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.
Ethylene Glycol Monomethyl Ether (EGME), a common chemical and solvent used in industry and in consumer goods, was used to test the hypothesis that mouse strains of differing basal fertility would respond differently to a reproductive toxicant. This study used Swiss CD-1 mice in a modified RACB protocol. The design was modified to use 30 pairs of mice/group instead of the usual 40/control and 20/treated group. Neither Task 3, the crossover mating test, nor 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 calculated consumption estimates of nearly equal to 60, 200, and 550 mg/kg/d. Water consumption was not reduced by EGME addition. No males and ten females died during Task 2: 1, 3, 3, and 3 in the control to high dose groups, respectively.
All pairs had at least one litter in all groups except the high dose, where only 30% of the pairs had at least one litter. Only 2 high dose pairs produced 4 litters, and none produced 5. In the control and low dose litters, 93-94% of pups were born alive, while that was reduced to 87% in the middle dose, and to 14% in the high dose group. The number of live pups/litter was reduced in the high dose group, from a control mean of 11.7, to nearly equal to 0.5. There was no effect on live pup weight.
The last litter was weaned for second-generation testing. Male and female pup survival in the middle dose group were reduced by 30-40%; there were no high-dose pups. Absolute pup weight in the middle dose group was reduced by nearly equal to 20% at weaning, but was not significantly different at earlier times.
The F0 mice were killed and necropsied after the last litter was weaned. While female body weight was unchanged, female kidney weights were increased by 7% and 8% in the low and high dose groups, respectively. In males, body weight was also unchanged, and kidney weight was increased only at the low dose, by 10%. Male liver weights were increased by 6% and 7% in the middle and high dose groups, respectively. Testis weight and epididymis weight were reduced in the high dose group by nearly equal to 16% and nearly equal to 13%, respectively. Abnormal sperm forms were increased in the high dose group by nearly equal to 6-fold.
The second generation mice were cohabited for a week at 74 ± 10 days of age. There were no high dose offspring for this Task. Only 50% of the middle dose group mated, and a third of the 20 cohabited pairs delivered any pups at 0.1% EGME. While there was no reduction in litter size in this F1 mating, there was a 10% reduction in the proportion of live-born F2 pups at 0.1%, and a 10% reduction in their weight adjusted for litter size.
After the F2 pups were delivered and assessed, all remaining animals were killed, and the F1 mice were necropsied. There were no adverse effects on female body or organ weights, or on male body weights. Liver weight (adjusted for body weight) was increased by nearly equal to 9% and 10%, and kidney weights (also adjusted) were increased by 9% and 7% in the low and middle dose groups, respectively. There was a 10% reduction in adjusted epididymis weight at the middle dose level. There were no changes in sperm parameters at either dose level.
This study showed that the greatest effect produced by EGME at these doses was on the ability to become pregnant and deliver live pups. The top dose (0.3% EGME in the drinking water) was severely toxic to reproduction, with only 8/27 pairs delivering any litters of any pups, live or dead. The middle dose level (0.1% EGME) had few detectable effects on F0 reproduction, but significant adverse effects on F1 reproductive success, based on a reduced fertility index, a reduced proportion of liveborn pups, and reduced F2 pup weight. The lowest dose used in this study, 0.03% EGME, was without adverse reproductive effect in Swiss CD-1 mice.