A sensitive and specific radioimmunoassay for enkephalins is described which discriminates between leucine-enkephalin and methionine-enkephalin. Total opiod peptide activity was assayed by the ability of brain extracts to complete for opiate receptor binding. In rats treated with morphine and/or naloxone, opiates were separated from opioid peptides by Dowex AG-50W column chromatography prior to radioreceptor assay. Chronic administration of morphine failed to alter immunoreactive enkephalin levels or total opioid activity in radioreceptor assays.
- Opioid peptides
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