In order to better delineate the profile of thermoregulatory action of alpha 1-adrenoceptor antagonists; corynanthine (CRN) and BMY 20064 (BMY), and alpha 2-adrenoceptor agonist; medetomidine (MDT) and B-HT 920 (BHT), the effect of intravenous administration of two doses of these drugs on rectal (Tre) and ear skin (Te) temperatures, metabolic rate (M), respiratory evaporative heat loss (Eres) and respiratory rate (Rr) were examined in febrile and non-febrile rabbits. 2. Results indicate that alpha 1-adrenoceptor antagonists as well as alpha 2-adrenoceptor agonists markedly lowered body temperature exhibiting antipyretic and hypothermic actions. The hypothermic and antipyretic effect after the CRN or BMY, and BHT or MDT, treatment was associated with inhibition of metabolic rate and/or with body heat redistributed to peripheral tissues and an increase of the potential for heat loss to the environment. 3. BMY also abolished the thermogenic response to cold. However, BMY did not affect metabolic heat production on exposure to a cold ambient temperature. This unexpected phenomenon is difficult to explain at the present moment. Possible mechanisms responsible for the thermoregulatory activity of BMY are discussed. 4. These results indicate that alpha 1- and alpha 2-adrenoceptor drugs' thermoregulatory actions are similar in event and suggest that both subtypes of alpha-adrenoceptor might be implicated functionally in a variety of thermoregulatory processes.
