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Hum. Reprod. Advance Access published online on April 14, 2005
Human Reproduction, doi:10.1093/humrep/deh795
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© The Author 2005. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org
Received July 29, 2004
Revised December 14, 2004
Accepted January 15, 2005

Article

Serum fluctuations of total and free tryptophan levels during the menstrual cycle are related to gonadotrophins and reflect brain serotonin utilization

N. Carretti 1*, P. Florio 1, A. Bertolin 1, C.V.L. Costa 2, G. Allegri 2, and G. Zilli 3

1 Department of Pediatrics, Obstetrics and Reproductive Medicine, University of Siena Policlinico ‘Le Scotte’, Viale Bracci, 53100 Siena, Italy
2 Department of Pharmaceutical Sciences, Italy
3 Department of Applied Mathematics, University of Padova, Siena and Padova, Italy

* To whom correspondence should be addressed.
N. Carretti, E-mail: carretti{at}unisi.it


  Abstract

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{beta}-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.

Keywords: central nervous system; menstrual cycle; neuroendocrine; ovary; serotonin.
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