Diurnal rhythms of immunoreactive N-acetylserotonin and melatonin in the serum of male rats

Immunoreactive N-acetylserotonin and melatonin in rat serum were extracted by ethyl acetate at less than or equal to pH 3 and chloroform at greater than or equal to pH 10, respectively, following protein precipitation and were quantified by radioimmunoassays. There were diurnal rhythms of N-acetylserotonin and melatonin in the serum of rats (housed in 121/12d; lights on from 06.00-18.00 h for two weeks). Serum melatonin levels 20.00-04.00 h are higher than those at 08.00-16.00 h. Serum N-acetylserotonin levels were, however, higher at 24.00-08.00 h and lower at 12.00-20.00 h. The concentration of N-acetylserotonin in individual samples ranged from a minimum of 0.45 ng/ml at 12.00 h to a maximum of 2.78 ng/ml at 08.00 h. The diurnal study on N-acetylserotonin levels in the rat serum was repeated and a similar result was obtained. The findings of the presence of N-acetylserotonin in the rat serum and a diurnal rhythm of serum N-acetylserotonin are in keeping with the notions that N-acetylserotonin may be secreted by the pineal gland and that N-acetylserotonin may be another indole with hormonal activities.