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in pregnant rats
Departments of 1 Physiology and Biophysics and 2 Pathology and Clinical Neurosciences, University of Calgary Health Sciences Centre, Calgary, Alberta, Canada T2N 4N1
Rats have an attenuated febrile
response to endogenous pyrogen near the term of pregnancy. Given the
fundamental role of E-series prostaglandins (PGEs) in mediating the
febrile response to blood-borne endogenous pyrogen, the present
experiments were carried out to determine whether PGEs increase in the
area surrounding the organum vasculosum laminae terminalis (peri-OVLT)
of near-term pregnant (P) rats as in nonpregnant (NP) rats after
intravenous (iv) administration of recombinant rat interleukin-1
(rrIL-1
). Core temperature was measured by telemetry and peri-OVLT
interstitial fluid was sampled in 12 NP and 12 P chronically
instrumented, Sprague-Dawley rats by microdialysis for determination of
total PGEs by radioimmunoassay. Basal core temperatures were higher in
NP compared with P rats (NP 37.9°C ± 0.5, P 36.9°C ± 0.4; P < 0.05), but basal peri-OVLT PGEs were similar
in both groups (NP 260 ± 153 pg/ml, P 278 ± 177 pg/ml;
P =not significant). Intravenous administration of rrIL-1
to NP rats produced a significant increase in core temperature with a
latency, magnitude, and duration of 10 min, 0.87°C, and at least 170 min, respectively; peri-OVLT PGEs were increased significantly by 30 min and averaged 270% above basal levels throughout the experiment. In
P rats, however, neither core temperature nor peri-OVLT PGEs increased
significantly after iv administration of rrIL-1
. Intravenous
administration of vehicle did not significantly alter core temperature
or peri-OVLT PGEs in either group of rats. Thus peri-OVLT PGEs do not
increase in P rats as they do in NP rats after iv administration of
rrIL-1
. The mechanism of this interesting component of the maternal
adaptation to pregnancy, which likely plays a major role in mediating
the attenuated febrile response to endogenous pyrogen near the term of
pregnancy, warrants further investigation.
cytokine; endogenous pyrogen; exogenous pyrogen; interleukin; microdialysis; organum vasculosum laminae terminalis
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