Decreased Serum and Pineal Concentrations of Melatonin and N-Acetylserotonin in Aged Male Hamsters

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Abstract
Serum and pineal concentrations of melatonin and N-acetylserotonin in 4-mo.-old (adult) and 15-mo.-old (senile) male hamsters were studied. The animals were adapted under 12:12 h light:dark cycle for a minimum of 1 mo. before they were decapitated at mid-light and mid-dark. Melatonin and N-acetylserotonin in the pineal and serum were extracted and quantified by radioimmunoassay. Diurnal variations (P < 0.05) were observed in the levels of pineal melatonin, pineal N-acetylserotonin and serum melatonin. There was, however, no day and night difference (P > 0.05) demonstrated in the levels of serum N-acetylserotonin in our studies. Moreover, the levels of pineal melatonin, pineal N-acetylserotonin and serum melatonin in the dark period and the level of serum melatonin in the light period of the adult hamster were higher (P < 0.05) than those of the senile animal, but the levels of serum N-acetylserotonin in the 2 age-groups studied demonstrated no significant differences (P > 0.05). In the hamster, the synthesis and secretion of pineal melatonin decrease with aging.