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

Placentophagia and the Tao of POEF

Placentophagia, ingestion of placenta and amniotic fluid, usually during parturition, is a behavioral feature of nearly all nonaquatic, placental mammals, and is a nexus for several interlocking behavioral phenomena. Placentophagia has not been typical of human cultures, but in recent years, some women in affluent societies have engaged in it, thereby bringing publicity to the behavior. First, we summarized benefits of placentophagia for nonhuman mammals, which include increased attractiveness of neonates, enhanced onset of maternal behavior, suppression of pseudopregnancy, and enhancement of opioid hypoalgesia by Placental Opioid-Enhancing Factor (POEF), a benefit that may extend well outside the context of parturition. The research on POEF in animals was discussed in detail. Then we discussed placentophagia (placentophagy) in humans, and whether there is validity to the claims of various benefits reported primarily in the pro-placentophagy literature, and, although human afterbirth shows POEF activity, the POEF effect has not yet been tested in humans. Finally, we discussed the general possible implications, for the management of pain and addiction, of isolating and characterizing POEF.

Peripartum effects of synthetic oxytocin: The good, the bad, and the unknown

The first clinical applications of oxytocin (OT) were in obstetrics as a hormone to start and speed up labor and to control postpartum hemorrhage. Discoveries in the 1960s and 1970s revealed that the effects of OT are not limited to its peripheral actions around birth and milk ejection. Indeed, OT also acts as a neuromodulator in the brain affecting fear memory, social attachment, and other forms of social behaviors. The peripheral and central effects of OT have been separately subject to extensive scrutiny. However, the effects of peripheral OT-particularly in the form of administration of synthetic OT (synOT) around birth-on the central nervous system are surprisingly understudied. Here, we provide a narrative review of the current evidence, suggest putative mechanisms of synOT action, and provide new directions and hypotheses for future studies to bridge the gaps between neuroscience, obstetrics, and psychiatry.

Consumption of Maternal Placenta in Humans and Nonhuman Mammals: Beneficial and Adverse Effects

Placentophagia is a common mammalian behavior, and the first scientific study of the potential effects of human maternal placentophagia on lactation was in 1917. More recently, in the 1970s, human placentophagia was reported in North America with a trend toward increased consumption. There are different hypotheses about the women and nonhuman mammals' motivation towards placentophagia, but few have been subject to hypotheses testing. In women, the controversy continues; on the one hand, researchers attribute benefits like increased breast milk, weight gain in newborns, decreased postpartum depression and fatigue, and improved mothers' mood. In contrast, bacterial or viral infections, hormonal, or trace elements that could become toxic for both the mother and baby are reported as possible health risks. Other reports argue a lack of scientific rigor to support the self-reported benefits of placentophagia. Also, the way the placenta is prepared (raw, cooked, dehydrated, processed, or encapsulated) alters its components, and thus the desired effects. This review provides relevant information and the different hypotheses and points of view around placentophagia. However, there are still questions to be resolved, and more studies are needed to confirm or reject the data generated so far about placentophagia in humans and nonhuman mammals.

Amniotic-fluid ingestion enhances central δ-opioid-induced hypoalgesia in rats in the cold-water tail-flick assay in a repeated-measures design

Placental Opioid Enhancing Factor (POEF) is found in amniotic fluid (AF) and placenta. When ingested, it enhances opioid-mediated pain relief. Our laboratory has shown that ingestion of AF specifically enhances the hypoalgesia associated with δ-opioid receptor activation in the brain. The specific biochemical compound in AF responsible for the enhancement of δ-opioid activity is of great interest as an analgesic adjunct for pain but is unknown at this time. Research efforts to isolate and characterize this biochemical compound are hampered by the lack of an algesiometric assay that allows repeated measurement of pain threshold and repeated exposure to δ-opioid receptor activation. The cold water tail-flick assay (CWTF) may be a sensitive and reliable pain threshold test of (a) all species of opioids that is (b) not subject to repeated-testing effects. Therefore the CWTF test is potentially ideal for the study of δ opioid systems in a repeated measures design. Here, we confirm these attributes of the CWTF test, and determined that (a) there are no repeated-exposure effects associated with the CWTF assay; (b) there are no repeated-exposure effects associated with repeated central injections of DPDPE ([D-Pen2,D-Pen5]-Enkephalin, a selective δ-opioid agonist) as measured by the CWTF assay; and (c) ingestion of AF in conjunction with a central injection of DPDPE produced the same hypoalgesic enhancement as previously found using another assay.

Human placentophagy: a review

Placentophagy or placentophagia, the postpartum ingestion of the placenta, is widespread among mammals; however, no contemporary human culture incorporates eating placenta postpartum as part of its traditions. At present, there is an increasing interest in placentophagy among postpartum women, especially in the United States. The placenta can be eaten raw, cooked, roasted, dehydrated, or encapsulated or through smoothies and tinctures. The most frequently used preparation appears to be placenta encapsulation after steaming and dehydration. Numerous companies offer to prepare the placenta for consumption, although the evidence for positive effects of human placentophagy is anecdotal and limited to self-reported surveys. Without any scientific evidence, individuals promoting placentophagy, especially in the form of placenta encapsulation, claim that it is associated with certain physical and psychosocial benefits. We found that there is no scientific evidence of any clinical benefit of placentophagy among humans, and no placental nutrients and hormones are retained in sufficient amounts after placenta encapsulation to be potentially helpful to the mother postpartum. In contrast to the belief of clinical benefits associated with human placentophagy, the Centers for Disease Control and Prevention recently issued a warning due to a case in which a newborn infant developed recurrent neonatal group B Streptococcus sepsis after the mother ingested contaminated placenta capsules containing Streptococcus agalactiae. The Centers for Disease Control and Prevention recommended that the intake of placenta capsules should be avoided owing to inadequate eradication of infectious pathogens during the encapsulation process. Therefore, in response to a woman who expresses an interest in placentophagy, physicians should inform her about the reported risks and the absence of clinical benefits associated with the ingestion. In addition, clinicians should inquire regarding a history of placenta ingestion in cases of postpartum maternal or neonatal infections such as group B Streptococcus sepsis. In conclusion, there is no professional responsibility on clinicians to offer placentophagy to pregnant women. Moreover, because placentophagy is potentially harmful with no documented benefit, counseling women should be directive: physicians should discourage this practice. Health care organizations should develop clear clinical guidelines to implement a scientific and professional approach to human placentophagy.

Placentophagy: therapeutic miracle or myth?

Postpartum women are consuming their placentas encapsulated, cooked, and raw for the prevention of postpartum depression (PPD), pain relief, and other health benefits. Placentophagy is supported by health advocates who assert that the placenta retains hormones and nutrients that are beneficial to the mother. A computerized search was conducted using PubMed, Medline Ovid, and PsychINFO between January 1950 and January 2014. Keywords included placentophagy, placentophagia, maternal placentophagia, maternal placentophagy, human placentophagia, and human placentophagy. A total of 49 articles were identified. Empirical studies of human or animal consumption of human placentas were included. Editorial commentaries were excluded. Animal placentophagy studies were chosen based on their relevance to human practice. Ten articles (four human, six animal) were selected for inclusion. A minority of women in developed countries perceive placentophagy to reduce PPD risk and enhance recovery. Experimental animal research in support of pain reduction has not been applied in humans. Studies investigating placenta consumption for facilitating uterine contraction, resumption of normal cyclic estrogen cycle, and milk production are inconclusive. The health benefits and risks of placentophagy require further investigation of the retained contents of raw, cooked, and encapsulated placenta and its effects on the postpartum woman.

Placentophagia in humans and nonhuman mammals: causes and consequences

Afterbirth ingestion by nonhuman mammalian mothers has a number of benefits: (1) increasing the interaction between the mother and infant; (2) potentiating pregnancy-mediated analgesia in the delivering mother; (3) potentiating maternal brain opioid circuits that facilitate the onset of caretaking behavior; and (4) suppressing postpartum pseudopregnancy. Childbirth is fraught with additional problems for which there are no practical nonhuman animal models: postpartum depression, failure to bond, hostility toward infants. Ingested afterbirth may contain components that ameliorate these problems, but the issue has not been tested empirically. The results of such studies, if positive, will be medically relevant. If negative, speculations and recommendations will persist, as it is not possible to prove the negative. A more challenging anthropological question is "why don't humans engage in placentophagia as a biological imperative?" Is it possible that there is more adaptive advantage in not doing so?

Effect of amniotic-fluid ingestion on vaginal-cervical-stimulation-induced Fos expression in female rats during estrus

Placental Opioid-Enhancing Factor (POEF) is a substance found in amniotic fluid (AF) that, when ingested, potentiates opioid-mediated, but not non-opioid-mediated, hypoalgesia. Vaginal-cervical stimulation (VCS) produces a stimulus-bound, partially opioid-mediated hypoalgesia that previous research has shown to be potentiated by AF ingestion. To understand the mechanism of opioid enhancement by POEF we investigated the pattern of neural activation after a bout of VCS that produced hypoalgesia, with and without co-administration of AF. Specifically, virgin Long-Evans rats showing vaginal estrus were handled briefly (control) or received VCS (75g pressure, 1 min), in a pattern that approximated early parturition rather than copulation, using a spring-loaded glass-rod probe. Rats were given an orogastric infusion (0.25 ml) of either AF or 0.9% saline resulting in four groups (VCS or handling; AF or saline). Rats were perfused 90 min after treatment and tissue was processed by immunohistochemistry for Fos. The number of Fos-immunoreactive cells was counted in structures previously shown to express Fos in response to VCS (the medial preoptic area, MPOA; the ventrolateral portion of the ventromedial hypothalamic nucleus, vlVMH; the arcuate nucleus, ARC). We found that this pattern of VCS did not produce a significant increase in Fos expression in the MPOA and vlVMH unless it was paired with AF. VCS produced a significant increase in Fos in the ARC. The interaction of AF and VCS on Fos expression in the MPOA suggests that POEF may enhance vaginal-cervical sensory input at parturition to facilitate sensitization of the MPOA, and presumably facilitate maternal-behavior onset.

Ingestion of amniotic fluid enhances the facilitative effect of VTA morphine on the onset of maternal behavior in virgin rats

Previous research has shown that injection of morphine into the ventral tegmental area (VTA) facilitates the onset of maternal behavior in virgin female rats, and injection of the opioid antagonist naltrexone into the VTA disrupts the onset of maternal behavior in parturient rats. Placentophagia -- ingestion of placenta and amniotic fluid, usually at parturition -- modifies central opioid processes. Ingestion of the active substance in placenta and amniotic fluid, Placental Opioid-Enhancing Factor (POEF), enhances the hypoalgesic effect of centrally administered morphine, and more specifically, enhances delta- and kappa-opioid-receptor-mediated hypoalgesia and attenuates mu-opioid-receptor-mediated hypoalgesia. POEF (in placenta or amniotic fluid) ingestion does not, by itself, produce hypoalgesia. In the present study, we tested the hypothesis that ingestion of amniotic fluid enhances the facilitative effect of opioid activity (unilateral morphine injection) in the VTA on the rate of onset of maternal behavior. Virgin female Long-Evans rats were given one intra-VTA injection of morphine sulfate (0.0, 0.01, or 0.03 microg, in saline) and an orogastric infusion of 0.25 ml amniotic fluid or saline once each day of the first three days of the 10-day testing period. Subjects were continuously exposed to foster pups that were replaced every 12 h; replacement of pups was followed by a 15-min observation period. Maternal behavior latency was determined by the first of two consecutive tests wherein the subject displayed pup retrieval, pup licking in the nest, and crouching over all foster pups, during the 15-min observation. We confirmed the previous finding that the VTA injection, alone, of 0.03 microg morphine shortened the latency to show maternal behavior and that 0.0 microg and 0.01 microg morphine did not. Ingestion of amniotic fluid (and therefore POEF) facilitated the onset of maternal behavior in rats receiving an intra-VTA microinjection of an otherwise subthreshold dose of morphine (0.01 microg).

In uniparentalPhodopus sungorus, new mothers, and fathers present during the birth of their offspring, are the only hamsters that readily consume fresh placenta

Placentophagia is common among parturient female mammals but non-parturient females generally refuse placenta. Biparental male dwarf hamsters (Phodopus campbelli) readily consume placenta. The present study quantified placentophagia and liver acceptance in the closely related Siberian hamster P. sungorus in which males do not participate in the birth and are not responsive to a displaced pup. Sexually naïve P. sungorus males and females refused both placenta and liver (all groups <10%). Reproductive females specifically consumed placenta on the day before (G17), and the day of, parturition (G18) (>80%). Males rejected both tissues on G17 and accepted placenta soon after the birth (G18) (80%) only if they were present during the birth. Palatability of the placenta was not responsible for the species difference as P. campbelli accepted P. sungorus placenta. Results are consistent with a neophobic reaction to both placenta (conspecific or heterospecific) and liver as P. sungorus also rejected P. campbelli placenta.

Amniotic fluid: not just fetal urine anymore

Amniotic fluid (AF) is a complex substance essential to fetal well-being. This article reviews recent discoveries and the current understanding of the origin and circulation of AF and its nutritive, protective, and diagnostic functions. Future directions for AF research are also discussed.

Placentophagia in naïve adults, new fathers, and new mothers in the biparental dwarf hamster,Phodopus campbelli

Placentophagia in mammals typically occurs only in females during the birth. Male hamsters, Phodopus campbelli, with an extensive paternal behavior repertoire eat placenta during the birth and as alloparental juveniles. Two fresh placentae were presented to sexually naïve males and females covering the developmental range from puberty through reproductive maturity and into senescence. Expectant parents and new mothers were also tested. Placentophagia occurred in both sexes at all developmental stages and was higher in reproductive than in naïve hamsters. Placentophagia declined with increasing age in females, but not males. Liver was readily accepted, but acceptance did not decline with age in females, and was not low in juvenile males, confirming that animals distinguished between the two tissues. Senescent females consumed both tissues willingly. In these paternal males, which do not experience pregnancy or parturition, and in naïve females that selectively refuse placenta, the stimuli influencing placentophagia remain unknown.

Ingested placenta blocks the effect of morphine on gut transit in Long–Evans rats

Opioids produce antinociception, and ingested placenta or amniotic fluid modifies that antinociception. More specifically, ingested placenta enhances the antinociception produced by selective activation of central kappa-opioid or delta-opioid receptors but attenuates that produced by activation of central mu-opioid receptors. Opioids also slow gut transit by acting on central or peripheral mu-opioid receptors. Therefore, we hypothesized that ingested placenta would reverse the slowing of gut transit that is produced by morphine, a preferential mu-opioid-receptor agonist. Rats were injected with morphine either centrally or systemically and fed placenta, after which gastrointestinal transit was evaluated. We report here that ingested placenta reversed the slowing of gut transit produced by centrally administered morphine but did not affect the slowing of gut transit produced by systemically administered morphine. These results suggest another likely consequence of placentophagia at parturition in mammals--reversal of opioid-mediated, pregnancy-based disruption of gastrointestinal function--as well as an important consideration in opioid-based treatments for pain in humans--enhancement of desirable effects with attenuation of adverse effects.

Placenta ingestion by rats enhances δ- and κ-opioid antinociception, but suppresses μ-opioid antinociception

Ingestion of placenta or amniotic fluid produces a dramatic enhancement of centrally mediated opioid antinociception in the rat. The present experiments investigated the role of each opioid receptor type (mu, delta, kappa) in the antinociception-modulating effects of Placental Opioid-Enhancing Factor (POEF-presumably the active substance). Antinociception was measured on a 52 degrees C hotplate in adult, female rats after they ingested placenta or control substance (1.0 g) and after they received an intracerebroventricular injection of a delta-specific ([D-Pen2,D-Pen5]enkephalin (DPDPE); 0, 30, 50, 62, or 70 nmol), mu-specific ([D-Ala2,N-MePhe4,Gly5-ol]enkephalin (DAMGO); 0, 0.21, 0.29, or 0.39 nmol), or kappa-specific (U-62066; spiradoline; 0, 100, 150, or 200 nmol) opioid receptor agonist. The results showed that ingestion of placenta potentiated delta- and kappa-opioid antinociception, but attenuated mu-opioid antinociception. This finding of POEF action as both opioid receptor-specific and complex provides an important basis for understanding the intrinsic pain-suppression mechanisms that are activated during parturition and modified by placentophagia, and important information for the possible use of POEF as an adjunct to opioids in pain management.

Placentophagia in rabbits: incidence across the reproductive cycle

Rabbits show placentophagia at parturition, but the regulation of this behavior and its incidence across the reproductive cycle are unknown. By testing estrous, midpregnant, prepartum (day 1), and postpartum (days 1 and 5) food-deprived rabbits with liver and placenta, we found an absence or infrequency (<%) of placentophagia in the former three groups, an invariable occurrence at parturition, and a persistence into postpartum days 1 and 5 (50 and 48%, respectively). Most placentophagic females also ate liver on postpartum day 1, but not on postpartum day 5. In different food-deprived rabbits, tested every 2 hr with placenta and food pellets, placentophagia incidence was 20% at 8 hr prepartum, 100% at parturition, and 67 and 21% at 8 and 24 hr postpartum, respectively. Most placentophagic rabbits also ate food pellets in postpartum (but not in prepartum) tests. Results suggest that somatosensory, hormonal, or both factors of the peripartum period regulate placentophagia expression.

Ingested bovine amniotic fluid enhances morphine antinociception in rats

Ingestion by rats of rat placenta or amniotic fluid enhances opioid-mediated, or partly opioid-mediated, antinociception produced by morphine injection, vaginal or cervical stimulation, late pregnancy, and foot shock. This phenomenon is believed to be produced by a placental opioid-enhancing factor (POEF). Ingestion by rats of human or dolphin placenta has also been shown to enhance opioid antinociception, suggesting that POEF may be common to many mammalian species. We tested bovine amniotic fluid (BAF) for its capacity to enhance morphine antinociception in female Long-Evans rats, as determined by percentage change from baseline tail-flick latency in response to radiant heat, and we report that 0.50 mL BAF effectively enhanced morphine antinociception but did not by itself produce antinociception. The efficacy of POEF across species suggests that POEF may have been functionally (and structurally) conserved during evolution. Furthermore, the availability of POEF at parturition, as well as its ability to enhance pregnancy-mediated antinociception without disrupting maternal behavior, offers a tenable explanation for the long-debated ultimate causality of placentophagia.

The analgesia-enhancing component of ingested amniotic fluid does not affect nicotine-induced antinociception in naltrexone-treated rats

Ingestion of amniotic fluid and placenta by rats has been shown to enhance opioid-mediated antinociception but not affect the nonopioid-mediated antinociception produced by aspirin, suggesting specificity for opioid-mediated processes. However, enhancement by the active substance(s) in amniotic fluid and placenta (POEF, for placental opioid-enhancing factor) of antinociception produced by other nonopioid mechanisms has yet to be examined. The present experiments tested whether ingestion of amniotic fluid enhances the antinociception produced by nicotine injection. In Experiment 1A, enhancement of morphine-mediated antinociception by ingestion of amniotic fluid was demonstrated in a hot-plate assay. In Experiment 1B, rats pretreated with naltrexone were given an orogastric infusion of amniotic fluid or control (0.25 ml), then injected with nicotine (0, 0.075, 0.125, or 0.225 mg/kg subcutaneously), then tested for antinociception in a hot-plate assay. Amniotic fluid ingestion did not enhance the antinociception produced by various doses of nicotine. In Experiment 2, rats pretreated with naltrexone were given an orogastric infusion of amniotic fluid (0, 0.125, 0.25, or 0.50 ml) and then injected with 0.125 mg/kg nicotine. None of the doses of amniotic fluid enhanced the nicotine-induced antinociception. The findings of these experiments lend support to our contention that the enhancement by POEF of antinociception is specific to opioid-mediated processes.

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.

Blockade of digestion by famotidine pretreatment does not interfere with the opioid-enhancing effect of ingested amniotic fluid

Ingestion of placenta or amniotic fluid by rats has been shown to enhance ongoing opioid-mediated antinociception, but does not, by itself, produce antinociception. This enhancement is produced by an active substance(s) in placenta and amniotic fluid that we have termed POEF for placental opioid-enhancing factor. Previous research has shown that enhancement requires mediation by the gastrointestinal system: gastric vagotomy blocks enhancement produced by ingested placenta; amniotic fluid injected SC or IP does not produce enhancement. The present study was designed to distinguish between two possible explanations for the blockade of the POEF effect produced by gastric vagotomy: that afferent information arising in vagal gastric receptors conveys the critical information to the CNS, or that disruption of vagal efferent action on digestion blocks the manufacture or activation of the POEF molecule in the gut. Famotidine is an H2-histamine receptor antagonist that reduces gastric acid and pepsin secretion to an extent at least as great as gastric vagotomy. Rats treated with either famotidine or a vehicle were fed placenta or a control substance, then stimulated with vaginal/cervical probing to produce antinociception that is partly opioid mediated. Famotidine did not block POEF enhancement of vaginal/cervical stimulation-induced analgesia in a tail flick latency test. These results suggest that enhancement by POEF does not require normal digestive processes or other processes inhibited by famotidine.

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

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.

Enhancement of opioid-mediated analgesia: a solution to the enigma of placentophagia

Two major consequences of placentophagia, the ingestion of afterbirth materials that occurs usually during mammalian parturition, have been uncovered in the past several years. The first is that increased contact, associated with ingesting placenta and amniotic fluid from the surface of the young, causes an accelerated onset of maternal behavior toward those young. The second, which probably has importance for a broader range of mammalian taxa than the first, is that ingestion of afterbirth materials produces enhancement of ongoing opioid-mediated analgesia. The active substance in placenta and amniotic fluid has been named POEF, for Placental Opioid-Enhancing Factor. Recent research on both consequences is summarized, with particular attention to POEF, the generalizability of the enhancement phenomenon, its locus and mode of action, and its significance for new approaches to the management of pain and addiction.