Needham Katie B, Dochtermann Ned A, Greives Timothy J
Department of Biological Sciences, North Dakota State University, Fargo, ND 58102, USA.
Department of Biological Sciences, North Dakota State University, Fargo, ND 58102, USA.
Gen Comp Endocrinol. 2017 May 15;246:211-217. doi: 10.1016/j.ygcen.2016.12.010. Epub 2016 Dec 23.
The hypothalamic-pituitary-gonadal (HPG) axis, with gonadotropin-releasing hormone (GnRH) initiating the endocrine cascade, regulates testosterone secretion. Testosterone, through its pleiotropic effects, plays a crucial role in coordinating morphology, physiology and behavior in a reproductive context. The concentration of circulating testosterone, however, varies over the course of the day and in response to other internal or external stimuli, potentially making it difficult to relate testosterone sampled at one time point with traits of interest. Many researchers now utilize the administration of exogenous GnRH to elicit a standardized stimulation of testosterone secretion. However, it has remained unclear if and how this exogenously stimulated activation of the HPG axis is related with endogenously regulated testosterone that is capable of influencing testosterone related traits. Repeated measures of a hormone can uncover consistent individual variation in hormonal differences at the HPG axis level, variation that potentially stems from underlying genetic variation in a population experiencing identical environmental cues. Thus, we asked, using the house sparrow (Passer domesticus), how daily endogenous variation in testosterone profiles relates to GnRH-induced testosterone secretion. Further, we explore the relationship between endogenous daily testosterone peaks and GnRH-induced testosterone with badge size, a morphological trait related with status within a social group. We found that GnRH-induced testosterone levels reflect a highly repeatable hormonal phenotype that is strongly correlated with nighttime testosterone levels. The results demonstrate the usefulness of GnRH-induced testosterone in studies aimed at understanding individual variation and selection on endogenously regulated testosterone levels and the potential importance of nighttime testosterone levels to physiology and behavior.
下丘脑 - 垂体 - 性腺（HPG）轴通过促性腺激素释放激素（GnRH）启动内分泌级联反应，调节睾酮分泌。睾酮通过其多效性作用，在生殖环境中协调形态、生理和行为方面发挥着关键作用。然而，循环睾酮的浓度在一天中会有所变化，并会对其他内部或外部刺激做出反应，这可能使得难以将某一时刻采集的睾酮与感兴趣的特征联系起来。现在许多研究人员利用外源性GnRH的给药来引发睾酮分泌的标准化刺激。然而，外源性刺激的HPG轴激活是否以及如何与能够影响睾酮相关特征的内源性调节睾酮相关，仍不清楚。对一种激素的重复测量可以揭示HPG轴水平上激素差异中一致的个体变异，这种变异可能源于在相同环境线索下群体中潜在的遗传变异。因此，我们以家麻雀（Passer domesticus）为研究对象，探究睾酮水平的每日内源性变化与GnRH诱导的睾酮分泌之间的关系。此外，我们还探讨了内源性每日睾酮峰值以及GnRH诱导的睾酮与徽章大小之间的关系，徽章大小是一种与社会群体中地位相关的形态特征。我们发现，GnRH诱导的睾酮水平反映了一种高度可重复的激素表型，与夜间睾酮水平密切相关。研究结果表明，GnRH诱导的睾酮在旨在理解内源性调节睾酮水平的个体变异和选择以及夜间睾酮水平对生理和行为的潜在重要性的研究中具有实用性。
