Background: Previous studies report that genes in the morphine biosynthetic pathway have been found in placental tissue. Prior researchers have shown that kappa opioid receptors are present in human placenta. We determined if a µ opiate receptor was present and which subtype was expressed in human placenta. We also sought to demonstrate a functional µ opiate receptor in human placenta.
Material/Methods: Polymerase chain reactions as well as DNA sequencing were performed to identify the µ opiate receptor subtypes present in human placenta. The functionality of the receptor was demonstrated by real time amperometric measurements of morphine induced NO release.
Results: The µ4 opiate receptor sequence was present as well as the µ1 opioid receptor transcript. The addition of morphine to placental tissue resulted in immediate nitric oxide release and this effect was blocked by naloxone.
Conclusions: In the present study, an intact morphine signaling system has been demonstrated in human placenta. Morphine signaling in human placenta probably functions to regulate the immune, vascular, and endocrine functions of this organ via NO.

Keywords: Protein Isoforms - metabolism, Pregnancy, Placenta - metabolism, Nitric Oxide Synthase - metabolism, Nitric Oxide - secretion, Narcotics - pharmacology, Narcotic Antagonists - pharmacology, Naloxone - pharmacology, Morphine - pharmacology, Receptors, Opioid, mu - metabolism, Reverse Transcriptase Polymerase Chain Reaction, Signal Transduction - physiology