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 min-1 kg-1 (for 3-8 min, at 7-10 min post bypass; n = 7) on both microaggregation 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) increased 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' aggregation, was not influenced by adrenaline infusion. In contrast, collagen (0.2 microgram/ml)-induced microaggregation in blood was enhanced by adrenaline (92% versus 41%, P = 0.02), with no change in controls (60% versus 53%, P = 0.61). 3. In controls, collagen (0.6 microgram/ml)-induced macroaggregation in platelet-rich plasma (extent of increase in light transmission, cm) was impaired at 10 min post bypass (5.3 versus 12.1 before bypass, P = 0.01), but was enhanced by adrenaline (7.0 versus 3.6 before infusion, P = 0.02). Platelet counts (x 10(9)/l) were decreased postbypass (155 versus 220, P = 0.02) and were not influenced by adrenaline infusion (167, P = 0.93).(ABSTRACT TRUNCATED AT 250 WORDS)