Distribution Pattern of Metorphamide Compared with Other Opioid Peptides from Proenkephalin and Prodynorphin in the Bovine Brain

Abstract

Metorphamide is a [Met]-enkephalin-containing opioid octapeptide with a C-terminal alpha-amide group. It is derived from proenkephalin and is, so far, the only endogenous opioid peptide with a particularly high affinity for mu opioid (morphine) receptors, a somewhat lesser affinity for kappa opioid receptors, and a relatively low affinity for delta 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 with the concentrations of eight other opioid peptides from proenkephalin and prodynorphin in identical extracts. The other opioid peptides were [Met]-enkephalyl-Arg6-Phe7 and [Met]-enkephalyl-Arg6-Gly7-Leu8 from proenkephalin; alpha-neoendorphin, beta-neoendorphin, dynorphin A(1-8), 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 proenkephalin-derived 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 mu 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 mu opioid receptor ligand.

The regulation of proenkephalin expression in a distinct population of glial cells.

“…Assay of proenkephalin peptides Proenkephalin peptide levels were determined by radioimmunoassay using specific antisera recognizing met-enkephalin-arg6-phe7 essentially as described by Sonders and Weber (1987). We used met-enkephalin-arg6-phe7 (Peninsula Laboratories, Belmont, CA) as the tracer and standard.…”

Subcellular Localization, Partial Purification, and Characterization of a Dynorphin Processing Endopeptidase from Bovine Pituitary

“…For example, Dyn A-8 is more abundant than Dyn A-17 in the midbrain, whereas the converse is true in the hippocampus (Cone et al, 1983). In the neurointermediate lobe of the bovine pituitary, there is four times more Dyn A-8 compared with Dyn A-17 (Sonders and Weber, 1987). The regional varia-C H A M CTERIZA TION OF A PITUITA R Y D YNOR PHIN CONVERTING ENZYME 32 1 tions of the relative proportions of the assorted cleavage products in brain and pituitary could be due to differences in the tissue levels of the processing enzymes.…”

“…The dynorphin precursor (prodynorphin) contains both dibasic and monobasic cleavage sites. Prodynorphin is expressed in pituitary, brain, and several other tissues (Civelli et al, 1985;Devi et al, 1987;Sonders and Weber, 1987). In the brain and neurointermediate lobe of the pituitary, prodynorphin is processed to produce a-and 0neo-endorphins (Kangawa et al, 198 1;Weber et a]., 19826), dynorphins (Dyn) A-17 and A-8 Weber et al, 1982a), Dyn B-13 (also designated "rimorphin") (Fischli et al, 1982;klpatrick et al, 1982), Dyn B-29 (also designated "leumorphin") (Nakao et al, 1983), and leucine-enkephalin (Leu-Enk) (Zamir et al, 1984).…”

“…The formation of Dyn B-13 from Dyn B-29 and Dyn A-8 from Dyn A-17 requires a monobasic cleavage between Thr and Arg and Ile and Arg, respectively. The relative amounts of these peptides vary between regions (Cone et al, 1983;Sonders and Weber, 1987). For example, Dyn A-8 is more abundant than Dyn A-17 in the midbrain, whereas the converse is true in the hippocampus (Cone et al, 1983).…”

Tissue Content of Opioid Peptides in the Myenteric Plexus‐Longitudinal Muscle of Guinea‐Pig Small Intestine

“…The high content of [Met'lenkephalin in the myenteric plexus could be due to metabolic conversion of BAM-18 and BAM-8 amide to the &selective [Met5]enkephalin. It is important to appreciate that the pattern of processing of proenkephalin and of prodynorphin varies widely in different regions and different species (Liston et al, 1984;White et al, 1986;Sonders and Weber, 1987).…”