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

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.

The placenta as a target of opioid drugs†

Opioid drugs are analgesics increasingly being prescribed to control pain associated with a wide range of causes. Usage of pregnant women has dramatically increased in the past decades. Neonates born to these women are at risk for neonatal abstinence syndrome (also referred to as neonatal opioid withdrawal syndrome). Negative birth outcomes linked with maternal opioid use disorder include compromised fetal growth, premature birth, reduced birthweight, and congenital defects. Such infants require lengthier hospital stays necessitating rising health care costs, and they are at greater risk for neurobehavioral and other diseases. Thus, it is essential to understand the genesis of such disorders. As the primary communication organ between mother and conceptus, the placenta itself is susceptible to opioid effects but may be key to understanding how these drugs affect long-term offspring health and potential avenue to prevent later diseases. In this review, we will consider the evidence that placental responses are regulated through an endogenous opioid system. However, maternal consumption of opioid drugs can also bind and act through opioid receptors express by trophoblast cells of the placenta. Thus, we will also discuss the current human and rodent studies that have examined the effects of opioids on the placenta. These drugs might affect placental hormones associated with maternal recognition of pregnancy, including placental lactogens and human chorionic gonadotropin in rodents and humans, respectively. A further understanding of how such drugs affect the placenta may open up new avenues for early diagnostic and remediation approaches.

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.

Perspectives from Patients and Healthcare Providers on the Practice of Maternal Placentophagy

PURPOSE

Placentophagy (maternal consumption of the placenta) has become increasingly prevalent in the past decade among women seeking to promote health and healing during the postpartum period. The purpose of this study was to assess patient and provider familiarity with and attitudes toward placentophagy, as well as patients' willingness to try placentophagy.

METHODS

Two cross-sectional surveys with questions regarding placentophagy practice were distributed to healthcare providers and patients. The provider survey was distributed via email listservers to international perinatal professional organizations and to obstetrics and gynecology, nurse midwifery, family medicine, and psychiatry departments at three urban hospitals. Patient surveys were administered in person at an urban hospital in Chicago, Illinois.

RESULTS

Approximately two thirds (66%; n = 100) of patients and most (89%; n = 161) of providers were familiar with placentophagy. Patients with a history of a self-reported mental health disorder were more likely to be willing to consider placentophagy and to believe that healthcare providers should discuss it with their patients.

CONCLUSIONS

Most providers and patients have heard of placentophagy but are unsure of its benefits and/or risks. Further research examining the potential therapeutic efficacy and/or risks of placentophagy is needed.

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.

Exposure to ethanol on prenatal days 19-20 increases ethanol intake and palatability in the infant rat: involvement of kappa and mu opioid receptors

Prenatal exposure to ethanol on gestation Days 19-20, but not 17-18, increases ethanol acceptance in infant rats. This effect seems to be a conditioned response acquired prenatally, mediated by the opioid system, which could be stimulated by ethanol's pharmacological properties (mu-opioid receptors) or by a component of the amniotic fluid from gestation-day 20 (kappa-inducing factor). The latter option was evaluated administering non-ethanol chemosensory stimuli on gestation Days 19-20 and testing postnatal intake and palatability. However, prenatal exposure to anise or vanilla increased neither intake nor palatability of these tastants on postnatal Day 14. In experiment 2, the role of ethanol's pharmacological effect was tested by administering ethanol and selective antagonists of mu and kappa opioid receptors prenatally. Blocking the mu-opioid receptor system completely reversed the effects on intake and palatability, while antagonizing kappa receptors only partially reduced the effects on palatability. This suggests that the pharmacological effect of ethanol on the fetal mu opioid system is the appetitive reinforcer, which induces the prenatally conditioned preference detected in the preweanling period.

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?

In search of human placentophagy: a cross-cultural survey of human placenta consumption, disposal practices, and cultural beliefs

Maternal placentophagy, the consumption of the placenta or "afterbirth" by the mother following parturition, is an ubiquitous behavior among eutherian mammals, including non-human primates. Here we report on a cross-cultural survey of 179 human societies regarding the consumption, treatment, and disposal of human placenta, in addition to accompanying cultural beliefs and perceptions about the organ. The conspicuous absence of cultural traditions associated with maternal placentophagy in the cross-cultural ethnographic record raises interesting questions relative to its ubiquitous presence among nearly all other mammals, and the reasons for its absence (or extreme rarity) among prehistoric/historic and contemporary human cultures.

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.

Opioid and progesterone signaling is obligatory for early human embryogenesis

The growth factors that drive the division and differentiation of stem cells during early human embryogenesis are unknown. The secretion of endorphins, progesterone (P(4)), human chorionic gonadotropin, 17beta-estradiol, and gonadotropin-releasing hormone by trophoblasts that lie adjacent to the embryoblast in the blastocyst suggests that these pregnancy-associated factors may directly signal the growth and development of the embryoblast. To test this hypothesis, we treated embryoblast-derived human embryonic stem cells (hESCs) with ICI 174,864, a delta-opioid receptor antagonist, and RU-486 (mifepristone), a P(4) receptor competitive antagonist. Both antagonists potently inhibited the differentiation of hESC into embryoid bodies, an in vitro structure akin to the blastocyst containing all three germ layers. Furthermore, these agents prevented the differentiation of hESC aggregates into columnar neuroectodermal cells and their organization into neural tube-like rosettes as determined morphologically. Immunoblot analyses confirmed the obligatory role of these hormones; both antagonists inhibited nestin expression, an early marker of neural precursor cells normally detected during rosette formation. Conversely, addition of P(4) to hESC aggregates induced nestin expression and the formation of neuroectodermal rosettes. These results demonstrate that trophoblast-associated hormones induce blastulation and neurulation during early human embryogenesis.

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).

Roles of different subtypes of opioid receptors in mediating the ventrolateral orbital cortex opioid-induced inhibition of mirror-neuropathic pain in the rat

Previous studies have demonstrated that opioid receptors in the prefrontal ventrolateral orbital cortex (VLO) are involved in anti-nociception. The aim of this current study was to examine whether opioid receptors in the VLO have effects on the hypersensitivity induced by contralateral L5 and L6 spinal nerve ligation (SNL), termed as mirror neuropathic pain (MNP) in the male rat. Morphine (1.0, 2.5, 5.0 microg) microinjected into the VLO contralateral to the SNL depressed the mechanical paw withdrawal assessed by von Frey filaments and the cold plate (4 degrees C)-induced paw lifting in a dose-dependent manner on the side without SNL. These effects were antagonized by microinjection of the non-selective opioid receptor antagonist naloxone (1.0 mug) into the same VLO site. Microinjection of endomorphin-1 (5.0 microg), a highly selective mu-opioid receptor agonist, and [d-Ala(2), d-Leu(5)]-enkephalin (DADLE, 10 microg), a delta-/mu-receptor agonist, also depressed the MNP. The effects of both drugs were blocked by selective mu-receptor antagonist beta-funaltrexamine (beta-FNA, 3.75 microg), but the effect of the DADLE was not influenced by the selective delta-receptor antagonist naltrindole (5.0 microg). Microinjection of the kappa-opioid receptor agonist spiradoline mesylate salt (U-62066) (100 microg) had no effect on the MNP. These results suggest that the VLO is involved in opioid-induced inhibition of the MNP and the effect is mediated by mu- (but not delta- and kappa-) opioid receptors.

μ- but not δ- and κ-opioid receptors in the ventrolateral orbital cortex mediate opioid-induced antiallodynia in a rat neuropathic pain model

Previous studies have indicated that the ventrolateral orbital cortex (VLO) is involved in opioid-mediated antinociception in the tail flick test and formalin test. The aim of the current study was to examine the effect of opioids microinjected into the VLO on allodynia in the rat L5/L6 spinal nerve ligation (SNL) model of neuropathic pain and determine the roles of different subtypes of opioid receptors in this effect. The allodynia was assessed by both mechanical (von Frey filaments) and cold plate (4 degrees C) stimuli. Morphine (1.0, 2.5, and 5.0 microg) microinjected into the VLO contralateral to the nerve ligation dose-dependently depressed the mechanical and cold allodynia and these effects were reversed by nonselective opioid receptor antagonist naloxone (1.0 microg) administrated into the same site. Microinjection of endomorphin-1 (5.0 microg), a highly selective mu-opioid receptor agonist, and [D-Ala2, D-Leu5]-enkephalin (DADLE, 10 microg), a delta-/mu-opioid receptor agonist, also depressed the allodynia, and the effects of both drugs were blocked by selective mu-receptor antagonist beta-funaltrexamine (beta-FNA, 3.75 microg), but the effects of DADLE were not influenced by the selective delta-receptor antagonist naltrindole (5.0 microg). Microinjection of U-62066 (100 microg), a kappa-opioid receptor agonist, into the VLO had no effect on the allodynia. These results suggest that the VLO is involved in opioid-induced antiallodynia and mu- but not delta- and kappa-opioid receptor mediates these effects in the rat with neuropathic pain.

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.

The roles of different subtypes of opioid receptors in mediating the nucleus submedius opioid-evoked antiallodynia in a neuropathic pain model of rats

Previous studies have indicated that thalamic nucleus submedius is involved in opioid-mediated antinociception in tail flick test and formalin test. The current study examined the effects of opioids microinjected into the thalamic nucleus submedius on the allodynia developed in neuropathic pain model rats, and determined the roles of different subtypes of opioid receptors in the thalamic nucleus submedius opioid-evoked antiallodynia. The allodynic behaviors induced by L5/L6 spinal nerve ligation were assessed by mechanical (von Frey filaments) and cold (4 degrees C plate) stimuli. Morphine (1.0, 2.5, and 5.0 microg) microinjected into the thalamic nucleus submedius contralateral to the nerve injury paw produced a dose-dependent inhibition of the mechanical and cold allodynia, and these effects were reversed by microinjection of the non-selective opioid receptor antagonist naloxone (1.0 microg) into the same site. Microinjection of endomorphin-1 (5.0 microg), a highly selective mu-opioid receptor agonist, and [D-Ala2, D-Leu5]-enkephalin (10 microg), a delta-/mu-opioid receptor agonist, also inhibited the allodynic behaviors, and these effects were blocked by selective mu-opioid receptor antagonist beta-funaltrexamine hydrochloride (3.75 microg). However, the [D-Ala2, D-Leu5]-enkephalin-evoked antiallodynic effects were not influenced by the selective delta-opioid receptor antagonist naltrindole (5.0 microg). Microinjection of the selective kappa-receptor agonist spiradoline mesylate salt (100 microg) into the thalamic nucleus submedius failed to alter the allodynia induced by spinal nerve ligation. These results suggest that the thalamic nucleus submedius is involved in opioid-evoked antiallodynia which is mediated by mu- but not delta- and kappa-opioid receptor in the neuropathic pain model rats.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

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.