Heparin inhibits bovine testicular hyaluronidase activity in myocardium of dogs with coronary artery occlusion

Abstract

Bovine testicular hyaluronidase (BTH) reduces experimental myocardial infarct size and ameliorates electrocardiographic signs of ischemia. This study was done to determine if heparin, an in vitro inhibitor of hyaluronidase activity, blocks the action of BTH in the myocardium of dogs after coronary artery occlusion. BTH was administered intravenously as 5,000 NF units/kg at 0.5 and 2.5 hours after coronary occlusion. Heparin was administered intravenously as a 150-unit/kg loading dose, followed by 10 units/kg per hour i.v., beginning 15 minutes before coronary occlusion. The area of myocardial ischemia at risk was assessed by a radiolabeled microsphere technique; the area that developed necrosis was assessed by a histochemical technique. In vivo activity of BTH was assessed by a colorimetric analysis of the BTH substrate, i.e., hyaluronic acid (HA), extracted from myocardial tissue. For biochemical analysis of HA, the heart was divided into anterior myocardium, which included ischemic tissue and posterior nonischemic myocardium. The myocardial HA content of dogs treated with BTH plus heparin (anterior, 3.44 ± 0.40 μg HA/mg protein; posterior, 3.69 ± 0.33 μg HA/mg protein) was not significantly different from control (anterior, 3.61 ± 0.29 μg HA/mg protein; posterior, 3.55 ± 0.23 μg HA/mg protein). In contrast, BTH lowered myocardial HA content (anterior, 2.16 ± 0.21 μg HA/mg protein; posterior, 2.08 ± 0.14 μg HA/mg protein) compared with either BTH plus heparin or control groups in both anterior myocardium (p = 0.006) and posterior myocardium (p = 0.001). Significant salvage of ischemic myocardium at risk of necrosis was observed in BTH-treated dogs compared with control dogs (area necrosis = 66.4 ± 11.7%area risk vs area necrosis = 97.5 ± 5.4% area risk, p = 0.037). Treatment with BTH did not produce significant salvage of ischemic myocardium in heparinized dogs (area necrosis = 82.4 ± 15.0% area risk). Thus, heparin inhibits in vivo activity of BTH in myocardium of dogs after coronary artery occlusion.