In vivo test systems for the quantitative and qualitative analysis of the biological activity of phytoestrogens

Many compounds of plant origin with the ability to bind to the estrogen receptor have been identified in the last decades. One of the most extensively used in vivo assays to characterise the estrogenic potency of these phytoestrogens and mechanisms of their action is the rodent uterotrophic assay. Various protocols exist for this test system, using immature, hypophysectomized, or ovariectomized rats and mice and oral or subcutaneous administration of the test compound. However, just monitoring the ability of a compound to stimulate uterine growth is not sufficient to characterize its estrogenicity. Over the last decades, an increasing number of estrogen sensitive tissues has been identified. Moreover, a variety of different molecular mechanisms have been discovered for the action of estrogens, including non-genomic actions. Therefore, an in vivo test design for estrogenicity should include an analysis of several estrogen sensitive parameters in different estrogen sensitive tissues. To distinguish between agonistic and antagonistic properties of a substance, combinations of the test compound with estrogens and antiestrogens should be analyzed. A reasonable supplement to this enhanced uterotrophic assay are selected estrogen sensitive tumor models, which can be used to test for potential chemopreventive properties of phytoestrogens.