Effect of postnatal exposure to benzo[a]pyrene on the uterus of immature rats

The objective of this study was to investigate the morphological effects of postnatal exposure to benzo[a]pyrene (B[a]P) on the development of the uterus, uterine estrogen receptor (ERα) expression, and the uterine response to estrogen stimulation using the uterotrophic bioassay in rats. Neonates were injected on each postnatal day (PND) 1-14 with B[a]P (0.1, 1.0 and 10.0 mg/kg), ethynylestradiol (EE; 1.0 μg/kg) or vehicle (control group). All animals were killed on PND 23. Postnatal administration of B[a]P with doses of 1.0 and 10.0 mg/kg induced significant (P<0.01) reduction of uterine weight and significantly lowered (P<0.05) ERα expression in the luminal epithelium. The increase in uterine weight and luminal epithelium heights after EE stimulation (1.0 μg/kg) on PND 20-22 was significantly higher (P<0.01) in all groups in comparison with corresponding non-stimulated groups. However, the uterotrophic response in rats postnatally exposed to EE and B[a]P was significantly lower (P<0.01) than in controls. In the control and EE groups, EE stimulation on PND 20-22 induced a significant (P<0.01) decrease in ERα immunoreactivity of the luminal epithelium. In contrast, rats postnatally treated with B[a]P showed no change in the density of ERα immunostaining when detected after estrogenic stimulation. The present study showed that postnatal exposure to B[a]P caused pathological changes in constitution and maturation of uterine ERα resulting in disturbed morphological development and uterine dysfunction in immature rats.