Effects of subcutaneous injection of capsaicin(5 mg/kg) on thermoregulation were studied in male Wistar rat. Oxygen consumption was measured for the evaluation of thermogenesis, and temperature of skin and colon was measured by thermistor probe, simultaneously under the general anesthesia with urethane, and the following results were obtained.
Skin temperature increased to 30.9 ± 2.0 ℃(mean ± SE) at 50 minutes after capsaicin injection and returned to basal state at 120 minutes(n=8). Temperature of colon decreased to 35.5 ± 0.3 ℃ and elevated form the baseline during 120 to 430 minutes after capsaicin injection. Oxygen consumption increased significantly from 6 minutes after capsaicin injection and showed maximum level(17.2 ± 0.4 mL/min/kg0.75) at 50 minutes. Theses oxygen consumptions were significantly increased until 400 minutes after capsaicin injection. However, there were no changes of oxygen consumption in control group(n = 5).
In the group of pretreatment with hexamethonium(n = 5) before 1 hour of capsaicin injection, oxygen consumption was increased to 18.0 ± 0.44 mL/min/kg0.75 at 60 minutes, and temperature changes of skin and colon were attenuated by capsaicin administration. In the group of resection of adrenal medulla, increment of oxygen consumption by capsaicin injections was attenuated during 20 to 100 minutes(15.0 ± 0.7 mL/min/kg0.75 at 60 minutes), and temperature of colon was more decreased significantly, while skin temperature changes were similar as control group.
The above results suggest that capsaicin may activate both heat production and loss simultaneously, and heat production and loss could be in independent action system.

Keywords: Capsaicin, Thermoregulation, Oxygen Consumption