Bone cell kinetics and function during experimental uremia.

Bone cell kinetics and function and chondrocyte kinetics were evaluated in uremic rats and their pair-fed controls using quantitative histology and 3H-thymidine labeling. The principle histologic abnormality in the proximal tibial metaphysis of uremic rats was a relative abundance of proliferating and differentiated bone cells. No mineralization abnormalities were observed. There was increased proliferation of bone cells and an increased rate of differentiation of osteoblasts and osteoclast nuclei in uremic animals. There was no change in chondrocyte kinetics, indicating a dissociation of the normal bone elongation and bone maturation processes. The data on osteoclast number and hard tissue suggest individual osteoclasts in uremic animals have sub-normal resorbing efficiency. It is proposed that the cell kinetic alterations are due to secondary hyperparathyroidism. The cause of osteoclast inefficiency is uncertain, but may be related to (1) deficiency of active products of vitamin D; (2) chronic uremia; and/or (3) chronic secondary hyperparathyroidism.