| Abstract: | The metabolism of tryptophan and tryptophan metabolites was investigated during the follicular, luteal and premenstrual phases of the menstrual cycle in 33 healthy women across one cycle. The metabolites of all three pathways of tryptophan ie the serotonergic pathway, the pyrollase pathway and the indole acetic acid pathway, were assayed from urinary prebreakfast samples collected on a repeated measures basis. Urinary 3 hydroxy kynurenine excretion was significantly elevated in the luteal phase (p=0.030). The relative activity of the serotonergic pathway to the kynurenergic pathway (identified by the ratios 5HT+HIAA/KY+HK and 5HT/KY+HK) were significantly elevated in both the luteal and premenstrual phases compared to the follicular phase (p=0.009 and p=0.005 respectively); indicating that the kynurenergic pathway of tryptophan metabolism may modulate serotonergic metabolism (via HK) during the menstrual cycle; and that the relative and not actual levels of serotonin metabolism may be the important factor when investigating any cyclical effects of the neurotransmitter serotonin. |
