Modifications of Febrile Temperature Regulation by Acclimation

Abstract

Fever is known to be rather an adjustment than a disturbance of the thermoregulatory system. The febrile body temperature elevation is caused by a concurrent shift of the control characteristics of all thermoregulatory effector mechanisms. Depending on ambient conditions, heat production and heat conservation mechanisms are activated and heat loss mechanisms are reduced (1). This process is usually explained by the concept of an adjustment of the control system to a shifted set point (2, 3). Acclimation, too, is a process which influences the regulatory mechanisms of the temperature control system. In general, thermo-adaptive modifications enable the organism to cope with a given environmental stress more efficiently. These modifications may consist, on the one hand, of morphological changes, which primarily modify the controlled system, such as changes in thermal insulation of the body shell. On the other hand, functional adaptive effects can alter effector-capacities or bring about adjustments of the control characteristics like shifts of threshold body temperatures for the activation of thermoregulatory effectors (4, 5). Adaptive alterations of control mechanisms have been found on the level of thermoreception (6) and of afferent pathways (7, 8). So the question arises which influences thermo-adaptive changes may have on the action of regulatory mechanisms during fever and on the extent of febrile temperature elevation. This question was investigated by studies on pyrogen-induced fever in acclimated rabbits.