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

Abstract

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-methoxy-tryptamine (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.

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

“…In experiments on the influence of pteridines on indole-metabolism, it was found that reduced neopterin had the strongest effect on the synthesis of MT (Van Benthem et aL, 1985 b) indicating a physiological function of MT. These and present data confirm the suggestion that aMT is not the only physiological important pineal MI; MT and probably other MI may also be considered as active pineal compounds.…”

Diurnal variations in serum neopterin levels are associated with the pineal hormone melatonin circadian rhythm in healthy human subjects

“…Biopterin is an essential enzymatic cofactor for tryptophan hydroxylase, an enzyme which plays an important role in neurotransmitters synthesis and it is a regulatory point in the melatonin synthesis pathway. It has been suggested a modulatory role of some pteridine compounds on the enzymes of the indole metabolism in the pineal gland [10]. In addition to this, melatonin is an effective downregulator of biopterin synthesis because of its effects on both the direct inhibition of cathalytic activity of the guanosine triphosphate cyclohydrolase I and the downregulation of its gene expression [11].…”