GRADIENT HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF ENKEPHALIN PEPTIDES, THEIR METABOLITES, AND ENZYME-INHIBITORS USING COMBINED ULTRAVIOLET AND ELECTROCHEMICAL DETECTION - II - APPLICATION TO OCULAR PERMEABILITY STUDIES IN-VITRO

A gradient HPLC method with combined ultraviolet (UV) and electrochemi cal detection (ED) was used to study the ocular permeability of [D-Ala (2)]-methionine enkephalinamide (MEA) in vitro. Coulometric ED was sel ective for MEA and its tyrosine-containing metabolites with quantitati on Limits between 20 and 60 nM (1.0-3.0 pmol per 50-mu l injection), w hereas UV detection at 205 nm allowed the determination of several aro matic metabolites and enzyme inhibitors with quantitation limits betwe en 40 and 500 nW (2.0-25.0 pmol), This method was capable of detecting permeability of MEA and metabolite formation in the cornea and conjun ctiva in vitro. Furthermore, effects of aminopeptidase inhibitor besta tin and enkephalinase inhibitor SCH 39370 on permeation and metabolism of MEA could be determined. (C) 1998 Elsevier Science B.V.