title: 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.
authors.affiliation: Department of Medicine, Wakayama Medical University, and Wakayama Rosai Hospital, Wakayama, Japan. tsudak@mail.wakayama-med.ac.jp
authors.forename: Kazushi
authors.initials: K
authors.lastname: Tsuda
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kinoshita-Shimamoto
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Mabuchi
authors.forename: Ichiro
authors.initials: I
authors.lastname: Nishio
mesh_terms: D001161:Arteriosclerosis / Q000517:prevention & control; D001794:Blood Pressure / Q000187:drug effects; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000187:drug effects*; D015914:Estrogen Replacement Therapy; D004967:Estrogens / Q000008:administration & dosage; D005260:Female; D006801:Humans; D006973:Hypertension / Q000517:prevention & control*; D008525:Medroxyprogesterone / Q000008:administration & dosage; D008560:Membrane Fluidity / Q000187:drug effects*; D008833:Microcirculation; D008875:Middle Aged; D012212:Rheology
chemical_list: D004967:Estrogens; D008525:Medroxyprogesterone