Abstract
Strain difference in thermoregulation under hot environment was studied among Wistar rat strains, especially in relation to thermal salivation and body water economics (BWE). Eight Wistar rat strains were exposed to an ambient temperature (Ta) of 42.5°C, 40%RH. Survival time (ST), saliva spreading (SS), body water loss (BWL), BWE, and wet weight of 3 salivary glands were determined. Strain difference in thermoregulatory ability was as large among Wistar rat strains as it was among non-Wistar rat strains. Crj: Wistar survived heat longer than the others. LEW/N Crj, HOS: Wistar, Wistar-Kyoto and Wistar/MS also survived heat longer than Jcl: Wistar, Wistar King A and Wistar/MK. Rats depend on extensive SS in order to survive the heat longer than 2 hr. BWE was highly efficient in strains showing more saliva spreading than others. There was no change in the wet weight of the submaxillary gland in terms of heat tolerance. These findings indicated that thermal salivation is a potential evaporative heat loss system in Ta higher than body temperature (Tb). Thermal salivation is supported by rapid body water mobilization in the early phase and by highly efficient BWE during the following long lasting hyperthermia.
