The effects of heparin and dextran sulphate on cultured mouse limb bones.

Heparin and the synthetic substitute dextran sulphate induce osteoporisis following prolonged administration to man or experimental animals. The possibility that this is brought about by a direct toxic effect on bone has been studied in tissue culture using explants of mouse radii, ulnae and tibiae. Fifty-three bones from new born or day old mice were cultured as controls, 73 with added heparin and 74 with added dextran sulphate at concentrations 0·1, 1·0 and 5·0 mg. per ml. Cultures were continued for 6 days. Control bones increased in length by approximately 22 per cent during this period and although little endochondral ossification occurred there was considerable periosteal and endosteal new bone formation. When heparin or dextran sulphate was added to the culture medium there was progressive impairment of linear growth with increasing concentrations of these substances. Thus at a concentration of 0·1 mg. per ml. there was little impairment of linear growth but at 5·0 mg. per ml. the bones increased in length by only approximately 15 per cent. With 1·0 and 5·0 mg. per ml. of heparin or dextran sulphate there was increased resorption of bone and impaired new bone formation. At the highest concentration of 5 mg. per ml. both substances almost completely inhibited new bone formation. Undecalcified sections showed no loss of mineral from the remaining diaphyseal bone and there was no impairment of alkaline phosphatase activity demonstrated histochemically. The concentrations of heparin or dextran sulphate required in the present tissue culture experiments to produce bone changes were higher than those achieved in the blood and tissue fluids of experimental animals even after prolonged administration. For the changes to be brought about by a direct effect of heparin or dextran sulphate on bone it would be necessary to postulate a selective accumulation of these substances in bone tissues.