Early and late hormonal responses to the microdose gonadotropin-releasing hormone agonist in normal menstruating women

OBJECTIVE: To assess the effect of a microdose gonadotropin-releasing hormone (GnRH) agonist on the LH, FSH, and E2 secretion in normal menstruating women. DESIGN: Prospective study. SETTING: Tertiary teaching hospital. PATIENT(S): Five normal menstruating women. INTERVENTION(S): Five microg of triptorelin was injected daily in 5 women for 7 days beginning from the cycle day 3. In the next cycle, the same amount of triptorelin was injected into the same women daily for 3 days. MAIN OUTCOME MEASURE(S): Serial serum FSH, LH, and E2 levels. RESULT(S): The FSH levels peaked (27.53 +/- 6.34 IU/L) after 5 hours, and the LH levels peaked (34.35 +/- 7.81 IU/L) by 4 hours. The increased gonadotropin levels persisted even after the second and third day of the GnRH-agonist injections, although the peak levels were not as high as observed with the first injection (19.56 IU/L in the second day, 9.15 IU/L in the third day for FSH; 32.18 IU/L in the second day, 13.59 IU/L in the third day for LH). The down-regulation of gonadotropins was established in 4 days. When the GnRH-agonist was administered for 7 days, the E2 level began to increase 6 days after the last injection. When the GnRH-agonist was administered for 3 days, the E2 level began to increase 3 days after the last injection. CONCLUSION(S): Pituitary down-regulation could be achieved even with a microdose of GnRH agonist. The increased level of gonadotropins persisted for 3 days at this dose. The duration of the down-regulation was influenced by the duration of GnRH-agonist administration.