Determination of pineal melatonin by high-performance liquid chromatography with electrochemical detection:...

High-pressure liquid chromatography with electrochemical detection has been used for the determination of melatonin in rat pineal glands and tissue explants. Rat pineal melatonin content was measured at 2-hr intervals during a 24-hr period by direct injection of supernatants from centrifuged pineal homogenates into a reversed-phase C18 column. The lower limit of sensitivity was 32 pg per gland for a 2:1 signal-to-noise ratio, which allows melatonin measurements during daytime. Both absolute values and circadian rhythmicity obtained with the present method are in agreement with previously validated radioimmunoassays. In addition, isoproterenol-induced release of melatonin from individual rat pineal explants was measured after chloroform extraction of the incubation medium.