Chromatographic identification of enkephalins in the guinea pig retina

Immunocytochemical localization of enkephalin-like peptides and binding of several opiate ligands have been reported previously in the mammalian retina. High-performance liquid chromatography was used to separate and identify the enkephalin-related peptides in the guinea pig retina. Enkephalin-immunoreactivity in the retina was separated into three distinct fractions, as determined by radioimmunoassay. Two of these fractions were identified as Met- and Leu-enkephalin, respectively. The immunoreactive fractions were also active in inhibiting the binding of [3H]enkephalin to rat brain membranes. All immunoreactive peptides had molecular weights similar to those of the enkephalins, as determined by gel chromatography. These techniques allow us to directly assay and identify enkephalin-related peptides in retinal tissues.