HEPARIN AND NONANTICOAGULANT HEPARIN PRESERVE REGIONAL MYOCARDIAL-CONTRACTILITY AFTER ISCHEMIA-REPERFUSION INJURY - ROLE OF NITRIC-OXIDE

Objectives: These studies were performed to determine the effect of he parin and nonanticoagulant heparin on myocardial function after ischem ia-reperfusion and to further evaluate the role that the nitric oxide- cyclic guanosine monophosphate pathway plays in mediating the effect o f heparin. Methods: Fifteen dogs were subjected to 15 minutes ischemia followed by 120 minutes reperfusion and pretreated with either saline solution, bovine heparin (6.0 mg/kg intravenously), or N-acetyl hepar in (6.0 mg/kg intravenously), a heparin derivative without anticoagula nt properties. The left anterior descending artery was occluded for 15 minutes and regional systolic shortening, a unitless measure of myoca rdial contractility, assessed during reperfusion, To evaluate the role of nitric oxide, the inhibitor N-omega-nitro-L-arginine, 1.5 mg/kg in tracoronary, was given before heparin administration, Myocardial level s of cyclic guanosine monophosphate, the second messenger of nitric ox ide, were also measured in the N-acetyl heparin group using radioimmun oassay. Results: Regional systolic shortening was significantly decrea sed in the saline group during 60 and 120 minutes compared with before ischemia (9.2 +/- 1.0 and 9.0 +/- 0.9 vs 12.2 +/- 1.2, p less than or equal to 0.0003), Heparin and N-acetyl heparin-treated dogs, however, showed preservation of systolic shortening throughout reperfusion, Ad ministration of nitro-L-arginine significantly attenuated the protecti ve effect of heparin (9.2 +/- 1.2 vs 12.7 +/- 1.1, p less than or equa l to 0.0001) and N-acetyl heparin (9.3 +/- 0.3 vs 12.8 +/- 0.1, p less than or equal to 0.0001) during 120 minutes reperfusion. Myocardial l evels of cyclic guanosine monophosphate were also significantly increa sed in the N-acetyl heparin group compared with saline (199.1 +/- 7.1 vs 103.5 +/- 4.5 pmol/mg, p less than or equal to 0.0001). Conclusions : Heparin preserves myocardial contractility after ischemia-reperfusio n independent of its anticoagulant properties. Furthermore, the protec tive effects of heparin during ischemia-reperfusion are mediated, at l east in part, through a nitric oxide-cyclic guanosine monophosphate pa thway.