Influence of Age on Pulsatile Luteinizing Hormone Release and Responsiveness of the Gonadotrophs to Sex Hormone Feedback in Men

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Abstract
The influence of aging on serum LH and testosterone (T) pulse frequency and gonadotroph sensitivity to an-drogen and estrogen feedback was studied in young (65 yr) Trappist monks. LH pulse frequency (sampling interval, 20 min) was significantly lower [0.25 ± 0.03 (±sem) vs. 0.38 ± 0.02 pulses/h; P < 0.01] in elderly (n = 21) than in young monks (n = 27); the pulse amplitudes were similar. Similarly, T pulse frequency was lower in the elderly than in the young monks (0.13 ± 0.04 vs. 0.23 ± 0.02 pulses/h; P < 0.01). In elderly men, the hypothalamo-pituitary complex was more sensitive to 5α-androstan-17β-ol-3-one feedback, as determined by the decrease in serum LH and T levels. Moreover, during 5α-androstan-17β-ol-3-one (125 mg/day, percutaneously, for 10 days) administration, the LH response to LHRH (100 μg, iv) was significantly higher in the elderly men compared to the pretreatment response. During estradiol (1.5 mg/day, percutaneously for 10 days) administration, the LH response to LHRH was decreased in the elderly men, but unchanged in the young men, suggesting greater responsiveness to estradiol in the elderly men. We conclude that in aged men, decreased testicular androgen secretion is not exclusively the consequence of a primary testicular alteration, but that important changes occur in hypothal-amo-pituitary function, specifically decreased LH pulse frequency and increased LH responsiveness to sex hormone feedback.

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