Effect of hyperbarism on collagenous protein metabolism in granulation tissue

Rats with subcutaneously implanted polyurethane sponges were exposed 6 hours daily for 7 days to high ambient atmospheric pressures (1.5, 2, 2.5 and 3 ATA). Another group was exposed 4 hours daily for 4 weeks to 3 ATA before inducing granulation tissue formation. 14C-proline was administered 16 hours before terminating the experiment. Free hydroxyproline, soluble and insoluble collagen and total noncollagenous protein were isolated from the 7-day granuloma and the amount and radioactivity of 14C-hydroxyproline and 14C-proline were determined. Seven days' graduated hyperbarism did not affect collagen synthesis; the maturation of collagen to insoluble forms was inhibited at 2 and 2.5 ATA, but not at 3 ATA. Stimulated degradation of collagen (free hydroxyproline) was observed at 2, 2.5 and 3 ATA. In animals subjected to long-term exposure at 3 ATA pressure, the collagen in the granuloma matured to insoluble forms more quickly. Biochemical changes were correlated with changes in the fine structure of the granulation tissue. The appearance of the fibroblast proteosynthetic apparatus was not influenced by hyperbarism. Progressive spherical transformation, fusion of mitochondria and lysosomal activation in the pericapillary fibroblasts occurred at 2, 2.5 and 3 ATA. In short-term experiment, the formation of cytosegresomes and cellular necrosis also contributed to the effect at 3 ATA, which is thus already a toxic pressure for granulation tissue.