Antithrombin III inhibits mesangial cell proliferation.

Thrombin stimulates and heparin and heparan sulfate inhibit mesangial cell proliferation. In addition, heparin has been shown to inhibit thrombin-stimulated smooth muscle cell proliferation. The anticoagulant action of heparin is mediated by antithrombin III. This study investigated whether heparin's antiproliferative action is also mediated by antithrombin III. To this end, the effect of antithrombin III on thrombin-stimulated mesangial cell growth was examined. As expected, thrombin stimulated DNA synthesis and cell growth in cultured human mesangial cells. The effect of thrombin on DNA synthesis and mesangial cell proliferation was inhibited by standard heparin and antithrombin III, separately or together. The magnitude of the inhibitory action of antithrombin III was equal to that of equimolar concentrations of heparin and that observed with the combination of the two. Experiments carried out in serum (hence antithrombin III)-free medium revealed that heparin's inhibitory effects are independent of antithrombin III. It was concluded that antithrombin III, an endogenous inhibitor of thrombin's coagulant activity, is an equally effective inhibitor of thrombin's mitogenic action.