Plasma concentration of thrombin-antithrombin complex in mutant mice. Plasma levels of thrombin-antithrombin (TAT) complexes were measured by ELISA. (A) Steady-state TAT levels in hyperfibrinogenemic mice (Hifib) and in hyperfibrinogenemic mice with superimposed thrombomodulin deficiency (HiFib/TMPro) are comparable to that measured in wild-type mice (wt). (B) Mice were injected intravenously with a bolus of 0.05 U of mouse α-thrombin to induce TAT-complex formation, and TAT levels were measured 10 minutes after thrombin infusion. Hyperfibrinogenemia suppresses the augmentation of TAT formation observed in mice with isolated thrombomodulin deficiency (TMPro). Values are given as apparent TAT concentration determined from a standard constructed with purified human TAT.