Effect of apelin on bleeding time in apelin^−/− mice and the role of APJ. (A) Tail-bleeding time in WT or apelin^−/− mice receiving an IV injection of PBS (control; ●, ▪) or apelin-13 (50 nmol/kg; ○, □). (B) Tail bleeding-time in WT mice injected with PBS (●), apelin-13 (50 nmol/kg; ○), F13A (500 nmol/kg; ▪), F13A (500 nmol/kg) plus apelin-13 (50 nmol/kg; □), MM54 (500 nmol/kg; ♦), or MM54 (500 nmol/kg) plus apelin-13 (50 nmol/kg; ♢). Each symbol represents 1 individual, and horizontal lines indicate the mean. Statistical significance was determined by 2-tailed Mann-Whitney test (***P < .0001).