Indoleamine metabolism in the pineal gland of the Chinese hamster, Cricetulus griseus

Diurnal profiles of melatonin synthesis-related indoles, catecholamines and their metabolites in the duck pineal organ

This study characterizes the diurnal profiles of ten melatonin synthesis-related indoles, the quantitative relations between these compounds, and daily variations in the contents of catecholamines and their metabolites in the domestic duck pineal organ. Fourteen-week-old birds, which were reared under a 12L:12D cycle, were killed at two-hour intervals. The indole contents were measured using HPLC with fluorescence detection, whereas the levels of catecholamines and their metabolites were measured using HPLC with electrochemical detection. All indole contents, except for tryptophan, showed significant diurnal variations. The 5-hydroxytryptophan level was approximately two-fold higher during the scotophase than during the photophase. The serotonin content increased during the first half of the photophase, remained elevated for approximately 10 h and then rapidly decreased in the middle of the scotophase. N-acetylserotonin showed the most prominent changes, with a more than 15-fold increase at night. The melatonin cycle demonstrated only an approximately 5-fold difference between the peak and nadir. The 5-methoxytryptamine content was markedly elevated during the scotophase. The 5-hydroxyindole acetic acid, 5-hydroxytryptophol, 5-methoxyindole acetic acid and 5-methoxytryptophol profiles were analogous to the serotonin rhythm. The norepinephrine and dopamine contents showed no significant changes. The DOPA, DOPAC and homovanillic acid levels were higher during the scotophase than during the photophase. Vanillylmandelic acid showed the opposite rhythm, with an elevated level during the daytime.

Circadian rhythm entrainment with melatonin, melatonin receptor antagonist S22153 or their combination in mice exposed to constant light

The ability of daily melatonin and the melatonin receptor antagonist, S22153, to entrain circadian system function was investigated in mice with atypical melatonin rhythm. B6D2F(1) mice were first synchronized to a LD 12:12 for approximately 2 wk, then exposed to continuous light (LL) until study completion. After 10-18 days of LL exposure, mice received daily subcutaneous (s.c.) melatonin at a dose of 0.1, 1 or 10 mg/kg/day (exp. 1) or daily intraperitoneal (i.p.) S22153 (20 mg/kg/day) with or without melatonin (1 mg/kg/day, exp. 2) at subjective zeitgeber time (ZT) 10 for 19 days. Then all the mice were exposed to LL for another 10 days. Spectral analysis showed that initial LL lengthened the period of both rhythms by approximately 1.5 hr as compared with LD 12:12. No entrainment of either rhythm was found in controls. Conversely, daily melatonin-only, S22153-only or their combination set the temperature and activity periods to approximately 24 hr and produced a significant increase of the circadian amplitude of both rhythms as compared with controls. However, after treatment withdrawal, the dominant period lengthened to approximately 25.5 hr in mice receiving either melatonin or S22153. On the contrary, the period remained close to 24 hr for the 10 days following withdrawal of combined S22153 and melatonin. Such sustained pharmacological resetting of circadian function could display therapeutic potential against external resynchronization resulting from defective photoperiodic entrainment.

Relationship of atypical melatonin rhythm with two circadian clock outputs in B6D2F(1) mice

Circadian rhythms in body temperature, locomotor activity, and the circadian changes of plasma and pineal melatonin content were investigated in B6D2F(1) mice synchronized by 12 h of light and 12 h of darkness. During 8 wk continuous recording, activity and temperature displayed a marked stable and reproducible circadian rhythm, with both peaks occurring near the middle of darkness. Both 24- and 12-h rhythmic components were also significantly detected. Mean plasma melatonin concentration rose steadily during the light span and reached a maximum (30.6 +/- 10.0 pg/ml) at 11 h after light onset (HALO), then gradually decreased after the onset of darkness to a nadir (4.7 +/- 0.4 pg/ml) at 20 HALO. Mean pineal content followed a pattern parallel to that of plasma concentration (peak at 11 HALO: 17.7 +/- 1.0 pg/gland; trough at 17 HALO: 4.7 +/- 1.0 pg/gland). In addition, a second sharp peak was observed at 21 HALO (20.2 +/- 3.5 pg/gland). Plasma and pineal contents displayed large and statistically significant circadian changes, with a composite rhythm of period (24 + 12 h). This mouse model has predominant production and secretion of melatonin during the day. This possibly contributes to a similar coupling between chronopharmacology mechanisms and the rest-activity cycle in these mice and in human subjects.