Amniotic fluid and placenta contain a substance (POEF, for Placental Opioid-Enhancing Factor) that, when ingested, enhances opioid-mediated analgesia in nonpregnant rats; ingestion of the substance by rats not experiencing opioid-mediated analgesia, however, does not produce analgesia. It is highly likely that periparturitional analgesia-enhancement is a significant benefit of ingestion of the afterbirth (placentophagia) during delivery. Here we report that prepartum ingestion of amniotic fluid (via orogastric infusion) does indeed enhance the endogenous-opioid-mediated analgesia evident at the end of pregnancy and during delivery; that the degree of enhancement is greater with 0.75 ml than with 0.25 ml; and that the prepartum enhancement of analgesia can be blocked with the opioid antagonist naloxone.
fluid ingestion enhances the central analgesic effect of morphine. BRAIN RES BULL 26(6) 851-855, 1991.-Amniotic fluid and placenta contain a substance (POEF) that when in gested enhances opioid-mediated analgesia produced by several agents (morphine injection, vaginal/cervical stimulation, late preg nancy, footshock) , but not that produced by aspirin injection. The present series of experiments employed quaternary naltrexone, an opioid antagonist that does not readily cross the blood-brain barrier, in conjunction with either peripheral or central administra tion of morphine, to determine whether amniotic-fluid ingestion (and therefore POEF ingestion) enhances opioid-mediated analge sia by affecting the central and/or peripheral actions of morphine. The results suggest that POEF affects only the central analgesic effects of morphine.
PHA RM ACOL BlOCH FM HEHA Y 511( I) 147-15 I. IlJ'I7.-lngestion of ;1I1111iotic fluid and placenta by rats h;ls been shown to enh;lllce opioid-mediated ,Intinociception but not arrect the nonopioid-mediated antinociception pl'llduced bv aspirin. su~ csting spccificity for opioid-mediated proccsses. Ilowcver. enhanccment hy the active substancc(s) in amniotic fluid and pia cc'nta (POEF. for placental o[Jioid-enhancing factor) of antinociception produced bv other nonopioidmech,lllisms 1m.. yet to be examine'll. Thc present experiments tested whether ingestion of amniotic fluid enlwnees thc antinociecption produced by nicotine injection. In ExperimLOnt I A. LOnhancelllent of morphine-mediated antinociception by ingestionl>f amniotic fluid W;h den]()nstrared in ,I hot-plate assay. In Experiment I B. rats prdreated with naltrexone werc given an orogastric infusion of amniotic fluid m contl'lll (0.25 ml). then injected with nicotine (0.0.075.0.125, or 0.225 mglkg subcut'lncously). then tested for antinocicc'ption in a hot-pl;lte 'ISS;ly. Amniotic fluid ingestion did not enhance the antinociccption produccd by v;nious doscs of nicotinLO. In Expcrimcnt 2. rats pretrcated with naltrcxone were given an orogaslric infusion of amniotic fluid (0.0.125. 11.25. or 0.50 ml) ;\Ild then injcctcd with n.125 m~lk~ nicotinc. None of the doscs of amniotic fluid enhanced thc nicotinc induccd <1n1 inocicept ion. Thc'findings of these expcr;'illents lend support 10 our contcntion that thc enhancemcnt bv POEF of
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