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

282 CHAPIN ET AL.
termination, which occurred B71 days later. The
remaining male pups from 4–5 litters/group from each
litter (11–17/group) were housed together. Singly housed
males were weighed and killed on PND 183–185, and
group-housed males were weighed and killed on PND
186–187. Equal numbers of males from each group were
killed each day. Liver, kidney, and reproductive organs
were weighed, and testicular sperm count and efficiency
were determined. Technicians were blinded to experimental
conditions. Measures taken to reduce stress to
animals included administering test agents by drip
feeding, minimal handling of pups, and minimal
environmental noise. Selection of 3 males from each
litter increased statistical power compared to previous
studies (Nagel et al., 1997; vom Saal et al., 1997).
Statistical analyses were dually conducted using the
individual offspring and the litter as the statistical unit.
Data were evaluated by ANOVA and Dunnett test.
Results from vehicle-treated and naïve controls were
pooled when there was no evidence of a vehicle effect.
Data from individually housed and group housed-males
were pooled when they did not differ significantly.
There were no significant differences in litter sizes or
percentage of males/litter. In female offspring from the
bisphenol A groups, there were no significant effects on
body weight or organ weights, including cervix, uterus,
vagina, and ovary. Age and weight at vaginal opening
were also unaffected in groups exposed to bisphenol A.
Vaginal opening was delayed in the diethylstilbestroltreated
group and in the naïve control group.
Significant effects included increased terminal body
weights in the low-dose group, increased testis weight in
both dose groups, and increased epididymis weight in
the high-dose group. Because testis and epididymis
weights relative to body weights were nearly identical
to controls [data not shown by study authors], the
authors considered the finding equivocal. Although
prostate weights were slightly higher in the bisphenol
A groups, there were no statistically significant effects on
prostate weight when adjusted for body weight and litter
effects. Daily sperm production was increased in both
dose groups, but the study authors considered the
finding equivocal due to low biological significance.
The study authors noted that the study failed to confirm
the increase in prostate weight and decrease in sperm
production reported in the studies by vom Saal et al.
(1997) and Nagel et al. (1997), but results were consistent
with those reported by Cagen et al. (1999a). Possible
reasons for variability between studies were stated as
differences in background sound level, diet, and animal
body weights. The study authors also mentioned the
possibility of genetic drift occurring in mice bred inhouse
in the vom Saal laboratory.
[The NTP Statistics Subpanel (NTP, 2001) essentially
reproduced the findings reported by Ashby et al.
(1999).]
Strengths/Weaknesses: Strengths are the rather close
replication of the designs of the studies by vom Saal et al.
(1998) and Nagel et al. (1997) with diet as the only major
difference, the use of both solo and group housed mice,
and the support of the conclusions by the NTP Statistics
Subpanel. The use of small samples is an understandable
weakness given that this study was designed to be a
replicate study. The lack of response of the positive
control DES group is problematic.
Utility (Adequacy) for CERHR Evaluation Process:
This study is inadequate for the evaluation process due
to absence of response of the positive control group and
small sample sizes.
Howdeshell et al. (1999), support not indicated,
examined the effect of prenatal bisphenol A exposure
on age of puberty in female mice. [No information was
provided about chow or composition of bedding and
cage materials.] CF-1 mice (n 5 21/group) were fed oil
vehicle [type of oil not specified] or bisphenol A [purity
not reported] at 0.0024 mg/kg bw/day on GD 11–17 [day
of vaginal plug not defined]. On GD 19, pups were
obtained by cesarean section. Intrauterine position of
pups (i.e., located next to male or female pups) was noted
at that time. Pups were fostered by untreated mothers
and weaned on PND 22. Body weights were measured,
and pups were monitored for vaginal opening and time
to estrus. Results were analyzed according to all pups
from each dose group or in relation to intrauterine
position. The study authors stated that fetuses positioned
between 2 male mice were exposed to the lowest levels of
17b-estradiol, while exposures to 17b-estradiol were
highest in fetuses positioned next to female fetuses. Data
were analyzed on a litter basis to control for maternal
effects. Age of vaginal opening was covaried with weight
at weaning. Numbers of female offspring evaluated were
75–111/group for body weight and 51–58/group for
vaginal opening. The study authors attempted to
evaluate females from each intrauterine position in each
litter. [No additional information was provided for
statistical analysis in this brief communication.]
Body weight at weaning was significantly increased in
females in the bisphenol A group. When analyzed
according to intrauterine position, body weights were
22% higher than controls in females who were not
positioned next to a male fetus and 9% higher in females
who had been positioned next to 1 male in utero. There
were no significant effects on age of vaginal opening. [It
was not clear if the data presented were covaried with
body weight.] Bisphenol A treatment significantly
reduced the period between vaginal opening and first
estrus by B2.5 days. When evaluated according to
intrauterine position, a significant decrease in time to
first estrous was observed in females who were not
positioned next to a male pup (accelerated by B5 days)
and in females positioned next to 1 male [B2 days]. No
statistically significant findings were observed in females
who had been positioned next to 2 males in utero. The
study authors concluded that prenatal exposure to
bisphenol A at environmentally relevant levels altered
postnatal growth and reproductive function in female
mice but that natural variations in individual endogenous
17b-estradiol levels influenced the response to
bisphenol A.
The results of this study were also discussed in a
publication by Howdeshell and vom Saal (2000), which
indicated that the work was supported by NIH and
reported additional findings. There was a bisphenol Aassociated
reduction in pup survival between birth and
weaning. Complete litter death occurred in 6 of 21
litters in the bisphenol A group compared to 1 of 21
litters in the control group. Significantly increased
body weight of male pups at weaning was also reported
for the bisphenol A group. Body weights were highest in
males who were positioned next to 2 female pups in
Birth Defects Research (Part B) 83:157–395, 2008