Aspirin enhances evaporation in hydrated and dehydrated rats.

The effect of acetysalicylic acid (aspirin) on thermoregulation in a warm environment was studied in hydrated and dehydrated adult rats to test the hypothesis that dehydration hyperthermia can be modified by an antipyretic drug. Metabolic rate (MR), evaporative water loss (EWL), and deep body temperature (Tb) were measured during 2 h of exposure to an ambient temperature of 36 degrees C after the rats had received an oral pellet of aspirin (100 mg.kg-1) or placebo. The dehydrated placebo group had a higher Tb and lower EWL than the hydrated placebo group. Aspirin increased MR and EWL in both hydrated and dehydrated animals. Aspirin did not affect Tb in hydrated rats, but reduced Tb by 0.2 degree C in dehydrated rats during the heat exposure. The elevation in EWL appears to be a thermoregulatory response to increased heat production in both hydrated and dehydrated animals after aspirin treatment. The possibility that aspirin may act in dehydrated animals to restore central thermosensitivity toward hydrated levels needs to be tested further.