title: Thermoregulatory responses in the rat to exercise in the heat following prolonged heat exposure.
abstract: To determine the effects of prolonged exposure to severe thermal stress on the subsequent ability to exercise in the heat, rats were exposed to a hot (35 degrees C) environment for 1, 2, 3, or 4 wk. At each of these weekly intervals the rats ran on a treadmill to hyperthermic exhaustion (41.5--43.0 degrees C), and tail-skin (Tt-sk) and rectal (Tre) temperatures were monitored. The results indicated that prolonged heat exposure did not enhance the rats' endurance capacity. Further, as the period of heat stress increased, there was a concomitant significant decrement in tail-skin vasodilation; indeed, after 3 and 4 wk at 35 degrees C Tt-sk reflects a complete shutdown of blood flow to the tail during exercise. Additionally, slight evaporative cooling from exogenous fluid (saliva or urine from the treadmill surface) might account for the low Tt-sk in relation to Tre and Ta. Hematocrit ratios ordinarily decreased from week to week during heat exposure, whereas body weights remained very consistent throughout the 4-wk interval. The mechanism of this decrement in vasodilation is undergoing further study.
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001833:Body Temperature Regulation; D006358:Hot Temperature; D008297:Male; D010807:Physical Endurance; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014664:Vasodilation