NITRIC-OXIDE FROM POLYMORPHONUCLEAR LEUKOCYTES MODULATES RED-BLOOD-CELL DEFORMABILITY INVITRO

We confirmed that iloprost is very potent in preserving the deformability of rabbit red blood cells (RBC). Incubation of RBC with a small number (up to 1.2 x 10(6) cells/ml) of polymorphonuclear leukocytes (PMNs) caused a gradual decline in RBC deformability. The addition of PMNs up to 2.8 x 10(6) cells/ml increased RBC deformability but, at higher concentrations, both in the presence and absence of a neutrophil activating cytokine (interleukin-8; IL-8), PMNs reduced the deformability of RBCs. In the presence of a small number of PMNs, the deformability of RBC was increased by nitric oxide (NO) donors, such as sydnonimine (SIN-1) or sodium nitroprusside, and reduced by the NO synthase inhibitor, N(G)-monomethyl-L-arginine. We suggest that the deformability of RBC is modulated by PMNs via the release of NO and that the NO concentration is of critical importance in this modulatory mechanism. NO seems to preserve or enhance RBC deformability within a certain range of concentrations, but these effects are reversed or eliminated at both too low and too high concentrations.