Ultrastructural changes in the mucosa of frozen-preserved canine ileum

Serial ultramicroscopic observations were made on four segments of canine ileum frozen to -50°C after use of 10% glycerol solution as a cryoprotectant. The observed alterations in cellular structure were progressive in degree during the perfusion, frozen and thawed, and revascularized stages. Normal fine structure was evident in the cells studied 1 month after freezing. There was a wide variation in the response of individual cells to the freezing process. Changes observed in the epithelial cells included swelling of mitochondria, distention and vesiculation of the endoplasmic reticulum, and rounding with dilation of the cisternal profiles of the Golgi apparatus. In the terminal stages prior to cell disruption, fragmentation of the microvilli was observed. Consistent or typical changes in the nuclei were not identified in this study. In the lamina propria, the capillary endothelium retained its integrity during perfusion but showed mitochondrial swelling. Late changes following freezing included disruption of endothelial cytoplasm. Minimal changes in smooth muscle cells were observed but included decrease in peripheral myofibrills and increase in condensed nuclear chromatin. Plasma cells were relatively unaffected by perfusion but showed vesiculation of the endoplasmic reticulum after freezing and thawing. It would appear that the morphological changes observed after freezing and thawing first appear after perfusion. The one ultrastructural change which may prove most useful in evaluating improved storage procedures is the gradual alteration in the rough endoplasmic reticulum, which develops over a broad range of experimental conditions.