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Department of Physiology and Biophysics, Health Sciences Centre, University of Calgary, Calgary, Alberta, Canada T2N 4N1
Received 20 May 1996; accepted in final form 18 December 1996.
Eliason, Heather L., and James E. Fewell. Influence of
pregnancy on the febrile response to ICV administration of
PGE1 in rats studied in a
thermocline. J. Appl. Physiol. 82(5):
1453-1458, 1997.
Rats near term of pregnancy have an attenuated
febrile response to intracerebroventricular (ICV) injection of
prostaglandin E1 (PGE1) when they are studied at
an ambient temperature below their thermoneutral zone. Given that
nonshivering thermogenesis in brown adipose tissue is impaired in
rodents near term of pregnancy, it is possible that the attenuated
febrile response is forced by impairment of this component of the
autonomic thermoregulatory response. If this were the case, then
near-term pregnant rats should develop a "normal" fever after
PGE1 administration if they were
studied in a thermocline where they could utilize behavioral as well as
autonomic thermoregulatory effectors to increase their body core
temperature (Tbc). Experiments
were, therefore, carried out on 13 nonpregnant and 14 pregnant
chronically instrumented rats in a thermocline (temperature gradient
10-40°C) to investigate their
Tbc responses to ICV injection of
PGE1. ICV injection of 0.2 µg
PGE1 produced significant
increases in Tbc and fever index in both nonpregnant and pregnant animals (day
19 of gestation); the increases, however, were
significantly attenuated in the pregnant compared with the nonpregnant
rats. Behavioral (e.g., selected ambient temperature) and autonomic
(e.g., oxygen consumption) thermoregulatory effectors were activated to
increase Tbc after ICV
PGE1 in both groups of animals,
but the duration of activation was shortened in pregnant compared with
nonpregnant rats. The abbreviated thermoregulatory effector responses
and the resulting attenuated febrile response to
PGE1 in the pregnant rats may have resulted from a pregnancy-related activation of an endogenous antipyretic system.
autonomic thermoregulation; behavioral thermoregulation; endogenous pyrogen; exogenous pyrogen; fever; prostaglandin; intracerebroventricular
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