Correlations between age and rat dermis modifications. Ultrastructural-morphometric evaluations and lysyl oxidase...

The extracellular matrix is a complex, integrated macromolecular system which plays a crucial role in the economy of each organ. In this study we focused our attention on the correlations between age and rat skin dermis. The latter was chosen as a model of the connective tissue, and was analyzed by means of electron microscopy and by measurement of the activity of lysyl oxidase, the enzyme involved in collagen and elastin crosslink formation. Ultrastructural and morphometric evaluations associated to body weight growth, showed a progressive increase in the amounts of extracellular components and a progressive reduction in the cell density. Skin from adult animals appeared characterized by a well organized matrix; by contrast, in old rats, we observed several degenerative features such as the disorganization of collagen bundles, the vacuolization of elastic fibers, and the atrophy of the mesenchimal cells. Morphometric evaluations in old animals showed a slight but significant reduction in the percentage of the total collagen measured, a fair stability in the area occupied by the elastin fibers, and an increase of the apparently non-structured matrix. The fact that lysyl oxidase activity was diminished in old rats does not corroborate the observation by several authors that increased collagen insolubility is a consequence of higher intra- and intermolecular crosslinking. This would suggest that other chemical modifications, such as crosslink oxidation or non enzymatic glycosylation, might be involved during the aging of connective tissue. The qualitative and quantitative modifications observed at all ages illustrate the correlation between connective tissue modifications and structural and/or functional properties of the skin.