W. C. Legerstee

Circadian rhythmicity of the activity of hydroxyindole-o-methyl transferase (HIOMT) in the formation of melatonin and 5-methoxytryptophol in the pineal, retina, and harderian gland of the golden hamster

The day and night rhythms in the activity of HIOMT in the formation of melatonin and of 5-methoxytryptophol have been determined in the pineal, retina and Harderian gland of the adult male golden hamster. In all hamsters used there was no detectable HIOMT activity in the deep pineal. In the superficial pineal HIOMT activity, involved in the synthesis of melatonin (Mel), was observed to be high at the end of the dark period and at the middle of the light period. Considering the HIOMT activity involved in the production of 5-methoxytryptophol (5-MTL), an increase in 5-MTL synthesis was observed only during the light period. Comparing the peak of Mel-production with that of 5-MTL it appears that during the light period the pineal produces more 5-MTL than Mel. In the Harderian glands, the circadian course of HIOMT activity involved in the synthesis of Mel seems to run parallel to that of the enzyme implicated in 5-MTL synthesis, both being stimulated at the end of the dark period. The activity of HIOMT in 5-MTL production is, however, always approximately 2 times higher than for Mel synthesis. In the retina the synthesis of Mel and 5-MTL is not significantly higher during the dark period than during the light period. However, the production of 5-MTL is larger than that of Mel. It appears that (1) with the exception of the end of the dark period, the extra-pineal synthesis of Mel and 5-MTL is always higher than that in the pineal; (2) the circadian synthesis of 5-methoxyindoles is different in each organ, and (3) in the pineal the circadian activity of HIOMT involved in 5-MTL formation is different from that of the same enzyme involved in the formation of Mel. The results are discussed.

Preliminary investigations on melatonin and 5-methoxytryptophol synthesis in the pineal, retina, and Harderian gland of the mole rat and in the pineal of the mouse “eyeless”

Hydroxyindole-O-methyltransferase (HIOMT) activity for the synthesis of melatonin and 5-methoxytryptophol, both 5-methoxyindoles, was measured in the pineal, the Harderian gland and the retina of the mole rat and in the pineal of the mouse “eyeless”. In the pineal and the Harderian gland of the mole rat a larger amount of 5-methoxytryptophol than of melatonin is synthesized. 5-Methoxyindole synthesis is extremely high in the Harderian gland, whereas in the retina HIOMT activity is low and variable. In the pineal of the mouse “eyeless”, a low 5-methoxyindole synthesis showing no circadian rhythm is demonstrated. It is concluded that, besides the generally accepted regulation of the indole metabolism by light, in species with atrophied eyes having Harderian glands (mole rat) and in species without eyes other factors than light might be responsible for the indole metabolism in the pineal gland.

Seasonal variations in HIOMT activity during the night in the pineal gland of 21 day old male Wistar rats.

In the pineal of 21-day old male Wistar rats hydroxyindole-O-methyl-transferase (HIOMT) activities involved in the synthesis of several 5-methoxyindoles were determined during the night in April, June, October and January. A high HIOMT activity for the synthesis of melatonin/5-methoxytryptophol was determined in the months of January and April. In June and October a decrease was observed. The activity maxima coincide with peaks of activity found for the synthesis of 5-methoxytryptophan. Synthesis of 5-methoxytryptamine occurred only in June and October, whereas the synthesis of 5-methoxyindole-3-acetic acid occurred only in January. From these results it may be concluded that January and April are the most active months of those tested for the melatonin/5-methoxytryptophol synthesis in the rat pineal gland. A possible physiological role of the 5-methoxyindoles other than melatonin and 5-methoxytryptophol is discussed.

Estimation of the methylating capacity in the pineal gland of the rat with special reference to the methylation of N-acetylserotonin and 5-hydroxytryptophol separately.

In the present paper, an extension is presented of an earlier described method, by which the methylating capacity of the pineal gland can be determined. Supplementary to the earlier method, the synthesis of melatonin and 5-methoxytryptophol can now be qualified and quantified separately.

Day and night rhythms in the methylation of N-acetylserotonin/5-hydroxytryptophol in the pineal gland of male rats of different ages

Next to a night rhythm of the methylation of N-acetylserotonin/5-hydroxytryptophol the presence of a daytime rhythm could also be established. Rhythmicity was studied in May during the night and in June during daytime in 21, 42 and 70 days old male Wistar rats. In 21 days old rats, moderate HIOMT activity was observed from 12 p.m.–4 a.m. In rats aged 42 and 70 days HIOMT activity was increased showing a peak at 4 a.m. In September this night maximum is observed at 12 p.m. in rats, aged 42 days. This points to the presence of a seasonal change in HIOMT rhythmicity during the night. During daytime a moderate HIOMT activity is present, which reaches a maximum at 2 p.m. in the 21 and 42 day old animals, while in the adult 70 days old rats activity starts to increase at 2 p.m. probably reaching a maximum at 6 p.m.

Circadian Rhythmicity in the Activity of HIOMT in the Formation of Melatonin and of 5-Methoxytryptophol in the Retina, Harderian Gland and Pineal of the Male Hamster

The day and night rhythms in the activity of HIOMT in the formation of melatonin and of 5-raethoxytryptophol have been determined in the retina, Harderian gland and pineal of adult male golden hamster. It appears that (1) with the exception of the end of the dark period, the extra-pineal synthesis of melatonin and 5-methoxytryptophol is always higher than that in the pineal; (2) the circadian synthesis of methoxyindoles is different in each organ, and (3) in the pineal the circadian activity of HIOMT involved in 5-methoxytryptophol formation is different from that of the enzyme involved in the formation of melatonin.

Seasonal Variations in HIOMT Activity During the Night in the Pineal Gland of Wistar Rats of Several Ages

ABSTRACT In the pineal of 10, 21 and 42 day old male Wistar rats hydroxyindole-O-methyltransferase (HIOMT) activities involved in the synthesis of several 5-methoxyindoles were investigated during the night in April, June, October and January. It was observed that during January and April melatonin/5-methoxytryptophol and 5-methoxytryptophan synthesis was highest. The synthesis of 5-methoxytryptamine and 5-me”thoxyindole-3-acetic acid does not coincide with melatonin/5-methoxytryptophol and 5-methoxytryptophan synthesis. Furthermore it was demonstrated that the maxima of HIOMT activities change in time during the seasons. The seasonal variations in HIOMT activity and a shift of the activity maxima demonstrate that indole metabolism is more complicated than is generally accepted.

Circadian rhythmicity in the methylation of 5-hydroxy-indoles and norepinephrine in the pineal gland of 10 day old rats

In pineals of 10 day old rats 5-hydroxytryptophan, 5-hydroxyindole-3-acetic acid, N-acetylserotonin/5-hydroxytryptophol and norepinephrine are methylated following a circadian rhythm. During the night HIOMT and COMT activities were measured for the above mentioned substrates, while HIOMT activity for 5-hydroxytryptophan and N-acetylserotonin/5-hydroxytryptophol was also determined during daytime.