Gill M S, Toogood A A, O'Neill P A, Adams J E, Thorner M O, Shalet S M, Clayton P E
Department of Medicine, University of Manchester, UK.
Clin Endocrinol (Oxf). 1997 Aug;47(2):161-7. doi: 10.1046/j.1365-2265.1997.2291056.x.
Growth hormone (GH) secretion declines with age and is affected by body composition. The signal that mediates the latter relationship remains III-defined. Leptin, the protein product of the adipocyte specific ob gene, is thought to accurately reflect fat mass and could therefore be a candidate to influence GH secretion. We have therefore investigated the relationship between GH status, leptin and body composition in normal and GH-deficient elderly subjects.
GH Secretion was assessed by 20-minute sampling over 24 hours and serum leptin concentrations were measured in a single morning, fasted sample.
Twenty-one GH deficient elderly patients (61-83 years) and 22 gender- and BMI-matched controls (61-88 years).
Body composition was assessed by dual-energy X-ray absorptiometry (DEXA). GH was measured in an ultrasensitive chemiluminescent assay and serum leptin was determined by radio-immunoassay.
Leptin was correlated with percentage body fat in both sexes (male r = 0.75, female r = 0.89, both P < 0.001). Male patients had increased fat mass (FM) (P < 0.01) and leptin concentrations (P < 0.05) but similar lean mass (LM) compared with controls. However, leptin concentration per unit FM was identical in both groups (P = 0.3). In contrast, female patients had lower LM (P < 0.05) but similar FM to controls, yet their leptin concentration per unit FM was twice that of the controls (P < 0.05). In multiple linear regression (MLR) leptin was determined positively by FM and negatively by LM (controls r2 = 76%; patients r2 = 73%, both P < 0.0001). When controlled for gender, GH secretion in the controls was correlated negatively with leptin (r = -0.68, P < 0.01) and negatively with percentage body fat (r = -0.73, P < 0.01). In MLR, using leptin as a marker of body composition, 66% of the variability in GH secretion in the controls could be explained by gender (38%) and by leptin (28%).
Both decreased lean mass and increased fat mass raise serum leptin concentrations in normal and growth hormone-deficient elderly subjects. Leptin is therefore a marker of body composition rather than fat mass alone. The influence of body composition on growth hormone secretion in the elderly may be mediated through leptin, acting as a peripheral signal from adipose tissue to decrease GH secretion.
生长激素（GH）分泌随年龄增长而下降，并受身体成分影响。介导后一种关系的信号仍未明确界定。瘦素是脂肪细胞特异性ob基因的蛋白质产物，被认为能准确反映脂肪量，因此可能是影响GH分泌的一个候选因素。因此，我们研究了正常和生长激素缺乏的老年受试者中GH状态、瘦素与身体成分之间的关系。
通过24小时内每20分钟采样一次来评估GH分泌，并在一个早晨的空腹样本中测量血清瘦素浓度。
21名生长激素缺乏的老年患者（61 - 83岁）和22名性别及体重指数匹配的对照者（61 - 88岁）。
通过双能X线吸收法（DEXA）评估身体成分。采用超灵敏化学发光分析法测量GH，通过放射免疫分析法测定血清瘦素。
瘦素与两性的体脂百分比均相关（男性r = 0.75，女性r = 0.89，P均< 0.001）。与对照组相比，男性患者的脂肪量（FM）增加（P < 0.01），瘦素浓度增加（P < 0.05），但瘦体重（LM）相似。然而，两组每单位FM的瘦素浓度相同（P = 0.3）。相比之下，女性患者的LM较低（P < 0.05），但FM与对照组相似，但其每单位FM的瘦素浓度是对照组的两倍（P < 0.05）。在多元线性回归（MLR）中，瘦素由FM正向决定，由LM负向决定（对照组r2 = 76%；患者组r2 = 73%，P均< 0.0001）。在控制性别后，对照组的GH分泌与瘦素呈负相关（r = -0.68，P < 0.01），与体脂百分比呈负相关（r = -0.73，P < 0.01）。在MLR中，以瘦素作为身体成分的标志物，对照组中GH分泌变异性的66%可由性别（38%）和瘦素（28%）解释。
在正常和生长激素缺乏的老年受试者中，瘦体重降低和脂肪量增加均会提高血清瘦素浓度。因此，瘦素是身体成分的一个标志物，而非仅为脂肪量的标志物。身体成分对老年人生长激素分泌的影响可能通过瘦素介导，瘦素作为来自脂肪组织的外周信号减少GH分泌。
