Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass.
Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 microg. mL(-1)) or the neutrophil stimulant fMLP (10(-7)M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers was studied in vitro.


METHODS
Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ohms) or fMLP (3.9 to 0 Ohms (p<0.0001). CPB had no additional effect. Heparinisation also reduced the platelet count from 127 (110-170) to 95 (64-117). The inhibition of macroaggregation could not be reversed by ex vivo heparinase.


METHODS
In vitro, the same heparin concentration, as measured in vivo (4 micromL(-1)), inhibited collagen-induced macroaggregation (20.3 to 14.7 Omega), but this effect was less than that observed ex vivo and was reversed by heparinase. In vitro heparin promoted fMLP macroaggregation (2.9 to 8.6 Omega). The inhibition of macroaggregation resulted from heparinisation, per se, rather than CPB and was insensitive to heparinase. There was less inhibition by in vitro heparin, which was reversible by heparinase, indicating a direct effect of heparin in vitro. The disparate findings are suggestive of an indirect action by heparin in vivo on macroaggregation, although heparin had a small direct stimulatory action on microaggregation.
Belcher
P R
PR
Department of Cardiac Surgery, University of Glasgow, Glasgow, United Kingdom. belcher@clinmed.gla.ac.uk
Muriithi
E W
EW
Milne
E M
EM
Wanikiat
P
P
Wheatley
D J
DJ
Armstrong
R A
RA
D000925:Anticoagulants / Q000494:pharmacology*; D002315:Cardiopulmonary Bypass; D003094:Collagen / Q000494:pharmacology; D001026:Coronary Artery Bypass; D005260:Female; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D010976:Platelet Count / Q000187:drug effects; D010979:Platelet Function Tests; D011994:Recombinant Proteins / Q000494:pharmacology
D000925:Anticoagulants; D006629:Hirudins; D010975:Platelet Aggregation Inhibitors; D011994:Recombinant Proteins; D009240:N-Formylmethionine Leucyl-Phenylalanine; D006493:Heparin; D003094:Collagen; C060225:desirudin