Tenover J S, Matsumoto A M, Plymate S R, Bremner W J
Geriatric Research, Education, and Clinical Center, Veterans Administration Medical Center, Seattle, Washington.
J Clin Endocrinol Metab. 1987 Dec;65(6):1118-26. doi: 10.1210/jcem-65-6-1118.
Serum testosterone (T) levels in men decline with age while serum LH levels, as measured by RIA, increase. To assess if the decline in serum T levels in healthy aging men is paralleled by an age-related decline in the bioavailable non-sex hormone-binding globulin (SHBG)-bound fraction of T and to determine whether there are age-related changes in LH secretion or LH control of T production, we studied 29 young (aged 22-35 yr) and 26 elderly (aged 65-84 yr) healthy men. All men had single random blood samples drawn, and 14 men in each age group underwent frequent blood sampling for 24 h, both before and after 7 days of clomiphene citrate (CC) administration. Both mean 24-h serum total T levels and non-SHBG-bound T were reduced in elderly men compared to those in young men (P less than 0.05), while estradiol and SHBG levels were similar in the 2 age groups. Serum FSH determined by RIA and LH by RIA and bioassay were higher in the elderly men compared to those in young men (P less than 0.05), but the ratios of LH bioactivity to immunoreactivity and the LH pulse frequency and amplitude were similar. After CC administration, mean serum total T and non-SHBG-bound levels in young men increased by 100% and 304%, respectively, while in older men these values increased by only 32% and 8%, respectively. However, CC-stimulated LH pulse characteristics and serum levels of estradiol, SHBG, FSH, and bioactive and immunoreactive LH were similar in the 2 groups. Thus, both at baseline and after CC stimulation, elderly men had significantly lower serum total T and non-SHBG-bound (bioavailable) T levels than did young men, despite similar or increased levels of bioactive LH and similar bioactive to immunoreactive LH ratios and LH pulse characteristics. These results suggest that major age-related changes in the hypothalamic-pituitary-testicular axis occur at the level of the testes and are manifested by decreased responsiveness to bioactive LH. Administration of CC to young and elderly men resulted in similar changes in LH pulse characteristics and LH bioactivity and immunoreactivity, suggesting preserved hypothalamic-pituitary responsiveness in the elderly.
男性血清睾酮（T）水平随年龄增长而下降，而通过放射免疫分析法（RIA）测定的血清促黄体生成素（LH）水平则升高。为了评估健康老年男性血清T水平的下降是否与T的生物可利用非性激素结合球蛋白（SHBG）结合部分的年龄相关下降平行，并确定LH分泌或LH对T产生的控制是否存在年龄相关变化，我们研究了29名年轻（22 - 35岁）和26名老年（65 - 84岁）健康男性。所有男性均采集单次随机血样，每个年龄组的14名男性在服用枸橼酸氯米芬（CC）7天前后均进行了24小时的频繁血样采集。与年轻男性相比，老年男性的24小时血清总T水平和非SHBG结合T均降低（P < 0.05），而两个年龄组的雌二醇和SHBG水平相似。通过RIA测定的血清促卵泡生成素（FSH）以及通过RIA和生物测定法测定的LH在老年男性中高于年轻男性（P < 0.05），但LH生物活性与免疫反应性的比值以及LH脉冲频率和幅度相似。服用CC后，年轻男性的平均血清总T和非SHBG结合水平分别增加了100%和304%，而老年男性的这些值仅分别增加了32%和8%。然而，两组中CC刺激后的LH脉冲特征以及雌二醇、SHBG、FSH和生物活性及免疫反应性LH的血清水平相似。因此，无论在基线还是CC刺激后，尽管生物活性LH水平相似或升高以及生物活性与免疫反应性LH比值和LH脉冲特征相似，但老年男性的血清总T和非SHBG结合（生物可利用）T水平均显著低于年轻男性。这些结果表明，下丘脑 - 垂体 - 睾丸轴的主要年龄相关变化发生在睾丸水平，并表现为对生物活性LH的反应性降低。对年轻和老年男性给予CC导致LH脉冲特征以及LH生物活性和免疫反应性出现相似变化，表明老年男性下丘脑 - 垂体反应性保留。
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