Hum. Reprod. Advance Access originally published online on April 14, 2005
Human Reproduction 2005 20(6):1548-1553; doi:10.1093/humrep/deh795
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Serum fluctuations of total and free tryptophan levels during the menstrual cycle are related to gonadotrophins and reflect brain serotonin utilization
1 Department of Pediatrics, Obstetrics and Reproductive Medicine, University of Siena Policlinico ‘Le Scotte’, Viale Bracci, 53100 Siena, 2 Department of Pharmaceutical Sciences and 3 Department of Applied Mathematics, University of Padova, Siena and Padova, Italy
4 To whom correspondence should be addressed. Email: carretti{at}unisi.it
BACKGROUND: Serotoninergic (5-HT) neurons are suggested to regulate estrous cycle in animal models. In the present study we evaluated whether a relationship exists between the serotoninergic precursors in the central nervous system and the gonadotrophin–ovarian cyclic function. METHODS: We measured 5-HT precursors [free (FT) and total (TT) tryptophan] and LH, FSH and 17
-estradiol (E2) levels in the serum of 15 fertile women with normal menstrual cycles during the follicular (cycle days 1–5, 7–11), mid-cycle (cycle days 14–16) and luteal (cycle days 17–19, 22–24) phases. RESULTS: TT and FT were significantly increased in the 7–11 and 17–19 cycle days and were decreased at mid-cycle (P<0.01), with a cyclic and opposite behaviour when compared to that of FSH and LH. Indeed, correlation analysis through the matrix of mean values showed that LH was negatively correlated to TT (r=–0.636) and FT (r=–0.574), as well as FSH (TT, r=–0.655; FT, r=–0.663), and that TT and FT were positively correlated to each other (r=0.801; P<0.001). Furthermore, whilst the two FT peaks reached approximately the same levels in the follicular and luteal phase, TT levels were 
30% higher in the luteal than in the follicular phase of the cycle: thus in the first (follicular) phase FT peak was relatively higher than that of TT, whereas the contrary occurred in the second (luteal) phase of the cycle. CONCLUSIONS: Both TT and FT levels have cyclic variations throughout the menstrual cycle, being lowest at mid-cycle (14–16 cycle days), concomitant with the highest LH and FSH concentrations, and higher before and after mid-cycle phase, coinciding with the lowest circulating LH/FSH levels. Since TT and FT levels in the plasma have cyclic changes, our study: (i) suggests that a consumption of serum serotonin precursors takes place concomitant with gonadotrophin release during menstrual cycle; (ii) may represent an in vivo model to investigate this relationship in women in different physiopathological conditions.
Key words: central nervous system/menstrual cycle/neuroendocrine/ovary/serotonin