Journal of Applied Physiology, Vol 49, Issue 6 979-984, Copyright © 1980 by American Physiological Society
Thermal control of respiratory evaporative heat loss in exercising dogs
J. B. Mercer and C. Jessen
Experiments were carried out to determine whether respiratory evaporative
heat loss (REHL) in exercising dogs is entirely under thermal control or
whether a nonthermal input is additionally involved. To determine body core
thermosensitivity, hypothalamic perfusion thermodes and intravascular heat
exchanges were chronically implanted in the animals. This allowed the
temperature of these two areas to be independently manipulated. At 30
degrees C air temperature, REHL was measured in three dogs during rest or
while running on a treadmill (6 km . h-1, 0 degree gradient). During
exercise, the threshold temperature was lowered by 9 degrees C, and the
slope of the heat-loss response was reduced to one-third as compared with
rest when hypothalamic temperature alone was clamped at various levels
between 30 degrees and 42 degrees C. However, when extrahypothalamic body
core temperature was additionally clamped, the decrease in threshold during
exercise was reduced to 0.43 degrees C, while the slope of the response was
identical to that during rest. The results suggest that by taking account
of total body core thermosensitivity, instead of hypothalamic
thermosensitivity, the alleged role of a nonthermal input is greatly
reduced. In addition, the results showed that the major pat of central
thermosensitivity must be attributed to the extrahypothalamic body core.
