RESUMO
BACKGROUND: The aim of this study was to develop a mathematical model of the hypothalamo-pituitary-gonadal axis that would reflect available data in humans. METHODS: A model of hormonal relationships at the early follicular and midluteal phases of the human menstrual cycle is proposed. FINDINGS: Two distinct temporal patterns of oscillatory behavior have been demonstrated for both pituitary and gonadal steroids in the early follicular phase: first, rapid oscillations in gonadotropin releasing hormone, follicle stimulating hormone and luteinizing hormone (Q approximate to 1 hour) that were an immediate consequence of the programmed equations. Second, there were slower, undulating, emergent rhythms in luteinizing hormone and follicle stimulating hormone, and also in estrogen, having oscillatory periods of 2-12 hours. There was also a longer-period (Q2-3 days) emergent rhythm in progesterone. In the mid-luteal phase, estrogen and progesterone rhythms were correlated, and all hormones showed an approximately 6-hour periodicity. CONCLUSIONS: To our knowledge, the oscillatory behavior of peripheral sex steroids in the follicular phase has not been previously noted.