Hormone replacement therapy improves membrane fluidity of erythrocytes in postmenopausal women: an electron paramagnetic resonance investigation

Abstract

Background Many studies have shown that hormone replacement therapy (HRT) might provide protection against the development of hypertension and arteriosclerosis in postmenopausal women. However, the precise mechanism underlying its benefits is unclear. This question was addressed in an electron spin resonance (EPR) study of membrane function of erythrocytes in postmenopausal women. The purpose of this study was to investigate the effects of HRT on membrane fluidity of erythrocytes in postmenopausal women by means of the EPR and spin-labeling method. Methods The healthy postmenopausal women were randomly divided into the HRT group ( n = 14) receiving the conjugated estrogen with medroxyprogesterone for 3 months and the non-HRT control group ( n = 14). We measured membrane fluidity of erythrocytes in postmenopausal women before and after the trial period. Results The HRT group showed a significant decrease in blood pressure (BP) after treatment (systolic BP 145.7 ± 5.5 v 123.3 ± 5.1 mm Hg, n = 14, mean ± SEM, P < .05). The order parameter (S) for 5-nitroxide stearate in the EPR spectra of erythrocyte membranes decreased significantly in the HRT group (S: 0.718 ± 0.002 v 0.695 ± 0.002, n = 14, P < .01). The finding indicated that HRT increased the membrane fluidity of erythrocytes and improved the microviscosity of the cell membranes in postmenopausal women. Conclusions These results are consistent with the hypothesis that HRT might have a beneficial effect on the membrane rheologic behavior of erythrocytes and the microcirculation in postmenopausal women.