Effects of acute stimulation with gonadotropin releasing hormone (GnRH) on biologically active serum luteinizing hormone (LH) in elderly men

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Abstract
This study was designed to characterize the response pattern of biologically active LH (BIO-LH) after Gonadotropin Releasing Hormone (GnRH) acute administration in healthy eiderly men, in comparison with normal young adult men. Serum levels of BIO-LH under basal conditions and in response to the iv injection of 0.1 mg synthetic GnRH were measured in 6 healthy elderly men (mean age 74.2 yr), as weli as in 9 normal young men (mean age 27.4yr). A sensitive in vitro bioassay, based upon testosterone production by mechanically dispersed mouse Leydig cells, was employed to assess LH biological activity. Levels of immunoreactive LH (RIA-LH) and basal testosterone (T) concentrations were determined by a double antibody radioimmunoassay technique. Mean basal levels of BIO-LH and RIA-LH were significantly increased in elderly men, compared to levels in young men, whereas the mean basal ratio of LH in vitro bioactivity to LH immunoreactivity (LH B/l ratio) and mean basal T concentrations were significantly lower in the elderly group. After GnRH administration, the B/l ratio of serum LH remained unchanged both in elderly and in young men. The mean relative maximum response for BIO-LH (BIO-LH Δ %) was significantly lower in elderly men than in the younger male subjects, whereas mean BIO-LH response areas (BIO-LH Δ areas) were not significantly different in the two groups. The mean peak response for both BIO-LH and RIA-LH was observed at 45 min in the elderly group and at 30 min in the younger subjects. Jn elderly men the mean percent decrement of LH serum concentrations after the peak was significantly lower than in young men, showing a slower rate of decline of serum LH from the peak values in the elderly group. Our data indicate that some age-related alterations in the synthesis, secretion and/or metabolic clearance rate of LH could be responsible for the altered pituitary responsiveness to GnRH administration shown in elderly men by this study.