Toxicological Sciences, Vol 50, 106-116, Copyright © 1999 by Society of Toxicology
MC Newland and PA Reile
Female rats were exposed to 0, 0.5, or 6 ppm Hg (as methylmercuric
chloride, 10 rats/group) in drinking water. For half the rats, exposure
began 4 weeks before mating and for the others, exposure began 7 weeks
before mating. All mating was done with an unexposed male. Maternal
exposure continued to post-natal day (PN) 16. Blood and whole-brain mercury
concentrations were determined in pups on PN 0 (birth) and PN 21 (weaning).
Maternal water consumption was monitored daily during gestation and
lactation. Maternal water consumption increased 2- to 3- fold through
gestation for all groups. Mercury levels in blood and brain were unrelated
to the duration of exposure before mating, although reproductive success
appeared to be so related. Mercury levels in both media were closely
related to consumption during gestation, but apparently maternal exposure
during lactation did not result in exposure to the nursing pups. Brain
mercury in offspring decreased between birth and weaning from 0.49 to 0.045
ppm in the low-dose rats and from 9.8 to 0.53 ppm in the high-dose rats.
The brain increased in weight only about 5.5-fold during this time,
indicating that there was minimal mercury exposure and some net loss from
brain during this period. Brain:blood ratios averaged about 0.14 at birth
and 0.24 at weaning, suggesting differential loss from neural and
non-neural tissue. These ratios are higher than those reported in studies
using less chronic exposure conditions or with adult rats. Brain
concentrations of mercury in females in the low-dose group were about
10-15% higher than those seen in their male siblings. At the higher dose,
the males had slightly higher levels of mercury in the brain than did their
female siblings at birth. The relationship between brain concentration (in
ppm) and cumulative mercury consumption, also expressed on a ppm basis
(cumulative mercury consumed divided by maternal body weight at
parturition), was not linear but was well described by a power-function
relationship: Hg = A*(cum exposure)b where the exponent, b, was 1.12 and
1.17 for blood and brain, respectively, at birth. This exponent was
indistinguishable from 1.0 for both media at weaning, indicating that the
relationship between exposure and blood and brain levels became linear.
ARTICLES
Blood and brain mercury levels after chronic gestational exposure to methylmercury in rats
Department of Psychology, Auburn University, Alabama 36849, USA. newlamc@mail.auburn.edu
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