Gender difference in vascular and platelet reactivity to thromboxane A(2)-mimetic U46619 and to endothelial dependent vasodilation in Zucker fatty (hypertensive, hyperinsulinemic) diabetic rats

Sex-Related Differences in Platelet Aggregation: A Literature Review Supplemented with Local Data from a Group of Generally Healthy Individuals

The process of platelet aggregation is often influenced by several factors including sex and age. A literature review confirmed the existence of sex-related differences in platelet aggregation. Although 68 out of 78 papers found such differences, there are still some controversies regarding these differences, which can be due to multiple factors (age, trigger, concomitant disease, sample handling, etc.). These outcomes are discussed in line with novel results obtained from a local study, in which blood samples from a total of 53 overall healthy women and men with ages ranging from 20 to 66 years were collected. Aggregation was induced with seven different triggers (ristocetin, thrombin receptor activating peptide 6 [TRAP-6], arachidonic acid [AA], platelet-activating factor 16 [PAF-16], ADP, collagen, or thromboxane A₂ analog U-46619) ex vivo. In addition, three FDA-approved antiplatelet drugs (vorapaxar, ticagrelor, or acetylsalicylic acid [ASA]) were also tested. In general, women had higher aggregation responses to some agonists (ADP, TRAP), as well as lower benefit from inhibitors (ASA, vorapaxar). The aggregatory responses to AA and TRAP decreased with age in both sexes, while responses to ADP, U-46619, and PAF were affected by age only in women. In conclusion, more studies are needed to decipher the biological importance of sex-related differences in platelet aggregation in part to enable personalized antiplatelet treatment.

Chronic ethanol vapor exposure potentiates cardiovascular responses to acute stress in male but not in female rats

BACKGROUND

Ethanol use is related to a wide variety of negative health outcomes, including cardiovascular diseases. Stress is also involved in numerous pathologies, such as cardiovascular diseases and psychiatric disorders. Sexual dimorphism is an important factor affecting cardiovascular response and has been proposed as a potential risk factor for sex-specific health problems in humans. Here, we evaluated the effect of prolonged ethanol vapor inhalation on arterial pressure, heart rate, and tail skin temperature responses to acute restraint stress, investigating differences between male and female rats.

METHODS

We exposed male and female Long-Evans rats to ethanol vapor for 14 h, followed by ethanol withdrawal for 10 h, for 30 consecutive days, or to room air (control groups). The animals underwent surgical implantation of a cannula into the femoral artery for assessment of arterial pressure and heart rate values. The tail skin temperature was measured as an indirect measurement of sympathetic vasomotor response.

RESULTS

Chronic ethanol vapor inhalation reduced basal heart rate in both female and male rats. Sex-related difference was observed in the decrease of tail cutaneous temperature evoked by stress, but not in the pressor and tachycardiac responses. Furthermore, prolonged ethanol inhalation enhanced the blood pressure and heart rate increase caused by acute restraint stress in male, but not in female rats. However, no effect of chronic ethanol vapor was observed in the tail cutaneous temperature response to restraint in either sex.

CONCLUSION

Chronic ethanol vapor exposure increased the cardiovascular reactivity to stress in male, but not in female rats.

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.

C-reactive protein for predicting prognosis and its gender-specific associations with diabetes mellitus and hypertension in the development of coronary artery spasm

Background

While hypertension is negatively associated with coronary artery spasm (CAS), scarce data are available on diabetes mellitus in relation to CAS. In addition, outcome prediction in patients with CAS is challenging due to the lack of appropriate biomarkers. Therefore, we sought to identify the roles that gender, high-sensitivity C-reactive protein (hs-CRP), diabetes mellitus and hypertension play in CAS development and prognosis.

Methodology/Prinicpal Findings

Patients (350 women and 547 men) undergoing diagnostic coronary angiography with or without proven CAS but without obstructive stenosis were evaluated at long-term follow-up (median 102 months). Diabetic women and diabetic men with low hs-CRP levels had a low and high risk of CAS (odds ratio [OR]: 0.16, 95% confidence interval [CI]: 0.01–1.88 and OR: 5.02, 95% CI: 1.03–24.54, respectively). The ORs of CAS in both women and men with the highest hs-CRP tertile (>3 mg/L) reduced from 4.41 to 1.45 and 2.98 to 1.52, respectively, if they had diabetes mellitus, and from 9.68 to 2.43 and 2.60 to 1.75, respectively, if they had hypertension. Hypertension had a more negative effect on CAS development in diabetic than non-diabetic women, which was not observed in men. The highest hs-CRP tertile was an independent predictor of adverse outcomes. Patients with the highest hs-CRP tertile had more coronary events than patients with the lowest hs-CRP tertitle (p = 0.021, log-rank test).

Conclusions

Diabetes mellitus contributes to CAS development in men with low hs-CRP levels, but not in women. There are negative effects of diabetes mellitus and hypertension on CAS development in patients with high hs-CRP levels and especially in women. Elevated hs-CRP level independently predicts adverse outcomes.

Considerations of sex and gender differences in preclinical and clinical trials

Women continue to be underrepresented in clinical trials, particularly in Phases I and II of experimental drug studies in spite of legislative guidelines in the USA, Canada, the European Union, Australia, and Japan requiring the inclusion of women in clinical trials. As such, women remain a vulnerable population subject to the adverse effects of pharmacological therapies. Thus, women experience higher rates of adverse drug reactions than do men and for women of reproductive age or who may be pregnant, therapeutic options may be limited. This chapter provides a brief history of inclusion of sex and gender as variables in clinical trials, summarizes governmental legislation for consideration of sex and gender in clinical trials and provides specific examples of drugs which have been withdrawn from the market because of side effects in women. Additional information related to sex and gender in preclinical testing, trial design, challenges to recruitment of women for clinical trials and statistical methods for analysis of data also is considered.

Angiotensin II type 2 receptor mediates sex differences in mice renal interlobar arteries response to angiotensin II

OBJECTIVE

Functional sex differences are described in several vascular beds. In the case of renal vessels, sex differences could influence processes like regulation of blood pressure and ion balance. Angiotensin II and nitric oxide are important regulators of renal vascular tone. Females have higher nitric oxide synthase expression, nitric oxide bioavailability and ratio of angiotensin II type 2/type 1 receptors. Thus, our objective was to examine whether renal interlobar arteries present sex differences in their response to angiotensin II, and whether angiotensin II type 2 receptors play a role in such differences.

METHODS

We investigated the isometric contraction and relaxation of interlobar arteries from female and male mice under blockade of nitric oxide synthases and angiotensin II type 2 receptors. We also investigated the expression of angiotensin II receptors (type 1 and 2) and endothelial nitric oxide synthase.

RESULTS

Significantly less intense contraction to angiotensin II were seen in arteries from females in comparison to male mice. Inhibition of nitric oxide synthases and endothelial removal abolished this difference. Angiotensin II type 2 receptors blockade enhanced contraction to angiotensin II in females, but not in males. Endothelial-dependent vasodilation was more dependent on nitric oxide in females than in males. Expression of angiotensin II type 1 and type 2 receptors was similar between sexes. Expression of endothelial nitric oxide synthase was higher in females.

CONCLUSION

A sex-specific, nitric oxide-mediated effect via angiotensin II type 2 receptors underlies the sex differences in the response of interlobar arteries to angiotensin II. Our findings may help understanding sex differences in renal hemodynamics and blood pressure control.

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.

Salt sensitivity of nitric oxide generation and blood pressure in mice with targeted knockout of the insulin receptor from the renal tubule

To elucidate the role of the insulin receptor (IR) on kidney nitric oxide generation and blood pressure (BP) control, we generated mice with targeted deletion of renal tubule IR using loxP recombination driven by a Ksp-cadherin promoter. Male knockout (KO) and wild-type (WT) littermates (~4 mo old) were transitioned through three 1-wk treatments: 1) low-NaCl diet (0.085%); 2) high-NaCl diet (HS; 5%); and 3) HS diet plus 3 mM tempol, a superoxide dismutase mimetic, in the drinking water. Mice were then switched to medium-NaCl (0.5%) diet for 5 days and kidneys harvested under pentobarbital anesthesia. Twenty-four-hour urinary nitrates plus nitrites were significantly higher in the WT mice under HS (2,067 ± 280 vs. 1,550 ± 230 nmol/day in WT and KO, respectively, P < 0.05). Tempol attenuated genotype differences in urinary nitrates plus nitrites. A rise in BP with HS was observed only in KO mice and not affected by tempol (mean arterial pressure, dark period, HS, 106 ± 5 vs. 119 ± 4 mmHg, for WT and KO, respectively, P < 0.05). Renal outer medullary protein levels of nitric oxide synthase (NOS) isoforms by Western blot (NOS1-3 and phosphorylated-S1177-NOS3) revealed significantly lower band density for NOS1 (130-kDa isoform) in the KO mice. A second study, when mice were euthanized under HS conditions, confirmed significantly lower NOS1 (130 kDa) in the KO, with an even more substantial (>50%) reduction of the 160-kDa NOS1 isoform. These studies suggest that the loss of renal IR signaling impairs renal nitric oxide production. This may be important in BP control, especially in insulin-resistant states, such as the metabolic syndrome.

Reference intervals for platelet aggregation assessed by multiple electrode platelet aggregometry

INTRODUCTION

Analyses of platelet aggregation in hirudin whole blood using Multiplate® was validated. Reference intervals for the most commonly used agonists were established, and the association between platelet aggregation, age, gender and haematological values was analysed.

MATERIAL AND METHODS

We included 121 healthy individuals to establish reference intervals and six healthy individuals for evaluation of the day-to-day variation. Platelet aggregation was evaluated on hirudin whole blood employing Multiplate® induced by arachidonic acid, ADP, collagen and ristocetin (RISTOlow and RISTOhigh). Measurements of haematological values were performed employing Sysmex K-4500.

RESULTS

We found no association between platelet aggregation and age (p>0.57 for all agonists, except RISTOlow: p=0.05). Platelet aggregation was significantly higher in women compared to men for all agonists (p<0.0003), except RISTOlow (p=0.05). A reference interval is presented as 95% confidence interval suitable for any age and both sex. Day-to-day variation was <11% for all agonists except for RISTOlow. No association was found between platelet aggregation and haematocrit or red blood cell count after adjusting for age and gender except for RISTOhigh. A positive significant association was found between platelet count and platelet aggregation (p<0.04). Finally, a significant positive association was found between platelet aggregation and white blood cell count for all agonists (p<0.05) except RISTOlow and RISTOhigh (p>0.05).

CONCLUSION

Reference intervals for platelet aggregation in healthy individuals (age: 17 to 66 years) were established in hirudin whole blood measured by Multiplate® employing the most commonly used agonists.

Does Gender have an Influence on Platelet Function and the Efficacy of Oral Antiplatelet Therapy?

The underlying pathophysiology of ischemic complications during acute coronary syndrome involves thrombus generation at sites of plaque rupture and endothelial erosion, in which platelet activation and aggregation play major roles. This review discusses whether there are intrinsic differences in thrombogenicity between genders. In trials of acute coronary syndromes with dual antiplatelet therapy strategies, women tend to experience more ischemic events. Controversy exists surrounding the protective role of estrogens in the premenopausal woman. In vitro studies support the attenuation of platelet function by estrogen. Sufficient data support the presence of gender differences in thrombogenicity to promote further investigation in this area.

The effect of menstrual cycle on platelet aggregation in reproductive-age women

Our aim was to assess the change in platelet activity along the menstrual cycle. We conducted a prospective observational study. The study group included 16 healthy women with regular menstrual cycles, which were compared to a control group of 14 healthy males. Exclusion criteria were age <18 years or >45 years, use of oral contraceptives or any other forms of hormonal therapy and medical disorders or medications that might affect platelet aggregation. Blood samples were taken from each of the women at four different phases of the menstrual cycle: day 1 +/- 1, day 7 +/- 1, day 14 +/- 1, and day 21 +/- 1. A single blood sample was taken from the males. Platelet aggregation was assessed in whole blood samples using the Multiplate analyzer with three different agonists (ADP, arachidonic acid (AA), and thrombin-receptor activating peptide (TRAP)). Platelet aggregation for each of the women at each of the phases of the menstrual cycle was expressed as the percentage change from the day 1 +/- 1 value. A total of 390 aggregation assays were performed. The mean aggregation activity was significantly higher in females compared with males, irrespective of the agonist used. For the TRAP and the ADP agonists, the relative platelet activity decreased along the menstrual cycle from day 1 towards day 21 and from day 7 towards day 21, respectively, although differences reached statistical significance only for day 21 (-12.4% +/- 3.2%, P < 0.05 for TRAP, and -9.5% +/- 3.9%, P < 0.05 for ADP). When using AA to induce platelet aggregation, the relative platelet activity was highest around the time of ovulation (11.0% +/- 4.7%) and was significantly lower on day 21 (-8.5% +/- 6.7%, P < 0.05). In conclusion, platelet aggregation activity is higher in females compared with males. The association between the phase of the menstrual cycle and platelet activity appears to vary with the type of agonist, but platelet aggregation is consistently lowest in the mid-luteal phase irrespective of the agonist used.

The role of rho kinase in sex-dependent vascular dysfunction in type 1 diabetes

We hypothesized that rho/rho kinase plays a role in sex differences in vascular dysfunction of diabetics. Contractions to serotonin were greater in isolated aortic rings from nondiabetic males versus females and increased further in streptozotocin-induced diabetic males but not females. The increased contractions to serotonin in males were reduced by inhibitors of rho kinase (fasudil, Y27632 and H1152) despite no change in expression of rhoA or rho kinase. Contractions to U46619 were not altered by fasudil or Y27632 or the presence of diabetes. In contrast to acute effects of fasudil, chronic treatment with fasudil increased contractions to serotonin in aorta from both non-diabetic and diabetic males. In summary, serotonin-induced contractions were increased in aorta from diabetic males but not females. Although administration of rho kinase inhibitors acutely decreased contractions to serotonin, long-term treatment with fasudil increased contractions. Long-term fasudil treatment may increase compensatory mechanisms to enhance vasoconstrictions.

Thrombosis and antithrombotic therapy in women

Sex-based differences in the prevalence and presentation of arterial and venous thrombosis exist, and emerging data indicate that men and women do not accrue equal benefit from antithrombotic therapy. Sex hormones alter procoagulant protein expression and the function of blood and vascular cells. Sex-based differences in platelet function have been reported, and in animal models, sex-based differences in thrombosis have been noted. Here we review plausible mechanisms that may explain how sex functions as a modifier of thrombosis and summarize clinical data on the interaction between sex and response to antithrombotic therapy.

Estrogen, inflammation, and platelet phenotype

BACKGROUND

Although exogenous estrogenic therapies increase the risk of thrombosis, the effects of estrogen on formed elements of blood are uncertain.

OBJECTIVE

This article examines the genomic and nongenomic actions of estrogen on platelet phenotype that may contribute to increased thrombotic risk.

METHODS

To determine aggregation, secretion, protein expression, and thrombin generation, platelets were collected from experimental animals of varying hormonal status and from women enrolled in the Kronos Early Estrogen Prevention Study.

RESULTS

Estrogen receptor beta predominates in circulating platelets. Estrogenic treatment in ovariectomized animals decreased platelet aggregation and adenosine triphosphate (ATP) secretion. However, acute exposure to 17beta-estradiol did not reverse decreases in platelet ATP secretion invoked by lipopolysaccharide. Thrombin generation was positively correlated to the number of circulating microvesicles expressing phosphatidylserine.

CONCLUSION

Assessing the effect of estrogen treatments on blood platelets may lead to new ways of identifying women at risk for adverse thrombotic events with such therapies.

Sex-specific differences in chromosome-dependent regulation of vascular reactivity in female consomic rat strains from a SSxBN cross

High-throughput studies in the Medical College of Wisconsin Program for Genomic Applications (Physgen) were designed to link chromosomes with physiological function in consomic strains derived from a cross between Dahl salt-sensitive SS/JrHsdMcwi (SS) and Brown Norway normotensive BN/NHsdMcwi (BN) rats. The specific goal of the vascular protocol was to characterize the responses of aortic rings from these strains to vasoconstrictor and vasodilator stimuli (phenylephrine, acetylcholine, sodium nitroprusside, and bath hypoxia) to identify chromosomes that either increase or decrease vascular reactivity to these vasoactive stimuli. Because previous studies demonstrated sex-specific quantitative trait loci (QTLs) related to regulation of cardiovascular phenotypes in an F2 cross between the parental strains, males and females of each consomic strain were included in all experiments. As there were significant sex-specific differences in aortic sensitivity to vasoconstrictor and vasodilator stimuli compared with the parental SS strain, we report the results of the females separately from the males. There were also sex-specific differences in aortic ring sensitivity to these vasoactive stimuli in consomic strains that were fed a high-salt diet (4% NaCl) for 3 wk to evaluate salt-induced changes in vascular reactivity. Differences in genetic architecture could contribute to sex-specific differences in the development and expression of cardiovascular diseases via differential regulation and expression of genes. Our findings are the first to link physiological traits with specific chromosomes in female SS rats and support the idea that sex is an important environmental variable that plays a role in the expression and regulation of genes.

Sex differences in renal nitric oxide synthase, NAD(P)H oxidase, and blood pressure in obese Zucker rats

BACKGROUND

By increasing renal oxidative stress, obesity may alter the protective effect of female sex on blood pressure (BP).

OBJECTIVES

The aim of this study was to determine whether female rats had altered expression and activity of renal nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase and nitric oxide synthase (NOS), enzymes important in superoxide and nitric oxide generation, respectively, and whether this relationship was altered in obesity.

METHODS

Male and female, lean and obese Zucker rats were fed progressively higher levels of NaCl over 54 days while BP was measured by radiotelemetry. Kidneys were harvested after euthanization.

RESULTS

A total of 32 (n=8/body type/sex) Zucker rats were examined. On a high-salt diet (4% NaC1), male and obese rats had significantly higher mean arterial blood pressure relative to female and lean rats (mm Hg: lean male=108, lean female=99, obese male=129, and obese female=123) and reduced renal cortical NOS activity (determined by 2-way analysis of variance; P<0.05 for sex and body type). Immunoblotting revealed that cortical endothelial NOS protein abundance was reduced in obese but not in male rats. Surprisingly, lean female rats had the highest outer medullary protein levels of several NADPH oxidase subunits, including gp91phox, p47phox, and p67phox (% of lean male: 207, 196, and 151, respectively; P<0.01 for all). However, renal NADPH activity was not increased in lean females, but was significantly increased in obese rats of both sexes (P<0.05).

CONCLUSIONS

High-NaCl diet increased BP modestly in obese females, but not at all in lean females, suggesting some loss of protection with obesity in female rats. Reduced cortical NOS activity (both in male and obese rats) and/or increased NADPH oxidase activity (obese rats) may have contributed to increased salt sensitivity of BP.

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.

Impaired hemorrhage tolerance in the obese Zucker rat model of metabolic syndrome

As obese Zucker rats (OZR) manifesting the metabolic syndrome exhibit enhanced vascular adrenergic constriction and potentially an enhanced adrenergic activity vs. lean Zucker rats (LZR), this study tested the hypothesis that OZR exhibit an improved tolerance to progressive hemorrhage. Preliminary experiments indicated that, corrected for body mass, total blood volume was reduced in OZR vs. LZR. Anesthetized LZR and OZR had a cremaster muscle prepared for in situ videomicroscopy and had renal, splanchnic, hindlimb, and skeletal muscle perfusion monitored with flow probes. Arterial pressure, arteriolar reactivity to norepinephrine, and tissue/organ perfusion were monitored after either infusion of phentolamine or successive withdrawals of 10% total blood volume. Phentolamine infusion indicated that regional adrenergic tone under control conditions differs substantially between LZR and OZR, whereas with hemorrhage OZR exhibit decompensation in arterial pressure before LZR. Renal, distal hindlimb, and skeletal muscle perfusion decreased more rapidly and to a greater extent in OZR vs. LZR after hemorrhage. In contrast, hemorrhage-induced reductions in splanchnic perfusion in OZR lagged behind those in LZR, although a similar maximum reduction was ultimately attained. With increasing hemorrhage, cremasteric arteriolar tone increased more in OZR than LZR, and this increase in active tone was entirely due to an elevated adrenergic contribution. Norepinephrine-induced arteriolar constriction was greater in OZR vs. LZR under control conditions and during hemorrhage, with arterioles from OZR demonstrating early closure vs. LZR. These results suggest that a combination of reduced blood volume and elevated peripheral adrenergic constriction contribute to impaired hemorrhage tolerance in OZR.

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.

Sickle cell trait and gender influence type 2 diabetic complications in African patients

BACKGROUND: Black and African patients with type 2 diabetes have a greater frequency and more severe vascular complications of the disease, even after correction for socioeconomic factors. Asymptomatic sickle cell trait (SCT; hemoglobin AS) is also common among black Africans and may independently cause endothelial damage, manifested as isolated target organ complication or infarction. We examined the possibility that patients with concurrent type 2 diabetes and SCT may be predisposed to more frequent or severe diabetic macro- or microvascular complications than those without SCT. METHODS: Fifty-two type 2 diabetic patients were divided into four groups, according to gender and hemoglobin genotype (normal: AA or SCT: AS). The groups were well matched for age and for clinical and demographic parameters. Diabetic complications were assessed in each patient and scored. Hemoglobin genotype was determined by hemoglobin-gel electrophoresis. Statistical comparisons were made between the groups. RESULTS: The composite complication score for vascular disease differed significantly according to gender and genotype (p<0.027 ANOVA). Male diabetics with SCT had a higher risk ratio (RR 1.6, p<0.02) for complications than those with normal hemoglobin; however, this was not the case with female diabetics. Among the male diabetics with SCT, there was a significantly greater proportion with proteinuria (p<0.02) or retinopathy (p<0.05) than among those with a normal hemoglobin genotype. Multiple regression analysis showed that gender and SCT were independent predictors of the vascular complication severity score and that exclusion of hemoglobin genotype weakened the predictability of the regression. A significantly higher proportion of male than female diabetics had at least one detectable complication. Systolic or diastolic blood pressure had no significant impact on the regressions. CONCLUSION: Male gender and SCT may adversely affect the expression of microvascular diabetic complications in Africans. Diabetic patients from populations predisposed to the sickle gene should be screened for the trait as part of their initial risk assessment. Large-scale studies on the impact of hemoglobin genotype on diabetic complications are clearly indicated.

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

BACKGROUND

Male Zucker diabetic rats exhibit a more severe endotheliopathy in comparison with their female diabetic litter mates. The plasma concentrations of both thromboxanes and endothelins are elevated in diabetes, and the receptor cross-talk between TXA(2) and ET-1 receptors may be enhanced in type-2 diabetic Zucker rats.

AIMS

To determine the role of the endogenous sex steroid hormones, testosterone and estradiol on the systemic and renal microvascular reactivity to ET-1, thromboxane-mimetic U46619, ET-TXA(2) receptor interaction, and the nitric oxide vasodilator system in Zucker hypertensive-diabetic rats.

METHODS

Male and female Zucker rats aged 8-10 weeks were each divided into two groups. The male rats were castrated or underwent a sham operation. The female rats were spayed (bilateral ovariectomy and hysterectomy) or had a sham operation. All rats were studied 4-6 weeks after the gonadectomy or sham operations. Blood glucose and insulin as well as plasma concentrations of testosterone and estradiol were determined. Haemodynamic studies were undertaken with determination of the dose-response curve for mean arterial pressure (MAP), renal cortical flow (RCF) and renal medullary blood flow (MBF) in response to ET-1 and U46619, and the effect of interdiction of the ET-TXA(2) interaction with ET-antagonists BQ610 and BQ788. The role of endogenous NO was assessed by its response to graded acetylcholine doses and to a L-NG-nitro-arginine methyl ester (L-NAME) infusion.

RESULTS

Castrated male rats had a significantly lower blood glucose concentration (295 +/- 33 mg dL(-1)) compared with their sham-controls (481 +/- 40 mg dL(-1)), P = 0.008. Mean arterial pressure tended to be lower in the castrated rats. Gonadectomy reduced the plasma testosterone and estradiol concentrations. Castration abolished the hypotensive action of U46619 compared with sham-operated male rats (P < 0.0001, anova). Conversely, the pressor action of U46619 seen in the sham-operated female rats was reversed to a profound hypotensive action in the spayed rats (P < 0.001, anova). The change in MAP after U46619 was inversely correlated to the plasma testosterone concentration (r = -0.73, P = 0.027). The paradoxical hypotensive response elicited by ET-1 in the Zucker diabetic rats of both sexes was abolished by castration only (P < 0.005, anova). Castration caused a significant (P = 0.011) augmentation of the vasodilator response to acetylcholine, while spaying caused a slight attenuation. Castration, but not spaying, resulted in significant increases in MBF after U46619 (P = 0.003, anova), ET-1 (P = 0.005, anova) and acetylcholine (P = 0.053, anova). The ET-(B) antagonist BQ788 augmented the U46619-induced rise in MAP in castrated male rats, and also abolished the U46619-induced increase in MBF (P < 0.01 anova). L-NAME (25 mg kg(-1)) increased MAP and decreased MBF in the gonadectomized and sham-operated rats, except for the castrated male Zucker rats, where it significantly increased MBF (+90 +/- 31 PU) (P = 0.0004, anova) despite the increase in MAP.

CONCLUSIONS

Testosterone and estradiol regulate systemic and microvascular reactivity to TXA(2) receptor stimulation in type-2 diabetic Zucker rats. The impact of testosterone on blood glucose concentration, blood pressure, and the systemic and renal microcirculatory response to ET-1 and NO, as well as the endothelin-thromboxane receptor cross talk, is greater, and opposite to that of estradiol. The effects of testosterone withdrawal may at least in part be mediated by the ET-B receptor subtype and NO generation. Androgen blockade should be investigated further for the reversal or delay of hypertensive-diabetic endotheliopathy.

Alteration in endothelin receptor sub-type responsiveness and in the endothelin-TXA(2) mimetic U46619 interaction, in type-2 hypertensive diabetic Zucker rats

BACKGROUND

Type-2 diabetes is characterized by endotheliopathy, which increases target organ damage and mortality. There is excessive endothelin-1 and TXA(2) production, and abnormal vascular reactivity to endothelin-1, manifested as a paradoxical hypotensive action in Zucker diabetic, but not lean rats. We examined the hypothesis that there is an alteration in the ET-A/ET-B receptor subtype sensitivity, and/or the interaction or cross-talk between ET-1 and TXA(2) in type-2 diabetes, using Zucker diabetic rats and their lean littermates.

MATERIALS AND METHODS

Hemodynamic studies were performed in lean and Zucker fatty diabetic rats of both sexes. Laser doppler flowmetry was used to measure renal cortical (RCF) and medullary blood flow (MBF) responses. Dose response curves for mean arterial blood pressure (MAP), MBF and RCF in response to ET-1, U46619, acetylcholine, and L-NAME (25mg/kg) were constructed after pre-treatment of the rats with either BQ610 1mg/kg i.v. or BQ788 0.5mg/kg i.v. The effects of BQ610 and BQ788 on whole blood impedance aggregation were also assessed.

RESULTS

BQ788, but not BQ610 abolished both the paradoxical hypotensive action of ET-1 in Zucker diabetic rats (n=7 each, P<0.001 ANOVA) as well as the dose-dependent rise in MBF (P<0.001 ANOVA). BQ788, but not BQ610 abolished the difference in response to ET-1 between lean and diabetic Zucker rats. U46619 caused a hypotensive action in male Zucker rats which was abolished by L-NAME 25mg/kg or indomethacin 10mg/kg i.v. The U46619 interaction with BQ788 on both MAP and MBF was significantly (P<0.03 ANOVA) different between lean and diabetic Zucker rats. BQ788, but not BQ610 attenuated both the MAP and MBF responses to acetylcholine or L-NAME P<0.02 ANOVA). However, BQ610 dose-dependently attenuated the slope of platelet aggregation in both lean and Zucker diabetic rats (P<0.02 ANOVA).

CONCLUSION

ET-B receptor antagonism abolished the abnormal vascular reactivity and MBF responses to ET-1, and also normalized the vasoactive responses to the level seen in healthy lean Zucker rats. ET-1 receptor blockade influences the responses to TXA(2) receptor activation. In the systemic and renal circulation, this interaction appears to be mostly ET-B receptor mediated, whilst in platelets, ET-A receptor role may be predominant. The interaction or cross-talk between ET-1 and TXA(2) is altered in the type-2 diabetic state. Collectively, these pathophysiological changes may contribute to the vicious circle of diabetic endotheliopathy.