DETERMINATION OF MELATONIN IN RAT PINEAL, PLASMA AND RETINA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A sensitive method for the routine measurement of endogenous melatonin (MEL) in pineal, retina and plasma rat tissues has been developed usi ng reversed-phase high-performance liquid chromatography with electroc hemical detection. Quantification limit for MEL was 0.2 ng/mg protein in pineal, 15 pg/ml in plasma and 2.0 pg/mg protein in retina. To impr ove both MEL quantification and the reproducibility of the assay, an i nternal standard was used when an extraction in organic solvent was re quired, in contrast with other available chromatographic methods. MEL values and the circadian profile obtained in this study from both rat pineal and plasma agree with those reported previously. This method al lows MEL detection in mammal retina, particularly in rat, where MEL le vels are very low. (C) 1998 Elsevier Science B.V.