San Diego Zoo Institute for Conservation Research, 15600 San Pasqual Valley Road, Escondido, California 92027, USA.
Endocrinology. 2012 Mar;153(3):1444-52. doi: 10.1210/en.2011-1962. Epub 2012 Jan 17.
The captive southern white rhinoceros (SWR; Ceratotherium simum simum) population serves as an important genetic reservoir critical to the conservation of this vulnerable species. Unfortunately, captive populations are declining due to the poor reproductive success of captive-born females. Captive female SWR exhibit reproductive problems suggested to result from continual ovarian follicular activity and prolonged exposure to endogenous estrogen. However, we investigated the potential role of exogenous dietary phytoestrogens in the reproductive failure of SWR by cloning and characterizing in vitro phytoestrogen binding and activation of recombinant SWR estrogen receptors (ESR). We compared those characteristics with recombinant greater one-horned rhinoceros (GOHR; Rhinoceros unicornis) ESR, a species that receives similar captive diets yet reproduces relatively well. Our results indicate that phytoestrogens bind rhino ESR in a manner similar to other vertebrate species, but there are no differences found in phytoestrogen binding affinity of SWR ESR compared with GOHR ESR. However, species-specific differences in ESR activation by phytoestrogens were detected. The phytoestrogen coumestrol stimulated greater maximal activation of SWR ESR1 than GOHR ESR1. SWR ESR2 were also more sensitive to phytoestrogens and were activated to a greater extent by both coumestrol and daidzein. The concentrations in which significant differences in ESR activation occurred (10(-7) to 10(-5) m) are consistent with circulating concentrations measured in other vertebrate species. Taken together, these findings suggest that phytoestrogens potentially pose a risk to the reproductive health of captive SWR. However, additional studies are needed to further clarify the physiological role of dietary phytoestrogens in the reduced fertility of this species.
圈养的南部白犀牛（SWR；Ceratotherium simum simum）种群是保护这一脆弱物种的重要遗传资源库。不幸的是，由于圈养出生的雌性繁殖成功率低，圈养种群正在减少。圈养雌性 SWR 表现出的繁殖问题被认为是由于持续的卵巢卵泡活动和长期暴露于内源性雌激素引起的。然而，我们通过克隆和体外鉴定植物雌激素结合和激活重组 SWR 雌激素受体（ESR）来研究外源性饮食植物雌激素在 SWR 生殖失败中的潜在作用。我们将这些特征与重组大独角犀牛（GOHR；Rhinoceros unicornis）ESR 进行了比较，后者接受类似的圈养饮食，但繁殖相对较好。我们的结果表明，植物雌激素以类似于其他脊椎动物物种的方式结合犀牛 ESR，但 SWR ESR 与 GOHR ESR 相比，植物雌激素结合亲和力没有差异。然而，检测到 ESR 对植物雌激素的激活存在种间差异。植物雌激素大豆素可刺激 SWR ESR1 的最大激活作用大于 GOHR ESR1。SWR ESR2 对植物雌激素也更敏感，大豆素和染料木黄酮均可使其更大程度地激活。在 ESR 激活中发生显著差异的浓度（10(-7) 至 10(-5) m）与在其他脊椎动物物种中测量到的循环浓度一致。综上所述，这些发现表明植物雌激素可能对圈养 SWR 的生殖健康构成风险。然而，需要进一步的研究来进一步阐明饮食植物雌激素在该物种生育能力下降中的生理作用。
