Ultrastructural studies of muscle cells and vascular endothelium immediately after freeze-thaw injury.

Abstract Little is known about the ultrastructural changes which occur in vascular endothelium immediately after an in vivo freezethaw insult, although most investigators will agree that tissue viability relates directly to the degree of vascular damage. In this study an electron microscopic examination of an in vivo model for frostbite injury was initiated. The horseradish peroxidase technique was utilized to follow early alterations in capillary flow and the independent effects of hypoxia, cooling to 2 °C, supercooling, and a single freeze-thaw insult were assessed. No precipitous changes in muscle cell mitochondria or capillary endothelium were detected as a result of brief hypoxia, cooling at 2 °C, or supercooling to −13 °C. Reducing the temperature by 1 °C/min until freezing occurred, continuing to cool for 10 min postheat of fusion, and rapidly rewarming resulted in consistent mitochondrial damage in muscle cells and marked degeneration of associated capillaries. Peroxidase injected iv prior to thawing was rarely localized in the capillaries of previously frozen muscle. Since peroxidase was found in the capillaries of unfrozen legs of the same animals, it is inferred that little or no flow occurred in most capillaries postthaw. Ultrastructural integrity of capillaries immediately after thawing may be a good index for predicting tissue loss. “In conducting the research described in this report, the investigators adhered to the ‘Guide for Laboratory Animal Facilities and Care,’ as promulgated by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, National Academy of Sciences-National Research Council.”