Depressed follicle-stimulating hormone, luteinizing hormone, and prolactin responses to the luteinizing hormone-releasing hormone, thyrotropin-releasing hormone, and metoclopramide test in endurance runners in the hard-training season.

The responses of serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to luteinizing hormone-releasing hormone (LH-RH) and the responses of prolactin (PRL) to thyrotropin-releasing hormone (TRH) and metoclopramide (MC) were measured in the late luteal phase of the cycle in 12 endurance runners and 11 control women and in 12 joggers and 7 control women. LH-RH (100 micrograms) and TRH (200 micrograms) were injected intravenously at the beginning of the test, and MC (10 mg) was injected 60 minutes later. Blood samples were obtained before and 20, 60, 80, and 120 minutes after the beginning of the test. Runners had significantly lower serum concentrations of estradiol and progesterone than control subjects, whereas the concentrations of FSH, LH, and PRL were similar at the beginning of the study. Compared with their controls, the runners had significantly lower FSH (P less than 0.05) and LH responses at 20 minutes (P less than 0.05) and lower LH responses at 80 minutes (P less than 0.01) to LH-RH and lower PRL responses to MC 20 minutes after MC injection (P less than 0.05). Joggers and their control subjects had similar LH, FSH, and PRL responses to these pharmacologic stimuli. It is concluded that decreased ovarian activity explains, at least partly, the lowered responses of FSH and LH to LH-RH and the lowered response of PRL to MC in endurance runners.