INCREASED OXIDATION OF PINEAL SEROTONIN AS A POSSIBLE EXPLANATION FORREDUCED MELATONIN SYNTHESIS IN THE AGING DJUNGARIAN HAMSTER (PHODOPUS-SUNGORUS)

Groups of young adult (1.7 months) and old adult (9.7 months) female D jungarian hamsters were exposed to short-day photoperiods (SD; 8L: 16D ) or long-day photoperiods (LD; 16L:8D) for 6 weeks. Pineal and serum melatonin rhythms were dampened in old SD animals when compared with y oung SD animals. The melatonin precursor serotonin showed diurnal vari ations with opposite phases. to melatonin synthesis. However, pineal s erotonin levels were even lower in old SD animals than in young SD ani mals, contrary to the expected accumulation of the precursor. The synt hesis of a metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA ), was significantly lower in younger hamsters, under both photoperiod s. These results indicate that the age-associated decline in the produ ction of melatonin is a consequence of an increased oxidation of its p recursors.