Enhanced responses to pulmonary vasoconstrictors. The vasoconstrictor challenges triggered enhanced pulmonary arterial pressure in the sickle mice and BM-S mice. (A) Hypoxic pulmonary vasoconstrictor response. Acute exposure to 10% oxygen increased pulmonary artery pressure in both sickle and mice receiving transplants with marrow from sickle mice compared with hemizygous controls. (B) Norepinephrine (0.3 μg/kg/min) was associated with increased pulmonary artery pressure in both sickle mice and BM-S mice compared with controls. This difference was also observed at other doses of norepinephrine (0.1 and 1.0 μg/kg/min, P < .05 for both, data not shown). (C) Angiotensin II (0.3 μg/kg/min) was also associated with increased pulmonary artery pressure in sickle mice and BM-S mice compared with controls. Similar results were observed at a lower dose (0.1 μg/kg intravenous bolus, P < .05, data not shown). Statistically significant differences from hemizygous controls are noted by *P < .05. Numbers represent mean ± SEM for n = 4-7 per group.