kg
-1 H2O (p < 0.05) in older and younger subjects, respectively.
Thirst ratings increased in both groups, but pre-HOI thirst
perception on a line rating scale was lower in older (69 +/- 8 mm)
than younger (94 +/- 6 mm, p < 0.05) subjects. Fifteen min of
HOI restored PV by 7.8+/-1.0% and 5.7+/-1.0%, in older and younger
subjects, but suppressed thirst rating in younger subjects only
(p<0.05). Fluid intake was reduced in HOI compared to TC in
younger (6.3 +/- 0.5 vs 14.3 +/- 2.2 ml x kg-1, p<0.05), but not
in older (6.7 +/- 2.1 vs 8.4 +/- 3.3 ml x kg-1) subjects. During HOI,
older subjects had smaller suppression of plasma renin activity and
aldosterone concentration but a greater increase in the plasma atrial
natriuretic peptide concentration (P[ANP], p < 0.05). HOI
increased fractional sodium excretion in both groups, but mean
arterial pressure increased only in the older subjects (p <
0.05). We conclude that the inhibitory influence of central volume
expansion on thirst and drinking behavior is diminished with aging.
Further, in contrast to younger people, HOI natriuresis is associated
with exaggerated increases in P[ANP] and arterial blood pressure in
older people, suggesting arterial baroreceptors may be involved in
the fluid regulatory response to central blood volume expansion in
older people.
Received 26 April 1996; accepted in final form 19 June 1996.
APS Manuscript Number R236-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96