[Effect of vitamin D3 on the formation of proteoglycans and tissue calcification]

Nonspecific calcinosis engendered by vitamin D3 is associated with extraosseous calcium deposits, in connection with which proteoglycans (PG) can be observed. After administration of vitamin D3 tissue samples from cardiac muscle and aorta of rats were taken and traced ultrahistochemically by means of the acriflavin-phosphotungstic acid contrast-method. The calcification began first with an increase in PG in the cell membranes of the sarcolemma, in the ground substance, and in the capillaries of the interstice. Subsequently circularly formed concentric layers of calcium encrustations appear in the above-mentioned locations. Large amounts of PG were also observed prior to the formation of crystalline fascicular calcium deposits in the ground substance and in the elastic fibers of the media of the aorta. This process began at the outer edges of the media and continued towards their interior, resulting in a loosening of the bond between the elastic fibers and the sarcoplasmic continuations of the smooth muscle cells. The extraosseous calcification resulting after the administration of vitamin D3 can therefore be considered not only as a result of hypercalcemia, but also as a result of stimulation of the production of ground substance through vitamin D3. This form of calcification represents a characteristic pathophysiological process which is differentiated from the dystrophic form in that it begins without previous cell damage.