Effects of perinatal polychlorinated biphenyls on adult female rat reproduction: development, reproductive physiology, and second generational effects

Abstract

Perinatal exposures to endocrine-disrupting chemicals, such as polychlorinated biphenyls (PCBs), can cause latent effects on reproductive function. Here, we tested whether PCBs administered during late pregnancy would compromise reproductive physiology in both the fetally exposed female offspring (F1 generation), as well as in their female offspring (F2 generation). Pregnant Sprague-Dawley rats were treated with the PCB mixture, Aroclor 1221 (A1221; 0, 0.1, 1, or 10 mg/kg), on Embryonic Days 16 and 18. Somatic and reproductive development of F1 and their F2 female offspring were monitored, including ages of eye opening, pubertal landmarks, and serum reproductive hormones. The results showed that low doses of A1221 given during this critical period of neuroendocrine development caused differential effects of A1221 on F1 and F2 female rats. In both generations, litter sex ratio was skewed toward females. In the F1 generation, additional effects were found, including a significant alteration of serum LH in the 1 mg/kg A1221 group. The F2 generation showed more profound alterations, particularly with respect to fluctuations in hormones and reproductive tract tissues across the estrous cycle. On proestrus, the day of the preovulatory GnRH/gonadotropin surge, F2 females whose mothers had been exposed perinatally to A1221 exhibited substantially suppressed LH and progesterone concentrations, and correspondingly smaller uterine and ovarian weights on estrus, compared with F2 descendants of control rats. These latter changes suggest a dysregulation of reproductive physiology. Thus, low levels of exposure to PCBs during late fetal development cause significant effects on the maturation and physiology of two generations of female offspring. These findings have implications for reproductive health and fertility of wildlife and humans.

Figure 1

F1 & F2 litter size and litter sex ratios. A. Numbers of pups (prior to culling) in the F1 generation group did not differ with treatment. B. Sex ratios did not differ in either the F1 or the F2 generations. Data here and in other figures are shown as mean ± SEM.

Figure 2

F1 and F2 body weight and anogenital distance were analyzed by repeated measures ANOVA across development. A. F1 body weights: ANOVA showed a significant difference only on P34, at which age the 1 mg/kg group was significantly heavier than all other treatment groups. B. F1 anogenital distance: No significant differences were detected. C. F2 body weights: On P40-42, the 1 mg/kg group was significantly lighter than the control or 0.1 mg/kg groups. D. F2 Anogenital Distance was unaffected by treatment. The letter a denotes a significant difference between the 1 mg/kg group with all other groups (p < 0.005). The letter b denotes a significant difference between the 1 mg/kg with the control and 0.1 mg/kg groups (p < 0.05).

Figure 3

F1 serum hormone levels. A. Serum progesterone. B. Serum Estradiol. C. Serum luteinizing hormone (LH). No significant differences were observed for progesterone and estradiol. The 1 mg/kg group had significantly higher LH levels than either the 0.1 or 10 mg/kg groups and tended to have higher LH levels than the control group, although this was non-significant (p = 0.0516). The letter a denotes a significant difference between the 1 mg/kg group with the 0.1 and 10 mg/kg groups (p < 0.05).

Figure 4

F1 ovarian and uterine weights, shown normalized to body weight. There were no significant differences between groups.

Figure 5

F2 serum hormone levels across the estrous cycle. A. Serum progesterone: Significant interactions between cycle stage and treatment occurred in F2 female rats on proestrus, during which the control group was different from all three A1221 treatment groups. On diestrus 2, significant differences were found for the 10 mg/kg group compared to the 0.1 and 1 mg/kg groups. Patterns of hormones across the cycle in control rats were significantly different from those in the A1221 F2 rats (see Results for details). B. Serum Estradiol: A significant effect of cycle stage (p < 0.001) was detected by two-way ANOVA, but no effect of treatment nor any interaction of treatment with cycle stage was detected. C. Serum LH: LH levels varied significantly by estrous cycle stage, and a significant interaction of treatment with cycle stage was also found. On proestrus, there were significant differences between control and all three A1221 treatment groups. Only the control and 10 mg/kg groups showed significant fluctuations in LH levels across the estrous cycle (see Results for details). The letter a denotes a significant difference between the control with the 0.1 mg/kg (p < 0.005) and the 1 and 10 mg/kg (p < 0.05) groups. The letter b denotes significance between the 10 mg/kg group with the 0.1 and 1 mg/kg groups (p < 0.05). The letter c denotes a difference between the control group with the three A1221 groups (p < 0.01 vs. 1 mg/kg; p < 0.05 vs. 0.1 and 10 mg/kg). N=4 to 7 pups per group.

Figure 6

F2 0varian and uterine weights on ∼P42, expressed as a percentage of body weight and shown here according to estrous cycle day. For the ovary (A), two-way ANOVA showed a significant effect of treatment and cycle stage, but no interaction. The control group was significantly different from the 0.1 mg/kg A1221 group (p < 0.05), and a showed a non-significant trend vs. the 1 mg/kg group (p = 0.0514). For the uterus (B) there was no significant effect of treatment, or interaction with treatment, although uterine size fluctuated significantly across the estrous cycle. *, ovary and uterine weights are significantly larger on estrus compared to all other days of the estrous cycle (p < 0.05).