Growth of the cartilages of the mid-line cranial base of the Wistar rat: an autoradiographic study using 35S-sulphate.

Matrix synthesis in the mid-line cranial base of the rat was studied using a single injection of 35S-sulphate in animals aged 4-80 days. High uptake of 35S-sulphate in the morphologically distinct zone of early hypertrophy led to it being renamed the Matrixogenic Zone. Relocation of 35S-sulphate label into the primary spongiosa was used to estimate the growth rate of each site of endochondral ossification. This showed a marked caudorostral and temporal gradient. In addition, there was a caudorostral and temporal gradient in hypertrophic cell size, but only a temporal gradient in the rate of cell loss.