CALCIUM CONCRETIONS IN THE PINEAL-GLAND OF AGED RATS - AN ULTRASTRUCTURAL AND MICROANALYTICAL STUDY OF THEIR BIOGENESIS

The genesis of calcium concretions in aged rats was studied by means o f transmission and scanning electron microscopy. The potassium pyroant imonate method, combined with X-ray microanalysis, allowed us to study the distribution of cations and calcium. Notable accumulations of cal cium (associated with phosphorus) were localized in vesicles, vacuoles , lipid droplets, lipo-pigments, and mitochondria of dark pinealocytes . The results obtained in the present investigation suggest that these organelles are involved in the genesis of the concretions. The presen ce of sulfur indicates the existence of an organic matrix. We propose that genesis takes place in dark pinealocytes, which contain more calc ium than light pinealocytes. Mineralization foci are sometimes associa ted with cellular debris and enlarge by further apposition of material . Two types of concretions, as determined by electron microscopy and c onfirmed by electron diffraction, could be observed: the ''amorphous'' type with concentric layers and the crystalline type with needle-shap ed crystals. Once formed, the concretions reach the extracellular spac e and the cell breaks down. Possible extracellular calcification is su ggested in the extracellular calcium-rich floculent material. The mine ralization process is interpreted as being an age-related phenomenon a nd mainly a consequence of the degeneration of pinealocytes.