Radioimmunoassay of melatonin in rat serum

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Abstract

  • 1.

    1. Melatonin was coupled to albumin by means of a Na-p-carboxybenzyl, a Na-propionic acid, methylene, or a diazotized p-aminobenzoic acid bridge and injected into rabbits or sheep.

  • 2.

    2. All coupling procedures stimulated antisera which bound melatonin with the greatest affinity; N-acetylserotonin and 6-hydroxymelatonin cross-reacted with the antisera at 3–5%. Other naturally occurring indolealkylamine derivatives showed less cross-reactivity.

  • 3.

    3. Coupling the hapten melatonin to protein through a bridge at or near the indole N can stimulate antisera which are relatively specific to melatonin and suggest that antisera which bind specifically to any other individual indolealkylamine derivative could be produced using these coupling procedures.

  • 4.

    4. Using the methylene bridged antisera, a radioimmunoassay for melatonin was developed and validated for rat serum. In addition to tests for reliability and parallelism, serum estimates of melatonin by radioimmunoassay correlated .98 with gas chromatography-mass spectrometry.

  • 5.

    5. Serum melatonin levels have a characteristic 24-hour rhythm with a crest late in the dark period (L:D 12:12). Following the injection of 50 ug of melatonin, serum levels reach 5–20 fold higher concentrations than physiological levels.

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