Mineralized deposits in the thoracic aorta of aged rats: Ultrastructural and electron probe x-ray microanalysis study

Abstract

The thoracic aorta of male and female virgin rats aged from 26–30 months was studied by electron microscopy and electron probe X-ray microanalysis. In all rats (but especially the oldest female) several types of calcified mineral deposits were identified: (a) Ovoid, membrane-bound, amorphous mineral interspersed with fine needle-like crystals; these were found in intact but degenerating arterial cells, and their size and distribution suggested that they were highly calcified mitochondria. (b) Extracellular spherular deposits located in pleomorphic necrotic debris; two distinct types; (i) amorphous or concentrically- layered spherites with characteristics electron-dense periphery, 0.25–0.8 μm diameter, Ca : P = 1.24 ± 0.02, and with significant Mg content (Ca : Mg = 16.7 ± 2.5); (ii) less regularly shaped granules composed of denser material, Ca : P more variable (1.30 ± 0.18), but not detectable Mg. (c) Spiculate crystal lumps which appeared to grow on the microvesicular component (25–100 nm) of the pleomorphic debris. No evidence was found of calcium deposition on or within elastic or collagen fibres. We concluded that age-related arterial calcification is probably initiated within the mitochondria of degenerating vascular smooth muscle cells, and possibly also in the extracellular spaces within lysed, submitochondrial particles.