Wu Julie M, Zelinski Mary B, Ingram Donald K, Ottinger Mary Ann
Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, USA.
Exp Biol Med (Maywood). 2005 Dec;230(11):818-28. doi: 10.1177/153537020523001106.
Aging of the reproductive system has been studied in numerous vertebrate species. Although there are wide variations in reproductive strategies and hormone cycle components, many of the fundamental changes that occur during aging are similar. Evolutionary hypotheses attempt to explain why menopause occurs, whereas cellular hypotheses attempt to explain how it occurs. It is commonly believed that a disruption in the hypothalamic-pituitary-gonadal axis is responsible for the onset of menopause. Data exist to demonstrate that the first signs of menopause occur at the level of the brain or the ovary. Thus, finding an appropriate and representative animal model is especially important for the advancement of menopause research. In primates, there is a gradual decline in the function of the hypothalamic-pituitary-gonadal (HPG) axis ultimately resulting in irregularities in menstrual cycles and increasingly sporadic incidence of ovulation. Rodents also exhibit a progressive deterioration in HPG axis function; however, they also experience a period of constant estrus accompanied by intermittent ovulations, reduced progesterone levels, and elevated circulating estradiol levels. It is remarkable to observe that females of other classes also demonstrate deterioration in HPG axis function and ovarian failure. Comparisons of aging in various taxa provide insight into fundamental biological mechanisms of aging that could underlie reproductive decline.
许多脊椎动物物种的生殖系统衰老已得到研究。尽管生殖策略和激素周期组成存在广泛差异，但衰老过程中发生的许多基本变化是相似的。进化假说试图解释绝经为何发生，而细胞假说则试图解释其发生机制。人们普遍认为，下丘脑 - 垂体 - 性腺轴的紊乱是绝经开始的原因。有数据表明，绝经的最初迹象出现在大脑或卵巢层面。因此，找到合适且具有代表性的动物模型对绝经研究的进展尤为重要。在灵长类动物中，下丘脑 - 垂体 - 性腺（HPG）轴功能逐渐下降，最终导致月经周期不规律以及排卵越来越不频繁。啮齿动物的HPG轴功能也会逐渐恶化；然而，它们还会经历一段持续发情期，伴有间歇性排卵、孕酮水平降低和循环雌二醇水平升高。值得注意的是，其他类别的雌性动物也表现出HPG轴功能恶化和卵巢功能衰竭。对不同分类群衰老情况的比较有助于深入了解可能导致生殖功能衰退的衰老基本生物学机制。
