Platelet recruitment on A23187-stimulated endothelium in vivo. (A) Dot plot representation of the time in seconds (s) until initiation of platelet tethering in vivo on endothelium of murine mesenteric venules stimulated with A23187 for the indicated number of mice (m). Means are represented as short horizontal lines; indicated 2-tailed P values were calculated by unpaired nonparametric Mann-Whitney test with Welch correction for nonequal variances. (B) Distribution of numbers of mesenteric vessels, reactive (▪) and nonreactive (□) with platelets, during analysis of tethering and firm adhesion, as indicated for the mentioned number of mice (m); indicated P values were calculated by 2 × 2 contingency table analysis and Fisher exact test with 2-sided P value. C indicates nontreated controls; +TSP-1, bolus of 80 μg/kg + infusion of 80 μg/kg/h; +4N1K, injection with calcein-labeled platelets preactivated with 100 μM of the CD47 activating peptide 4N1K; and +Tsp1^-/- platelets and +WT platelets, cross-design experiments with platelet injection in WT and Tsp1^-/- mice, respectively.