Effect of age and salicylate on rectal temperature during heat exposure

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.