THE ANALGESIA-ENHANCING COMPONENT OF INGESTED AMNIOTIC-FLUID DOES NOTAFFECT NICOTINE-INDUCED ANTINOCICEPTION IN NALTREXONE-TREATED RATS

Ingestion of amniotic fluid and placenta by rats has been shown to enh ance opioid-mediated antinociception but not affect the nonopioid-medi ated antinociception produced by aspirin, suggesting specificity for o pioid-mediated processes. However, enhancement by the active substance (s) in amniotic fluid and placenta (POEF, for placental opioid-enhanci ng factor) of antinociception produced by other nonopioid mechanisms h as yet to be examined. The present experiments tested whether ingestio n of amniotic fluid enhances the antinociception produced by nicotine injection. In Experiment IA, enhancement of morphine-mediated antinoci ception by ingestion of amniotic fluid was demonstrated in a hot-plate assay. In Experiment 1B, rats pretreated with naltrexone were given a n orogastric infusion of amniotic fluid or control (0.25 mi), then inj ected with nicotine (0, 0.075, 0.125, or 0.225 mg/kg subcutaneously), then tested for antinociception in a hot-plate assay. Amniotic fluid i ngestion did not enhance the antinociception produced by various doses of nicotine. In Experiment 2, rats pretreated with naltrexone were gi ven an orogastric infusion of amniotic fluid (0, 0.125, 0.25, or 0.50 mi) and then injected with 0.125 mg/kg nicotine. None of the doses of amniotic fluid enhanced the nicotine-induced antinociception. The find ings of these experiments lend support to our contention that the enha ncement by POEF of antinociception is specific to opioid-mediated proc esses. (C) 1997 Elsevier Science Inc.