Thermoregulation of the rabbit during the late phase of endotoxin fever

Abstract

In the late phase of the fever occurring 120 or more min after i.v. injection of endotoxin (1 microgram/kg) to female rabbits, marked shifts of thresholds for respiratory evaporative heat loss and for peripheral vasodilatation to higher body core temperatures were observed. In contrast, the threshold body core temperature for cold thermogenesis was shifted downwards. As a result, the interthreshold zone was widened. Within the body temperature range of 37.4 to 39.9 degrees C neither heat production or heat loss mechanisms were operant and the body temperature was determined mainly by passive heat transfer between the body and the environment. Outside this zone, the sensitivities of the heat and cold defence activities to changes in body core temperature appeared to be unchanged.

Gaseous Mediators in Temperature Regulation

“…It is important to point out, though, that this upward shift in the thermogenesis threshold has been reported only in the earliest stages of the systemic inflammatory response. In other stages of the response, an increase in the thermogenesis threshold is not always present (138,146,285,380), which is consistent with the many reports of rodents being unable to develop fever at room (subneutral) temperatures [for a discussion, see Refs. (284,355)].…”

“…(8,26)]. In endothermic species, LPS also produces consistent increases in the temperature thresholds for activation of skin vasodilation and respiratory heat loss, which then defend a higher level of T b (138,146,379,380). Therefore, it appears that the most natural way to produce a fever is by means of heat conservation in a warm environment.…”

“…Initially proposed by Hammel (136), this model was refined over the years (34,40), but its basis always laid on the conjecture that a single signal-reference comparator would coordinate the activity of all thermoeffectors. Over the past decade, however, the set-point model of thermoregulation has been questioned by several authors (156,217,279) in view of the realization that thermoeffectors can be activated or inhibited independently of each other in the course of thermoregulatory responses (11,282,285,297,380), a property that cannot be accounted by a single comparator. These lines of evidence reinforce Partridge's call for caution when employing manmade engineering principles to explain biological control systems that emerged in layers over the course of evolution (258).…”

Effects of Ambient Temperature on Thermoregulation during Fever in Cats

“…Results presented here are in agreement with previous studies on thermoregulation during endotoxin-induced fever in the rabbit [20]. A similarity between the thermoregulatory disturbances during the late phase o f endotoxin fever and those described for hypothalamic-lesioned animals [24] is reported by Vybiral et al [20].…”

Fever and fever syndrome. Current problems.

“…Recently this observation of threshold dissociation in pyrogen-induced fever was confirmed by studies on rabbits in which the stimulus response relationships between core temperature and various thermoregulatory effectors were determined before and during the course of endotoxin fever [53]. Both Thcv and Thsh increased during the early phase of LPS fever; however, during the second phase, Thcv remained elevated whereas Thsh decreased even below its normal value, resulting in the expansion of the inter-threshold zone between heat and cold defence activation from about 0.5 to 3.0°C.…”