Journal of Applied Physiology, Vol 54, Issue 4 1115-1119, Copyright © 1983 by American Physiological Society
Effect of triiodothyronine on body temperature at rest and during exercise in dogs
J. M. Stager
To determine the effect of the thyroid hormones on body temperature at rest
and during exercise, five mongrel dogs were trained to run on a treadmill
and then treated with exogenous triiodothyronine (T3) (1 mg/kg) to elevate
circulating T3 levels or propylthiouracil (PTU) (200 mg/day for 14 days) to
lower endogenous T3 levels. When compared with levels in euthyroid controls
at rest and during exercise, rectal temperature (Tre) was increased (P less
than or equal to 0.01 and P less than or equal to 0.02, rest and exercise,
respectively) in T3-treated dogs and decreased (P less than 0.05 and P less
than 0.01) in the PTU-treated dogs. Although the rise in Tre from rest to
exercise in the PTU trial was slightly less than that of the control runs
(1.23 vs 1.44 degrees C, respectively; P = 0.05), it was similar to the
rise in Tre observed in the T3 experiments (1.37 degrees C). Because T3
treatment resulted in an elevation in exercise oxygen consumption (VO2),
untreated dogs were run at elevated work loads such that their VO2 matched
that recorded when pretreated with T3. Exercise Tre in these experiments
was lower (P less than 0.02) than after T3 treatment, even though the
exercise metabolic rates were equivalent. It was concluded that 1) although
T3 alters body temperature, the magnitude of the rise in Tre during
exercise is not dependent on T3 concentration and 2) the effects of T3 on
body temperature at rest and during exercise are mediated through
mechanisms other than alterations in metabolic rate.
