Decreased serum and pineal concentrations of melatonin and N-acetylserotonin in aged male hamsters.

Serum and pineal concentrations of melatonin and N-acetylserotonin in 4-month-old (adult) and 15-month-old (senile) male hamsters were studied. The animals were adapted under 12:12 h light:dark cycle for a minimum of 1 month 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 less than 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 greater than 0.05) demonstrated in the levels of serum 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 less than 0.05) than those of the senile animal, but the levels of serum N-acetylserotonin in the two age-groups studied demonstrated no significant differences (p greater than 0.05). Our studies indicate that in the hamster, the synthesis and secretion of pineal melatonin decrease with aging.