Kuiri-Hänninen Tanja, Sankilampi Ulla, Dunkel Leo
Department of Pediatrics, Kuopio University Hospital, University of Eastern Finland, Kuopio, Finland.
Horm Res Paediatr. 2014;82(2):73-80. doi: 10.1159/000362414. Epub 2014 Jul 5.
The hypothalamic-pituitary-gonadal (HPG) axis is active in the midgestational foetus but silenced towards term because of the negative feedback effects mediated by the placental hormones. This restraint is removed at birth, leading to reactivation of the axis and an increase in gonadotrophin levels. Gonadotrophin levels are high during the first 3 months of life but decrease towards the age of 6 months except for FSH levels in girls that remain elevated until 3-4 years of age. After this, the HPG axis remains quiescent until puberty. The postnatal gonadotrophin surge results in gonadal activation in both sexes. In boys, testosterone levels rise to a peak at 1-3 months of age and then decline following LH levels. Postnatal HPG axis activation is associated with penile and testicular growth and therefore considered important for the development of male genitalia. In girls, elevated gonadotrophin levels result in the maturation of ovarian follicles and in an increase in oestradiol levels. Biological significance and possible long-term consequences of this minipuberty remain elusive, as do the mechanisms that silence the HPG axis until puberty. However, the first months of life provide a 'window of opportunity' for functional studies of the HPG axis prior to pubertal development.
下丘脑 - 垂体 - 性腺（HPG）轴在妊娠中期胎儿中活跃，但由于胎盘激素介导的负反馈作用，在足月时会受到抑制。这种抑制在出生时被解除，导致该轴重新激活，促性腺激素水平升高。促性腺激素水平在出生后的前3个月较高，但到6个月大时会下降，不过女孩的促卵泡生成素（FSH）水平会一直升高到3 - 4岁。在此之后，HPG轴在青春期前一直处于静止状态。出生后促性腺激素激增导致两性性腺激活。在男孩中，睾酮水平在1 - 3个月大时升至峰值，然后随着促黄体生成素（LH）水平下降。出生后HPG轴的激活与阴茎和睾丸的生长有关，因此被认为对男性生殖器的发育很重要。在女孩中，促性腺激素水平升高会导致卵巢卵泡成熟和雌二醇水平增加。这种小青春期的生物学意义和可能的长期后果仍然不明，使HPG轴在青春期前保持沉默的机制也是如此。然而，生命的最初几个月为青春期前发育阶段HPG轴的功能研究提供了一个“机会窗口”。
