Organohalogen concentrations and a gross and histologic ...

42
Results and comparisons
The polar bear liver was similar to domestic carnivorous species although
interlobular fibrous septa seemed to lack as in brown bear (Ursus arctos)
(MacLachlan and Cullen 1995, Prunescu et al. 2003). Five different tissue
changes were found in the light microscopic evaluation of the liver tissue: fat
accumulation, mild to moderate mononuclear cell infiltrations, portal fibrosis,
bile duct proliferations and nuclear dislocation. The lipid accumulation
was thought to be a result of blubber intake (Ramsay and Stirling 1988;
Messier et al. 1992, Dietz et al. 2004), but if organohalogen toxicity (PCBs)
plays a role in this morphological appearance cannot be ruled out (e.g. Kimbrough
et al. 1971, Kimbrough et al. 1972, Bruckner et al. 1974, Bergman et al.
1992b, MacLachlan and Cullen 1995, Parkinson 1996). Regarding the lipid
granulomas these were thought to be a result of randomly distributed infectious
agens in the parenchyma via the portal vein probably ”caught” in the
narrow space of Disse (MacLachlan and Cullen 1995). There were no age related
differences in the degree of mononuclear cell infiltrations while indications
of positive age relation was found for portal fibrosis (Table 6). No
such age difference were found for bile duct proliferations, but these were
found to be highly related to the degree of portal fibrosis. Overall, there was
no significant difference in the prevalence of histopathological changes between
adult females and adult males (Table 6).
Seasonal variations was found for hepatocytic lipid content (subadults) and
fibrosis (adults) with both being lower in Aug-Oct compared to the rest of
the year. Regarding the bile duct proliferation and mononuclear cell accumulations
around portal triads, these could be a result of chronic inflammation
(liver injury) (MacLachlan and Cullen 1995), and has been described
in mink (Mustela vison) exposed to PCBs (Bergman et al. 1992a) as well as
free-ranging Atlantic bottlenose dolphins (Tursiops truncatus) (Rawson et al.
1993) and Arctic beluga whales (Delphinapterus leucas) (Woshner et al. 2002)
exposed to mercury. Whether this is due to organohalogens and/or other
environmental factors cannot be concluded. In our analysis we found significant
differences in mean concentrations of organohalogens between
groups of histopathological changes. However, these were not consistent
probably due to low sample size. As discussed earlier, high individual variability
due to age, sex, season, metabolic capacity and individual sensibility
to organohalogens could also play a role. Due to low sample size we could
not analyze relations between histopathological changes and individual levels
of skull bone mineral density either.
Table 6
Results of histological examination of liver tissue from 88 polar bears sampled in East Greenland, 1999-2002 given as frequencies (no.
of observations in paranthesis). Changes considered were lipid content of Ito-cells (lipid), mononuclear portal cell infiltrations (infiltrations),
granulomes (often lipid granulomes), portal fibrosis (fibrosis) and bile duct proliferation (proliferation). Histopathological findings
were classified according to severity (absent, mild and moderate). Sub: subadults of both sexes, AdF: adult females and AdM: adult
males. In few cases of autolysis and freeze damage, one or more of the changes considered could not be evaluated.
Group Lipid Infiltrations Granulomes Fibrosis Proliferation
Absent 41%
(14)
Mild 26%
(9)
Moderate 32%
(11)
Sub AdF AdM Sub AdF AdM Sub AdF AdM Sub AdF AdM Sub AdF AdM
10%
(3)
10%
(3)
80%
(23)
0%
(0)
16%
(4)
84%
(21)
3%
(1)
66%
(21)
31%
(10)
8%
(2)
72%
(18)
20%
(5)
21%
(5)
54%
(13)
25%
(6)
16%
(5)
68%
(21)
16%
(5)
52%
(13)
36%
(9)
12%
(3)
33%
(8)
54%
(13)
13%
(3)
55%
(17)
45%
(14)
48%
(12)
52%
(13)
33%
(8)
67%
(16)
68%
(21)
32%
(10)
56%
(14)
44%
(11)
. . . . . .
Total 34 29 25 32 25 24 31 25 24 31 25 24 31 25 24
58%
(14)
42%
(10)