Interactions between erythrocytes and vascular endothelium have been implicated in the pathogenesis of vaso-occlusion in
sickle cell anemia. Sickle erythrocytes adhere to endothelial cells and facilitate trapping of rigid sickle cells in microvessels. Compensatory dilation of precapillary arterioles may mitigate the occlusion. The endothelium regulates vasoreactivity by elaborating
endothelium-derived relaxing factor (EDRF), a small molecule that passes freely into vascular smooth muscle where it initiates vasorelaxation by activating
soluble guanylate cyclase in the smooth muscle cell cytoplasm. Endothelial release of EDRF can be stimulated by agonists such as
acetylcholine. It is highly sensitive to decomposition by
superoxide anions and is rapidly bound and inactivated by
oxyhemoglobin in
solution. The purpose of this study was to determine whether sickle cell interaction with endothelium disrupts this mechanism of endothelial regulation of vasomotor tone. Transverse strips of rabbit aorta, mounted isometrically in organ
baths, were contracted with
norepinephrine, and relaxation responses to
acetylcholine or other agonists were determined. Responses were measured under control conditions and again in the presence of
oxyhemoglobin A or S, or erythrocytes or ghosts from normal control subjects or patients with homozygous
sickle cell anemia. Sickle erythrocytes inhibited vasorelaxation to
acetylcholine by 83%. Approximately half of the inhibition was attributable to a small amount of
oxyhemoglobin S that was leaked into the
buffer from the erythrocytes. Consistent with this, sickle erythrocyte ghosts inhibited vasorelaxation to
acetylcholine by up to 45%. Ghosts from normal erythrocytes did not inhibit vasorelaxation to
acetylcholine, and the inhibition seen with normal erythrocytes was entirely attributable to leakage of
oxyhemoglobin A into the bath
buffer.(ABSTRACT TRUNCATED AT 250 WORDS)