Vascular Abnormalities and Pulmonary Hypertension in the Berkeley Sickle Mouse.

Clinically, pulmonary hypertension is a major risk factor for mortality in adults with sickle cell disease. Contributing factors probably include red cell hemolysis and vaso-occlusive injury with their associated oxidative and inflammatory stimuli. Previously, we have described RBC hemolysis and endothelial oxidative stress in the Berkeley sickle mouse model and extend those studies in this work to investigate cardiovascular and endothelial dysfunction. Eight to ten month old homozygous and hemizygous Berkeley sickle mice and C57BL/6 control mice were used for all aspects of these experiments. In vivo measurements of mean arterial pressure and right ventricular pressures were conducted in fully anesthetized mice using a pressure transducer inserted in the carotid and right ventricle respectively. Following in vivo readings hearts were excised for measurement of ventricular mass. The ascending aorta was removed and cut into 5 mm rings for in vitro studies of agonist- induced contractility and relaxation. The mean arterial pressure of the hemizygous sickle mice (70.6 ± 3.4) was significantly lower than the control mice (86.0 ± 3.1) and the mean arterial pressure of homozygous sickle mice (59.0 ± 2.2 mmHg) was significantly lower than the hemizygous and control mice (p≤0.05 and p≤0.001, respectively). The right ventricular pressure showed a trend that approached significance (p= 0.08) such that pressures in homozygous mice were ≥ than those in hemizygous which were ≥ than those in control mice. Increased basal cardiac output was suggested by significant left ventricular hypertrophy. In vitro examination of potassium chloride activation of voltage gated calcium channels showed no significant difference in sensitivity or maximal contraction. Similarly, there was no difference in sensitivity to the α₁ agonist, phenylephrine. However, both hemi- and homozygous mice showed a significant reduction in maximal force of contraction (normalized to cross sectional area when compared to controls. Maximal acetylcholine induced relaxation of aortic rings was significantly reduced (p≤0.05) in homozygous sickle mice compared to controls. The same effect was not seen with sodium nitroprusside induced relaxation indicating that the acetylcholine effect was not due to effects on the smooth muscle but was endothelium-dependent. The Berkeley mouse model shows cardiac hypertrophy consistent with the increased cardiac output associated with chronic anemia and a reduced basal mean arterial blood pressure similar to that seen in humans. 8–10 month old mice have increased right ventricular pressure and RV mass indicative of pulmonary hypertension. Further endothelial dysfunction is characterized by a reduction in the maximal relaxation elicited by acetylcholine. Therefore, the Berkeley mouse is a good model for investigating sickle related endothelial dysfunction.