[Matrix vesicles in various "elastic" organs].

Matrix vesicles (MV) have been found during normal development in the rabbit and rat aorta and pulmonary trunk as well as in the elastic cartilage of the rat external ear. In spite of the morphological variability of MV, two basic types can be ruled out: MV with dense osmiophilic content, and light or electron-translucent MV. MV of the first type are considered to be extracellular lysosomes. MV in the vessel wall are predominantly localized in the subendothelium, and the border-zones between media and endothelium or media and adventitia; in elastic cartilage they are localized near the perichondrium. Especially often they can be seen at the place of contact between elastic and other fibers of the intercellular space. They can even penetrate the elastic membranes and plates. The parts of the organs mentioned encounter higher functional demands and are more active during development and growth. The MV appear almost exclusively a short time before birth, and predominantly during the first 20-60 days of postnatal life. Their origin may be due to exocytosis and the detachment of parts (Mikroapokrinie) of endothelial cells, smooth muscle cells, fibrocytes and chondrocytes. The MV are considered to be a substrate for subsidiary extracellular mechanisms of adaptation during the normal ontogenesis of the elastic tissue of these organs.