Peptide histidine isoleucine (PHI) immunoreactivity in the rat retina: identification and characterisation by radioimmunoassay, immunohistochemistry and high-performance liquid chromatography.

The presence of peptide histidine isoleucine immunoreactivity (PHI-IR) in the retinae of male Wistar rats has been demonstrated using a specific radioimmunoassay (RIA), immunohistochemistry (IHC) and high performance liquid chromatography (HPLC). PHI levels (mean +/- S.E.M.) of 16.68 +/- 1.61 ng/g wet weight of normal retinal tissue were measured by RIA. IHC showed PHI-IR to be localized to a population of amacrine cells distributed along the proximal aspect of the inner nuclear layer and to processes in laminae I and IV of the inner plexiform layer. PHI-IR in retinal extracts was shown to coelute with a synthetic porcine PHI standard on a reverse phase HPLC system. Additionally levels of PHI-IR were significantly increased (P less than 0.001) with light adaptation.