Electron paramagnetic resonance investigation on modulatory effect of 17beta-estradiol on membrane fluidity of erythrocytes in postmenopausal women

Oestradiol: any role in cardiovascular risk factors in female centenarians of Hainan?

Background

Previous studies reported that low level of oestradiol (E2) was associated with higher risk of cardiovascular disease (CVD). However, little study examined the relationship between E2 and CVD in longevous women, which were deficient in serum E2 for the post-menopausal status. Therefore, this study aims to explore the association between E2 and CVD risk factors in a group of female centenarians of Hainan, China.

Methods

A total of 413 female centenarians (aged from 100 to 115) from China Hainan Centenarian Cohort Study (CHCCS) were enrolled in this study. Home interviews were conducted to collected data on demographic characteristics, health-related lifestyles, and anthropometrics. The level of serum E2 was assessed in the Clinical Laboratory of Hainan branch of PLA General Hospital. The variables of CVD risk factors, including blood pressures, lipids and blood glucose, were measured through standard procedures.

Results

Significant negative correlations between levels of serum E2 and TC, HDL-C, and LDL-C were observed in this study. Compared with the highest group of E2, the odds ratio and 95% confidence intervals of high LDL-C in groups 3, 2 and 1 were OR1.94 (CI0.82–4.62), OR3.61 (CI1.27–10.25) and OR9.29 (CI2.08–41.53), respectively. Similarly, the prevalence of hypertension was decreased with the increase of serum E2. The odds ratio and 95% confidence intervals of stage-2 hypertension in groups 3, 2 and 1 versus highest E2 group were OR1.34 (CI0.49–3.72), OR1.36 (CI0.47–3.99) and OR1.38 (CI0.45–4.20), respectively.

Conclusions

This study examined the relationship between E2 and CVD risk factors in a group of community-based female centenarians. A negative correlations between serum E2 levels and CVD risk factors, i.e. high level of LDL-C, TC, and hypertension were observed in this population. Besides, the level of serum E2 is also negatively correlated with HDL-C. Further studies on the correlation between serum E2 and CVD risk factors, especially dyslipidemia, in longevous and post-menopausal women are warranted.

Gold nanoparticle uptake is enhanced by estradiol in MCF-7 breast cancer cells

Purpose: In the present study, we investigated the effects of 17β-estradiol (E₂) on membrane roughness and gold nanoparticle (AuNP) uptake in MCF-7 breast cancer cells. Methods: Estrogen receptor (ER)-positive breast cancer cells (MCF-7) were exposed to bare 20 nm AuNPs in the presence and absence of 1×10^-9 M E₂ for different time intervals for up to 24 hrs. The effects of AuNP incorporation and E₂ incubation on the MCF-7 cell surface roughness were measured using atomic force microscopy (AFM). Endocytic vesicle formation was studied using confocal laser scanning microscopy (CLSM). Finally, the results were confirmed by hyperspectral optical microscopy. Results: High-resolution AFM images of the surfaces of MCF-7 membranes (up to 250 nm²) were obtained. The incubation of cells for 12 hrs with AuNP and E₂ increased the cell membrane roughness by 95% and 30% compared with the groups treated with vehicle (ethanol) or AuNPs only, respectively. This effect was blocked by an ER antagonist (7α,17β-[9-[(4,4,5,5,5-Pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol [ICI] 182,780). Higher amounts of AuNPs were localized inside MCF-7 cells around the nucleus, even after 6 hrs of E₂ incubation, compared with vehicle-treated cells. Endolysosome formation was induced by E₂, which may be associated with an increase in AuNP-uptake. Conclusions: E₂ enhances AuNP incorporation in MCF-7 cells by modulating of plasma membrane roughness and inducing lysosomal endocytosis. These findings provide new insights into combined nanotherapies and hormone therapies for breast cancer.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Correlation between genetic polymorphisms within the MAPK1/HIF-1/HO-1 signaling pathway and risk or prognosis of perimenopausal coronary artery disease

BACKGROUND

Mitogen-activated protein kinase-1 (MAPK1), as well as its downstream factors of hypoxia-inducible factor-1 (HIF-1) and heme oxygenase-1 (HO-1), have been documented to be involved in modulating development of coronary artery disease (CAD).

HYPOTHESIS

Genetic mutations within the MAPK1/HIF-1/HO-1 signaling pathway could alter the risk of perimenopausal CAD in Chinese patients.

METHODS

Peripheral blood samples were gathered from 589 CAD patients and 860 healthy controls, and 12 potential single-nucleotide polymorphisms (SNPs) were obtained from HapMap database and previously published studies. Genotyping of SNPs was implemented with the TaqMan SNP Genotyping Assays. Odds ratios (OR) and 95% confidence intervals (CI) were utilized to evaluate the correlations between SNPs and CAD risk.

RESULTS

Regarding MAPK1 , rs6928 (OR: 1.71, 95% CI: 1.47-1.98, P < 0.05), rs9340 (OR: 0.85, 95% CI: 0.73-0.99, P < 0.05), and rs11913721 (OR: 0.70, 95% CI: 0.52-0.95, P < 0.05) were remarkably associated with susceptibility to perimenopausal CAD. Of these, rs9340 and rs11913721 were also regarded as protective factors for perimenopausal CAD patients. Moreover, results of HIF-1 indicated noticeable correlations between combined SNPs of rs1087314 and rs2057482 and risk of perimenopausal CAD (OR: 1.24, 95% CI: 1.01-1.53, P < 0.05; and OR: 0.71, 95% CI: 0.55-0.91, P < 0.05, respectively). Nonetheless, rs2071746 in HO-1 was found to be only associated with perimenopausal CAD risk (OR: 0.67, 95% CI: 0.58-0.78, P < 0.05).

CONCLUSIONS

The genetic mutations within MAPK1 (rs6928, rs9340, rs11913721), HIF-1 (rs1087314, rs2057482), and HO-1 (rs2071746) could alter susceptibility to perimenopausal CAD in this Chinese population.

Chronic kidney disease predicts impaired membrane microviscosity of red blood cells in hypertensive and normotensive subjects

Current evidence indicates that abnormalities in physical properties of the cell membranes may be strongly linked to hypertension and other circulatory disorders. Recent studies have shown that chronic kidney disease (CKD) might be a risk factor for cardiovascular and cerebrovascular outcomes. The purpose of the present study was to examine the possible relationship between kidney function and membrane fluidity (a reciprocal value of membrane microviscosity) of red blood cells (RBCs) in hypertensive and normotensive subjects using an electron spin resonance (ESR) and spin-labeling method. The order parameter (S) for the ESR spin-label agent (5-nitroxide stearate) in RBC membranes was significantly higher in hypertensive subjects than in normotensive subjects, indicating that membrane fluidity was decreased in hypertension. The order parameter (S) of RBCs was inversely correlated with estimated glomerular filtration rate (eGFR), suggesting that a decreased eGFR value might be associated with reduced membrane fluidity of RBCs. Multivariate regression analysis also demonstrated that, after adjustment for general risk factors, eGFR might be a significant predictor of membrane fluidity of RBCs. The reduced levels of both membrane fluidity of RBCs and eGFR were associated with increased plasma 8-iso-prostaglandin F2α (an index of oxidative stress) and decreased plasma nitric oxide (NO)-metabolites, suggesting that kidney function could be a determinant of membrane microviscosity of RBCs, at least in part, via oxidative stress- and NO-dependent mechanisms. The ESR study suggests that CKD might have a close correlation with impaired rheologic behavior of RBCs and microcirculatory disorders in hypertensive subjects.

Isoflavone supplementation reduces DNA oxidative damage and increases O-β-N-acetyl-D-glucosaminidase activity in healthy women

Phenolic compounds are believed to boost the human antioxidant defense system and health; therefore, the aim of this research was to investigate the hypothesis that soy isoflavones (IFs) provide antioxidant protection in healthy women by evaluating DNA resistance to oxidative damage and O-β-N-acetyl-D-glucosaminidase (OGA) activity. An IF supplement (80 mg/d) was given to 9 postmenopausal women and 13 young women for 6 months and then stopped up to the 14th month. The women were allowed to consume their normal diet. Blood samples were collected at the beginning of the study after 2, 4, and 6 months and then at the 8th and 14th months. Plasma concentrations of genistein and daidzein, total antioxidant capacity, plasma vitamin status, markers of oxidative stress (red blood cell membrane fluidity, activity of the red blood cell cytosolic enzyme OGA and lymphocyte DNA susceptibility to oxidative stress), and serum lipid profile were analyzed. Analysis of variance for repeated measures was used for statistical analysis. Plasma concentrations of IFs rose significantly during the supplementation period, and plasma total antioxidant capacity increased in young women; membrane fluidity and OGA activity increased, and DNA oxidative damage decreased (P < .05) at 4 months, then returned to the basal level. There was a significant inverse correlation between DNA damage and plasma IF concentrations (P < .01). The results indicated a positive effect of IF supplementation on oxidative stress in women, thus suggesting that the healthful action ascribed to soy consumption may be partially related to the antioxidant potential of IFs.

Associations between High-Sensitivity C-Reactive Protein and Membrane Fluidity of Red Blood Cells in Hypertensive Elderly Men: An Electron Spin Resonance Study

Recent evidence indicates that high-sensitivity C-reactive protein (hs-CRP), an acute phase of an inflammatory marker, might be associated with atherosclerosis, hypertension, and other cardiovascular diseases. The present study was performed to assess the possible link between plasma hs-CRP and membrane fluidity (a reciprocal value of membrane microviscosity) in hypertensive elderly men. We measured the membrane fluidity of red blood cells (RBCs) in hypertensive and normotensive elderly men using an electron spin resonance and spin-labeling method. Membrane fluidity of RBCs was decreased in hypertensive elderly men compared with normotensive elderly men. Plasma hs-CRP levels were significantly higher in hypertensive elderly men than in normotensive elderly men. In contrast, plasma nitric-oxide- (NO-) metabolite levels were lower in hypertensive elderly men than in normotensive elderly men. The reduced membrane fluidity of RBCs was associated with increased plasma hs-CRP and decreased plasma NO-metabolite levels. In a multivariate regression analysis, plasma hs-CRP was an independent determinant of membrane fluidity of RBCs after adjustment for general risk factors. The results suggest that CRP might have a close correlation with the rheologic behavior of RBCs and the microcirculation and would contribute, at least in part, to the circulatory dysfunction and vascular complications in hypertensive elderly men.

Roles of adiponectin and oxidative stress in the regulation of membrane microviscosity of red blood cells in hypertensive men-an electron spin resonance study

This study was undertaken to investigate possible relationships among plasma adiponectin, 8-iso-prostaglandin F2α (8-iso-PG F2α: an index of oxidative stress), and membrane fluidity (a reciprocal value of microviscosity) in hypertensive and normotensive men using an electron spin resonance-method. The order parameter (S) for the spin-label agent (5-nitroxide stearate) in red blood cell (RBC) membranes was higher in hypertensive men than in normotensive men, indicating that membrane fluidity was decreased in hypertension. Plasma adiponectin and NO metabolites levels were lower in hypertensive men than in normotensive men. In contrast, plasma 8-iso-PG F2α levels were increased in hypertensive men compared with normotensive men. Plasma adiponectin concentration was correlated with plasma NO-metabolites, and inversely correlated with plasma 8-iso-PG F2α. The order parameter (S) of RBCs was inversely correlated with plasma adiponectin and plasma NO metabolite levels, and positively correlated with plasma 8-iso-PG F2α, suggesting that the reduced membrane fluidity of RBCs might be associated with hypoadiponectinemia, endothelial dysfunction, and increased oxidative stress. In a multivariate regression analysis, adiponectin and 8-iso-PG F2α were significant determinants of membrane fluidity of RBCs after adjustment for general risk factors. These results suggest that adiponectin and oxidative stress might have a close correlation with rheologic behavior and microcirculation in hypertension.

Oxidative stress and membrane fluidity of red blood cells in hypertensive and normotensive men: an electron spin resonance investigation

Recent evidence indicates that oxidative stress might actively participate in the pathophysiology of hypertension, atherosclerosis, and other cardiovascular diseases. The purpose of the present study was to assess the possible link between oxidative stress and membrane fluidity in hypertensive and normotensive men. We measured the membrane fluidity (a reciprocal value of membrane microviscosity) of red blood cells (RBCs) in hypertensive and normotensive men using an electron spin resonance (ESR) and spin-labeling method. Membrane fluidity of RBCs was decreased in hypertensive men compared with normotensive men. The levels of plasma 8-Iso-prostaglandin F2alpha (8-Iso-PG F2alpha : an index of oxidative stress) were significantly higher in hypertensive men than in normotensive men. In contrast, plasma nitric oxide (NO)-metabolite levels were significantly lower in hypertensive men than in normotensive men. In the overall analysis of hypertensive and normotensive men, plasma 8-Iso-PG F2alpha levels were inversely correlated with plasma NO-metabolites. Furthermore, the reduced membrane fluidity of RBCs was associated with increased plasma 8-Iso-PG F2alpha and decreased plasma NO-metabolite levels. In a multivariate regression analysis, plasma 8-Iso-PG F2alpha was found to be an independent determinant of membrane fluidity of RBCs. The results of the present study suggest that oxidative stress might have a close correlation with the rheologic behavior of RBCs and the microcirculation in hypertensive men.

Electron paramagnetic resonance investigation on modulatory effect of benidipine on membrane fluidity of erythrocytes in essential hypertension

It has been shown that benidipine, a long-lasting calcium (Ca) channel blocker, may exert its protective effect against vascular disorders by increasing nitric oxide (NO) production. The purpose of the present study was to investigate whether orally administered benidipine might influence the membrane function in patients with essential hypertension. We measured the membrane fluidity of erythrocytes by using an electron paramagnetic resonance (EPR) and spin-labeling method. In the preliminary study using erythrocytes obtained from healthy volunteers, benidipine decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS in the EPR spectra in vitro. The finding indicated that benidipine increased the membrane fluidity and improved the microviscosity of erythrocytes. In addition, it was demonstrated that the effect of benidipine on membrane fluidity of erythrocytes was significantly potentiated by the NO-substrate, L-arginine. In the separate series of the study, we observed that orally administered benidipine for 4 weeks significantly increased the membrane fluidity of erythrocytes with a concomitant increase in plasma NO metabolite levels in hypertensive subjects. The results of the present study demonstrated that benidipine might increase the membrane fluidity and improve the microviscosity of erythrocytes both in vitro and in vivo, to some extent, by the NO-dependent mechanism. Furthermore, it is strongly suggested that orally administered benidipine might have a beneficial effect on the rheologic behavior of erythrocytes and the improvement of the microcirculation in hypertensive subjects.

Experimental and computational studies investigating trehalose protection of HepG2 cells from palmitate-induced toxicity

Understanding the mechanism of saturated fatty acid-induced hepatocyte toxicity may provide insight into cures for diseases such as obesity-associated cirrhosis. Trehalose, a nonreducing disaccharide shown to protect proteins and cellular membranes from inactivation or denaturation caused by different stress conditions, also protects hepatocytes from palmitate-induced toxicity. Our results suggest that trehalose serves as a free radical scavenger and alleviates damage from hydrogen peroxide secreted by the compromised cells. We also observe that trehalose protects HepG2 cells by interacting with the plasma membrane to counteract the changes in membrane fluidity induced by palmitate. The experimental results are supported by molecular dynamics simulations of model cell membranes that closely reflect the experimental conditions. Simulations were performed to understand the specific interactions between lipid bilayers, palmitate, and trehalose. The simulations results reveal the early stages of how palmitate induces biophysical changes to the cellular membrane and the role of trehalose in protecting the membrane structure.

Adiponectin and membrane fluidity of erythrocytes in normotensive and hypertensive men

OBJECTIVE

Abnormalities in physicochemical properties of the cell membranes may underlie the defects that are strongly linked to hypertension. Recent evidence indicates that adiponectin may have protective effects against cardiovascular diseases. The purpose of the present study was to assess the possible link between plasma adiponectin and membrane fluidity in normotensive (NT) and hypertensive (HT) men.

RESEARCH METHODS AND PROCEDURES

We measured the membrane fluidity (a reciprocal value of membrane microviscosity) of erythrocytes in NT and HT men by using an electron paramagnetic resonance and spin-labeling method.

RESULTS

The order parameter (S) for the spin label agent (5-nitroxide stearate) and the peak height ratio (h0/h(-1)) for 16-nitroxide stearate in the electron paramagnetic resonance spectra of erythrocytes were significantly higher in HT men than in NT men, indicating that membrane fluidity of erythrocytes was decreased in HT men compared with NT men. Both of plasma adiponectin and nitric oxide (NO) metabolite levels were significantly lower in HT men than in NT men. The plasma adiponectin levels were correlated with plasma NO metabolites. The S and the h0/h(-1) of erythrocytes were inversely correlated with the plasma adiponectin and NO metabolite levels, indicating that the decreased membrane fluidity of erythrocytes was associated with hypoadiponectinemia and reduced plasma NO metabolites.

DISCUSSION

The results of the present study demonstrated that plasma adiponectin levels were lower in HT men than in NT men and that hypoadiponectinemia was associated with decreased membrane fluidity of erythrocytes. The finding suggests that adiponectin may be linked to the rheologic behavior of the erythrocytes and the microcirculation in men, at least in part, by the NO-dependent mechanism.

cGMP (guanosine 3′,5′-cyclic monophosphate) transport across human erythrocyte membranes

Human erythrocytes produce cGMP that can be eliminated by phosphodiesterases or active efflux transporters. The efflux can be studied under controlled conditions as ATP-dependent uptake into inside-out membrane vesicles. However, widely differing values for the transport rates have been reported. We have here examined factors that influence the uptake rates measured and thus may explain these discrepancies. Both the ionic composition of the buffer used during uptake and the mode of vesicle preparation were found to affect the observed transport rates. Furthermore it was apparent that different blood donors expressed on their erythrocytes different amounts of both MRP4 and MRP5, transporters that have been putatively linked to cGMP efflux across erythrocyte membranes. These differences in expression were reflected in differences in rates of cGMP uptake into inside-out erythrocyte membrane vesicles. Calculations based on the transport rates observed using vesicles suggest that efflux may be the principal means for eliminating cGMP from human erythrocytes.

Estrogen, mitochondria, and growth of cancer and non-cancer cells

In this review, we discuss estrogen actions on mitochondrial function and the possible implications on cell growth. Mitochondria are important targets of estrogen action. Therefore, an in-depth analysis of interaction between estrogen and mitochondria; and mitochondrial signaling to nucleus are pertinent to the development of new therapy strategies for the treatment of estrogen-dependent diseases related to mitochondrial disorders, including cancer.

Effects of mild aerobic physical exercise on membrane fluidity of erythrocytes in essential hypertension

1. The present study was undertaken to investigate the effects of aerobic physical exercise on membrane function in mild essential hypertension. 2. Hypertensive patients were divided into an exercise group (n = 8) and a non-exercise (control) group (n = 8). Physical exercise within the intensity of the anaerobic threshold level was performed twice a week for 6 months. Membrane fluidity of erythrocytes was examined by means of electron paramagnetic resonance (EPR) and spin-labelling methods before and after the trial period in both groups. 3. After physical exercise, blood pressure decreased significantly. 4. Compared with the non-exercise group, in the exercise group both the order parameter (S) and the peak height ratio (ho/h-1) in the EPR spectra of erythrocytes were significantly reduced (S, 0.717 +/- 0.004 vs 0.691 +/- 0.008, respectively (n = 8), P < 0.05; ho/h-1, 5.38 +/- 0.06 vs 4.89 +/- 0.06, respectively (n = 8), P < 0.05). These findings indicated that exercise increased membrane fluidity and improved the membrane microviscosity of erythrocytes. 5. There was no direct correlation between blood pressure reduction and the exercise-induced increase in membrane fluidity of erythrocytes. 6. In the non-exercise (control) group, blood pressure and membrane fluidity were not changed after a 6 month follow-up period. 7. The results show that aerobic physical exercise increased erythrocyte membrane fluidity and improved the rigidity of cell membranes in hypertensive patients. The improvement of rheological properties of erythrocytes may explain, in part, the cellular mechanisms for the beneficial effects of physical exercise in hypertension.

Effect of oestrone on membrane fluidity of erythrocytes is mediated by a nitric oxide-dependent pathway: An electron paramagnetic resonance study

1. It has been recognized that hormone replacement therapy (HRT) may have a beneficial effect on protection against cardiovascular diseases. Oestrone is the major component of conjugated equiline oestrogens, which are commonly used in HRT. The present study was performed in order to investigate the effects of oestrone on the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labelling method. 2. In an in vitro study, oestrone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-nitroxide stearate (16-NS) obtained from EPR spectra of erythrocyte membranes. This finding indicated that oestrone may increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. 3. The effect of oestrone was significantly potentiated by the nitric oxide (NO) donor s-nitroso-N-acetylpenicillamine and the cGMP analogue 8-bromo-cGMP. 4. In contrast, the change in membrane fluidity induced by oestrone was antagonized by the NO synthase inhibitors NG-nitro-l-arginine methyl ester and asymmetric dimethyl-l-arginine. 5. The results of the present study show that oestrone significantly increases membrane fluidity and improves the rigidity of cell membranes, which is partially mediated by a NO- and cGMP-dependent pathway. Furthermore, the data may be consistent with the hypothesis that oestrone could have a beneficial effect on the rheological behaviour of erythrocytes and have a crucial role in the regulation of the microcirculation.

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism—an electron paramagnetic resonance investigation

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, L-arginine and S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester (L-NAME) and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.

Synergistic role of progesterone and nitric oxide in the regulation of membrane fluidity of erythrocytes in humans: an electron paramagnetic resonance investigation

BACKGROUND

It has been shown that progesterone may actively participate in the regulation of blood pressure and other cardiovascular regulations. However, the precise mechanism underlying its effects is unclear.

METHODS

In the present study, we examined the effects of progesterone on membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method.

RESULTS

In an in vitro study, progesterone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. The finding indicates that progesterone might increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. The effect of progesterone was significantly potentiated by the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP) and a cyclic guanosine monophosphate (cGMP) analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by progesterone was attenuated in the presence of the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester (L-NAME) and asymmetric dimethyl-L-arginine (ADMA).

CONCLUSIONS

The results of the present study showed that progesterone increased the membrane fluidity of erythrocytes and ameliorated the rigidity of cell membranes, at least in part, by an NO-dependent mechanism. Furthermore, the data strongly suggest that progesterone might be involved in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in humans.