Estriol improves membrane fluidity of erythrocytes by the nitric oxide-dependent mechanism: An electron paramagnetic resonance study

The present in vitro study was performed to investigate the effects of estr iol (E3) on membrane fluidity of erythrocytes by means of an electron param agnetic resonance (EPR) and spin-labeling method. E3 was shown to significa ntly decrease the order parameter (S) for 5-nitroxide stearate (5-NS) and t he peak height ratio (h(o)/h(-1)) for 16-NS obtained from EPR spectra of er ythrocyte membranes. This finding indicated that E3 might increase the memb rane fluidity of erythrocytes, The effect of E3 was significantly potentiat ed by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine 3',5'-mono-phosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change in the membrane fluidity induced by E3 was antagonize d by the NO synthase inhibitor, L-N-G-nitroarginine-methyl-ester (L-NAME), and asymmetric dimethyl-L-arginine (ADMA), The results of the present study showed that E3 significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- a nd cGMP-dependent pathway. Furthermore, the data might be consistent with t he hypothesis that E3 could have a beneficial effect on the theological beh avior of erythrocytes and may play a crucial role in the regulation of micr ocirculation.