Differential Sensitivity to Prepubertal Xenoestrogen Disruption in C57 and CD10 Mice.

Abstract

Mice are routinely used as model organisms to study the effects of endocrine disrupting chemicals. Different strains of mice differ in their sensitivity to endocrine disruption and the difference in sensitivity may be life stage and or tissue dependent. Previous work has shown that C57BL/6 (C57) and CD-1 mouse strains have differential sensitivity to prepubertal xenoestrogen disruption of the testis. In order to identify mechanisms of differential strain sensitivity to prepubertal xenoestrogen exposure C57 or CD10 mice were backcrossed > seven times to Estrogen Receptor action INdicator (ERIN) mice that contain a transgene with an estrogen responsive promoter linked to the reporter gene beta-galactosidase. At weaning mice were group housed and exposed to ethinyl estradiol [(EE2) 1, 10, or 100 micro-g/kg body weight)] via their drinking water (vehicle control = 0.1% ethanol). Mice were maintained on treated drinking water until collection at 48 days of age. Body, testes, preputial gland, seminal vesicle, and coagulating gland weights were obtained at necropsy. The presence of preputial separation, which is a marker of puberty, and semen in the seminal vesicles was also noted at necropsy. We confirmed that the backcrossed ERIN mice were very similar to their respective wildtype parent strains and exhibited the same differential sensitivity to prepubertal xenoestrogen exposure. Overall, the C57 mice were more sensitive to prepubertal xenoestrogen disruption of the male reproductive tract. The effect on testis weight and preputial separation were the most striking, where C57 mice were over 33-times more sensitive than CD10 mice (IC50 was not reached in CD10 mice). Testes from C57 mice exposed to 1, 10, or 100 micro-g/kg EE2 were 12%, 79%, and 89% smaller, respectively, than those from vehicle exposed mice, whereas testes from CD10 mice were 3%, 11% and 13% smaller than those from vehicle exposed mice. The differential sensitivity of preputial separation was striking at the dose of 10 micro-g/kg EE2, where none of the C57 mice displayed preputial separation while all of the CD10 mice did. Even at the highest EE2 dose, 80% of the CD10 mice still showed preputial separation. This indicates that C57 mice were over 33-times more sensitive to inhibition of puberty than CD10 mice. The preputial glands, seminal vesicles, and coagulating glands decreased in weight following prepubertal xenoestrogen exposure. These tissues were 8-11 times more sensitive to disruption by EE2 in C57 mice than CD10 mice. Preputial gland weight was the most sensitive marker for prepubertal xenoestrogen disruption (IC50 of 1 and 10 micro-g/kg for C57 and CD10 mice, respectively). In summary, C57 mice were much more sensitive to testis disruption by prepubertal xenoestrogen exposure than CD10 mice. The differential sensitivity to estrogen disruption between C57 and CD10 mice, appears to be life stage dependent, however, as we have not found differences in sensitivity to disruption from adult xenoestrogen exposures. Furthermore, the ERIN transgenic mice backcrosses responded very similarly to wildtype mice following prepubertal EE2 exposure and will be used to examine the mechanisms of differential prepubertal disruption by xenoestrogens. (poster)