Figure 4

Relative increases in norepinephrine-induced expression of P-selectin in arterial (black bars) and jugular venous (grey bars) platelets isolated from severe traumatic brain injury (TBI) patients and peripheral venous platelets taken from healthy controls (white bars) expressed as a percentage of baseline values. Baseline values were determined in platelets not stimulated in vitro with norepinephrine. During the first week, the norepinephrine-mediated increase in P-selectin-positive platelets was significantly reduced compared with controls. In the second week, the norepinephrine-mediated increase in P-selectin expression significantly exceeded changes seen in the first week and in healthy volunteers. Overall, there was no significant difference between arterial and jugular venous platelets. During the second week, the TRAP-mediated increase in P-selectin-positive platelets significantly exceeded the TRAP-induced activation observed during the first week. ^#P <0.001 second week versus first week; ⁺P <0.01 patients versus controls; * P <0.01 norepinephrine of greater than 500 nM versus norepinephrine of less than 10 μM. TRAP, thrombin receptor-activating peptide.