J. van Benthem

Day/night rhythmicity in the methylating capacities for different 5-hydroxyindoles in the pineal, the retina and the Harderian gland of the golden hamster (Mesocricetus auratus) during the annual seasons.

In the pineal, the Harderian gland and the retina of the golden hamster the day/night capacity for the synthesis of different methoxyindoles is investigated under natural conditions for one 24-hour period in the months of December, March and June. The amounts of the methoxyindoles and the diurnal rhythms in the synthesis are different in the various months during which the tests were performed. There is a striking increase in the synthesis of melatonin and methoxytryptophol in all three organs in June as compared with December. Equally striking is the high synthesis of methoxytryptamine in the pineal in June, whereas this compound was not formed in the Harderian gland and the retina in this month. Methoxytryptophan synthesis was not observed in June in any of the three organs. Methoxyindoleacetic acid rhythmicity shows a pattern more or less identical to that of melatonin and methoxytryptophol. A high synthesis exists at the end of the June day, but greater fluctuations during the days of the two other months. Acetylmethoxytryptophol is synthesized in the pineal during the night in March, but in the late afternoon in June. The largest quantity of this compound is found in the Harderian gland in December, in the pineal in March and in the retina in June. The largest amounts of melatonin and methoxytryptophol are synthesized when gonadal weight is largest. The possible correlation between the amounts synthesized, the rhythmicities in synthesis and the reproductive system is discussed.

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.

Rhythmic synthesis of various 5-methoxyindoles in the pineal gland of male adult golden hamsters, kept under the same artificial conditions throughout the year

Until now the day/night and seasonal rhythmicity in the synthesis of 5-methoxyindoles (MI) is thought to be regulated by environmental factors, especially photoperiod and temperature. Endogenous factors are also implicated in the generation of N-acetyltransferase and hydroxyindole-O-methyltransferase activity rhythms. In the present experiments seasonal rhythmicity in the synthesis of MI in the pineal gland was investigated in hamsters kept under the same artificial conditions throughout the year. Though the environmental conditions were the same, day/night and seasonal rhythmicity in the production of MI in the pineal were observed indicating the existence of endogenous factors influencing the rhythmicities. In November, most of the MI showed the highest synthesis, MA and ML excepted, which were especially produced in July and September. The results obtained sustain the hypothesis that aMT is synthesized from MT rather than from aHT. Moreover, the rhythmicities in aMT synthesis are not identical to those found in aMT concentration as described in the literature. This indicates that synthesis and concentration of a compound are not comparable. At the end of the light period, when aMT injections have an antigonadotropic effect, a peak of aMT synthesis was always present. Although MI synthesis showed seasonal rhythmicity, no reproductive cycle occurred in the hamsters. At present, the concept that the pro- and/or antigonadal effects of the pineal are mediated by aMT seems to be the most acceptable. The present results, however, indicate that aMT and perhaps other MI, often regarded as factors influencing gonadal growth in golden hamsters, are not the only factors involved.

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.

Daily and seasonal rhythmicity in the methylation of pineal indolic compounds in adult male golden hamsters, kept under natural conditions

Seasonal rhythmicity in the reproductive cycle was demonstrated in golden hamsters exposed to natural conditions. Testes regress in weight and function from October up to April. Reproductive functional testes are found in June. Although less marked, body weight also shows seasonal variations: a retarded growth in winter and early spring. In the pineal gland of these animals diurnal and seasonal rhythmicity was found in the synthesis of various MI. It has been concluded that rhythms in the pineal of animals kept under artificial conditions are often more pronounced as compared to those in hamsters kept under natural conditions. Melatonin (aMT) synthesis was observed during the day as well as during the night. A certain resemblance in patterns of day/night rhythms as to aMT and 5-methoxytryptamine (MT) production was reported suggesting a physiological role of MT. To facilitate the discussion on seasonal rhythmicity the average synthesis per day of the 5-methoxyindoles (MI) was calculated. During the period of gonadal regression in fall and early winter, MT and aMT, which are both generally accepted as pineal antigonadotropins, showed opposite patterns in rhythms of mean synthesis; MT decreased but aMT increased from October up to December. It was suggested that under natural conditions MT may induce and aMT maintain gonadal atrophy. Furthermore, also other MI showed relatively high amounts of production, at least in November. The period of recrudescence was characterized by a high synthesis of 5-methoxytryptophan (MW), 5-methoxytryptophol (ML) and O-acetyl-5-methoxytryptophol (aML). This confirms an earlier suggestion that aML can be considered a counter-antigonadotropic substance of the hamster pineal gland. Therefore it was concluded that, apart from MT and aMT, also other MI may be of physiological importance in the regulation of gonadal atrophy.

Pteridines in the Pineal and Effects of These Substances on the Indole Metabolism of This Organ

Pteridines are very light sensitive substances. The first compounds of this class were isolated as a yellow pigment from the wings of the brimstone butterfly by Wieland and Schopf (1925) and as the white pigment from the wings of the cabbage butterfly by Schopf and Wieland (1926). These pigments were named xanthopterin and leucopterin indicating the colour and source of the compounds. The real chemical structure of these substances was not solved until 1940 by Purrmann. The structure of a third insect pigment, isoxanthopterin was also elucidated by Purrmann in 1941. The well-known structure folic acid, and its derivatives which play a key role in metabolism, contains also a pteridine ring. For a survey of the most important literature in the pteridine field till 1969, see Blakly’s “Biochemistry of folic acid and related pteridines”.

The influence of light of different wavelengths on the methylating capacity of the pineal gland of male golden hamsters in relation to reproduction.

In the present experiments the influence of light of different wavelengths on pineal indole metabolism in relation to reproduction was studied. Therefore, during autumn and winter male golden hamsters were kept under natural conditions but for the sunlight which was filtered exposing the hamsters to either normal (control), red or blue light. During the gradually shortening photoperiod at the start of the experiments under normal light conditions, a marked decrease of FSH and LH plasma content as well as testicular weight was found, indicating the onset of gonadal atrophy. During this period a high synthesis of 5-methoxytryptophan (MW) and 5-methoxytryptamine (MT) was determined. The synthesis of other 5-methoxyindoles (MI) was low, while O-acetyl-5-methoxytryptophol (aML) synthesis even markedly decreased. Red and blue light did not cause significant changes in MI synthesis. As long as MT synthesis is high (under blue light), there is no increase in FSH content and testes weight is still decreasing. This influence of blue light confirms the putative antigonadotropic properties of MT. The increase of FSH content at week 9 was the first indication that recrudescence had started. At week 19, this recrudescence was also manifested in the increasing testes weight. The synthesis of melatonin (aMT), 5-methoxytryptophol (ML), 5-methoxyindole-3-acetic acid (MA) and aML increased whereas the production of MT decreased. Blue light exposure caused a significantly higher increase of synthesis of ML, MA, aML and, not-significantly, of aMT, whereas red light caused a significantly lower synthesis of MA. It was concluded that MT, a putative antigonadotropic, and aML, a putative counter-antigonadotropic, are probably important pineal compounds that transduce the photoperiodic messages, which cause either gonadal atrophy or recrudescence. The effect of blue light on indole metabolism and the reproductive cycle was more clear than that of red light. From the present results of blue light on indole metabolism, it was suggested that blue light delayed gonadal atrophy and stimulated gonadal growth, compared to red light. An opposite effect of red light was less obvious.

The effect of reduced neopterin on the synthesis of several methylated indoles in the pineal gland of adult male golden hamsters, kept under standardized conditions

In the present study the effect was tested of reduced neopterin (RN) on the methylating capacity of the pineal gland of adult, male golden hamsters, housed under standardized conditions throughout the year. An effect of RN on the synthesis of a number of methylated compounds was, indeed, demonstrated. It is concluded that RN not only influences the indole metabolism by being the cofactor of tryptophan-hydroxylase, but that it might be involved in the regulation of other enzymes as well. Incubation with RN was most effective at the end of the light period. As this is also the time at which melatonin (aMT) injections cause gonadal atrophy in hamsters, kept under long photoperiod, this time of the day may be very important for aMT synthesis. A season-bound influence of RN was also demonstrated. The effect of RN was stimulatory in September, November and January for 5-methoxytryptamine (MT) and in November for 5-methoxytryptophan (MW) synthesis, but inhibitory in July. Furthermore, the effect of RN was stimulating for 5-methoxyindole-3-acetic acid (MA) and aMT in September, while the influence in the other months tested was absent or slightly inhibiting. These results suggest that the influence of RN in the pineal may be regulatory to various enzymes of the indole metabolism.