In the cellular secretion theory of mineral deposition, extracellular
matrix vesicles are believed to play an integral role in hard tissue
mineralization (1). Membrane limited matrix vesicles arise from the plasma
membrane of epiphyseal chondrocytes and tooth odontoblasts by a budding
process (2, 3). Nutritional and hormonal factors have been postulated to
play essential roles in mineral deposition and apparently have a direct
effect on matrix vesicles of calcifying cartilage as concluded by Anderson
and Sajdera (4).
Immature (75-85 gm) Long-Evans hooded rats were hypophysectomized by the
parapharyngeal approach and maintained fourteen (14) days post-surgery. At
this time, the animals were anesthetized and perfusion fixed in cacodylate
buffered 2.5% glutaraldehyde. The proximal tibias were quickly dissected out
and split sagittally. One half was used for light microscopy (LM) and the
other for electron microscopy (EM). The halves used for EM were cut into
blocks approximately 1×3 mm. The tissue blocks were prepared for ultra-thin
sectioning and transmission EM. The tissue was oriented so as to section
through the epiphyseal growth plate from the zone of proliferating cartilage
on down through the hypertrophic zone and into the initial trabecular bone.
Sections were studied stained (double heavy metal) and unstained.
