Monograph on the Potential Human Reproductive and ... - OEHHA

258 CHAPIN ET AL.
the findings of this study, the study authors concluded
that prenatal and lactational exposure of rats to bisphenol
A does not appear to affect thyroid function.
Strengths/Weaknesses: Strengths of this study include
the use of a range of dose levels of bisphenol A.
Weaknesses include the limited endpoints addressed
(thyroid function), concern that the number of animals
used (6 dams per treatment group) may not provide
adequate statistical power to assess changes in hormone
levels and response given the variability inherent in these
measures, and failure to account for litter in the analyses.
Utility (Adequacy) for CERHR Evaluation Process:
As presented, this study is inadequate because it is
unclear whether there were adequate controls for litter
effects.
Zoeller et al. (2005), supported in part by NIH,
examined the effect of bisphenol A exposure on the
thyroid of developing rats. Sprague–Dawley rats were
housed in plastic cages. [No information was provided
about composition of feed or bedding materials.]
Before initiation of dosing, rats were trained to eat an
untreated wafer each day. On GD 6 (day of vaginal plug
not defined) through the remainder of the experiment
(the remainder of the gestation and lactation periods), 9
rats/group were given a wafer dosed with bisphenol A
[purity not reported] at levels resulting in exposure to 0
(methanol vehicle), 1, 10, or 50 mg/kg bw/day. Doses
were based on those used in the study by Tyl et al.
(2002b). Pups (n 5 7–9/group/sex/time period) were
weighed and killed on PND 4, 8, 15, or 35 (day of birth
not defined). During each of those time periods, serum
thyroxin was measured by RIA. On PND 15, brains of
male pups were sectioned and examined for presence of
RC3/neurogranin mRNA, a thyroid hormone-responsive
gene, using an in situ hybridization and autoradiography
technique. Serum thyroid-stimulating hormone was
measured using an unspecified method in 6–8 male
pups/group (1/litter) on PND 15. Statistical analyses
included ANOVA and Bonferroni t-test.
The text of the study indicated a significant reduction
in maternal body weight gain during pregnancy in the
high-dose group, while Figure 1 of the study indicated a
significant reduction in maternal body weight gain
during pregnancy at all dose levels. Maternal
body weight gain during the lactation period was
unaffected by bisphenol A treatment. Bisphenol A
exposure had no effect on litter size at birth. [Data were
not shown by study authors.] Bisphenol A had no effect
on pup body weights on PND 4, 8, or 15. On PND 15, but
at no other time period, there was a significant increase
in serum thyroxin levels in all dose groups of male and
female pups [percent increases compared to controls
were B11, 35, and 37% in each respective dose group.]
Significant increases in expression of RC3/neurogranin
mRNA were observed in the upper and lower dentate
gyrus in males from each treatment group [with no
apparent dose–response relationship]. Expression of
RC3/neurogranin mRNA in cortex was unaffected by
bisphenol A treatment. No significant effects were
observed for thyroid-stimulating hormone levels in
males on PND 15. The study authors concluded that
bisphenol A acts as a thyroid antagonist at these
concentrations.
Strengths/Weaknesses: Strengths of the study include
use of a range of doses and examination of a role of
bisphenol A as a thyroid hormone antagonist. Weaknesses
include the lack of litter-based analysis.
Utility (Adequacy) for CERHR Evaluation Process:
This study is inadequate based on inappropriate statistics
(i.e., not accounting for repeated measures over time or
the use of more than one pup per litter for a given
endpoint).
3.2.3.3 Studies with neurobehavioral endpoints:
Kwon et al. (2000), from CIIT, examined the effects of
bisphenol A exposure during pre- and postnatal development
on reproductive endpoints and the SDN-POA of
rats. Sprague–Dawley rats were fed NIH-07 feed and
housed in polycarbonate cages with cellulose fiber-chip
bedding. Water was provided in glass bottles with
Teflon-lined caps. Pregnant rats were randomly assigned
to groups according to body weight. Rats (n 5 8/group)
were gavaged with bisphenol A (B99% purity) at 0 (corn
oil vehicle), 3.2, 32, or 320 mg/kg bw/day from GD 11
(GD 0 5 day of sperm detection) through PND 20,
excluding the day of parturition. It was not stated if the
day of parturition was considered PND 0 or 1. A positive
control group was treated with 15 mg/kg bw/day
diethylstilbestrol. Rats were examined for clinical signs
of toxicity and weighed during the study. Pups were
weighed on PND 1 and 7. Pups were weaned on PND 21.
After pups were weaned, dams were killed for assessment
of body and organ weights. On PND 10, brains
were collected from 1–3 female offspring/litter from 6–8
litters/group for measurement of SDN-POA volume. All
remaining female pups were examined for age of vaginal
opening and day of first estrus, and estrous cyclicity was
monitored for 22 days, beginning at B4 months of age.
Lordosis behavior was examined at 6 months of age in 1–
2 female offspring/litter from 7–9 litters/group that had
been ovariectomized 2 weeks before reproductive
behavior testing and primed with estradiol benzoate
and progesterone. Male offspring were killed on PND
180 for measurement of body and reproductive
organ weights and histopathological evaluation of
ventral prostates fixed in 10% neutral buffered formalin.
[Based on information presented in the Results
section, it also appears that ovaries and uteri were
examined in an unspecified number of female offspring
at 6 months of age.] Statistical analyses included
ANOVA, Dunnett test, ANCOVA, and pair-wise comparison
of least square means. The litter was considered the
experimental unit.
Bisphenol A treatment had no significant effect on
maternal body weight during pregnancy or lactation or
on maternal liver, kidney, adrenal, ovary, or uterus
weights. There was no effect on number of live pups/
litter at birth or pup weight on PND 1 or 7. In female
offspring, bisphenol A exposure had no significant effect
on volume of SDN-POA, age or weight at vaginal
opening or first estrus, estrous cyclicity, or mean lordosis
intensity. In male offspring, there were no significant
effects on body weight or weights of testis, epididymis,
seminal vesicle, or prostate. The study authors noted that
a 23% increase in ventral prostate weight in the highdose
group did not reach statistical significance. No
treatment-related histopathological alterations were reported
for ventral prostate, ovary, or uterus. Effects
observed in the diethylstilbestrol group included increased
maternal liver weight, increased SDN-POA
volume in female offspring, and disrupted estrous
Birth Defects Research (Part B) 83:157–395, 2008