A specific radioimmunoassay for [Leu] and [Met]enkephalin applied to a HPLC separation of human CSF.

Highly specific antisera have been raised to [Leu]enkephalin and applied in a radioimmunoassay that is sufficiently sensitive and precise for the measurement of enkephalin pentapeptides in body fluids. Extraction of CSF by Sep-pak cartridges, followed by reverse-phase HPLC to separate [Leu] and [Met]enkephalin prior to assay, has assessed their concentrations as 59-170 pmol/l and 0.5-30 pmol/l, respectively, in three patients with chronic pain. The reproducibility of the HPLC separation step was checked by adding to the sample a synthetic analogue of very low cross-reactivity in UV detectable quantities. The assay procedure described is generally applicable to the assessment of [Leu] and [Met]enkephalin concentrations in CSF.