Amniotic Fluid Ingestion Enhances\ud Opioid-Mediated But Not\ud Nonopioid-Mediated Analgesia

Ingestion of amniotic fluid or placenta by rats has been shown to enhance several types of opioid-mediated analgesia: that induced by morphine, footshock, vaginal/cervical stimulation, and late pregnancy. This enhancement has also been blocked by administration of opioid antagonists. The present study was designed to examine further the specificity of the enhancement effect for opioid-mediated analgesia by testing for enhancement following administration of aspirin, a nonopioid analgesic. The formalin test was used as the pain threshold assay. Amniotic fluid or beef bouillon was administered by orogastric tube to rats that were treated either with morphine sulfate or saline. or pretreated with naltrexone, then treated with aspirin or vehicle. Both morphine and aspirin treatments produced analgesia. Amniotic fluid significantly enhanced the analgesia produced by morphine, but did not enhance the analgesia produced by aspirin, further suggesting that the enhancing effect of amniotic fluid ingestion is specific for opioid-mediated analgesia, such as that existing at the start of parturition

Gastric vagotomy blocks opioid analgesia enhancement produced by placenta ingestion

Ingestion of amniotic fluid or placenta by rats has been shown to enhance opioid-mediated analgesia induced by morphine injection, footshock, vaginal/cervical stimulation, or late pregnancy. This enhancement by ingestion appears to be specific to the central actions of opioids. The present study was designed to examine the possibility that information traveling via the vagus nerve might be involved in mediating this effect. Rats that had undergone either selective gastric vagotomy or sham vagotomy were injected with either morphine sulfate or vehicle and fed either placenta or a meat control. Enhancement was observed in rats that had undergone sham vagotomy but not in those that had undergone gastric vagotomy. These results support an interpretation of vagal involvement in the enhancement of opioid-mediated analgesia by placenta

Placental opioid-enhancing factor (POEF): Generalizability of effects

A substance in amniotic fluid and placenta (POEF for Placental Opioid-Enhancing Factor) has been shown to enhance opiate- or opioid-mediated analgesia in rats. Recent studies have only touched on the generalizability of the phenomenon. The present studies further tested the generalizability of the POEF effect: they examined sex specificity of the mechanism, whether POEF activity exists in afterbirth material of species other than the rat; whether POEF activity exists in tissue other than afterbirth material; whether POEF activity could be demonstrated after injection rather than ingestion of afterbirth material; and whether POEF enhances all opioid-mediated phenomena. We found that (a) POEF is effective in male rats as well as in female rats; (b) POEF activity exists in human and dolphin afterbirth material; (c) ingestion of pregnant-rat liver does not produce enhancement of opioid-mediated analgesia; (d) POEF does not seem to be effective when amniotic fluid is injected either IPO or SC; and (e) POEF does not modify morphine-induced hyperthermia

Ingestion of amniotic fluid by postpartum rats enhances morphine antinociception without liability to maternal behavior

Ingestion of amniotic fluid or placenta by rats has been shown to enhance opioid-mediated analgesia induced by morphine injection, foot shock, vaginal/cervical stimulation, or late pregnancy. The present study was designed to determine whether this mechanism might be a means of providing greater analgesia during the periparturitional period without contributing to the disruption of maternal behavior (measured primarily as retrieval) that can result from excessive opioid levels. Postpartum primiparous rats, injected with either 2 or 3 mg/kg morphine sulfate or vehicle and given orogastric infusions of either amniotic fluid or saline, were tested for maternal behavior. Pain threshold (determined by tail-flick latency test) in rats injected with 2 mg/kg morphine and infused with amniotic fluid was elevated to a level that did not differ significantly from that of a separate group of rats injected with 3 mg/kg morphine and infused with saline. This enhanced analgesia was not, however, accompanied by the significant disruption of maternal behavior found among the rats receiving the higher morphine dose