Evidence for Decreased Luteinizing Hormone-Releasing Hormone Pulse Frequency in Men with Selective Elevations of Follicle-Stimulating Hormone*

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Abstract
To examine the hypothes is that the frequencyof endogenous pulsatile LHRH stimulation controls the relativesecretion of FSH and LH from the pituitary, we studied menwith elevated FSH levels and normal LH levels to determinewhether they have an altered frequency of pulsatile LHRHsecretion compared to normal men. Because peripheral bloodmeasurements of LHRH do not reflect the pulsatile characteristicsof hypothalamic LHRH secretion, and it is generallyaccepted that the pulse frequency of LH secretion is an index ofthe frequency of endogenous LHRH pulsation, we used LH pulsefrequency as the indicator of LHRH pulse frequency. Frequentblood sampling was performed to characterize LH pulse patternsin five men with selective elevations of FSH and seven agematchednormal men. Beginning at 0800–0930 h, blood sampleswere obtained every 10 min for 24 h through an indwelling ivcatheter. Serum LH and FSH levels were measured by RIA ineach sample, and the pattern of LH secretion was determined.Testosterone (T), estradiol, sex hormone-binding globulin, andfree T were measured in a pooled serum sample from each man.Men with selective elevations of FSH had fewer LH pulses per 24 h (mean ± SEM, 10.6 ± 0.5) than the control group (12.9 ±0.6; P < 0.01). There was no statistically significant differencein LH pulse amplitude (23 ± 4 vs. 17 ± 3 ng⁄ml). There were nostatistically significant differences in T (4.9 ± 0.5 us. 6.1 ± 0.5ng⁄ml), estradiol (23 ± 7 vs. 31 ± 5 pg⁄ml), sex hormone-bindingglobulin (7.7 ± 1.4 vs. 7.7 ± 1.2 ng bound dihydrotestosterone⁄ml), or free T (0.16 ± 0.02 vs. 0.23 ± 0.04 ng⁄ml) in these menvs. normal subjects. We conclude that 1) compared to normalmen, men with selectively elevated FSH levels have decreasedLH pulse frequency, which suggests decreased LHRH pulsefrequency; and 2) the relative secretion rates of LH and FSH bythe pituitary may be regulated by the frequency of pulsatileLHRH secretion from the hypothalamus. (J Clin EndocrinolMetab60: 197, 1985)