Effects of ambient temperature on thermoregulation during fever in cats.

Effects of ambient thermal loads on thermoregulatory responses and on the shape of fever curves were studied during muramyl-dipeptide-(MDP)-induced fever in cats. They were implanted with electrodes for chronic recording of electromyograms and cortical and subcutaneous temperatures. A febrile response was induced following intravenous injection of muramyl dipeptide. (1) During the initial phase of fever, the recruitment of heat gain responses and suppression of heat loss responses did not depend on the ambient temperature (Ta). (2) The relative contribution of each thermoregulatory mechanism varied with Ta. (3) Ta did not affect the amplitude of the first febrile peak. However, a second peak in body temperature seen in MDP-induced fever was absent in warm Ta of 30 and 37 degrees C.