Colonic heating patterns and the variation of thermal resistance among rats.
Wright-G; Knecht-E; Wasserman-D
J Appl Physiol: Respir Environ Exercise Physiol 1977 Jul; 43(1):59-64
The characteristics of the rat colonic heating curve as related to ambient exposure conditions, hypertension, and dehydration were studied. Heat resistance was also determined over a 12 hour interval. Three basic heating patterns were identified. Type 1 rats exhibited a linear heating pattern from the resting to the lethal temperature. Type 11 subjects showed an initial rapid rate of core temperature elevation which preceded a relatively well defined convexity of the curve; this resulted in a secondary rate of heating which was maintained to the lethal temperature. Type 111 animals had the longest mean survival times and were characterized by a three stage heating curve; equilibrium was attained, followed by a marked decrease in core temperature. This was followed by a dramatic rise in body temperature that continued to the lethal temperature. Where total survival time differed among the treatment groups, those groups which had decreased thermal resistance generally had a higher percentage of Type 1 and Type 11 individuals. A significant decrease in the upper thermal limit during the early afternoon was observed. The reason for this fluctuation was not understood, but it was coincident with differences in the preexposure state of hydration. The authors suggest that the differences in lethal temperatures observed in rats be used as a model for the study of the heat death mechanism.
Laboratory-animals; Environment; Thermal-resistance; Exposure-limits; Body-mechanics; Mortality; Reaction-time; Models; Biological-rhythms;
Author Keywords: thermoregulation; lethal temperature; heat stress
Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology