Resistance to heat stress in the spontaneously hypertensive rat

Thermal resistance as determined by survival time was examined in different age groups of spontaneously hypertensive (SHR) rats during terminal heating. A comparison with age or weight matched controls indicated that the thermal resistance of SHR animals was markedly inferior to that of normotensive animals as evidenced by 56% and 36% decreases in the total heating time to the lethal temperature, respectively. The decrease in thermal resistance in SHR animals occurred after 8 weeks of age and was coincident with the elevation of mean blood pressure to about 150 mmHg. The observation of significantly decreased total body water and rates of evaporation at critical colonic temperatures (39-40 degrees C) suggested the possibility of a reduced ability for water mobilization for thermoregulatory purposes in hypertensive animals although it appeared that other factors affecting heat gain or loss were involved.