Amniotic-fluid ingestion by parturient rats enhances pregnancy-mediated analgesia

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.