Blood was collected and plasma prepared as in Figure 1. Plasma from individual littermate animals was diluted 1:5 in 0.9% saline containing 2 mg/ml BSA. (A) The aPTT was measured in 3 animals from each indicated group (in duplicate) both with and without APC (final concentration, 2.5 nM) and normalized to control (male lit^m/+ –pGH). The APC was mixed with CaCl₂, which was used to trigger the reaction. There was a small but nonsignificant increase in the normalized aPTT in female (open circles) versus male (filled squares) control animals. The aPTT was increased in male and female lit^m/m –pGH animals relative to lit^m/+ –pGH or lit^m/m +pGH animals. The aPTT was increased significantly in all groups by the addition of APC; however, the effect or APC was especially pronounced in lit^m/m –pGH animals relative to lit^m/+ –pGH or lit^m/m +pGH (*P < 0.05, **P < 0.01, ***P < 0.001; ANOVA with Bonferroni’s post-hoc test). (B) The raw aPTT plus APC was divided by the aPTT minus APC to generate an APC ratio for each group. The APC ratio is inversely proportional to APC resistance and was nonsignificantly higher in female lit^m/+ –pGH than male control animals. The APC ratio was significantly increased in male lit^m/m –pGH animals relative to lit^m/+ –pGH or lit^m/m +pGH animals and female lit^m/m –pGH animals relative to lit^m/m +pGH animals, suggesting that APC resistance is mediated by circulating GH concentration (*P < 0.05, **P < 0.01; ANOVA with Bonferroni’s post-hoc test).