Mice expressing fII^WE exhibit an extended time-to-occlusion in mesenteric arterioles after FeCl₃ injury. Thrombus formation was evaluated and quantified using intravital videomicroscopy. (A) The time to initial formation of a thrombus greater than 30 μm was similar between cohorts of wild-type (fII^WT/WT) and fII^WT/WE mice (●), with average times of 6.7 ± 0.3 minutes and 6.6 ± 0.3 minutes, respectively. Similar results were obtained for this parameter in cohorts of fII^WT/WT animals and heterozygous mice carrying one fII null allele and one wild-type fII allele (fII^WT/Null) and known to carry 50% of the normal level of entirely wild-type prothrombin; the average values in cohorts of fII^WT/Null and littermate wild-type mice were 6.3 ± 0.2 minutes and 6.4 ± 0.2 minutes, respectively (○). (B) The time to complete vessel occlusion and cessation of blood flow after injury in fII^WT/WE mice was significantly extended relative to wild-type mice, 15.0 ± 1.2 minutes compared with 10.6 ± 0.6 minutes, respectively. In contrast, the time-to-occlusion after injury in fII^WT/Null mice carrying 50% of normal wild-type prothrombin (average time of 11.7 ± 1.0 minutes) was distinctly shorter than fII^WT/WE mice and virtually identical to that of fII^WT/WT control mice (average time of 11.7 ± 1.1 minutes). Horizontal bars represent the mean of each group, and data were analyzed using the Student t test.