Morphological aspects of early and late collagen degradation in granulation tissue.

A sequential histologic, ultrastructural and immuno pathologic study was carried out in the Selye's inflammatory pouch model to observe extracellular matrix and cellular changes during granulation tissue formation. Besides changes involving different components of the connective tissue, it was observed that collagen resorption occurred under a biphasic process. At an early phase (3rd to 15th day), in which exudative inflammatory changes predominated, signs of collagen synthesis and degradation were seen simultaneously. Extracellular breakdown and internalization of collagen fragments within fibroblasts and myofibroblasts were observed. Later on (30th to 60th day), changes affecting collagen had a different ultrastructural appearance. Collagen fragmentation, focal "lytic" and "electron dense" changes occurred in the extracellular space specially at the periphery of fibroblasts, myofibroblasts and smooth muscle cells. Collagen degradation, thus seems to be a continuous process in granulation tissue, occurring with different morphologies at different times.