Metabolism of collagen in bone of adjuvant induced arthritic rat

The metabolism of collagen was examined in bones of rats rendered adjuvant arthritis and matched controls using radioactive isotopic tracer techniques. The rate of the synthesis was studied after the incorporation of tritiated labeled proline into the total bone collagen and determining the content of total hydroxyproline and estimating the specific and total activities of radioactive labeled hydroxyproline. The rate of the catabolism was examined by measuring the activities of various collagen degrading proteolytic enzymes in the bone extract and by estimating the total content of hydroxyproline excreted in the urine. The degradation of collagen was also followed by measuring the specific and total radioactivities of (3H)-hydroxyproline in the urine. When (3H)-proline was injected into the adjuvant arthritic rat, the specific and total radioactivities of (3H)-hydroxyproline in bone collagen were reduced significantly in diseased bone. The activities of various enzymes involved in the catabolism of collagen and other extracellular matrix components were appreciably elevated (about 2-3 fold) in the bone extract of arthritic rat. Similarly, the specific and total activities of (3H)-hydroxyproline in urine samples were also greatly increased in arthritic rats. In addition, the decreased content of hydroxyproline in total bone collagen was accompanied by the increased excretion of urinary hydroxyproline in adjuvant arthritic rats. The results clearly suggest that the arthritic disease induces the qualitative and quantitative changes in bone composition and causes the alteration in the metabolism of collagen in diseased tissue. These observations could therefore, explain in part, the altered response of connective tissue of bone to inflammation and arthritis.