Ultrastructure of the fibrous subaortic "ring" in dogs with discrete subaortic stenosis.

The subaortic fibrous "ring" in Newfoundland dogs with discrete subaortic stenosis is characterized by the presence of large, uni- and multinucleated, rounded connective tissue cells that resemble chondrocytes in several respects. Connective tissue adjacent to these cells is rich in acid mucopolysaccharides, small but cross-banded collagen fibrils, and small, poorly developed elastic fibers. The chondrocyte-like cells contain numerous cisternae of rough surfaced endoplasmic reticulum and prominent Golgi complexes, and they are surrounded by thick, concentrically arranged layers of basement membrane-like material. The differentiation of cellular and extracellular components of connective tissue in subaortic fibrous rings clearly differs in humans and in dogs with discrete subaortic stenosis.