Vitellogenin induction assay

Petty et al. (1998, 2000) used a vitellogenin (VGT) assay to assess the endocrine disrupting potential of contaminants in purified SPMD extracts. VGT is an egg yolk phosphoprotein precursor that is synthesized in the liver of female teleosts in response to estrogen from the ovary (Bailey, 1957). A wide variety of environmental contaminants have been shown to have estrogenic activity (Colborn et al., 1993). Equal portions of purified extracts from SPMDs, exposed in the Missouri River after the flood of 1993 and from the IWWTP at the Nogales Wash deployment were individually injected into immature rainbow trout (Oncorhynchus mykiss) as described in Section 6.4. The SPMD extracts contained elevated levels of complex mixtures of contaminants, including PAHs and pesticides. The fish injected with these sample extracts exhibited VGT induction, while no induction was observed in fish injected with any of the blank sample extracts. 

Several assays, such as the ultra-sensitive luminescent ELRA developed by Seifert (2004) with a detection limit of 20 ng L-1 for 17 (3-estradiol, have been reported in the literature. Although these assays are simple to use, many factors, such as differences in culture conditions, cell density or cell-line clones, affect the potency of estrogenic substances, and that makes the standardization of these methods difficult. The induction of several proteins or enzyme activities (e.g. the increasing levels of alkaline phosphatase, cathepsin D, prolactin and vitellogenin as a consequence of progestogens) has also been used to study estrogenicity. However, expression of these proteins or enzyme activities is restricted to specific cell lines and cannot be extrapolated to other tissues or species. 

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