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Endogenous analgesia in the pregnant rat: an artifact of weight-dependent measures?

Authors
Type
Published Article
Journal
Brain Research
0006-8993
Publisher
Elsevier
Publication Date
Volume
373
Issue
1-2
Pages
316–323
Identifiers
PMID: 3719314
Source
Medline
License
Unknown

Abstract

It has been reported that pregnancy produces an opioid-mediated, endogenous analgesia in the rat. In an attempt to confirm this finding, we used 5 different analgesic measures to compare the responsiveness of pregnant and non-pregnant female rats to painful stimuli. Pregnant and non-pregnant rats differed only when assessed by measures that were highly correlated with body weight. Furthermore, the reduced pain responsiveness of pregnant rats was not prevented by administration of the opioid antagonists, naloxone or naltrexone. We can find no evidence for an endogenous analgesia of pregnancy; instead, our results suggest that findings of a diminished response to painful stimuli in pregnant rats may be an artifact related to the greater body mass/weight of the pregnant animals.

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