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Activation of southern white rhinoceros (Ceratotherium simum simum) estrogen receptors by phytoestrogens and their potential role in thereproductive failure of captive-born females
Citation:
Tubbs, C., P. C. HARTIG, M. C. CARDON, N. Varga, AND M. Milnes. Activation of southern white rhinoceros (Ceratotherium simum simum) estrogen receptors by phytoestrogens and their potential role in thereproductive failure of captive-born females. JOURNAL OF ENDOCRINOLOGY. Society for Endocrinology, Bristol, 153(3):14444-52, (2012).
Impact/Purpose:
Taken together, these findings suggest that phytoestrogen 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.
Description:
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 (ESRs). We compared those characteristics to recombinant greater one-homed rhinoceros (GOHR; Rhinoceros unicornis) ESRs; a species that receives similar captive diets yet reproduces relatively well. Our results indicate that phytoestrogens bind rhino ESRs in a manner similar to other vertebrate species, but there are no differences found in phytoestrogen binding affinity of SWR ESRs compared to GOHR ESRs. However, species-specific differences in ESR activation by phytoestrogens were detected. The phytoestrogen coumestrol stimulated greater maximal activation of SWR ESRI than GOHR ESRI. SWR ESR2s were also more sensitive to phytoestrogens and were activated to a greater extent by both coumestrol and daidzein. The concentrations where significant differences in ESR activation occurred (l0-7 -10-5 M), are consistent with circulating concentrations measured in other vertebrate species. Taken together, these findings suggest that phytoestrogen 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.
