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The mechanisms that most likely underly the attenuated response of plasma LH to antiopioids or antiestrogens and the reduced frequency of large amplitude LH pulses in elderly men are decreased LHRH release and/or decreased sensitivity of the gonadotrophs to LHRH. To test the latter hypothesis, the LH response, measured both as bioactivity (B) and immunoactivity (IR), to increasing doses of LHRH ranging from 0.625-5 micrograms, administered as an iv bolus, was evaluated in 10 young (20-45 yr old) and 10 elderly (64-78 yr old) monks. Both basal B- and IR-LH levels were significantly higher in elderly men. The maximal response to each dose was similar in young and elderly men when measured as IR-LH, but the B-LH response was higher in elderly men. The B/IR LH ratio increased with increasing LH levels. The mean half-life of plasma IR-LH in the elderly was significantly longer than that in the group of young men and significantly longer than the mean half-life of B-LH. It is concluded that the sensitivity of the gonadotrophs to LHRH is not decreased in elderly men. This suggests that the attenuated response of LH levels to antiopioids and antiestrogens, respectively, as well as the reduced number of spontaneous high amplitude LH pulses in elderly men may, instead, be the consequence of the release of a decreased mass of LHRH at each pulse.
Kaufman et al. (Sat,) studied this question.