Proteoglycans were identified and localized histochemically and ultrastructurally in normal and hyperplastic arterial intimas in nonhuman primates (Macaca nemestrina). These regions were consistently more alcianophilic than the adjacent medial layers and this alcianophilia was absent after treatment with glycosaminoglycan- degradative enzymes. Ultrastructurally, the intimal intercellular matrix consisted of numerous, irregularly shaped, 200-500-A diameter granules possessing 30--60-A diameter filamentous projections, and these granules were dispersed between collagen and elastic fibers. The granules exhibited a marked affinity for ruthenium red and were interconnected via their filamentous projections. The ruthenium red- positive granules were intimately associated with the plasma membrane of intimal smooth muscle cells and attached to collagen fibrils and elastic fibers. The matrix granules were completely removed after testicular hyaluronidase or chondroitinase ABC digestion but only partially removed after leech hyaluronidase treatment. These results suggest that the matrix granules contain some hyaluronic acid and one or more isomers of chondroitin sulfate. In addition to the large ruthenium red-positive matrix granules, a smaller class of ruthenium red-positive granule (100--200-A diameter) was present within the basement membranes beneath the endothelium and surrounding the smooth muscle cells. Ruthenium red also exhibited an affinity for the surface coat of the smooth muscle cells. The potential importance of proteoglycans in arterial intimal hyperplasia is discussed
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