Fleming M W, Dailey R A
Endocrinology. 1985 May;116(5):1893-8. doi: 10.1210/endo-116-5-1893.
The transition at puberty to adult hormonal patterns has been hypothesized to involve a shift in the sensitivity of the hypothalamic-hypophysial axis to hormonal stimulation. Prepuberal gilts were treated with GnRH or estradiol-benzoate (EB) to compare responsiveness of the pituitary at 40, 80, 120, and 160 days of age. Mean BW at each was 15.6, 36.3, 56.4, and 70.7 kg, respectively. Gilts were injected with GnRH (625 ng/kg; iv) or EB (600 micrograms/kg; im) or with vehicles. Blood samples were collected at 10-min intervals for 3 h after injection of GnRH or vehicle or 4-h intervals for 96 h after injection with EB or vehicle. Plasma concentrations of LH and FSH were measured by RIA, and data were analyzed by a general linear model for split plot design. Pretreatment basal concentrations of LH and FSH decreased between 40 and 160 days of age from 1.7 to less than 0.7 ng/ml and from 29.9-4.1 ng/ml, respectively. GnRH-induced surges of LH became more synchronous relative to time of injection and decreased in maximum concentration with age. In the youngest gilts, multiple surges of LH were released after a single injection of GnRH. The magnitude of the initial release of LH decreased with age from 5.6-2.7 ng/ml. Gilts treated with EB had two or more surges of LH at all ages. However, the concentration of the surge was greatest and occurred synchronously 12 h earlier in the 160-day-old gilts than at other ages. Therefore, sensitivity to EB was enhanced both in response time and amount of LH released. Concentrations of FSH were highly variable among gilts, and treatment with GnRH or EB induced an adult-like release of gonadotropins only at 160 days of age. Maturation of the surge mechanism involved at least two distinct alterations for LH. First there was a reduction in the amount of LH released in response to GnRH after day 40. Second an increase in the precision (timing) and magnitude of the surge of LH in response to EB was seen as gilts approached puberty.
据推测，青春期向成人激素模式的转变涉及下丘脑 - 垂体轴对激素刺激敏感性的变化。对青春期前的小母猪用促性腺激素释放激素（GnRH）或苯甲酸雌二醇（EB）进行处理，以比较其在40、80、120和160日龄时垂体的反应性。各年龄段的平均体重分别为15.6、36.3、56.4和70.7千克。给小母猪注射GnRH（625纳克/千克；静脉注射）或EB（600微克/千克；肌肉注射）或注射溶剂。注射GnRH或溶剂后，每隔10分钟采集一次血样，共采集3小时；注射EB或溶剂后，每隔4小时采集一次血样，共采集96小时。用放射免疫分析法测定血浆中促黄体生成素（LH）和促卵泡生成素（FSH）的浓度，并采用裂区设计的通用线性模型对数据进行分析。LH和FSH的预处理基础浓度在40至160日龄之间分别从1.7纳克/毫升降至低于0.7纳克/毫升，以及从29.9纳克/毫升降至4.1纳克/毫升。GnRH诱导的LH峰值相对于注射时间变得更加同步，并且最大浓度随年龄增长而降低。在最年幼的小母猪中，单次注射GnRH后会释放多个LH峰值。LH的初始释放量随年龄增长从5.6纳克/毫升降至2.7纳克/毫升。用EB处理的小母猪在所有年龄段都有两个或更多的LH峰值。然而，在160日龄的小母猪中，峰值浓度最高，且比其他年龄段提前12小时同步出现。因此，对EB的敏感性在反应时间和LH释放量方面均有所增强。小母猪之间FSH的浓度差异很大，并且只有在160日龄时，用GnRH或EB处理才会诱导出类似成年动物的促性腺激素释放。LH激增机制的成熟至少涉及两个不同的变化。首先，40日龄后，对GnRH反应释放的LH量减少。其次，随着小母猪接近青春期，对EB反应的LH激增的精确性（时间）和幅度增加。
