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

Hydroxyindole-O-methyltransferase activity in ocular and brain structures of rabbit and hen

Relative activities of hydroxyindole-O-methyltransferase (HIOMT) of some brain and ocular structures of the rabbit and hen were analyzed using different 5-hydroxyindoles, i.e., N-acetylserotonin (NAS), 5-hydroxytryptophol (HTOL), 5-hydroxytryptophan (HTP), 5-hydroxytryptamine (HT), and 5-hydroxy-3-indoleacetic acid (HIAA), as enzyme substrates. Pineal glands of both species, as well as hen retina, are capable of producing, to varying degrees, melatonin, 5-methoxytryptophol, and 5-methoxytryptamine. Hen choroid and iris-ciliary body O-methylated NAS and HTOL, whereas rabbit choroid and, to a much lesser extent, hypothalamus and cerebral cortex all O-methylated only NAS. No measurable HIOMT activity was found in hen brain. NAS was a preferred substrate for HIOMT in the hen tissues, whereas in the rabbit pineal gland NAS and HTOL were equally good substrates for HIOMT. Other tested 5-hydroxyindoles, i.e., HTP, HT, and HIAA, were poor methyl acceptors. Of the tissues examined, the highest HIOMT activity was found in the hen pineal gland, followed by the rabbit pineal gland and hen retina. No significant differences between day and nighttime enzyme activities were observed in the pineal gland and retina of either species. The data suggest that in vertebrates some nervous and ocular tissues possess the potential to produce 5-methoxyindole compounds; however, the HIOMT-catalyzed process shows remarkable substrate-, tissue- and species-dependent variations.

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 different photoperiods on the methylating capacity of the pineal gland of adult, male golden hamsters, with special reference to 5-methoxyindoles

Testes weight, plasma FSH and LH concentration and pineal methylating capacity were compared in hamsters housed under either long (LD14:10) or short (LD8:16) photoperiods. Hamsters housed for 14 weeks under short photoperiod showed gonadal atrophy, which was complete after 6 weeks. Also plasma FSH and LH concentration showed a marked decline after transfer to short photoperiod. However, after 14 weeks the concentration of FSH and LH as well as testes weight increased again. Under both photoperiods day/night rhythms in plasma FSH and LH concentration were measured. Under both light regimes the concentrations did not show significant differences. Under long as well as short photoperiods in the pineal gland of animals no significant differences were found in the daily synthesis of various MI tested. Only the synthesis of ML was significantly higher in the pineal of hamsters housed under short photoperiod. The function of this higher synthesis of ML remains unknown. Although the maxima of the rhythm for the various MI found under different LD regimes did not differ in magnitude or duration, their location in respect to the onset of darkness was different. It is suggested that this specific location is of more physiological importance than the quantity or duration of synthesis, concentration or release of MI. At the moment the day/night rhythms were determined there were indications that recrudescence of the testes had already started. It is suggested that this recrudescence is responsible for the fact that no differences in the synthesis of MI were found comparing the influence of both photoperiods. After 14 weeks of exposure to short photoperiod, aML synthesis was, in contrast to the synthesis of the other MI, (not significantly) higher under LD8:16. Moreover, opposite results for aMT and aML synthesis during darkness were found. It is suggested that the ratio of synthesis of these compounds is of physiological significance.