Disparate effects of adhesion and degranulation of platelets on myocardial and coronary function in postischaemic hearts.

OBJECTIVE Beside the major effect of acute thrombus formation, little is known about the interaction of platelets with the coronary endothelium in an ischaemia-reperfusion situation. The present study was designed to investigate, separately, the consequences of platelet adhesion and degranulation during myocardial reperfusion. METHODS Isolated guinea pig hearts perfused with Krebs-Henseleit buffer and performing pressure-volume work were used. We infringed myocardial function by imposing ischaemia (20 min of low-flow perfusion with 1 ml/min and 10 min of global ischaemia) and reperfusion (15 min with 5 ml/min). During low-flow perfusion, the coronary endothelium was stimulated by thrombin before and during infusion of a bolus: 10(8) washed human platelets +/- the Arg-Gly-Asp (RGD) analogon lamifiban, the supernatant of 10(8) thrombin-stimulated platelets, fibrinogen (2 microM), lamifiban (2 microM) or Tyrode's solution (control group). The parameter external heart work (EHW), determined pre- and postischaemically, served as criterion for recovery of myocardial function. Additionally, the formation of capillary transudate was measured during the reperfusion phase to assess coronary permeability. Coronary perfusion pressure was monitored continuously and myocardial production of lactate and consumption of pyruvate were measured. Electron microscopy of hearts was performed after platelet application to verify platelet adhesion in the coronary system. RESULTS Recovery of EHW by hearts without platelet application was 64 +/- 3% and was significantly reduced to 49 +/- 5% by platelet infusion (n = 8 each). Infusion of supernatant of thrombin-stimulated platelets did not impair recovery of heart work. In the reperfusion phase (6th-10th min), hearts that either had received platelets or supernatant of platelets exhibited a significantly reduced production of capillary transudate (70 microliters/min vs. 180 microliters/min for the controls). Intracoronary bolus application of fibrinogen or lamifiban also reduced coronary leak. Coronary perfusion pressure and metabolic parameters were not statistically different between the groups at any time. CONCLUSIONS Platelet adhesion to the coronary endothelium in a situation of myocardial ischaemia impairs cardiac recovery, whereas constituents released by platelets may have beneficial effects on the integrity of the coronary endothelium. In particular, fibrinogen seems to contribute to the permeability reducing effect, possibly by interaction with endothelial receptors recognising the RGD sequence.