Febrile and metabolic tolerance to endotoxin and human recombinant interleukin-1 beta in rabbits

We investigated whether or not tolerance of the febrile and metabolic responses to human recombinant interleukin-1 beta (IL-1 beta) develops in rabbits. Febrile tolerance to bacterial endotoxin was induced by daily injections of lipopolysaccharide (LPS, 5.0 micrograms/kg iv). In LPS-tolerant rabbits, the second phase of the biphasic fever induced by intravenous injections of LPS (5.0 micrograms/kg) or IL-1 beta (2.0 micrograms/kg) was significantly reduced. However, the first phase was almost the same as that observed in normal rabbits. Five daily injections of IL-1 beta (2.0 micrograms/kg iv) resulted in the development of tolerance of the febrile response to IL-1 beta. In IL-1 beta-tolerant rabbits, the second peak of the biphasic fever was significantly reduced. In addition, decreases in leukocyte count and plasma zinc induced by intravenous injections of LPS or IL-1 beta were significantly reduced in LPS- or IL-1 beta-tolerant rabbits. However the monophasic fever induced by a smaller dose of IL-1 beta (0.5 microgram/kg iv) and the first peak of the IL-1 biphasic fever were almost the same as those observed in normal rabbits. Febrile responses induced in LPS- or IL-1 beta-tolerant rabbits by intracerebroventricular injections of LPS (5.0 ng) or IL-1 beta (2.0 ng) were similar to those observed in normal rabbits. The present results suggest that tolerance of the febrile and metabolic responses to IL-1 beta is developed after repeated injections of IL-1 beta and that reduced responsiveness to IL-1 beta is partly involved in the development of LPS tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraperitoneal injections of prostaglandin E2 attenuate hyperthermia induced by restraint or interleukin-1 in rats

1. The purpose of this study was to investigate the effect of the intraperitoneal (I.P.), intravenous (I.V.) or intrapreoptic area (POA) injection of prostaglandin E2 (PGE2) on the body temperature of restrained and unrestrained rats. The effect of I.P. PGE2 on the body temperature of rats during fever induced by I.P. injection of interleukin-1 beta (IL-1 beta) was also investigated. 2. Prior to injection, restrained rats had body temperatures of approximately 1 degree C higher than unrestrained rats. The I.P. injection of PGE2 (0.05 and 0.5 mg kg-1) caused body temperature to fall towards the pre-restraint levels in a dose-dependent manner. This fall in body temperature was preceded by a sharp increase in tail skin temperature that was also dependent on dose. The I.P. injection of PGE2 had no effect on the body temperature of unrestrained animals. 3. The I.V. injection of PGE2 caused very little change in the body temperature of restrained rats. However, when injected I.V. into unrestrained animals, PGE2 caused dose-dependent fevers. The injection of PGE2 (50 ng) into the POA resulted in fever in both restrained and unrestrained animals. 4. The I.P. injection of IL-1 beta (10 micrograms kg-1) caused a biphasic fever that lasted at least 420 min. The I.P. injection of PGE2 180 min after the injection of IL-1 beta caused a transient decrease in the rats' body temperature. This drop in body temperature was not associated with a decrease in metabolic rate. 5. These data support the hypothesis that during restraint stress hyperthermia and IL-1 beta fever, the I.P. injection of PGE2 acts peripherally to lower the body temperature of rats.

Role of vasopressin in the blockade of the development of morphine tolerance by footshock and psychological stress

To elucidate the underlying mechanism for the blockade of the development of morphine analgesic tolerance by footshock and psychological stress, we examined the role of arginine vasopressin in this process. Daily pretreatment with intracerebroventricular anti-arginine vasopressin antiserum suppressed the development of tolerance to morphine. The radioimmunoassayable arginine vasopressin content was decreased in the hypothalamus but not in other regions of mouse brain after exposure to an acute footshock or psychological stress. However, this change disappeared after 5 daily repeated treatments. Neither the development of morphine tolerance nor the brain levels of arginine vasopressin were affected by exposure to forced swimming stress. Neither a single nor 5 daily treatments with morphine induced any appreciable changes in arginine vasopressin content. However, morphine in combination with footshock, lowered this content as did, be it insignificantly, the combination of morphine and psychological stress after chronic treatment. Blockade by footshock and psychological stress of the tolerance development was dose-dependently abolished by daily pretreatment with intracerebroventricular arginine vasopressin. These findings suggest that arginine vasopressin plays a critical role in the blockade, by footshock and psychological stress, of the development of analgesic tolerance to morphine.