[Hypothalamic amenorrhea. Different patterns in the pulsatile secretion of LH during 24 hours and different responses to the stimulation test with GnRH].

In 12 patients with hypothalamic amenorrhea and in 5 normal women, plasma gonadotropins (LH and FSH) were assayed before and 20, 30, 60, and 120 minutes after stimulation with 10 mcg GnRH i.v. and 24 hours after stimulation with 100 mcg GnRH i.v. In four patients and in controls the pulsatile secretion of LH was evaluated by blood sampling at 15 minute intervals for the 24-hour period. All patients showed different increases in LH after administration of 10 mcg and 100 mcg at 60 and 120 minutes. In two patients, with decreased LH pulse frequency, the gonadotropin increase is dose-dependent in respect to GnRH. In the other two, with normal LH pulse frequency, no difference was shown. In conclusion, this study suggests that the mechanism responsible for amenorrhea is due to reduced frequency of pulsatile GnRH secretion. However, in some patients LH pulse frequency was within the normal range. The double GnRH test (10 or 100 mcg) may be useful in distinguishing these different forms of amenorrhea.