Effect of age and salicylate on rectal temperature during heat exposure

Abstract

Fischer 344, male rats (ages 8, 14, 28 months) were exposed for one hour to ambient temperatures of 21°, 32° and 38°C, 50% rh. The animals were treated with either 50 mg·kg−1 of sodium salicylate or saline and rectal temperatures were determined at 0, 30 and 60 minutes of exposure. At 32° and 38°C, 50% relative humidity (rh), a significant rise in rectal temperature was observed in all saline treated animals. During the 38°C, 50% rh exposure, the 28-month old animals exhibited a significantly greater rise in rectal temperatures at 60 minutes of exposure than 8 and 14 month old animals. Salicylate treatment resulted in a significantly greater rise in rectal temperatures for the 28-month old than for the 8 and 14-month old animals at 30 and 60 minutes during a 38°C, 50% rh exposure. Comparing saline and salicylate treatment, the 28-month old salicylate treated animals had a significantly greater rise in rectal temperature at 30 and 60 minutes during the 32°C, 50% rh exposure. The 38°C, 50% rh exposure resulted in a significantly greater rise in rectal temperature for all three ages at 50 minutes of exposure. The 28-month old animals also exhibited significantly greater rectal temperatures at 30 minutes of exposure. It was concluded from these experiments that the thermoregulatory mechanism(s) of 28-month old animals exposed to a high ambient temperature is less effective than that of the younger 8 and 14-month old animals. Salicylate administrations may further stress the thermoregulatory mechanism(s) of the older animals.