Distribution of immunoreactive metorphamide (adrenorphin) in discrete regions of the rat brain: comparison with Met-enkephalin-Arg6-Gly7-Leu8

Survey of distribution of substance P, vasoactive intestinal polypeptide, cholecystokinin, neurotensin, Met-enkephalin, bombesin and PHI in the spinal cord of cat, dog, sloth and monkey

Levels of substance P (sP), peptide-histidine-isoleucine (PHI), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), neurotensin (NT), bombesin (BOM) and methionine-enkephalin (Met-Enk) like immunoreactivity were measured in cat, dog, primate and sloth cervical, thoracic, lumbar and sacral dorsal and ventral horns and dorsal root ganglia. The levels of peptides in the cat sacral cord and the principal peaks of immunoreactivity on a 10-60% acetonitrile gradient on a C18 reverse phase high performance liquid chromatography (HPLC) were sP (sP1-11: 369 ng/g), PHI (PHI: 271 ng/g), VIP (VIP1-28: 210 ng/g), Met-Enk (Met1-5 and extended forms: 257 ng/g), BOM (BOM1-10 and GRP1-27: 20 ng/g), CCK (CCK-8: 15 ng/g) and NT (NT1-13: 10 ng/g). Consideration of the rostrocaudal levels revealed an approximately even distribution with the exception of VIP and PHI which showed sacral/cervical ratios of 79 and 63. For sP, Met-Enk and BOM dorsal/ventral ratios were greater than 1 at all spinal levels. For VIP, PHI and CCK these ratios were greater than 1 only in the sacral cord. Dorsal root ganglion (DRG) levels of sP, VIP, PHI were readily measurable in single ganglia and covaried with the respective levels in the dorsal cord. Pooled samples of spinal ganglia and the trigeminal ganglia revealed that the relative levels of peptide immunoreactivity were: sP (25 ng/g); VIP (26 ng/g); PHI (28 ng/g); Met-Enk (6 ng/g); CCK (2 ng/g); NT (1 ng/g); and BOM (1 ng/g).

The significance of multiple CNS opioid receptor types: a review of critical considerations relating to technical details and anatomy in the study of central opioid actions

The study of the CNS actions of opioids is complicated by the presence of both multiple opioid receptors and endogenous ligands in the brain. The recent descriptions of opioid isoreceptors, of tonic opioid systems, and of multiple opioid receptors on a single neuron are further technical details which must be considered. In the use of various opiates and opioid peptides to study physiological systems, the multiple opioid affinities of these compounds, as well as potential non-opioid actions, must be controlled for in the experimental design. In conjunction with the multiple receptor affinities of various opiates is the problem of receptor dualism with some drugs; particularly with the agonist/antagonist analgesics. Species differences in the relative proportions of different opioid receptor populations also limit any generalizations of a finding in one species. These limitations in the study of opioid receptors will be discussed with reference to previous neurochemical, neuroendocrine, electrophysiological and behavioral reports of multiple opioid receptors.

Distribution pattern of metorphamide compared with other opioid peptides from proenkephalin and prodynorphin in the bovine brain

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.

Metorphamide levels in chromaffin cells increase after treatment with reserpine

Exposure of bovine chromaffin cells in primary culture to 0.01-1 microM reserpine caused a dose- and time-dependent increase in intracellular levels of the amidated enkephalin peptide metorphamide. Maximal levels (approximately 800% of control) were obtained at 0.1 microM reserpine and increased levels were apparent by 16 h of treatment. Metorphamide increases were at least fivefold more than that of either Met- or Leu-enkephalin, suggesting that reserpine stimulates both enkephalin processing and amidation in the secretory vesicle. Treatment with elevated potassium, which increases enkephalin levels by stimulating production of preproenkephalin messenger RNA, elicited an increase in metorphamide levels equivalent to, but not greater than, the increase in Met-enkephalin pentapeptide. The ratio of Met-enkephalin to metorphamide in untreated chromaffin cells is approximately 140:1, whereas the final Met-enkephalin: metorphamide ratio in reserpinized chromaffin cells is approximately 30:1, similar to the Met-enkephalin:metorphamide ratio in enkephalinergic neurons of the CNS.