Morphine induced analgesia is attenuated in post-partum lactating rats.
The analgesic effects of morphine administration were determined in post-partum, lactating female rats, as well as in intact, cycling females during the diestrous stage of the estrous cycle. All doses of morphine (2.5, 5 and 10 mg/kg, iv) produced a significant analgesic response in both post-partum and diestrous females using the hot water tail immersion latency test. However, the analgesic response in the post-partum females was significantly less than during diestrus at all doses tested. In addition, pretreatment with the mu 1 specific antagonist, Naloxonazine, significantly blunted the analgesic response in diestrous females, but did not significantly affect analgesia in post-partum females. These results indicate that morphine is less effective in producing analgesia in post-partum females. The mu 1 opiate receptor site does not appear to be involved in the analgesia produced during the post-partum period.
Department of Zoology, Miami University, Oxford, OH 45056.
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Janik
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Callahan
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Rabii
D000698:Analgesia; D000818:Animals; D004031:Diestrus; D005260:Female; D007275:Injections, Intravenous; D007774:Lactation / Q000502:physiology*; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D049590:Postpartum Period / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects
D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine; C034643:naloxonazine