DIURNAL CHANGES IN THE CONTENT OF INDOLEAMINES CATECHOLAMINES, AND METHOXYINDOLES IN THE PINEAL-GLAND OF THE DJUNGARIAN HAMSTER (PHODOPUS-SUNGORUS) - EFFECT OF PHOTOPERIOD

Previous studies in Syrian hamster have shown that the correlations be tween the daily fluctuations in the contents of pineal indoleamines an d methoxyindoles are influenced by the photoperiod, and that dopamine may play a role in the regulation of pineal function. The present stud y investigated the 24 hour changes in the content of 5-hydroxytryptoph an (5-HTP), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), N-a cetylserotonin (NAS), melatonin, 5-methoxytryptophol (5-MT), noradrena line (NA), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) i n the pineal gland of female Djungarian hamsters exposed to long (LP; LD 16:8) or short (SP; LD 10:14) photoperiods for 10 weeks. Pronounced nocturnal increases of N-acetylserotonin and melatonin content were o bserved irrespective of the photoperiod regime. The content of 5-HT wa s markedly decreased during the first hour of the night in LP. which c ontrasted with the lack of changes in NAS and melatonin content at thi s time. In SP, an increased 5-HTP content and a less obvious decrease in 5-HT content was observed during the night, although melatonin and NAS content were even higher than in LP. Similar daily patterns as for 5-HT were observed in the 5-HT oxidative metabolites (5-HIAA and 5-MT ). When considering values throughout the day, a poor correlation for 5-HT vs., NAS and melatonin content was observed, which was particular ly evident during the nighttime. These data indicate that the daily va riation of pineal indoles may not only be dependent on changes in the N-acetyltransferase activity but also in other mechanisms regulating p inealocyte 5-HT availability. As previously reported in other species of hamster, pineal NA content did not show daily variations in LP cond itions, although a nocturnal increase was detected in SP In contrast, pronounced nocturnal increases were observed in the content of DA and its acid metabolite, DOPAC, irrespective of the photoperiod. These dat a indicate the existence of an increased dopaminergic turnover during the night and further support a role for DA in the regulation of melat onin synthesis and in the synchronization of the pineal functions.