Quantitation of ultrastructural changes in mouse pancreatic acinar cells caused by foreign serum

Quantitative changes in the pancreatic acinar cell organelles were studied in BALB/c mice injected with 1.0 ml fresh rabbit serum intraperitoneally. Groups of 5 mice were killed at 0, 1, 3, 6 and 12 h after the serum injection. Pancreatic tissue was processed for electron microscopy by glutaraldehyde and osmium tetroxide fixation and Epon embedding. The proportions of acinar cell cytoplasm (volume fractions) occupied by zymogen granules, granular endoplasmic reticulum, Golgi apparatus, mitochondria and lysosomes (including autophagosomes) were determined by the point counting method from electron micrographs. The volume fraction of lysosomes increased during the first 3 h and remained markedly elevated up to 12 h. The volume fractions of zymogen granules increased from 12 to 28% in 12 h. It was concluded that the secretory mechanism of pancreatic acinar cells was injured by the foreign serum. The injury caused accumulation of zymogen granules and increased autophagic activity in the acinar cells.