Carbonic Anhydrase Localization in Normal and Osteochondrotic Joint Cartilage of Growing Pigs

The histochemical localization of carbonic anhydrase in the normal and osteochondrotic epiphyseal growth cartilage from 15 growing pigs (6 to 18 weeks old) was studied. All animals were clinically normal. The entire thickness of the articular-epiphyseal cartilage complex from the femoral condyles was fixed in 2% glutaraldehyde and embedded in a water-soluble glycolmethacrylate. Sections (1–2 μm) were incubated on the surface of a medium containing cobalt, phosphate, and bicarbonate. A black precipitate formed at sites of enzymatic activity. This method shows the activity of all different isoenzymes of carbonic anhydrase. The specificity was checked by adding the carbonic anhydrase inhibitor acetazolamide to the incubation medium. Osteochondrosis in the epiphyseal growth cartilage was characterized by chondronecrotic areas in resting, proliferative, hypertrophic, and calcifying regions. When the hypertrophic and calcifying regions were involved, insufficient cartilage calcification and focally impaired ossification were seen. The chondronecrotic areas were surrounded by groups of morphologically viable cells, or so-called “clusters.” Carbonic anhydrase was present in chondrocytes of hypertrophic and calcifying regions of the normal growth cartilage and in osteoclasts and erythrocytes. No evidence of carbonic anhydrase activity was found in the articular cartilage or in the resting region of normal growth cartilage in any of the pigs. No enzyme activity was found in the osteochondrotic cartilage, either in clusters or dead cells. The lack of carbonic anhydrase in the osteochondrotic cartilage demonstrated in this study may result in an inability to produce the alkaline matrix necessary for calcification and could be one reason for the insufficient calcification typical of this cartilage.