Light microscopic changes consisted of nuclear displacement from the normal central cytoplasmic location in parenchymal cells, mononuclear cell infiltrations (mainly portally and as lipid granulomas), mild bile duct proliferation accompanied by fibrosis, and fat accumulation in hepatocytes and pluripotent Ito cells.
In the case of Ito cells and bile duct hyperplasia accompanied by portal fibrosis, we performed the chisquare test within subadult, adult, and old bears to determine age dependency.
In the case of lipid granulomas, the relationship to OHCs was analyzed based on the presence or absence of Ito cells.
Finally, we found a trend of livers with visible Ito cells showing a larger frequency of fatty granulomas, compared with livers without visible Ito cells (p < 0.
The fact that liver tissue, rich in visible Ito cells, had a higher number of lipid granulomas indicates that microorganisms (originating from the blood supply) play a role in the random multifocal necrosis (rupture of Ito cells) observed (Kelly 1993; MacLachlan and Cullen 1995).
In polar bears, the Ito cells are one of the major accumulation and storage sites for lipophilic vitamin A (Leighton et al.
Degree of change [% (n)] Histologic Absent Mild Moderate Severe liver change Portal mononuclear cell infiltrations 82 (65) 8 (6) 8 (6) 2 (2) Random mononuclear cell infiltrations 87 (69) 11 (9) 1 (1) 0 (0) Hepatocytic intracellular fat 0 (0) 16 (13) 24 (19) 60 (47) Lipid granulomas 24 (19) 35 (28) 32 (25) 9 (7) Lipid accumulation in Ito cells 25 (20) 18 (14) 24 (19) 33 (26) Mild bile duct hyperplasia with fibrosis 92 (73) 8 0 (0) 0 (0) Histologic Age Sex Season liver change [(F)p] [(F)p] [(F)p] Portal mononuclear cell infiltrations NS NS NS Random mononuclear cell infiltrations NS NS NS Hepatocytic intracellular fat NS NS NS Lipid granulomas NS NS NS Lipid accumulation in Ito cells (8) * NS NS Mild bile duct hyperplasia with fibrosis (11) * NS NS NS, not significant.
05), whereas Ito cell lipid accumulation was highly related to age (p < 0.
It has been proposed that this displacement is related to the high vitamin A accumulation (natural storage) in Ito cell cytoplasmic lipid droplets and hepatocytes, accumulated through the extensive feeding on blubber from ringed seal and bearded seal (Kakela et al.
1992; Ramsay and Stirling 1988), and a seasonal pattern in Ito cell numbers may be expected as was the case for the fatty tissue lipid percentage (Dietz et al.