四、血清瘦素与性早熟
Palmert等的研究表明：中枢性性早熟(CPP)女孩夜间血清瘦素水平超过白天血清瘦素水平 的38%，而CPP男孩超过22%〔21〕，其机制不明。用GnRH类似物抑制CPP男、女孩 垂体-性腺轴后，男孩睾酮明显下降，而血清瘦素水平则由(3.5±0.8)μg/L上升到( 9.5±3.1)μg/L。女孩在E2降低后血清瘦素水平并没有明显的改变，进一步表明男孩青 春期睾酮的分泌抑制了瘦素的产生，而女孩雌激素的改变并没有对瘦素产生调节作用。 CPP男、女孩经治疗抑制垂体-性腺轴后，夜间血清瘦素水平仍较白天增高，提示瘦素 的昼夜节律并不依赖垂体-性腺轴的活性〔22〕。
五、瘦素与性延迟
国外有关瘦素与性延迟的研究还不多。动物实验发现：饥饿可使幼鼠血清中瘦素水平下 降，性征不发育，性功能延迟。当给予充足食物后，血清中瘦素水平迅速提高，紧接着性 发育开始(雌鼠阴道打开)。在持续限制摄食的情况下，中枢注射瘦素也会引起性的成熟 〔11〕。有此可见，瘦素与性延迟也密切相关。
Arslanian等对年龄在14.9～16.5岁诊断为青春期延迟的男孩用睾酮制剂治疗4个月后，血清 瘦素水平由治疗前的(20.5±7.4)μg/L下降为(9.6±3.6)μg/L，同时体脂含量及体脂百 分率也明显下降。可以看出：青春期延迟的男孩有一个较高水平的瘦素，经睾酮治疗后， 随着体脂的下降血清瘦素水平也明显减低〔23〕。
Jockenhovel等对睾丸功能减退者，用睾酮替代治疗也发现：在治疗前患者血清瘦素水平 较正常人高三倍，尽管患者和正常人有相近的BMI。经治疗后患者血清瘦素水平也明显下 降。认为，睾丸功能减退者可能存在有瘦素抵抗状态，这种状态可以被雄激素诱导减低血 清瘦素水平而纠正，这样可以恢复患者对瘦素作用的反应〔18〕。
综上所述，瘦素对青春期的发动以及青春期发育都有一定的作用。青春期的发动是由于下 丘脑GnRH的脉冲释放峰度和频率增加所致。近年来研究发现：许多调控因子，包括类固醇、 神经介质、肽类激素等都能影响GnRH的分泌，这些因子可以兴奋和抑制GnRH的释放，有的更 具有兴奋/抑制的双向效应，即在特定情况下对GnRH分泌的调控转换成相反的作用〔24 〕。因此，青春期发动的确切机制以及瘦素的作用原理还有待进一步的研究。
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