Comparison of Whole Calvarial Bones and Long Bones During Early Growth in Rats. II. Turnover of Calcified and Uncalcified Collagen Masses

The increase of total collagen and its destruction were compared for whole calvaria and long bones from young growing rats prelabeled in utero with 3H-L-proline. Rats were compared from birth to 16 weeks of age. Long bones and calvaria were isolated as intact anatomical units for autoradiography or separated by collagenase into calified and uncalcified collagens. Autoradiography using 14C-L-proline demonstrated eccentric modeling of bone collagen. With growth the mass of calcified collagen (bone) increased rapidly in calvaria and long bones. A similar increase in the mass of uncalcified collagen (mainly cartilage) occured in the long bones; a very small increase occurred in the fibrous tissue of calvaria. Total and specific radioactivities of collagens at each age were compared to that present at birth. With growth remodeling an almost complete loss of pre-existing radioactive collagen occurred from uncalcified fibrous tissue of calvaria as compared to a smaller but substantial loss from the uncalcified cartilage of long bones. A marked loss of calcifed collagen occurred in long bones as compared to a smaller loss from calvarial bones. The istopic data indicate a large turnover of fibrous tissue (type I collagen) with growth remodeling as compared to a smaller turnover of bone (calcified, type I collagen) and cartilage (typc I collagen). The turnover rate of skeletal collagens depends upon whether the collagen is calcified or not, and not upon the type of collagen.