Organohalogen concentrations and a gross and histologic ...

Relationship between histology and BMD
We measured the bone mineral density (BMD) within groups of histology
(absent, mild and moderate) in 44 subadult, adult female and adult male
polar bears (Table 3). The sample size for subadults and adult males were
too small to evaluate the relationship between histopathological changes
and BMD. For adult females, there was no significant difference in BMD
levels between groups of mild and moderate histopathological changes. Levels,
age relations and the negative correlations between ∑-PCBs, ∑-DDTs,
dieldrin and ∑-CHLs, respectively, and skull BMD are reported in Sonne et
al., (Accepted with revision).
Table 3
Mean (SD) levels of of Bone Mineral Density (BMD; g hydroxyapatite/cm 2 ) in the skull of 44
East Greenland polar bears investigated for liver lesions during 1999-2002. The concentrations
are divided on age/sex groups (subadults, adult females and adult males respectively)
and liver histological changes based on the results from Table 1. Number of samples are
given in paranthesis. “.” indicates missing data. n.s. indicate no statistical significant differences
between the three means of the specific age/se s . x group at 5% level. ‡ could not be evaluated
due to low sampling size.
Histopathology Subadults ‡
Adult females n.s.
Adult males ‡
Absent . . 2.2 (1)
Mild 1.7±0.4 (19) 1.9±0.1 (10) n.s.
2.3±0.3 (10)
Moderate . 2±0.2 (3) n.s.
2.6 (1)
Discussion
Nuclear dislocation was found in nearly all individuals. Studies by Sato et
al., (2001) of polar bears from Svalbard revealed the same, and it was proposed
that it could be related to the high vitamin A accumulation (natural
storage) in Ito-cells, accumulated through the ”fatty” Arctic marine food
chains. In mammalian species, the dislocation is usually associated with
hepatitis, carcinomas, hyperplasia (adenomatous) or regeneration (Ibid.).
However, in the study by Sato et al., (2001) such histopathological changes
were not found. Whether the histological changes in the East Greenland
polar bears could be associated to the nuclear dispositioning, could not be
evaluated from our study because all individuals exhibited some or all of the
histopathological changes. If there was a link between nuclear dislocation
and organohalogens or hepatocytic lipid accumulation (e.g. MacLachlan and
Cullen 1995) could not be evaluated either.
Lipid
The Ito-cells are the accumulation and storage site for lipids and vitamin A
in polar bears (Leighton et al., 1988, Senoo et al.,1999, 2001). In the present
study, fat accumulation (lipids) were found in hepatocytes and Ito-cells
(centrolobularily and centroacinary respectively). Polar bears are hyperphagiae
from April to July, where they build up their fat deposits (Ramsay
and Stirling 1988; Messier et al., 1992). Based on samples from the same polar
bears as used in the present study, Dietz et al., (2004) showed a highly seasonal
pattern in the lipid-% in adipose tissue, with the lowest levels in
spring (Mar-May) during hyperphagia and the highest during Sept. In the
present investigation, the seasonal difference in hepatocytic lipid content of
subadults (Apr-Jul higher than Aug-Oct) probably reflected the high seal
blubber consumption in spring (Ramsay and Stirling 1988; Messier et al.,
1992).
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