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.
Ethoxacetic Acid (EAA), the active metabolite of 2-ethoxyethanol (a widely used glycol ether), was tested to assess its effects on reproduction in Swiss mice using the RACB protocol. This was performed as part of a larger structure-activity program, evaluating numerous glycol ethers and their metabolites. From the range finding study (Task 1), doses of 0.2, 0.6, and 1.0% in water were selected for the continuous breeding phase of the study. These concentrations produced estimated average doses of nearly equal to 303, 669, and 968 mg/kg/d.
Four female mice died during Task 2, 2 each in the middle and high dose groups. The deaths were due to partner-induced wounds. In Task 2, high dose mice gained less weight than the other mice, so that at necropsy, body weights were reduced by nearly equal to 13%. The number of litters per pair was reduced by 19% at the high dose, while the number of live pups per litter was decreased at both the middle dose (25%) and high dose (53%) levels. Adjusted live pup weight was reduced by 3% at the low dose and by 9% at the high dose. The mean adjusted live pup weight was the same value in the low and middle dose groups, but the variance was slightly higher for the middle dose group, making the difference from control not statistically significant. Cumulative days to litter increased by 5-9 days in the high dose group, an increase that was observed for all litters.
Task 4, the assessment of the second generation, was not conducted in this study (see the description in the Introductory section).
Since adverse effects on fertility and reproduction were observed in Task 2, Task 3 (the crossover study) was conducted using the controls and high dose mice. In pairs with EAA-treated females, the number of live pups per litter decreased by 50% and adjusted live pup weight was reduced by 9%. Pairs with treated males were not different from controls.
After the evaluation of the Task 3 litters, the F0 control and high dose adults were killed and necropsied. In EAA-treated females, relative kidney weight increased by 21%, while body weight was reduced by nearly equal to 14%. The estrous cycle was nearly equal to 15% longer in EAA-treated females than in controls (4.9 days vs. 5.6 days). In high dose males, body weight was nearly equal to 12% less than controls, absolute testis weight was 13% lower than controls, while relative epididymis and seminal vesicle weights were reduced by 8% and 11%, respectively. For the high dose mice, the proportion of abnormal sperm increased from a control value of nearly equal to 4%, to 10%.
In conclusion, EAA had significant effects on both females and males. The increased estrous cycle length probably underlies the reduced number of litters/pair, while the Task 3 reduction in pups/litter and pup weight clearly mimics those effects seen in Task 2. The adverse effects on male reproductive organ weight and sperm morphology were not reflected in functional changes.