Sex hormone regulation of systemic endothelial and renal microvascular reactivity in type-2 diabetes: studies in gonadectomized and sham-operated Zucker diabetic rats

Improvement of Cardiovascular Function in Aging Females by the Prolonged Activation of G Protein-Coupled Estrogen Receptor

Ample evidence suggests that estrogen replacement therapy is associated with beneficial effects with regard to cardiovascular diseases when the therapy is initiated temporally close to menopause but not when it is initiated later. Little is known about the complex interactions between hormone receptors after menopause. Coronary artery function and cardiac function were measured in rats that had either received no treatment or had been pretreated with an androgen receptor (AR) antagonist and/or a GPER agonist G-1. ICI 182,780 was used to block the classical estrogen receptors (ERs) to investigate their complex interactions with GPER. The beneficial effects of GPER were only observed by blocking ARs and classical ERs in aged female rats. The results demonstrate that GPER activation is a potential therapeutic target for the inhibition of age-dependent coronary artery dysfunction and cardiac dysfunction under the condition of blocking ARs and classical ERs after menopause. CLINICAL RELEVANCE: The risk of cardiovascular disease in postmenopausal women significantly increased. The role of sex hormones and their receptors during this process is still complicated. Our present study demonstrated that the imbalance of androgen and estrogen may contribute to the impairment of vascular reactivity and subsequent cardiac function. Treatment with GPER agonist G1 combined with the inhibition of ERα and ERβ could improve vascular function and reduce the myocardial ischemia reperfusion injury. These findings may provide the novel and effective strategy for the treatment of cardiovascular diseases in postmenopausal women.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Association of imbalanced sex hormone production with excessive procoagulation factor SerpinF2 in preeclampsia

BACKGROUND

Preeclampsia, a serious pregnancy-associated syndrome, is the leading cause of maternal and perinatal morbidity and mortality. Significant exacerbation of the hypercoagulation status as well as imbalanced steroid hormones have been reported in developed preeclampsia. However, it remains unclear whether the two pathological changes are directly associated.

METHOD AND RESULTS

Our proteomic analysis revealed a significantly elevated SerpinF2/α2-antiplasmin level in preeclampsia plasma. Measurement of the longitudinally gestational change of plasmin-α2-antiplasmin (PAP) complex, testosterone, estradiol in preeclampsia patients and normal pregnant women demonstrated that the circulating PAP and testosterone levels in the early-onset preeclampsia (E-PE) patients were substantially higher, whereas estradiol concentration was significantly lower than that in normal pregnant controls from early pregnancy throughout gestation. Correlation analysis revealed that circulating PAP is in positive correlation with the concentration of testosterone, and in negative correlation with estradiol in E-PE patients. In E-PE placenta, the productions and activities of 17β-hydroxysteroid dehydrogenases 3 and aromatase, the essential enzymes for testosterone and estradiol synthesis, were compromised. In human renal and trophoblastic cells, testosterone and estradiol could regulate SerpinF2 expression in opposite ways. In addition, obvious fibrin deposition was colocalized with SerpinF2 in intervillous spaces and the area surrounding syncytiotrophoblasts in E-PE placenta.

CONCLUSION

The findings reveal a tight correlation between the imbalanced steroid hormone production and the procoagulation factor in E-PE patients, which provide potential biomarkers to predict preeclampsia, and bring new insight into the pathogenesis of preeclampsia.

Regulation of blood pressure is influenced by gender: A study in obese Zucker rats

AIM

The present study determined the role of renin-angiotensin system (RAS), endothelin system, and eicosanoid system in the blood pressure (BP) regulation in male and female Zucker rats, and whether the pressor response change similarly in lean and obese animals.

MATERIAL AND METHODS

In female (f) and male (m), lean (L) and obese (O) Zucker rats (ZR) at 22 weeks old, we evaluated the role of the 3 mentioned systems using the following treatments: 1) enalapril (angiotensin I converting enzyme inhibitor), 2) the ABT-627 (endothelin receptor A (ET_A) antagonist), and 3) the 1-aminobenzotriazol (1-ABT: eicosanoid synthesis inhibitor).

KEY FINDINGS

MAP by radiotelemetry was similar and significantly higher in mOZR (120 ± 2 mm Hg) and fOZR (116 ± 4 mm Hg) (p < 0.05 vs. m-, fLZR), than mLZR (105 ± 3 mm Hg) and fLZR (106 ± 1 mm Hg), that were also similar. Enalapril reduced MAP more in mOZR (23%) and mLZR (26%), than fLZR (20%, p < 0.905 vs. mLZR) or fOZR (9%; p < 0.05 vs. other groups). After 10 days of drug-free and recovery period, ABT-627 reduced MAP in fLZR and mLZR by similar amounts (102 ± 4 to 92 ± 3 mm Hg, n = 6; p < 0.05 and 105 ± 2 vs. 92 ± 3 mm Hg, n = 6; p < 0.05, respectively), but did not affect either fOZR or mOZR. After another 10 days of drug-free and recovery period, 1-ABT reduced MAP in fOZR (116 ± 4 to 95 ± 2, n = 6; p < 0.05), and did not affect all other groups.

SIGNIFICANCE

We show that the mechanisms responsible for elevated BP in male and female OZR and LZR are different, and suggest that obesity may cause an increase in BP via different mechanisms in men and women as well.

Estrogen deprivation aggravates cardiac hypertrophy in nonobese Type 2 diabetic Goto-Kakizaki (GK) rats

Both Type 2 diabetes mellitus (T2DM) and estrogen deprivation have been shown to be associated with the development of cardiovascular disease and adverse cardiac remodeling. However, the role of estrogen deprivation on adverse cardiac remodeling in nonobese T2DM rats has not been clearly elucidated. We hypothesized that estrogen-deprivation aggravates adverse cardiac remodeling in Goto–Kakizaki (GK) rats. Wild-type (WT) and GK rats at the age of 9 months old were divided into two subgroups to have either a sham operation (WTS, GKS) or a bilateral ovariectomy (WTO, GKO) (n = 6/subgroup). Four months after the operation, the rats were killed, and the heart was excised rapidly. Metabolic parameters, cardiomyocytes hypertrophy, cardiac fibrosis, and biochemical parameters were determined. GK rats had hyperglycemia with hypoinsulinemia, and estrogen deprivation did not increase the severity of T2DM. Cardiac hypertrophy, cardiac oxidative stress, and phosphor-antinuclear factor κB were higher in WTO and GKS rats than WTS rats, and they markedly increased in GKO rats compared with GKS rats. Furthermore, cardiac fibrosis, transforming growth factor-β, Bax, phosphor-p38, and peroxisome proliferator- activated receptor γ coactivator-1α expression were increased in GKS and GKO rats compared with the lean rats. However, mitochondrial dynamics proteins including dynamin-related protein 1 and mitofusin-2 were not altered by T2DM and estrogen deprivation. Although estrogen deprivation did not aggravate T2DM in GK rats, it increased the severity of cardiac hypertrophy by provoking cardiac inflammation and oxidative stress in nonobese GK rats.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Sex and Gender Differences in Risk, Pathophysiology and Complications of Type 2 Diabetes Mellitus

The steep rise of type 2 diabetes mellitus (T2DM) and associated complications go along with mounting evidence of clinically important sex and gender differences. T2DM is more frequently diagnosed at lower age and body mass index in men; however, the most prominent risk factor, which is obesity, is more common in women. Generally, large sex-ratio differences across countries are observed. Diversities in biology, culture, lifestyle, environment, and socioeconomic status impact differences between males and females in predisposition, development, and clinical presentation. Genetic effects and epigenetic mechanisms, nutritional factors and sedentary lifestyle affect risk and complications differently in both sexes. Furthermore, sex hormones have a great impact on energy metabolism, body composition, vascular function, and inflammatory responses. Thus, endocrine imbalances relate to unfavorable cardiometabolic traits, observable in women with androgen excess or men with hypogonadism. Both biological and psychosocial factors are responsible for sex and gender differences in diabetes risk and outcome. Overall, psychosocial stress appears to have greater impact on women rather than on men. In addition, women have greater increases of cardiovascular risk, myocardial infarction, and stroke mortality than men, compared with nondiabetic subjects. However, when dialysis therapy is initiated, mortality is comparable in both males and females. Diabetes appears to attenuate the protective effect of the female sex in the development of cardiac diseases and nephropathy. Endocrine and behavioral factors are involved in gender inequalities and affect the outcome. More research regarding sex-dimorphic pathophysiological mechanisms of T2DM and its complications could contribute to more personalized diabetes care in the future and would thus promote more awareness in terms of sex- and gender-specific risk factors.

G-protein coupled receptor 30 (GPR30): a novel regulator of endothelial inflammation

Estrogen, the female sex hormone, is known to exert anti-inflammatory and anti-atherogenic effects. Traditionally, estrogen effects were believed to be largely mediated through the classical estrogen receptors (ERs). However, there is increasing evidence that G-protein coupled receptor 30 (GPR30), a novel estrogen receptor, can mediate many estrogenic effects on the vasculature. Despite this, the localization and functional significance of GPR30 in the human vascular endothelium remains poorly understood. Given this background, we examined the subcellular location and potential anti-inflammatory roles of GPR30 using human umbilical vein endothelial cells as a model system. Inflammatory changes were induced by treatment with tumor necrosis factor (TNF), a pro-inflammatory cytokine involved in atherogenesis and many other inflammatory conditions. We found that GPR30 was located predominantly in the endothelial cell nuclei. Treatment with the selective GPR30 agonist G-1 partially attenuated the TNF induced upregulation of pro-inflammatory proteins such as intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). This effect was completely abolished by the selective GPR30 antagonist G-15, suggesting that it was indeed mediated in a GPR30 dependent manner. Interestingly, estrogen alone had no effects on TNF-treated endothelium. Concomitant activation of the classical ERs blocked the anti-inflammatory effects of G-1, indicating opposing effects of GPR30 and the classical ERs. Our findings demonstrate that endothelial GPR30 is a novel regulator of the inflammatory response which could be a potential therapeutic target against atherosclerosis and other inflammatory diseases.

A comparison of serum androgens in pre-eclamptic and normotensive pregnant women during the third trimester of pregnancy

OBJECTIVE

To compare the serum androgens level during the third trimester of pregnancy between normotensive and pre-eclamptic women.

METHOD

A case-control study was performed on 64 pregnant women with the gestational age of 28-34 weeks. 32 women were pre-eclamptic (case group), and 32 women were normotensive till term gestation (control group). The serum level of androgens including sex hormone binding globulin (SHBG), total and free testosterone, androstenedione (ADD), and dehydroepiandrosterone sulfate (DHEA-S), were compared between the two groups.

RESULTS

The women of the two groups had no statistically significant difference according to age, gestational age, BMI (body mass index), parity and fetal sex. Serum level of SHBG (90.86 ± 9.30 vs. 55.86 ± 8.02 nmol/l, p = 0.02), total testosterone (3.70 ± 0.57 vs. 2.06 ± 0.24 ng/ml, p = 0.01), free testosterone (1.28 ± 0. 17 vs. 0. 74 ± 0.07 pg/ml, p = 0.01), and ADD (2.47 ± 0.10 vs. 2.17 ± 0.10 ng/ml, p = 0.04), was higher in the pre-eclamptic women. However, there was no difference between the two groups for DHEA-S (0.75 ± 0.18 vs. 0.51 ± 0.08 μg/ml, p = 0.19).

CONCLUSION

Serum androgen levels during third trimester of pregnancy are higher in pre-eclamptic women and this may propose an effect of androgens in the pathogenesis of pre-eclampsia.

Modulation of phase-II enzyme activities in benzene treated ovariectomized rats

The aim of the study was to determine the influence of ovariectomy on phase II enzymes viz. glutathione-S-transferase (GST), glutathione peroxidase (GPX) and catalase (CAT) in liver and kidney of female rats treated with benzene. The results showed the significant decrease of the GST and GPX activity in benzene treated rats after ovariectomy. However progesterone supplementation stimulated the activity of GST and GPX in liver and kidney of benzene treated non ovariectomized and ovariectomized rats. Progesterone supplementation to benzene treated ovariectomized rats helps to gain in CAT activity. Our results on DNA damage using single cell gel electrophoresis also confirmed our findings on antioxidant enzymes. The results showed that lack of protective progesterone against benzene toxicity is reflected in alterations in antioxidant enzyme activities. However progesterone therapy to benzene treated ovariectomized rats results in activating the antioxidant defence system. Since female workers are engaged in industrial sector, these results are important from occupational health point of view. Benzene exposure affects their reproductive health. Nevertheless, it could be modulated by suitable hormonal therapy.

Endothelin in the female vasculature: a role in aging?

Cardiovascular diseases are the leading cause of morbidity and mortality in the world. Aging is associated with an increased incidence of cardiovascular disease. Premenopausal women are relatively protected from vascular alterations compared with age-matched men, likely due to higher levels of the female sex hormones. However, these vasoprotective effects in women are attenuated after menopause. Thus, the vascular system in aging women is affected by both the aging process as well as loss of hormonal protection, positioning women of this age group at a high risk for cardiovascular diseases such as hypertension, myocardial infarction, and stroke. The endothelin system in general and endothelin-1 (ET-1) in particular plays an important role in the pathogenesis of vascular dysfunction associated with aging. Evidence suggests that the female sex steroids can interfere with the vascular expression and actions of ET-1 via several mechanisms, which may further contribute to pathological processes in the vasculature of aging women. In this review, we have summarized hormone-dependent vascular pathways whereby ET-1 may mediate the deleterious effects of aging in postmenopausal females.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Protective effects of antioxidant-fortified diet on renal function and metabolic profile in obese Zucker rat

Oxidative stress contributes to the pathophysiology of type 2 diabetes mellitus and its complications, including nephropathy. The current study was designed to test the hypothesis that a diet fortified with antioxidants would be beneficial to delay or prevent the progression of this disease. Male and female Zucker fa/fa rats were fed a control or an antioxidant (AO)-fortified diet starting at 4 weeks of age. Metabolic parameters, renal function, and renal histopathology were analyzed at 6, 13, and 20 weeks of age. Females on the AO diet had significantly lower blood glucose at 6 and 13 weeks, less severe renal pathology at 20 weeks, and higher glomerular filtration rates (GFR) at 20 weeks than age-matched females on the regular diet (P < 0.05). Metabolic parameters including blood glucose, insulin resistance, and serum cholesterol, and mean arterial pressure (MAP), worsened with age in both males and females, as expected. GFR decreased and renal pathology also became more severe with age. Finally, females on the AO diet had higher GFRs and lower MAP at 20 weeks than males on the same diet. This may denote a protective effect of the AO diet in females, but not in males. These findings may have implications for the role of antioxidants as therapy in humans with T2DM.

Effects of gonadectomy on glucocorticoid metabolism in obese Zucker rats

Glucocorticoids are metabolized by 11beta-hydroxysteroid dehydrogenase 1 (11betaHSD1) and the A-ring reductases (5alpha- and 5beta-reductases). Dysregulation of these enzymes has been reported in liver and adipose tissue in obese humans and animals, potentially leading to altered intracellular glucocorticoid concentrations and compensatory activation of the hypothalamic-pituitary-adrenal axis. This dysregulation of glucocorticoid metabolism in obesity is poorly understood. We hypothesized that changes in glucocorticoid metabolism in obesity are mediated by alterations in androgen action. Steroid metabolism was studied in obese and lean male Zucker rats (age 10 wk, 10 animals per group) 4 wk after gonadectomy or sham surgery. Oral glucose tolerance tests were performed, and activities and abundances of mRNAs for steroid metabolizing enzymes were quantified in liver and adipose tissue. Gonadectomy did not consistently alter weight gain, glucose intolerance, or hyperinsulinemia in obese animals. Gonadectomy increased adrenal mass (P < 0.05), suppressed 11betaHSD1 activity and/or mRNA in liver and adipose, increased 5alpha-reductase 1 mRNA in liver (P < 0.05), and increased 5beta-reductase activity only in obese animals (P < 0.05). Differences in hepatic 11betaHSD1 mRNA expression and adipose activity between lean and obese animals were normalized by gonadectomy, whereas obese gonadectomized animals maintained elevated liver 5alpha-reductase and had an exaggerated elevation of 5beta-reductase activity. We conclude that androgens tonically increase 11betaHSD1 in liver and adipose tissue in male rats and contribute to the dysregulation of 11betaHSD1 in obesity. By contrast, androgens tonically suppress hepatic A-ring reductases in male rats and do not contribute to dysregulation of these enzymes in obesity.

Lipid peroxidation in ovariectomized and pinealectomized rats: the effects of estradiol and progesterone supplementation

In the present study, we investigated the effect of estradiol and progesterone supplementation on oxidant and antioxidant parameters of renal tissue in ovariectomized and pinealectomized rats. The study was carried out on 36 adult, Sprague-Dawley strain female rats, 6 months of age and weighing 200-250 g. The rats were divided into six groups, each group included six rats: Group 1: Sham-ovariectomized (Sham-Ovx); Group 2: Ovariectomized (Ovx); Group 3: Ovx and estradiol (E) and progesterone (P) supplemented (Ovx+E-P); Group 4: Ovariectomized and sham pinealectomy (Ovx+sham Pnx); Group 5: Ovariectomized+Pinealectomized (Ovx+Pnx); Group 6: Ovariectomized+Pinealectomized+Hormone Supplemented group (Ovx+Pnx+E-P). The levels of malondialdehyde (MDA), reduced glutathione (GSH) and glutathione peroxidase (GSH-Px) were analysed in renal tissues of rats. The highest and the lowest levels of MDA were determined in Groups 5 and 1 respectively (p < 0.001). However, GSH and GSH-Px levels demonstrated statistically important decreases in groups 2, 4, 5 (p < 0.001). The findings of this study demonstrate that ovariectomy leads to oxidative damage in renal tissue. Pinealectomy in addition to ovariectomy greatly increases the oxidative damage. However, female sex hormones supplementations to the Ovx and/or Ovx+Pnx rats protected against lipid peroxidation by activating the antioxidant system.

Lipid peroxidation in liver tissue of ovariectomized and pinealectomized rats: effect of estradiol and progesterone supplementation

The present study aimed to determine the effect of estradiol-progesterone supplementation and pinealectomy on lipid peroxidation of liver tissue in ovariectomized rats. The study was carried out on 36 adult Sprague-Dawley female rats, which weighed 200-250 g. The rats were divided into 6 groups: Group 1: Sham Ovariectomy (Sham-Ovx), Group 2: Ovariectomy (Ovx), Group 3: Ovx + Estradiol-Progesterone supplementation (Ovx + H), Group 4: Sham Pinealectomy and Ovx (Sham Pnx -Ovx), Group 5: Ovx -Pnx, Group 6: Ovx -Pnx + H. Malondialdehyde (MDA), reduced form of glutathione (GSH) and glutathione peroxidase (GSH-Px) levels were determined in liver tissue of rats. The highest MDA levels and the lowest GSH-Px levels were determined in the ovariectomized-pinealectomized group, whereas the lowest MDA was in the Sham-Ovx group, and the highest GSH-Px levels were found in the Sham-Ovx and Ovx + Hormone supplemented group. Furthermore, the highest GSH levels were in group 1 and lowest levels were in group 5. The findings of this study demonstrate that ovariectomy led to lipid peroxidation in liver tissues of rats. Pinealectomy in addition to ovariectomy, increases lipid peroxidation, but, estradiol and progesterone supplementations to the ovariectomized-pinealectomized rats protect against lipid peroxidation to a significant extent.

The Effect of Flutamide on Systemic and Renal Hemodynamics in Zucker Diabetic Rats: Paradoxic Renal Vasodilator Response to Endothelin-1 and TXA2 Receptor Activation in Female Sex

BACKGROUND

There is increasing evidence that endogenous sex hormones regulate vascular reactivity, and testosterone may contribute to the worse prognosis for renal disease in men. Male Zucker diabetic rats exhibit improved renal hemodynamic responses after castration. It is, however, unclear whether endogenous testosterone affects renal and systemic microcirculatory responses in the female sex, especially in type 2 diabetes.

AIM

To test the hypothesis that endogenous testosterone in the female Zucker diabetic rat exerts a pathophysiologically relevant modulation of endothelial and renal microvascular function.

METHODS

Female Zucker diabetic rats (FZDR) aged 5-6 weeks and from the same litter were divided into 2 groups (n = 6-8 each). The experimental group received the androgen receptor blocker flutamide, dissolved in alcohol and added to their drinking water (500 mL) at 20 mg/rat/week. The control FZDR received only the alcohol vehicle added to the same volume of drinking water. Both FZDR groups were treated for 3 months before undergoing the hemodynamic studies. A sex comparison control group of male Zucker diabetic rats (MZDR), also aged 5-6 weeks, was studied, following same protocol. Mean arterial pressure (MAP) and renal cortical blood flow (RCF) response to phenylephrine, acetylcholine, TXA2-mimetic U46619, endothelin-1 (ET-1), angiotensin II, and L-NG-nitro arginine methyl ester were studied. Furthermore, the role of protein kinase C in the responses was assessed using phorbol-12,13 dibutyrate 10(-4) M. The impact of flutamide on body weights and blood glucose of the rats were also determined.

RESULTS

Flutamide-treated FZDR had a significant reduction in body weight/adiposity to 432 +/- 44 g, compared to controls at 553 +/- 37 g (P = 0.045), and random blood glucose concentration of 185 +/- 44 g/dL, compared to the control FZDR at 475 +/- 34 g/dL (P = 0.002). Vehicle-treated FZDR (n = 6-8), exhibited little or no systemic or renal response to any of the agonists. By contrast, flutamide treatment of FZDR (n = 5-7) caused a normalization of the dose-dependent MAP and RCF pressor response to phenylephrine [P < 0.005, analysis of variance (ANOVA)] and the vasodilator response to acetylcholine (P <. 0.01, ANOVA). Flutamide-treated FZDR showed enhanced pressor response to U46619 (P = 0.024, ANOVA), ET-1, and angiotensin II (P < 0.03, ANOVA). Surprisingly, the augmented systemic pressor action of U46619 and ET-1 was accompanied by a renal vasodilator action, with paradoxic RCF increases to U46619 (P < 0.003, ANOVA) and to ET-1 (P < 0.001, ANOVA) only in flutamide-treated FZDR. By contrast, flutamide-treated MZDR exhibited no significant change in body weight and an attenuation of the vasoconstrictor responses and enhanced nitric oxide-mediated dilatation compared with male controls. However, no specific effect on ET-1 or TXA2 receptor-mediated renal perfusion was discernible. Both L-NG-nitro arginine methyl ester and the protein kinase C agonist phorbol-12,13 dibutyrate [10(-4)M] significantly increased MAP and reduced RCF (P < 0.03) in the experimental FZDR compared with their controls.

CONCLUSION

Flutamide administration to FZDR resulted in the reversal of abnormal systemic and renal alpha-1-mediated vasoconstriction and enhanced nitric oxide-mediated vasodilation. Flutamide caused a paradoxic but specific increase in renal perfusion during ET-1 and TXA2 receptor activation, which could be renoprotective in females. The salutary effects of flutamide on vascular reactivity in the FZDR may be mediated by a protein kinase C-dependent mechanism. These results are compatible with the notion that endogenous testosterone may regulate systemic and renal microcirculation in the female sex and in the type 2 diabetic state.

Castration reduces platelet thromboxane A2 receptor density and aggregability

BACKGROUND

Exogenously administered testosterone upregulates platelet thromboxane A2 (TXA2) receptors and increases aggregation response to thromboxane mimetics in healthy male volunteers. However, the biological impact of endogenous testosterone on platelet TXA2 receptor expression, especially in older men at risk of coronary artery disease, is unclear.

AIM

To investigate the impact of reduction in circulating testosterone on platelet TXA2 receptor expression in older men.

DESIGN

Cross-sectional case-control study.

METHODS

We studied surgically and/or medically castrated men with prostate cancer (group A, n = 8, aged 71 +/- 8 years) and age-matched, uncastrated urology patients (group B, n = 7, aged 67 +/- 9 years). Plasma testosterone was measured by radioimmunoassay. Platelet TXA2 receptor expression was assessed by radioligand binding studies using radioactive 125I-BOP. Platelet aggregation responses to TXA2-mimetic I-BOP, and to thrombin, were also studied.

RESULTS

Group A had significantly lower plasma testosterone than group B (16 +/- 5 ng/dl vs. 308 +/- 47 ng/dl, p<0.001). Platelet TXA2 receptor density (B(max)) but not affinity (K(d)) was lower in group A (0.50 +/- 0.12 vs. 1.01 +/- 0.17 pmol/mg protein, p = 0.03). Maximum platelet aggregation response to I-BOP (E(max)), but not sensitivity (EC50) was lower in group A (53 +/- 2% vs. 63 +/- 2%, p = 0.003 ANOVA). In vitro, high concentrations of hydroxyflutamide (100 microM) competitively inhibited U46619-induced platelet aggregation in washed platelets, without affecting the binding of 125I-BOP to platelet TXA2 receptors.

DISCUSSION

Endogenous testosterone regulates platelet TXA2 receptor B(max) and the E(max) aggregation response to thromboxane mimetic I-BOP. Blockade of androgen receptors or inhibition of testosterone production may reduce platelet aggregation responses. Preliminary evidence suggests the presence of functional androgen receptors on human platelets, which may regulate TXA2 receptor expression.