Reticulocyte counts do not predict epinephrine responsiveness.
SS RBC adhesion was measured in the flow adhesion assay (“Materials and methods”). SS RBCs were treated with 1 × 10−8 M epinephrine for 1 minute or with buffer control. (A) Fold change in adhesion was plotted against percentage of reticulocyte counts (n = 21). (B) Percentage of reticulocyte counts was measured in 4 different SS patients at 2 separate time points. The 2 time points for each patient are connected by a solid line to show the relationship between epinephrine-stimulated adhesion and temporal reticulocyte counts. (C) Adherent SS RBCs were stained immediately following a flow adhesion assay (“Materials and methods”). The percentage of reticulocytes/1000 SS RBCs was counted microscopically for basal and epinephrine-stimulated conditions. Arrows indicate cells classified as reticulocytes. (Reticulocytes in A, C, and D were detected by methylene blue staining. In A and B, basal adhesion is normalized to 1.) (D) Between the most immature reticulocytes and the senescent RBCs exist as a continuum of RBCs at different stages of maturation. Methylene blue staining detects only the reticulocytes containing sufficient remnant RNA to allow visualization. Panels A, B, and C all suggest that these detectable reticulocytes are not responsible for the epinephrine-stimulated adhesion, whereas Figure 3B shows that the responsive population is likely not the senescent, dense RBCs. Therefore, the responsive population likely exists between these extremes, as indicated by the (*).
