EVAPORATIVE COOLING IN THE RAT: INTERACTION WITH HEAT LOSS FROM THE TAIL

¹ Department of Psychology, University of Pittsburgh, Pittsburgh, Pennsylvania
² Department of Biology, Syracuse University, Syracuse, New York

There are two major thermolytic responses of rats to inescapable heat stress: cutaneous vasodilatation and grooming behavior. The former response increases heat loss by radiation, conduction, and convection, primarily from vascularized exposed surfaces such as the tail, and depends upon the positive thermal gradient between the rat and its environment that occurs at ambient temperatures of 32-40°C. The latter response increases heat loss by evaporation of saliva groomed onto body surfaces and becomes increasingly important as ambient temperatures approach 40-41°C and the positive thermal gradient diminishes. These two mechanisms are not independent of one another. For example, rats develop more pronounced hyperthermia following surgical removal of salivary function, thereby increasing the positive thermal gradient and facilitating heat loss. Similarly, rats increase evaporative cooling by salivary grooming following amputation of the tail. Removal of either saliva or the tail impairs the rat's ability to regulate body temperature, while removal of both leaves the rat most vulnerable to heat stress.

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The technical assistance of Jen-shew Yen and Richard E. A. Porter is gratefully acknowledged. This study was supported by Research Grant MA-3192 from the Medical Research Council of Canada and by Research Grants GB-12344 and GB-28830 from the National Science Foundation of the U.S.A.