IMPAIRED PLATELET-AGGREGATION AFTER CARDIOPULMONARY BYPASS IN MAN - ENHANCEMENT OF COLLAGEN-INDUCED AGGREGATION IN WHOLE-BLOOD AND PLASMA BY ADRENALINE EX-VIVO

1. We tested the effect of intravenous adrenaline at 0.55-1.10 nmol mi n(-1) kg(-1) (for 3-8 min, at 7-10 min post bypass; n = 7) on both mic roaggregation in hirudinized whole blood, using platelet counting, and macroaggregation in platelet-rich plasma, using optical aggregometry. Control (n = 12) blood samples were taken before and at 10 and 20 min after bypass. 2. Post-bypass plasma adrenaline levels (nmol/l) increa sed slightly in controls (1.0 versus 0.7 at 10 min, medians; P = 0.05) and markedly with adrenaline infusion (36 versus 0.5 before infusion, P = 0.02). Microaggregation (percentage decrease in single platelets) in stirred blood, reflecting largely ADP-dependent 'spontaneous' aggr egation, was not influenced by adrenaline infusion. In contrast, colla gen (0.2 mu g/ml)-induced microaggregation in blood was enhanced by ad renaline (92% versus 41%, P = 0.02), with no change in controls (60% v ersus 53%, P = 0.61). 3. In controls, collagen (0.6 mu g/ml)-induced m acroaggregation in platelet-rich plasma (extent of increase in light t ransmission, cm) was impaired at 10 min post bypass (5.3 versus 12.1 b efore bypass, P = 0.01), but was enhanced by adrenaline (7.0 versus 3. 6 before infusion, P = 0.02). Platelet counts (x 10(9)/1) were decreas ed postbypass (155 versus 220, P = 0.02) and were not influenced by ad renaline infusion (167, P = 0.93). 4. In conclusion, following bypass and at normocalcaemia, adrenaline enhances collagen-induced aggregatio n in both plasma and whole blood ex vivo, independently of any change in platelet counts, but has no effect on stirring-induced 'spontaneous ' aggregation in blood.