Environmentally relevant xenoestrogen tissue concentrations correlated to biological responses in mice

The effects of xenoestrogens have been extensively studied in rodents, generally under single, high-dose conditions. Using a continuous-release, low-dose system in ovariectomized mice, we correlated the estrogenic end points of uterine epithelial height (UEH) and vaginal epithelial thickness (VET) with concentrations of two organochlorine pesticide isomers in fat and blood. Silastic capsules containing a range of doses of either ss-hexachlorocyclohexane (ss-HCH) or o, p'-dichlorodiphenyltrichloroethane (o,p'-DDT) were implanted subcutaneously, and animals were killed after 1 week. Average blood levels achieved by the various doses were 4.2-620 ng/mL for o,p'-DDT and 5.0-300 ng/mL for ss-HCH. Fat concentrations of o,p'-DDT and ss-HCH correlated linearly to blood levels (o,p'-DDT, r(2) = 0.94; ss-HCH, r(2) = 0.83). Fat concentrations (nanograms per gram of tissue) were higher than blood concentrations (nanograms per milliliter) by 90 +/- 5- and 120 +/- 9-fold (mean +/- SE) for o, p'-DDT and ss-HCH, respectively. The VET ranged from 12 +/- 0.9 microm in controls to 114 +/- 8 microm in treated animals, and was correlated to blood levels of either treatment compound. The UEH ranged from an average of 7.7 +/- 0.3 microm in controls to 26 +/- 2 microm in high-dose o,p'-DDT-treated animals. The UEH was also correlated with ss-HCH concentration, but it plateaued at approximately 11 microm at the highest doses. The lowest blood concentrations that produced statistically significant increases in VET or UEH were 18 +/- 2 ng/mL o,p'-DDT and 42 +/- 4 ng/mL ss-HCH. These values are within the same order of magnitude of blood concentrations found in some human subjects from the general population, suggesting that human blood concentrations of these organochlorines may reach estrogenic levels.