Suppression by heparin of injury-induced myointimal thickening

To ascertain the effect of heparin upon intimal smooth muscle cell proliferation after arterial endothelial injury, we subjected young male Sprague-Dawley rats to right carotid air injury and infused them with heparin intravenously for 5, 10, and 14 days after surgery. Control animals received lactated Ringer's solution. Marked inhibition of intimal smooth muscle cell proliferation was observed in the heparinized rats as compared to controls. This profound heparin effect may be due to the enhancement by heparin of antithrombin III inhibition of thrombin and suggests a hitherto unsuspected role of the clotting system in an injury-induced smooth muscle cell proliferation.