| Abstract: | We tested the hypothesis that the neuroendocrine control of gonadotropin secretion is altered in certain women distance runners with secondary amenorrhea. To this end, we quantitated the frequency and amplitude of spontaneous pulsatile LH secretion during a 24-h interval in nine such women. The ability of the pituitary gland to release LH normally was assessed by administration of graded bolus doses of GnRH during the subsequent 8 h. Compared to normally menstruating women, six of nine amenorrheic distance runners had a distinct reduction in spontaneous LH pulse frequency, with one, three, six, five, four, or two pulses per 24 h (normal, 8-15 pulses/24 h). This reduction in LH pulse frequency occurred without any significant alterations in plasma concentrations of estradiol and free testosterone or 24-h integrated serum concentrations of LH, FSH, or PRL. Moreover, in long-distance runners, the capacity of the pituitary gland to release LH was normal or accentuated in response to exogenous pulses of GnRH. In the six women athletes with diminished spontaneous LH pulsatility, acute ovarian responsiveness also was normal, since serum estradiol concentrations increased normally in response to the GnRH-induced LH pulses. Although long-distance runners had significantly lower estimated percent body fat compared to control women, specific changes in pulsatile gonadotropin release did not correlate with degree of body leanness. In summary, certain long-distance runners with secondary amenorrhea or severe oligomenorrhea have unambiguously decreased spontaneous LH pulse frequency with intact pituitary responsiveness to GnRH. This neuroendocrine disturbance may be relevant to exercise-associated amenorrhea, since pulsatile LH release is a prerequisite for cyclic ovarian function. We speculate that such alterations in pulsatile LH release in exercising women reflect an adaptive response of the hypothalamic pulse generator controlling the intermittent GnRH signal to the pituitary gland. The basis for amenorrhea in the remaining runners who have normal pulsatile properties of LH release is not known. |
