Journal of Applied Physiology, Vol 66, Issue 4 1749-1755, Copyright © 1989 by American Physiological Society
Plasma volume expansion in rats: effects on thermoregulation and exercise
R. P. Francesconi, M. Bosselaers, C. Matthew and R. W. Hubbard
US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007.
Administration of polyethylene glycol (PEG, intraperitoneal, 3 ml, 30%
solution) to adult male rats (300 g) resulted in an approximately 20%
increment in plasma volume (PV) 24 h after PEG injection. When these
animals were exercised (9.14 m/min, level treadmill) in a warm (30 degrees
C, 30-40% relative humidity) environment, their mean endurance was
increased from 67.9 (saline-treated controls, CONT) to 93.6 min (P less
than 0.01). Total water loss was increased from 12.2 (CONT) to 17.2 g (PEG,
P less than 0.01). Atropine administration (ATR, 200 micrograms/kg, tail
vein) significantly (P less than 0.05) reduced both the endurance and the
salivary water loss of CONT and PEG-treated rats, whereas it increased the
heating rate (P less than 0.01) of both groups. PEG treatment reduced (P
less than 0.01) the hematocrit and circulating protein levels both before
and subsequent to exercise in the warm environment. Clinical chemical
indexes of heat/exercise injury were generally unaffected by
pharmacological intervention, whereas clinical chemical responses to
exercise were related to the endurance time of each group. We concluded
that expansion of PV by PEG provided significant beneficial effects on
performance and thermoregulation during exercise in a warm environment.
