Influence of tetracycline on the calcification of epiphyseal rat cartilage. Transmission and scanning electron-microscopic studies.

Tetracyclines are known to interfere with bone calcification. We therefore studied their effects on matrix vesicle production and initial calcification of cartilage. 15-day-old rats were injected intraperitoneally with oxytetracycline 100 mg/kg, 6 consecutive injections every 12 h. Epiphyseal plates were examined by scanning and transmission electron microscopy and compared to light microscopy findings. It was found that high doses of tetracyclines cause degeneration of the chondrocytes in the proliferating and hypertrophic zones. Chondrocytes had short processes with only few matrix vesicles covering their surface. In the chondrocytic lacunae of the longitudinal septa of hypertrophic and calcifying cartilage there were fewer matrix vesicles as compared to controls, and their ability to aggregate and form mineralized calcospherites was impaired. This was further proven when bones were immersed in 7% NaOCl or ashed, as minerals containing calcospherites were hardly seen. It is therefore presumed that interference with intracellular and probably extracellular accumulation of calcium by tetracycline might inhibit matrix vesicle production and aggregation, thus inhibiting calcification.