Animal model of chondrocyte apoptosis in the epiphyseal cartilage of the neonatal bone

Apoptosis is considered to be the mechanism responsible for the death of chondrocytes during endochondral bone formation. It is also claimed that apoptosis of the chondrocytes is age related and that the apoptotic index increases with age. However, a detailed analysis of the apoptotic activity of the neonatal epiphyseal cartilage is lacking. A model that evaluates apoptosis in the femoral rat epiphyseal cartilage both quantitatively and qualitatively is reported. Apoptotic incidence in the epiphyseal cartilage reached a maximum at age 6 days, but the age in our study did not significantly affect the percentile rate of apoptotic chondrocytes (P > 0.05, Kruskal-Wallis test). Apoptosis in the zone of hypertrophic cartilage played the most important role in the growth plate's homeostasis. Morphologic evidence of apoptosis was necessary in addition to positive nick end labeling of cells. Electron microscopy studies revealed atypical modes of programmed death of the growth plate chondrocytes in addition to the classical apoptotic mode.