CARTILAGE OR BONE INDUCTION BY ARTICULAR CARTILAGE

Observations with Radioisotope Labelling Techniques

¹ Bone Research Laboratory, Division of Orthopaedics, Department of Surgery, School of Medicine, University of California, Los Angeles; Los Angeles, California, United States of America

1. Isografts of articular cartilage of young rats, with mucoproteins labelled with ³⁵S, extracellular fibrous proteins labelled with ³H-glycine, and nuclei labelled with ³H-thymidine, were transplanted into the anterior chamber of the eye.

2. Thin split-thickness transplants of the cells of the gliding surface of immature articular cartilage induced the formation of fibrous tissue.

3. Thick transplants and subsurface slices of immature articular cartilage, containing germinal cells of the epiphysial cartilage, induced the formation of new bone consistently within 4 weeks.

4. Full-thickness transplants in articular cartilage from senile rats induced only the formation of fibrous tissue.

5. Slices of growing cartilage, devitalised by cryolysis, or extraction of acid-soluble proteins, produced scanty deposits of bone or cartilage, or both, but only infrequently and generally after a lag phase extending from six to twelve weeks.

6. Reduction in the amount of mucoprotein in the cartilage matrix by papain, and suppression of the resynthesis of tissue proteins by cortisone, retarded but did not prevent bone induction.

7. Bone induction is the product of a series of interactions between inducing cells and responding cells by intracellular and intercellular reactions too complex to characterise in physico-chemical terms at this time.