Epinephrine enhances platelet-neutrophil adhesion in whole blood in vitro

Previous studies showed that alpha- or beta-adrenoceptor stimulation by catecholamines influenced neutrophil function, cytokine liberation, and platelet aggregability. We investigated whether adrenergic stimulation with epinephrine also alters platelet-neutrophil adhesion. This might be of specific interest in the critically ill, because the increased association of platelets and neutrophils has been shown to be of key importance in inflammation and thrombosis. For this purpose, whole blood was incubated with increasing concentrations of epinephrine (10 nM, 100 nM, and 1 microM). To distinguish receptor-specific effects, a subset of samples was incubated with propranolol (10 microM) or phentolamine (10 microM) before exposure to epinephrine. After incubation, another subset of samples was also stimulated with 100 nM of N-formyl-methionyl-leucyl-phenylalanine. All samples were stained, and platelet-neutrophil adhesion and CD45, L-selectin, CD11b, P-selectin glycoprotein ligand-1, glycoprotein IIb/IIIa, and P-selectin expression were measured by two-color flow cytometry. Epinephrine significantly enhanced platelet-neutrophil adhesion and P-selectin and glycoprotein IIb/IIIa expression on platelets. CD11b and L-selectin expression on unstimulated neutrophils remained unchanged, whereas N-formyl-methionyl-leucyl-phenylalanine-induced upregulation of CD11b and downregulation of L-selectin were suppressed by epinephrine. beta-Adrenergic blockade before incubation with epinephrine increased platelet-neutrophil aggregates and adhesion molecule expression (CD11b, P-selectin, and glycoprotein IIb/IIIa) even further. These results demonstrate that epinephrine enhances platelet-neutrophil adhesion. The alpha-adrenergic receptor-mediated increase in P-selectin and glycoprotein IIb/IIIa expression on platelets may contribute substantially to this effect. Our study shows that inotropic support enhances the platelet-neutrophil interaction, which might be crucial for critically ill patients.