The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Task 1, normally used to set doses for the continuous cohabitation phase, were conducted, because sufficient data were already available on affected sex and the optimal doses to use. In all three studies, dose levels of EGME in drinking water for Task 2 were set at 0.03%, 0.1%, and 0.3% EGME, w/v. For this study, these concentrations produced estimated consumption values of nearly equal to 50, 170, and 500 mg/kg/d. Water consumption was not reduced by EGME addition. One male and two females died in the control group during Task 2, and 1 male, 1 female, and 2 males died in the low to high dose groups, respectively. These deaths were judged not to be treatment-related.
While 23/27 control pairs delivered any pups, only 7/28 high dose pairs had any pups. Of those, 5 pairs delivered only 1 litter, and no high-dose pair delivered more than two litters. Thus, the mean number of litters per fertile pair declined from 3.57 (control) to 1.29 (high dose). Additionally, there were no live pups ever delivered at the high dose. The mean number of live pups/litter declined at the middle dose, from a control value of 8.0, to 6.9. A greater proportion of pups were born dead in the middle dose group (18%, vs. a control value of 8%). The mean pup weight adjusted for litter size increased at the low and middle doses by nearly equal to 2% and 4%, respectively.
The pups from the last litter were reared by their dam until weaning. In control litters, 75% and 87% of male and female pups, respectively, survived until weaning. In the middle dose group, these values were reduced to 33% and 28%, respectively. Absolute female pup weight was reduced only at weaning by nearly equal to 35%.; male pup weight was not significantly decreased.
After weaning the F1 mice, all remaining F0 mice were killed and necropsied. There were no changes in female body or organ weights. Male mice in the high dose group weighed 10% less than controls, and the adjusted liver weight for the middle dose males was increased by nearly equal to 6%. At the high dose, absolute testis weight was decreased by nearly equal to 30%, relative epididymis weight was decreased by nearly equal to 11%, the % of motile epididymal sperm and epididymal sperm density were decreased by nearly equal to 30% and nearly equal to 34%, respectively. The % abnormal sperm was increased at the middle and high doses, from a control value of 29%, to 37% and 96% abnormally-formed sperm, respectively.
At 74 ± 10 days of age, F1 mice were cohabited for a week within treatment groups. While there were sufficient F1's to make 20 non-sib pairs in the control and low-dose groups, there were sufficient middle-dose animals to form only 6 breeding pairs. Five of those 6 mated, but none delivered a litter of live pups (vs. 14/20 that delivered live young in the control group). Thus, F2 pups were available from only the low dose group and the controls. There were no differences between these groups in pup weight, mean pup number, viability, or proportion of males.
After the F2 pups were delivered and assessed, all mice were killed, and the F1 mice were necropsied. While there was no effect on female body weight, there was a 50% reduction in ovary weight at the middle dose (n=6), and a 26% increase in adjusted kidney weight. In males, there were no changes in body weight, while middle dose males showed a 25% increase in relative kidney weight and a 34% reduction in prostate weight. Seminal vesicle weight was reduced in the low and middle dose groups by 6% and 15%. Abnormal sperm forms were increased in the middle dose group, from a control value of 25%, to a treated value of 43% abnormal. Epididymal sperm density in the low dose was reduced by 11%; the 23% reduction in the middle dose group was not significant due to the small number of mice.
In summary, this strain had fewer pups/litter, and fewer litters/pair overall compared to the Swiss CD-1 strain, but more than the C3H strain. EGME completely inhibited successful reproduction at the top dose. The middle dose level (0.1%) was toxic, based on reductions in pup number and increases in abnormal sperm forms. In this strain, the low dose produced adverse effects in the second generation (reduced seminal vesicle weight and epididymal sperm count) that were not seen with the other strains at this dose. Compared to the Swiss mice, C57's had lower basal fertility, and were more affected by EGME exposure. This supports the hypothesis that strains of lower basal fecundity evidence greater reproductive toxicity than more robust and fertile strains when challenged with a toxicant.