Are Phe-Met-Arg-Phe-NH2 immunoreactive peptides endacoids modulating opiate antinociception?
Phe-Met-Arg-Phe-NH2 (FMRF-NH2) was initially isolated from the macrocallista nimbosa clam and subsequently existence of FMRF-NH2-like immunoreactivity (FMRF-NH2-IR) was detected in mammalian CNS. Due to the structural similarity between FMRF-NH2 and the C-terminal extended form of met5-enkephalin, met5-enkephalin-arg6-phe7 (YGGFMRF), a possible interaction between these two peptides was explored. FMRF-NH2 injected intrathecally decreases the antinociceptive action of YGGFMRF or morphine. However, the FMRF-NH2-IR present in rat and bovine brains differs from FMRF-NH2. Intrathecally injected FMRF-NH2-IR partially purified from bovine brain reduces YGGFMRF antinociception. The antagonism elicited by FMRF-NH2 can be reversed by proglumide, which was reported to act as a CCK antagonist. In order to characterize the biological profile of FMRF-NH2-IR, the effect of proglumide and of the FMRF-NH2 antibody on morphine analgesia was tested. Both the IgG isolated from FMRF-NH2 antiserum and proglumide were found to potentiate the morphine analgesia. The results taken together suggest that endogenous FMRF-NH2-IR modulates opioid antinociception; perhaps by acting as an endogenous naloxone.
D000818:Animals; D049872:Bivalvia / Q000032:analysis; D001923:Brain Chemistry; D002417:Cattle; D019835:FMRFamide; D007124:Immunoenzyme Techniques; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology; D009020:Morphine / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects; D009842:Oligopeptides / Q000302:isolation & purification* / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology; D011377:Proglumide / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000032:analysis
D009842:Oligopeptides; D019835:FMRFamide; D009020:Morphine; D011377:Proglumide