Department of Biological Sciences, University of Memphis, 3778 Walker Avenue, Memphis, TN 38111, USA; Biology Department, Millikin University, 1184 West Main Street, Decatur, IL 62522, USA.
Gen Comp Endocrinol. 2013 Dec 1;194:168-74. doi: 10.1016/j.ygcen.2013.09.016. Epub 2013 Oct 1.
In most vertebrates, production of reproductive hormones wanes with age, co-occurring with a decline in reproductive output. Measurement of these hormones can serve as a key marker of the onset of reproductive senescence. Longitudinal studies of physiological parameters in populations of free-living animals are relatively uncommon; however, we have monitored baseline concentrations of hormones for nine years in a population of Florida scrub-jays (Aphelocoma coerulescens). We hypothesized that concentrations of circulating reproductive hormones change with age, and predicted declines in reproductive hormones in the oldest jays. We found that baseline levels of luteinizing hormone (LH) and testosterone (T) were relatively low in both young and old male breeders and reach their highest levels in birds aged 4-7years. Conversely, we found no age-related patterns in baseline levels of LH or estradiol in female jays. In males we determined which component of the hypothalamo-pituitary-gonadal (HPG) axis is responsible for observed age-based differences, by challenging males of different ages with gonadotropin-releasing hormone (GnRH); thereby allowing assessment of pituitary and gonadal responsiveness by measuring plasma concentrations of luteinizing hormone and testosterone, respectively. The magnitude of increase in levels of both LH and T in response to GnRH challenge decreased with age in male breeders. Combined with the baseline levels, the results from the GnRH challenge suggest that younger birds have the capability to produce higher levels of reproductive hormone, whereas the old birds may be constrained by senescence in their ability to produce these hormones.
在大多数脊椎动物中，随着年龄的增长，生殖激素的产生会减弱，同时生殖能力也会下降。这些激素的测量可以作为生殖衰老开始的关键标志物。在自由生活动物的种群中，对生理参数进行纵向研究相对较少；然而，我们已经在佛罗里达州灌丛鸦（Aphelocoma coerulescens）的一个种群中监测了九年的激素基础浓度。我们假设循环生殖激素的浓度随年龄而变化，并预测最老的鸦的生殖激素下降。我们发现，无论是年轻还是年老的雄性繁殖者，其促黄体激素（LH）和睾酮（T）的基础水平都相对较低，在 4-7 岁的鸟类中达到最高水平。相反，我们在雌性灌丛鸦的 LH 或雌二醇的基础水平中没有发现与年龄相关的模式。在雄性中，我们通过用促性腺激素释放激素（GnRH）挑战不同年龄的雄性来确定下丘脑-垂体-性腺（HPG）轴的哪个组成部分是导致观察到的基于年龄的差异的原因；从而通过测量黄体生成素和睾酮的血浆浓度分别评估垂体和性腺的反应性。对 GnRH 挑战的反应中 LH 和 T 水平的增加幅度随着雄性繁殖者年龄的增长而降低。结合基础水平，GnRH 挑战的结果表明，年轻的鸟类有能力产生更高水平的生殖激素，而老年鸟类可能因衰老而无法产生这些激素。
