Characterization of lipid accumulation in the gallbladder mucosa of the ground squirrel fed a lithogenic diet

Richardson's ground squirrels (Spermophilus richardsonii) of both sexes were fed a 2 per cent cholesterol‐enriched diet for intervals of 12, 18, and 24 h; 3, 5, and 7 days; and 2, 3, 10, and 20 weeks. It was shown that free (unesterified) cholesterol, phospholipid, and cholesterol ester accumulated in specific regions of the gallbladder mucosa during cholelithiasis. Electron microscopy revealed the presence of lipids inter‐ and intracellularly as early as 12 h after ingestion. By 7 days, lipids were seen in dilated endoplasmic reticulum, as well as in supranuclear and basal regions of epithelial cells. Histochemical localization revealed free cholesterol in dilated endoplasmic reticulum and residual bodies at the ultrastructural level. Neutral lipid was observed by light microscopy in the supranuclear and basal regions of the cells. In 10‐ and 20‐week treated animals, lipid droplets were also seen in the lamina propria and macrophages. The lesion induced by cholesterol ingestion persisted throughout the experimental period, and while different from that in human tissue, it was similar to those observed in experimental canine cholesterosis.