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Distribution Pattern of Metorphamide Compared with Other Opioid Peptides from Proenkephalin and Prodynorphin in the Bovine Brain
Author(s) -
Senders Mark,
Weber Eckard
Publication year - 1987
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1987.tb00946.x
Subject(s) - proenkephalin , dynorphin , opioid peptide , dynorphin a , chemistry , opioid , endocrinology , medicine , enkephalin , endorphins , opioid receptor , receptor , biochemistry , biology
Metorphamide is a [Met]‐enkephalin‐containing opioid octapeptide with a C‐terminal α‐amide group. It is derived from proenkephalin and is, so far, the only endogenous opioid peptide with a particularly high affinity for μ opioid (morphine) receptors, a somewhat lesser affinity for K opioid receptors, and a relatively low affinity for δ opioid receptors. The concentrations of metorphamide in the bovine caudate nucleus, the hypothalamus, the spinal cord, and the neurointermediate pituitary were determined by radioimmunoassay and chromatography separation procedures. Metorphamide concentrations were compared withthe concentrations of eight other opioid peptides from proenkephalin and prodynorphin in identical extracts. The other opioid peptides were [Met]‐enkephaIyl‐Arg 6 ‐Phe 7 and [Met]‐enkephalyl‐Arg 6 ‐Gly 7 ‐Leu 8 from proenkephalin; α‐ neoendorphin, β‐neoendorphin, dynorphin A(l‐8), dynorphin A(1–17), and dynorphin B from prodynorphin; and [Leu]‐enkephalin, which can be derived from either precursor. All opioid peptides were present in all four bovine neural tissues investigated. Metorphamide concentrations were lower than the concentrations of the other proenkephalinderived opioid peptides. They were, however, similar to the concentrations of the prodynorphin‐derived opioid peptides in the same tissues. Marked differences in the relative ratios of the opioids derived from prodynorphin across brain regions were observed, a finding suggesting differential posttranslational processing. Differences in the ratios of the proenkephalin‐derived opioids across brain regions were less pronounced. The results from this study together with previous findings on metorphamide's μ opioid receptor binding and bioactivities suggest that the amounts of metorphamide in the bovine brain are sufficient to make this peptide a candidate for a physiologically significant endogenous μ opioid receptor ligand.