Effect of maternal exposure to endocrine disrupting chemicals on reproduction and mammary gland development in female Sprague-Dawley rats

Abstract

The aim of the study is to determine whether low doses of "endocrine disrupting chemicals" (EDCs) affect the development and proliferative activity of the mammary glands (MGs). Adult parous/nulliparous female Sprague-Dawley (SD) rats were treated from post-natal day (PND) 1 until PND 180 with diethylphthalate (DEP), methylparaben (MPB), triclosan (TCS) and a mixture at doses comparable to human exposure. The doses (mg/kg b.w./day) were: DEP=0.173; MPB=0.105; TCS=0.05. EDC treatment resulted in mortality rates >20% in pups as early as lactation day 7. Significant morphological/histological changes were observed at the end of lactation in the MGs of EDC-treated dams. The total transcriptome profile as well as lactation-related genes in MGs also corroborate the morphological findings as more profound gene expression changes are present only at the weaning period. The study highlights the heightened sensitivity of the MGs during critical windows of exposure, particularly pregnancy and lactation, with an impact on pups' survival.

Keywords: Endocrine disruptors; Mammary glands; Rats; Windows of susceptibility.

FIGURE 1

Outline of generation and treatment of experimental animals. A: F0 generation corresponds to breeders of the studied animals (F1), treated from delivery until weaning of the pups. B: The F1 generation was divided into two groups: nulliparous females treated from PND 1 until PND 181and parous females treated from PND 1 until PND 181, mated at PND 97 and observed during their pregnancy and lactation of their offspring. the F2 generation. For each group, at LD 28 (PND 146), corresponding to the end of lactation for parous rats, three animals per experimental group were sacrificed and mammary glands analyzed. At PND 181 all females were sacrificed and mammary gland examined. Solid triangles (▼) represent conclusion of exposure and sacrifice of animals.

FIGURE 2

Representative morphological and histological features of hematoxylin and eosin-stained paraffin sections of nulliparous female Sprague Dawleys rats, sacrificed at PND 181. Both the vehicle control (A,B) and treated (in this case with MPB) groups (C, D) showed normal ducts, epithelia, and stroma

FIGURE 3

Mammary gland from “Dams at the end of lactation-LD 28” Sprague-Dawley rat, 21-weeks old, sacrificed at LD 28 (after the weaning of their pups). Olive oil control (A,100X), DEP (B, 100X), MPB (C, 100X), TCS (D, 100X), MIX (E, 100X).

FIGURE 4

Representative morphological and histological features of hematoxylin and eosin-stained paraffin sections of parous female Sprague Dawleys rats, sacrificed at PND 181. Both the vehicle control (A, B) and treated (in this case with DEP) groups (C,D) showed residual secretory content in the collapsed alveolar and ducts structures

FIGURE 5

Hierarchical clustering of significantly differentially expressed probe sets between TCS and OIL at PND 146 (LD 28) (FDR < 0.25, 1-way ANOVA). Yellow corresponds to up-regulated gene expression, blue to down-regulated gene expression.