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