Sickle cell vaso-occlusion.

A polymerizable cell is a requirement for sickle cell vaso-occlusion, but other factors clearly modulate the course of the disease. Hemolysis produces a young red cell population that is capable of adhesion and may result in polymer formation in cells that would otherwise have remained deformable during transit through the microcirculation owing to prolonged delay time for polymerization. In addition, a young red cell population will have a higher activity of K:Cl cotransport, which is capable of rapidly dehydrating cells under acid conditions, thus promoting a vicious circle of hemolysis and adhesion. Transient occlusion may stimulate the release of vasoactive substances, which may lead to involvement of a larger area. In the past, research aimed at reducing the incidence of painful crisis was primarily focused on antisickling agents. Currently, hydroxyurea, which increases the level of fetal hemoglobin, which may be described as a natural antisickling agent, is undergoing clinical trials. Future research may involve agents that inhibit sickle cell adhesion, K:Cl cotransport, or vasoactive substances.