Gender differences in vascular reactivity to endothelin-1 (1-31) in mesenteric arteries from diabetic mice

Sex and Gender Related Differences in Diabetic Kidney Disease

Diversity in sex and gender are important considerations in the pathogenesis, prognostication, research, and management of diabetic kidney disease (DKD). Sex and gender differences in the disease risk, disease-specific mechanisms, and outcomes in DKD may be attributed to biological differences between males and females at the cellular and tissue level, inconsistencies in the diagnostic and assessment tools used in chronic kidney disease and DKD, as well societal differences in the way men, women, and gender-diverse individuals self-manage and interact with health care systems. This review outlines key considerations related to the impact of sex on DKD, specifically elaborating on how they contribute to observed differences in disease epidemiology, pathogenesis, and treatment strategies. We also highlight the effect of gender on DKD progression and care.

Sex-related differences in diabetic kidney disease: A review on the mechanisms and potential therapeutic implications

Sexual dimorphism may play a key role in the pathogenesis of diabetic kidney disease (DKD) and explain differences observed in disease phenotypes, responses to interventions, and disease progression between men and women with diabetes. Therefore, omitting the consideration of sex as a biological factor may result in delayed diagnoses and suboptimal therapies. This review will summarize the effects of sexual dimorphism on putative metabolic and molecular mechanisms underlying DKD, and the potential implications of these differences on therapeutic interventions. To successfully implement precision medicine, we require a better understanding of sexual dimorphism in the pathophysiologic progression of DKD. Such insights can unveil sex-specific therapeutic targets that have the potential to maximize efficacy while minimizing adverse events.

NTPDase1 Modulates Smooth Muscle Contraction in Mice Bladder by Regulating Nucleotide Receptor Activation Distinctly in Male and Female

Nucleotides released by smooth muscle cells (SMCs) and by innervating nerve terminals activate specific P2 receptors and modulate bladder contraction. We hypothesized that cell surface enzymes regulate SMC contraction in mice bladder by controlling the concentration of nucleotides. We showed by immunohistochemistry, enzymatic histochemistry, and biochemical activities that nucleoside triphosphate diphosphohydrolase-1 (NTPDase1) and ecto-5′-nucleotidase were the major ectonucleotidases expressed by SMCs in the bladder. RT-qPCR revealed that, among the nucleotide receptors, there was higher expression of P2X1, P2Y₁, and P2Y₆ receptors. Ex vivo, nucleotides induced a more potent contraction of bladder strips isolated from NTPDase1 deficient (Entpd1^−/−) mice compared to wild type controls. The strongest responses were obtained with uridine 5′-triphosphate (UTP) and uridine 5′-diphosphate (UDP), suggesting the involvement of P2Y₆ receptors, which was confirmed with P2ry6^−/− bladder strips. Interestingly, this response was reduced in female bladders. Our results also suggest the participation of P2X1, P2Y₂ and/or P2Y₄, and P2Y₁₂ in these contractions. A reduced response to the thromboxane analogue U46619 was also observed in wild type, Entpd1^−/−, and P2ry6^−/− female bladders showing another difference due to sex. In summary, NTPDase1 modulates the activation of nucleotide receptors in mouse bladder SMCs, and contractions induced by P2Y₆ receptor activation were weaker in female bladders.

Successful induction of diabetes in mice demonstrates no gender difference in development of early diabetic retinopathy

Purpose

Female mice have been found to be resistant to streptozotocin (STZ)-induced diabetes, and pre-clinical research related to diabetic complications commonly omits females. The purpose of this study was to develop a method to induce diabetes in female mice, and to determine if retinas of diabetic female mice develop molecular changes and histopathological abnormalities comparable to those which develop in male diabetic mice.

Methods

To induce diabetes, animals of both sexes received daily intraperitoneal (i.p.) injection of STZ for 5 consecutive days at 55 mg/kg BW (a dose that is known to induce diabetes in male mice) or for females, 75 mg/kg BW of STZ. Retinal abnormalities that have been implicated in the development of the retinopathy (superoxide generation and expression of inflammatory proteins, iNOS and ICAM-1) were evaluated at 2 months of diabetes, and retinal capillary degeneration was evaluated at 8 months of diabetes.

Results

Daily i.p. injection of STZ for 5 consecutive days at a concentration of 55 mg/kg BW was sufficient to induce diabetes in 100% of male mice, but only 33% of female mice. However, females did become hyperglycemic when the dose of STZ administered was increased to 75 mg/kg BW. The resulting STZ-induced hyperglycemia in female and male mice was sustained for at least 8 months. After induction of the diabetes, both sexes responded similarly with respect to the oxidative stress, expression of iNOS, and degeneration of retinal capillaries, but differed in the limited population evaluated with respect to expression of ICAM-1.

Conclusions

The resistance of female mice to STZ-induced diabetes can be overcome by increasing the dose of STZ used. Female mice can, and should, be included in pre-clinical studies of diabetes and its complications.

Mesenteric arterial dysfunction in the UC Davis Type 2 Diabetes Mellitus rat model is dependent on pre-diabetic versus diabetic status and is sexually dimorphic

Previous reports suggest that diabetes may differentially affect the vascular beds of females and males. However, there is insufficient evidence to establish the timeline of the vascular dysfunction in diabetes, specifically in relation to sex. Here, we determined whether mesenteric arterial function is altered in UC Davis Type-2 Diabetes Mellitus (UCD-T2DM) rats and if this occurs as early as the pre-diabetic stage of the disease. Specifically, we investigated whether vascular dysfunction differs between pre-diabetic or diabetic status and if this varies by sex. We measured the responses to endothelium-dependent and -independent vasorelaxant as well as vasoconstrictor agents and explored the potential mechanisms involved in sex-specific development of arterial dysfunction in UCD-T2DM rats. In addition, indices of insulin sensitivity were assessed. We report the reduced insulin sensitivity in pre-diabetic males and diabetic females. Vascular relaxation to acetylcholine was impaired to a greater extent in mesenteric artery from males in the pre-diabetic stage than in their female counterparts. In contrast, the arteries from females with diabetes exhibited a greater impairment to acetylcholine compared with diabetic males. Additionally, the sensitivity of mesenteric artery to contractile agents in females, but not in males, after the onset of diabetes was increased. Our data suggest that the reduced insulin sensitivity through AKT may predispose vessels to injury in the pre-diabetic stage in males. On the other hand, reduced insulin sensitivity as well as enhanced responsiveness to contractile agents may predispose arteries to injury in the diabetic stage in females.

Impact of Diabetes Mellitus in Women Undergoing Percutaneous Coronary Intervention With Drug-Eluting Stents

BACKGROUND

Data examining the impact of diabetes mellitus (DM) on ischemic risk after percutaneous coronary intervention in women are limited as most clinical trial participants are male. We evaluated (1) the impact of DM on ischemic outcomes in women undergoing drug-eluting stent (DES) implantation and (2) whether the outcomes of new- versus early-generation DES vary by DM status.

METHODS AND RESULTS

We pooled patient-level data of 10 448 women undergoing percutaneous coronary intervention with DES from 26 randomized trials. Baseline characteristics and 3-year clinical outcomes were stratified according to DM status (noninsulin-dependent and insulin-dependent) and DES generation. The primary end point was the composite of all-cause death or myocardial infarction. Secondary end points were definite or probable stent thrombosis and target lesion revascularization. Compared with women without DM (n=7154, 68.5%), adjusted risks (adjusted hazard ratios [95% CI]) for death or myocardial infarction among women with noninsulin-dependent DM (n=2241, 21.4%) and insulin-dependent DM (n=1053, 10.1%) were 1.30 (1.11-1.53) and 1.71 (1.41-2.07), respectively ( P_trend<0.001). Similar trends were observed for def/prob stent thrombosis and target lesion revascularization. Compared with early-generation DES, use of newer-generation DES was associated with significant reductions in death or myocardial infarction in the absence of DM whereas differences were nonsignificant in the presence of DM, with similar findings for def/prob stent thrombosis and target lesion revascularization.

CONCLUSIONS

The presence of DM is associated with substantial, graded, and durable risks for ischemic events among women undergoing percutaneous coronary intervention with DES. The safety and efficacy profile of newer-generation DES is preserved among women without DM, while benefits are nonsignificant among women with DM.

Afferent arteriole responsiveness to endothelin receptor activation: does sex matter?

BACKGROUND

The pathogenesis of hypertension is distinct between men and women. Endothelin-1 (ET-1) is a potential contributor to sex differences in the pathophysiology of hypertension. ET-1 participates in blood pressure regulation through activation of endothelin A (ET_A) and endothelin B (ET_B) receptors including those in the vasculature. Previous studies demonstrated that sex and sex hormones evoke discrepancies in ET-1-mediated control of vascular tone in different vascular beds. However, little is known about sex- and sex hormone-related differences in ET-1-dependent renal microvascular reactivity. Accordingly, we hypothesized that loss of sex hormones impairs afferent arteriole reactivity to ET-1.

METHODS

Male and female Sprague Dawley rats were subjected to gonadectomy or sham surgery (n = 6/group). After 3 weeks, kidneys from those rats were prepared for assessment of renal microvascular responses to ET-1 (ET_A and ET_B agonist, 10^-12 to 10^-8 M) and sarafotoxin 6c (S6c, ET_B agonist, 10^-12 to 10^-8 M) using the blood-perfused juxtamedullary nephron preparation.

RESULTS

Control afferent arteriole diameters at 100 mmHg were similar between sham male and female rats averaging 14.6 ± 0.3 and 15.3 ± 0.3 μm, respectively. Gonadectomy had no significant effect on control arteriole diameter. In sham males, ET-1 produced significant concentration-dependent decreases in afferent arteriole diameter, with 10^-8 M ET-1 decreasing diameter by 84 ± 1%. ET-1 induced similar concentration-dependent vasoconstrictor responses in sham female rats, with 10^-8 M ET-1 decreasing the diameter by 82 ± 1%. The afferent arteriolar vasoconstrictor responses to ET-1 were unchanged by ovariectomy or orchiectomy. Selective ET_B receptor activation by S6c induced a concentration-dependent decline in afferent arteriole diameter, with 10^-8 M S6c decreasing diameter by 77 ± 3 and 76 ± 3% in sham male and female rats, respectively. Notably, ovariectomy augmented the vasoconstrictor response to S6c (10^-12 to 10^-9 M), whereas orchiectomy had no significant impact on the responsiveness to ET_B receptor activation.

CONCLUSION

These data demonstrate that sex does not significantly influence afferent arteriole reactivity to ET receptor activation. Gonadectomy potentiated the responsiveness of the afferent arteriole to ET_B-induced vasoconstriction in females, but not males, suggesting that female sex hormones influence ET_B-mediated vasoconstriction in the renal microcirculation.

Diastolic dysfunction is more apparent in STZ-induced diabetic female mice, despite less pronounced hyperglycemia

Diabetic cardiomyopathy is a distinct pathology characterized by early emergence of diastolic dysfunction. Increased cardiovascular risk associated with diabetes is more marked for women, but an understanding of the role of diastolic dysfunction in female susceptibility to diabetic cardiomyopathy is lacking. To investigate the sex-specific relationship between systemic diabetic status and in vivo occurrence of diastolic dysfunction, diabetes was induced in male and female mice by streptozotocin (5x daily i.p. 55 mg/kg). Echocardiography was performed at 7 weeks post-diabetes induction, cardiac collagen content assessed by picrosirius red staining, and gene expression measured using qPCR. The extent of diabetes-associated hyperglycemia was more marked in males than females (males: 25.8 ± 1.2 vs 9.1 ± 0.4 mM; females: 13.5 ± 1.5 vs 8.4 ± 0.4 mM, p < 0.05) yet in vivo diastolic dysfunction was evident in female (E/E' 54% increase, p < 0.05) but not male diabetic mice. Cardiac structural abnormalities (left ventricular wall thinning, collagen deposition) were similar in male and female diabetic mice. Female-specific gene expression changes in glucose metabolic and autophagy-related genes were evident. This study demonstrates that STZ-induced diabetic female mice exhibit a heightened susceptibility to diastolic dysfunction, despite exhibiting a lower extent of hyperglycemia than male mice. These findings highlight the importance of early echocardiographic screening of asymptomatic prediabetic at-risk patients.

Effect of Long-Term Diabetes on Serotonin-Mediated Contraction in Carotid Arteries from Streptozotocin-Induced Diabetic Male and Female Rats

An accumulating body of evidence suggests that males and females differ in vascular function in arteries under pathophysiological states. In this study, we tested whether there was a sex difference associated with serotonin (5-hydroxytryptamine, 5-HT)-mediated contraction in the carotid arteries of long-term streptozotocin (STZ)-induced diabetic rats [viz. 23 or 24 weeks after STZ (65 mg/kg, intravenously (i.v.)) injection starting at 8 weeks old of rats]. In the control group, the 5-HT- and high-K⁺-induced contractions were greater in females than in males. In both sexes, treatment with STZ led to a decrease of 5-HT-induced contraction in carotid arteries compared to controls. In STZ-induced diabetic rats, the carotid arterial 5-HT-induced contraction was greater in female rats than in diabetic male rats. The high-K⁺-induced contraction was greater in diabetic female rats than in either age-matched female controls or diabetic male rats. Expression of the 5-HT_2A receptor, which is the main receptor for 5-HT-induced contraction in rat carotid arteries, was similar among the four groups. These results suggest that decreased 5-HT-induced carotid arterial contraction is seen in both sexes under long-term STZ-induced diabetic conditions. Further, this reduction seems to be weaker in females than in males. This alteration of 5-HT-induced contraction may be partly associated with increased voltage-dependent Ca²⁺ channel activity.

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.

Oestrogen receptor alpha in pulmonary hypertension

Aims

Pulmonary arterial hypertension (PAH) occurs more frequently in women with mutations in bone morphogenetic protein receptor type 2 (BMPR2) and dysfunctional BMPR2 signalling underpinning heritable PAH. We have previously shown that serotonin can uncover a pulmonary hypertensive phenotype in BMPR2^+/− mice and that oestrogen can increase serotinergic signalling in human pulmonary arterial smooth muscle cells (hPASMCs). Hence, here we wished to characterize the expression of oestrogen receptors (ERs) in male and female human pulmonary arteries and have examined the influence of oestrogen and serotonin on BMPR2 and ERα expression.

Methods and results

By immunohistochemistry, we showed that ERα, ERβ, and G-protein-coupled receptors are expressed in human pulmonary arteries localizing mainly to the smooth muscle layer which also expresses the serotonin transporter (SERT). Protein expression of ERα protein was higher in female PAH patient hPASMCs compared with male and serotonin also increased the expression of ERα. 17β-estradiol induced proliferation of hPASMCs via ERα activation and this engaged mitogen-activated protein kinase and Akt signalling. Female mice over-expressing SERT (SERT⁺ mice) develop PH and the ERα antagonist MPP attenuated the development of PH in normoxic and hypoxic female SERT⁺ mice. The therapeutic effects of MPP were accompanied by increased expression of BMPR2 in mouse lung.

Conclusion

ERα is highly expressed in female hPASMCs from PAH patients and mediates oestrogen-induced proliferation of hPASMCs via mitogen-activated protein kinase and Akt signalling. Serotonin can increase ERα expression in hPASMCs and antagonism of ERα reverses serotonin-dependent PH in the mouse and increases BMPR2 expression.

Activation of ErbB2 and Downstream Signalling via Rho Kinases and ERK1/2 Contributes to Diabetes-Induced Vascular Dysfunction

Diabetes mellitus leads to vascular complications but the underlying signalling mechanisms are not fully understood. Here, we examined the role of ErbB2 (HER2/Neu), a transmembrane receptor tyrosine kinase of the ErbB/EGFR (epidermal growth factor receptor) family, in mediating diabetes-induced vascular dysfunction in an experimental model of type 1 diabetes. Chronic treatment of streptozotocin-induced diabetic rats (1 mg/kg/alt diem) or acute, ex-vivo (10(-6), 10(-5) M) administration of AG825, a specific inhibitor of ErbB2, significantly corrected the diabetes-induced hyper-reactivity of the perfused mesenteric vascular bed (MVB) to the vasoconstrictor, norephinephrine (NE) and the attenuated responsiveness to the vasodilator, carbachol. Diabetes led to enhanced phosphorylation of ErbB2 at multiple tyrosine (Y) residues (Y1221/1222, Y1248 and Y877) in the MVB that could be attenuated by chronic AG825 treatment. Diabetes- or high glucose-mediated upregulation of ErbB2 phosphorylation was coupled with activation of Rho kinases (ROCKs) and ERK1/2 in MVB and in cultured vascular smooth muscle cells (VSMC) that were attenuated upon treatment with either chronic or acute AG825 or with anti-ErbB2 siRNA. ErbB2 likley heterodimerizes with EGFR, as evidenced by increased co-association in diabetic MVB, and further supported by our finding that ERK1/2 and ROCKs are common downstream effectors since their activation could also be blocked by AG1478. Our results show for the first time that ErbB2 is an upstream effector of ROCKs and ERK1/2 in mediating diabetes-induced vascular dysfunction. Thus, potential strategies aimed at modifying actions of signal transduction pathways involving ErbB2 pathway may prove to be beneficial in treatment of diabetes-induced vascular complications.

Sex, sex steroids, and diabetic cardiomyopathy: making the case for experimental focus

More than three decades ago, the Framingham study revealed that cardiovascular risk is elevated for all diabetics and that this jeopardy is substantially accentuated for women in particular. Numerous studies have subsequently documented worsened cardiac outcomes for women. Given that estrogen and insulin exert major regulatory effects through common intracellular signaling pathways prominent in maintenance of cardiomyocyte function, a sex-hormone:diabetic-disease interaction is plausible. Underlying aspects of female cardiovascular pathophysiology that exaggerate cardiovascular diabetic risk may be identified, including increased vulnerability to coronary microvascular disease, age-dependent impairment of insulin-sensitivity, and differential susceptibility to hyperglycemia. Since Framingham, considerable progress has been made in the development of experimental models of diabetic disease states, including a diversity of genetic rodent models. Ample evidence indicates that animal models of both type 1 and 2 diabetes variably recapitulate aspects of diabetic cardiomyopathy including diastolic and systolic dysfunction, and cardiac structural pathology including fibrosis, loss of compliance, and in some instances ventricular hypertrophy. Perplexingly, little of this work has explored the relevance and mechanisms of sexual dimorphism in diabetic cardiomyopathy. Only a small number of experimental studies have addressed this question, yet the prospects for gaining important mechanistic insights from further experimental enquiry are considerable. The case for experimental interrogation of sex differences, and of sex steroid influences in the aetiology of diabetic cardiomyopathy, is particularly compelling-providing incentive for future investigation with ultimate therapeutic potential.

Mitogen-activated protein kinases regulate vascular reactivity after hemorrhagic shock through myosin light chain phosphorylation pathway

BACKGROUND

Vascular hyporeactivity played an important role in many critical illness including shock or sepsis, but the mechanisms are incompletely understood. The objective of the present study was to investigate the roles of major mitogen-activated protein kinases (MAPKs extracellular signal-regulated kinase [ERK], p38 MAPK, and jun NH2-terminal kinase [JNK]) on vascular reactivity and the mechanisms.

METHODS

With superior mesenteric arteries from hemorrhagic shock rats, the role of p38 MAPK, ERK, and JNK in the regulation of vascular reactivity following shock and their relationship to myosin light chain (MLC20) phosphorylation-dependent pathway was observed.

RESULTS

ERK, p38 MAPK, and JNK activities in superior mesenteric arteries were increased at early shock and decreased at late shock. Stimulation of MAPKs with angiotensin II (AngII) increased the vascular reactivity, calcium sensitivity, and MLC20 phosphorylation. The increasing effect of AngII on vascular reactivity was antagonized by ERK, p38 MAPK, and JNK inhibitors, while the effect of AngII on calcium sensitivity was only blocked by ERK and p38 MAPK inhibitor, but not by JNK inhibitor. AngII increased the activity of protein kinase C-dependent phosphatase inhibitor of 17-kD (CPI17), integrin-linked kinase (ILK), and zipper-interacting protein kinase (ZIPK), The effect of AngII on CPI17 was blocked by ERK and p38 MAPK inhibitor, while the effect of AngII on ILK and ZIPK was only blocked by ERK inhibitor.

CONCLUSION

MAPKs participated in the regulation of vascular reactivity during shock. ERK and p38 MAPK is mainly through ILK, ZIPK, and CPI17-mediated MLC20 phosphorylation-dependent pathway, while JNK may be involved in the regulation of vascular reactivity by other mechanisms.

Sex differences in mesenteric endothelial function of streptozotocin-induced diabetic rats: a shift in the relative importance of EDRFs

Several studies suggest that diabetes affects male and female vascular beds differently. However, the mechanisms underlying the interaction of sex and diabetes remain to be investigated. This study investigates whether there are 1) sex differences in the development of abnormal vascular responses and 2) changes in the relative contributions of endothelium-derived relaxing factors in modulating vascular reactivity of mesenteric arteries taken from streptozotocin (STZ)-induced diabetic rats at early and intermediate stages of the disease (1 and 8 wk, respectively). We also investigated the mesenteric expression of the mRNAs for endothelial nitric oxide (NO) synthase (eNOS) and NADPH oxidase (Nox) in STZ-induced diabetes in both sexes. Vascular responses to acetylcholine (ACh) in mesenteric arterial rings precontracted with phenylephrine were measured before and after pretreatment with indomethacin (cyclooxygenase inhibitor), N(ω)-nitro-L-arginine methyl ester (NOS inhibitor), or barium chloride (K(ir) blocker) plus ouabain (Na(+)-K(+)-ATPase inhibitor). We demonstrated that ACh-induced relaxations were significantly impaired in mesenteric arteries from both male and female diabetic rats at 1 and 8 wk. However, at 8 wk the extent of impairment was significantly greater in diabetic females than diabetic males. Our data also showed that in females, the levels of eNOS, Nox2, and Nox4 mRNA expression and the relative importance of NO to the regulation of vascular reactivity were substantially enhanced, whereas the importance of endothelium-derived hyperpolarizing factor (EDHF) was significantly reduced at both 1 and 8 wk after the induction of diabetes. This study reveals the predisposition of female rat mesenteric arteries to vascular injury after the induction of diabetes may be due to a shift away from a putative EDHF, initially the major vasodilatory factor, toward a greater reliance on NO.

Aminoguanidine normalizes ET-1-induced aortic contraction in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats by suppressing Jab1-mediated increase in ET(A)-receptor expression

Circulating levels of endothelin (ET)-1 are increased in the diabetic state, as is endogenous ET(A)-receptor-mediated vasoconstriction. However, the responsible mechanisms remain unknown. We hypothesized that ET-1-induced vasoconstriction is augmented in type 2 diabetes with hyperglycemia through an increment in advanced glycation end-products (AGEs). So, we investigated whether treatment with aminoguanidine (AG), an inhibitor of AGEs, would normalize the ET-1-induced contraction induced by ET-1 in strips of thoracic aortas isolated from OLETF rats at the chronic stage of diabetes. In such aortas (vs. those from age-matched genetic control LETO rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of HIF1α/ECE1/plasma ET-1 and plasma CML-AGEs were increased, (3) the ET-1-stimulated ERK phosphorylation mediated by ET(A)-R was increased, (4) the expression level of Jab1-modified ET(A)-R protein was reduced, and (5) the expression level of O-GlcNAcylated ET(A)-R protein was increased. Aortas isolated from such OLETF rats that had been treated with AG (50mg/kg/day for 10 weeks) exhibited reduced ET-1-induced contraction, suppressed ET-1-stimulated ERK phosphorylation accompanied by down-regulation of ET(A)-R, and increased modification of ET(A)-R by Jab1. Such AG-treated rats exhibited normalized plasma ET-1 and CML-AGE levels, and their aortas exhibited decreased HIF1α/ECE1 expression. However, such AG treatment did not alter the elevated levels of plasma glucose or insulin, or systolic blood pressure seen in OLETF rats. These data from the OLETF model suggest that within the timescale studied here, AG normalizes ET-1-induced aortic contraction by suppressing ET(A)-R/ERK activities and/or by normalizing the imbalance between Jab1 and O-GlcNAc in type 2 diabetes.

Akt/eNOS pathway activation in endothelium-dependent relaxation is preserved in aortas from female, but not from male, type 2 diabetic mice

Cardiovascular problems are major causes of morbidity and mortality, the main problems being coronary artery disease and atherosclerosis, in type 2 diabetes mellitus. However, female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. Our aim was to investigate possible gender differences in the activation of Akt/eNOS signaling in aortas from a mouse type 2 diabetic model. Nonfasting plasma glucose was significantly above control in the diabetic mice (both males and females). Plasma insulin was not different between the age-matched controls and the diabetic mice (of either gender). In diabetic males (vs male controls and/or diabetic females): (a) systemic blood pressure was elevated, (b) the clonidine- and insulin-induced Akt-dependent aortic relaxations were impaired, but the ACh-induced Akt-independent and SNP-induced endothelium-independent aortic relaxations were not, (c) Akt and eNOS expression levels were lower, (d) both Akt phosphorylation at Ser(473) and eNOS phosphorylation at Ser(1177) in the aorta were lower under clonidine- or insulin-stimulation, but not under ACh-stimulation. These results suggest that in mice: (i) endothelial functions mediated via the Akt/eNOS pathway are abrogated in type 2 diabetes only in males and (ii) in females (vs males), eNOS expression is elevated and the endothelium resists dysfunction.

Gender differences in vascular reactivity of aortas from streptozotocin-induced diabetic mice

The aim of the present study was to assess gender differences in diabetes-related vascular reactivity in murine aortas. Diabetes is a risk factor for ischemic heart disease, cerebral ischemia, and atherosclerosis, conditions in which endothelial dysfunction plays a pathogenetic role. We examined vascular responses in aortas isolated from streptozotocin (STZ)-induced type 1 diabetic mice and age-matched control mice, and looked for gender differences in the diabetes-induced changes in these responses. For each gender, the plasma adiponectin levels were lower in diabetic mice than in the controls, and they were significantly higher in females than in males. The acetylcholine (ACh)-induced endothelium-dependent relaxation of aortic rings was impaired (vs. that in the age-matched controls) in diabetic male mice, but not in diabetic female mice. The sodium nitroprusside-induced endothelium-independent aortic relaxation was not altered by diabetes in either male or female mice. The norepinephrine-induced aortic contraction was enhanced (vs. that in the control group) in diabetic female mice, but not in diabetic male mice, whereas in the presence of N(G)-nitro-L-arginine neither gender exhibited a significant diabetes-induced change in this contraction. The clonidine-induced and insulin-induced endothelium-dependent aortic relaxations were impaired only in the diabetic female group (vs. the age-matched controls). These results suggest that: a) in male diabetic mice, which exhibited low adiponectin levels, these were impairments of both the aortic relaxation and nitric oxide (NO) production induced by ACh, whereas b) in female diabetic mice, there were impairments of the aortic relaxations induced by both insulin and clonidine.

Endothelin-1 and diabetic complications: focus on the vasculature

Diabetes is not only an endocrine but also a vascular disease. Cardiovascular complications are the leading cause of morbidity and mortality associated with diabetes. Diabetes affects both large and small vessels and hence diabetic complications are broadly classified as microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (heart disease, stroke and peripheral arterial disease) complications. Endothelial dysfunction, defined as an imbalance of endothelium-derived vasoconstrictor and vasodilator substances, is a common denominator in the pathogenesis and progression of both macro and microvascular complications. While the pathophysiology of diabetic complications is complex, endothelin-1 (ET-1), a potent vasoconstrictor with proliferative, profibrotic, and proinflammatory properties, may contribute to many facets of diabetic vascular disease. This review will focus on the effects of ET-1 on function and structure of microvessels (retina, skin and mesenteric arteries) and macrovessels (coronary and cerebral arteries) and also discuss the relative role(s) of endothelin A (ET(A)) and ET(B) receptors in mediating ET-1 actions.

Enhancement of mesenteric artery contraction to 5-HT depends on Rho kinase and Src kinase pathways in the ob/ob mouse model of type 2 diabetes

BACKGROUND AND PURPOSE

Arteries from hypertensive subjects are reportedly hyperresponsive to 5-hydroxytryptamine (5-HT), but it remains unclear whether this is true in chronic type 2 diabetes. We have assessed responses to 5-HT shown by mesenteric arteries from type 2 diabetic ob/ob mice (27-32 weeks old) and have identified the molecular mechanisms involved.

EXPERIMENTAL APPROACH

Contractions of mesenteric rings to 5-HT were examined in vitro. Activation of mesenteric RhoA, Rho kinase and Src was measured by Western blotting or by modified enzyme-linked immunosorbent assay.

KEY RESULTS

Concentration-dependent contractions to 5-HT were greater in mesenteric rings from the ob/ob than in those from the age-matched control ('Lean') group. In each group, there was no significant change in the 5-HT-induced contractions after inhibition of nitric oxide synthase (with N(G)-nitro-L-arginine), of cyclooxygenase (with indomethacin) or of protein kinase C (with chelerythrine). However inhibition of the MEK/ERK pathway (with PD98059) decreased the response to 5-HT. Although the diabetes-related enhancement of the 5-HT response was preserved with each of these inhibitors, enhancement was abolished by a Rho kinase inhibitor (Y27632) and by Src kinase inhibitors (PP1 analogue or Src kinase inhibitor I). 5-HT-induced activation of RhoA, Rho kinase and Src kinase in mesenteric arteries was greater in the ob/ob than in the Lean group, but the expression of RhoA, Rho kinase isoforms and Src did not differ between these groups.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the enhancement of 5-HT-induced contraction in mesenteric arteries from ob/ob mice may be attributable to increased activation of RhoA/Rho kinase and Src kinase.

Gender-specific reduction in contraction is associated with increased estrogen receptor expression in single vascular smooth muscle cells of female rat

Gender differences in the incidence of cardiovascular disease have been related to plasma estrogen levels; however, the role of vascular estrogen receptor (ER) subtypes in these sex differences is less clear. We tested whether the gender differences in vascular smooth muscle (VSM) function reflect differential expression/activity of ERalpha, ERbeta and the newly-identified GPR30. Single aortic VSM cells (VSMCs) were freshly isolated from male and female Sprague-Dawley rats, and their contraction to phenylephrine (PHE, 10(-5) M), AngII (10(-7) M) and membrane-depolarization by KCl (51 mM) was measured in the absence or presence of 10(-6) M 17beta-estradiol (E2, stimulant of most ERs), PPT (ERalpha agonist), DPN (ERbeta agonist), and ICI 182,780 (an ERalpha/ERbeta antagonist with GPR30 agonistic properties). The cells were fixed and fluorescently labeled with ERalpha, ERbeta or GPR30 antibody, and the subcellular distribution of ERs was examined using digital imaging microscopy. The mRNA expression and protein amount of aortic ER subtypes was examined using RT-PCR and Western blots. PHE, AngII, and KCl caused less contraction in VSMCs of females than males. Pretreatment of VSMCs with E2 reduced PHE-, AngII- and KCl-induced contraction in both males and females. PPT caused similar inhibition of PHE-, AngII- and KCl-induced contraction as E2, suggesting a role of ERalpha. DPN mainly inhibited PHE and KCl contraction, suggesting an interaction between ERbeta and Ca(2+) channels. ICI 182,780 did not reduce aortic VSMC contraction, suggesting little role for GPR30. RT-PCR and Western blots revealed greater expression of ERalpha and ERbeta in VSMCs of females than males, but similar amounts of GPR30. The total immunofluorescence signal for ERalpha and ERbeta was greater in VSMCs of females than males, and was largely localized in the nucleus. GPR30 fluorescence was similar in VSMCs of males and females, and was mainly in the cytosol. In PPT treated cells, nuclear ERalpha signal was enhanced. DPN did not affect the distribution of ERbeta, and ICI 182,780 did not significantly increase GPR30 in the cell surface. Thus, ER subtypes demonstrate similar responsiveness to specific agonists in VSMCs of male and female rats. The reduced contraction in VSMCs of females could be due to gender-related increase in the expression of ERalpha and ERbeta.

Ovariectomy in aged versus young rats augments matrix metalloproteinase-mediated vasoconstriction in mesenteric arteries

OBJECTIVE

Ovarian deficiency is known to undermine vasoprotective mechanisms and accelerate cardiovascular disease in postmenopausal women. In a rat model of menopause (aged ovariectomized [Ovx] rats), we recently revealed a vasoconstrictor pathway mediated by matrix metalloproteinases (MMPs) via cleavage of big endothelin-1 (ET-1). However, the specific impact of aging and/or Ovx on this pathway remains unknown. We hypothesized that aging exacerbates MMP-mediated vasoconstriction in an ovary-deficient state.

METHODS

Young and aged female Sprague-Dawley rats, either intact or Ovx, were assessed for MMP-dependent vasoreactivity. Dose responses to big ET-1 in the absence or presence of an MMP inhibitor (GM6001) were tested on small mesenteric arteries using a pressure myograph system. MMP levels in the vascular tissue were measured by gelatin zymography.

RESULTS

Both young Ovx and aged Ovx animals demonstrated a similar increase in the vasoconstriction to big ET-1 compared with the age-matched intact groups. MMP inhibition attenuated big ET-1 response in both Ovx groups and aged controls, but this effect was more pronounced in aged Ovx arteries (area under the curve reduction, 3.8 +/- 0.6 units in aged Ovx rats vs 1.5 +/- 0.5 units in young Ovx rats or 1.8 +/- 0.6 units in aged intact rats; P < 0.05). MMP-2 activity in the vascular tissue increased with age and was further augmented by Ovx.

CONCLUSIONS

Regardless of age, ovarian loss increases vascular reactivity to big ET-1, which is mediated, in part, by MMP. Superimposed with advancing age, ovarian deficiency further increases the proconstrictor role of MMP, which corresponds with higher MMP-2 levels in the aging vessel wall. MMP-mediated vasoconstriction may be a mechanism contributing to vascular dysfunction in postmenopausal women.

Endothelin-1 induces contraction of female rat internal pudendal and clitoral arteries through ET(A) receptor and rho-kinase activation

INTRODUCTION

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, acts mainly through the Gprotein-coupled ET(A) receptor (ET(A)R). Increased vascular ET-1 production and constrictor sensitivity have been observed in various cardiovascular diseases, including hypertension, as well as erectile dysfunction. The internal pudendal artery (IPA) supplies blood to the vagina and clitoris. Inadequate blood flow through the IPA may lead to insufficient vaginal engorgement and clitoral tumescence.

AIM

Characterize the effects of ET-1 on the IPA and clitoral artery (CA).

METHODS

IPA and CA from female Sprague Dawley rats (225-250 g) were mounted in myograph chambers. Arterial segments were submitted to increasing concentrations of ET-1 (10-10-10-6 M). Segments were incubated with the ET(A)R antagonist, atrasentan (10-8 M) or the Rho-kinase inhibitor, Y-27632 (10-6 M) 30 minutes prior to agonist exposure. All E(max) values are expressed as % KCl-induced maximal contraction. ET(A)R, RhoA, and Rho-kinase expression from IPA was evaluated by Western blot. mRNA of preproET-1, ET(A)R, ET(B)R, RhoA, and Rho-kinase were measured by real time PCR.

MAIN OUTCOME MEASURES

ET-1 constrictor sensitivity in IPA and CA, protein expression and messenger RNA levels of ET-1-mediated constriction components.

RESULTS

ET-1 concentration-dependently contracted IPA (% Contraction and pD2, respectively: 156 ± 18, 8.2 ± 0.1) and CA (163 ± 12, 8.8 ± 0.08), while ET(A)R antagonism reduced ET-1-mediated contraction (IPA: 104 ± 23, 6.4 ± 0.2; CA: 112 ± 17, 6.6 ± 0.08). Pretreatment with Y-27632 significantly shifted ET-1 pD2 in IPA (108 ± 24, 7.9 ± 0.1) and CA (147 ± 58 and 8.0 ± 0.25). Protein expression of ET(A)R, ET(B)R, RhoA, and Rho-kinase were detected in IPA. IPA and CA contained preproET-1, ET(A)R, ET(B)R, RhoA, and Rho-kinase message.

CONCLUSION

We observed that the IPA and CA are sensitive to ET-1, signaling through the ET(A)R and Rho-kinase pathway. These data indicate that ET-1 may play a role in vaginal and clitoral blood flow and may be important in pathologies where ET-1 levels are elevated.

Estrogen receptor-mediated enhancement of venous relaxation in female rat: implications in sex-related differences in varicose veins

BACKGROUND

A greater incidence of varicose veins has been reported in premenopausal women than in men. We hypothesized that the sex differences in venous function reflect reduced constriction and enhanced venous dilation in women due to direct venous relaxation effects of estrogen on specific estrogen receptors (ER).

METHODS

Circular segments of inferior vena cava (IVC) from male and female Sprague-Dawley rats were suspended between two wires, and isometric contraction (in mg/mg tissue) to phenylephrine, angiotensin II (AngII), and 96 mM KCl was measured. To investigate sex differences in venous smooth muscle, Ca(2+) release from the intracellular stores, and Ca(2+) entry from the extracellular space, the transient phenylephrine contraction in 0 Ca(2+) Krebs was measured. Extracellular CaCl(2) (0.1, 0.3, 0.6, 1, 2.5 mM) was added, and the [Ca(2+)](e)-dependent contraction was measured. To investigate sex differences in venous endothelial function, acetylcholine-induced relaxation was measured. To test the role of specific ERs, the amount of venous tissue ERs was measured using Western blots, and the venous relaxation in response to 17beta-estradiol (E2, activator of most ERs), 4,4,'4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)-tris-phenol (PPT; ERalpha agonist), 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; ERbeta agonist), and ICI 182,780 (ERalpha/ERbeta antagonist, and G protein-coupled receptor 30 [GPR30] agonist) was measured in IVC segments nontreated or treated with the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME).

RESULTS

Phenylephrine caused concentration-dependent contraction that was less in female (max 104.2 +/- 16.2) than male IVC (172.4 +/- 20.4). AngII (10(-6))-induced contraction was also less in female (81.0 +/- 11.1) than male IVC (122.5 +/- 15.0). Phenylephrine contraction in 0 Ca(2+) Krebs was insignificantly less in female (4.8 +/- 1.8) than male IVC (7.2 +/- 1.7), suggesting little difference in the intracellular Ca(2+) release mechanism. In contrast, the [Ca(2+)](e)-dependent contraction was significantly reduced in female than male IVC. Also, contraction to membrane depolarization by 96 mM KCl, which stimulates Ca(2+) influx, was less in female (129.7 +/- 16.7) than male IVC (319.7 +/- 30.4), supporting sex differences in Ca(2+) entry. Acetylcholine relaxation was greater in female (max 80.6% +/- 4.1%) than male IVC (max 48.0% +/- 6.1%), suggesting sex differences in the endothelium-dependent relaxation pathway. Western blots revealed greater amounts of ERalpha, ERbeta, and GPR30 in female than male IVC. ER agonists caused concentration-dependent relaxation of phenylephrine contraction in female IVC. E2-induced relaxation (max 76.5% +/- 3.4%) was more than DPN (74.8% +/- 9.1%), PPT (71.4% +/- 12.5%), and ICI 182,780 (67.4% +/- 7.8%), and was similar in L-NAME-treated and nontreated IVC.

CONCLUSION

The reduced alpha-adrenergic, AngII, depolarization-induced, and [Ca(2+)](e)-dependent venous contraction in female rats is consistent with sex differences in the Ca(2+) entry mechanisms, possibly due to enhanced endothelium-dependent vasodilation and increased ER expression/activity in female rats. E2/ER-mediated venous relaxation in female rats is not prevented by NOS blockade, suggesting activation of an NO-independent relaxation pathway. The decreased venous contraction and enhanced E2/ER-mediated venous relaxation would lead to more distensible veins in female rats.

Short-term angiotensin-1 receptor antagonism in type 2 diabetic Goto-Kakizaki rats normalizes endothelin-1-induced mesenteric artery contraction

Endothelin (ET)-1 and angiotensin II (Ang II) are likely candidates for a key role in diabetic vascular complications. We demonstrated previously that an enhanced ET-1-induced contraction is present in mesenteric arteries from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes. Here, we investigated whether short-term treatment of such rats with losartan, an angiotensin type 1 receptor antagonist, might normalize the ET-1-induced contraction. In mesenteric arteries from GK rats at the chronic stage (34-38 weeks) (vs. those from age-matched control Wistar rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of ET-1 and Ang II were increased, (3) ET-1-stimulated ERK2 phosphorylation was increased, and (4) the ACh-induced endothelium-dependent relaxation was reduced. Mesenteric arteries isolated from such GK rats following treatment with losartan (25mg/kg/day for 2 weeks) exhibited reduced ET-1- and Ang II-induced contractions, suppressed ET-1-stimulated ERK phosphorylation, and increased ACh-induced relaxation, while the rats exhibited normalized plasma NO metabolism and their mesenteric arteries exhibited increased basal NO formation. However, such losartan treatment did not alter the increased levels of ET-1 and Ang II seen in GK mesenteric arteries. Our data suggest that within the timescale studied here, losartan normalizes ET-1-induced mesenteric artery contraction through a suppression of ERK activities and/or by normalizing endothelial function.

Diabetes-associated changes and role of N epsilon-(carboxymethyl)lysine in big ET-1-induced coronary vasoconstriction

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N(epsilon)-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose-response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.

Sex-related decrease in [Ca2+]i signaling and Ca2+-dependent contraction in inferior vena cava of female rat

Sex differences in the incidence of varicose veins have been suggested; however, the venous mechanisms involved are unclear. We hypothesized sex-related differences in venous function and underlying distinctions in intracellular free calcium, [Ca(2+)](i), signaling and Ca(2+)-dependent mechanisms of venous contraction. Circular segments of inferior vena cava (IVC) from male and female Sprague-Dawley rats were suspended between two hooks, labeled with fura-2, and placed in a cuvet inside a spectrofluorometer for simultaneous measurement of isometric contraction and the 340/380 fluorescence ratio (indicative of [Ca(2+)](i)). In male IVC, phenylephrine (PHE; 10(-5) M) caused significant increase in contraction and [Ca(2+)](i). In female IVC, PHE-induced contraction was significantly reduced, but [Ca(2+)](i) did not differ significantly from males. Membrane depolarization by KCl (96 mM), which stimulates Ca(2+) influx, caused parallel increases in contraction and [Ca(2+)](i) in male IVC, and the KCl-induced contraction was significantly reduced in parallel with [Ca(2+)](i) in female IVC. In male IVC stimulated with 0 Ca(2+) KCl solution, the addition of increasing concentrations of extracellular Ca(2+) ([Ca(2+)](e)) (0.1, 0.3, 0.6, 1, and 2.5 mM) caused stepwise increases in contraction and [Ca(2+)](i), and both the KCl-induced [Ca(2+)](e)-contraction curve and the [Ca(2+)](e)-[Ca(2+)](i) curve were reduced in female IVC, suggesting reduced Ca(2+) entry via voltage-gated channels. The PHE-induced [Ca(2+)](e)-contraction curve was significantly reduced in females, but the [Ca(2+)](e)-[Ca(2+)](i) curve was similar in female and male IVC, suggesting the involvement of other mechanisms in addition to Ca(2+) entry. The [Ca(2+)](e)-contraction and [Ca(2+)](e)-[Ca(2+)](i) curves were used to construct the [Ca(2+)](i)-contraction relationship. The KCl-induced [Ca(2+)](i)-contraction relationship was superimposed in male and female IVC. In contrast, the PHE-induced [Ca(2+)](i)-contraction relationship was reduced and located to the right in female compared with male IVC, suggesting reduced [Ca(2+)](i) sensitivity of the venous contractile myofilaments. The reduced contraction, [Ca(2+)](i), and [Ca(2+)](i) sensitivity in female veins render them more prone to dilation. These sex-specific reductions in venous function, if they also occur in human veins, may play a role in the greater incidence of varicose veins in females.

Mechanisms underlying enhanced vasorelaxant response to protease-activated receptor 2-activating peptide in type 2 diabetic Goto-Kakizaki rat mesenteric artery

Protease-activated receptor 2 (PAR2) is a G-protein-coupled receptor that is proteolytically activated by certain endogenous proteases, such as trypsin, tryptase, and factor Xa. PAR2 can also be activated by synthetic peptides if their sequence mimics the tethered ligand exposed after receptor cleavage. Although it is known that PAR2 modulates vascular reactivity, it is unclear whether at the chronic stage of type 2 diabetes there are alterations in PAR2-mediated vascular responses. We investigated this issue by exposing mesenteric artery rings to PAR2-activating peptide (PAR2-AP; SLIGRL-NH(2)), the arteries used being obtained from later-stage (32-40-week-old) type 2 diabetic Goto-Kakizaki (GK) rats. The PAR2-AP-induced relaxation was enhanced in GK rats (vs. age-matched Wistar rats), whereas the ACh-induced relaxation was weaker in GK than in Wistar rats. In both groups, the PAR2-AP-induced relaxation was largely blocked by endothelial denudation or by N(G)-nitro-L-arginine [nitric oxide (NO) synthase inhibitor] treatment, but it was unaffected by indomethacin (cyclooxygenase inhibitor) treatment. Both the NO production induced by PAR2-AP and the PAR2 protein expression were significantly increased in mesenteric arteries from GK rats (vs. Wistar rats). These data are the first to indicate that the PAR2-AP-induced endothelium-dependent relaxation is enhanced in mesenteric arteries isolated from type 2 diabetic GK rats at the chronic stage, and they further suggest that the enhancement may be due to an increased expression of PAR2 receptors in this artery.

Gender differences in endothelial function in aortas from type 2 diabetic model mice

Type 2 diabetes mellitus is associated with high mortality and morbidity, mainly due to coronary artery disease and atherosclerosis, although female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. Our main aim was to investigate gender differences in endothelial function in aortas from type 2 diabetic model mice. The nonfasting plasma glucose level was significantly elevated in diabetic mice (both males and females). The plasma insulin level was not different between controls and diabetics (either gender). The plasma adiponectin level was decreased by diabetes, and was lower in males. In control aortas (from males or females), the clonidine-induced relaxation was abolished by Akt-inhibitor treatment. In diabetic males (versus both control males and diabetic females): a) the clonidine- and insulin-induced endothelium-dependent aortic relaxations were impaired, but the acetylcholine (ACh)-induced and sodium nitroprusside (SNP)-induced aortic relaxations were not, b) the norepinephrine (NE)-induced aortic contractile response was enhanced, c) systemic blood pressure was elevated, and d) the clonidine-stimulated Ser-473 phosphorylation of Akt in the aorta was decreased. These results suggest that endothelial functions dependent on the Akt pathway are abrogated by type 2 diabetes only in male mice.

Impaired vascular function in small resistance arteries of LOX-1 overexpressing mice on high-fat diet

AIMS

LOX-1 is a major vascular receptor for oxidized low-density lipoprotein (oxLDL). In this study, we analysed the impact of LOX-1 overexpression and high dietary fat intake on vascular function in small resistance arteries.

METHODS AND RESULTS

Relaxation of mesenteric arteries was measured using a wire myograph. Compared with the control group, mice overexpressing LOX-1 on a high-fat diet (FD) had preserved vascular smooth muscle relaxation, but impaired endothelium-dependent relaxation via NO. Vascular NO availability was decreased by exaggerated formation of reactive oxygen species and decreased endothelial NO synthase expression. Endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation via cytochrome P450 metabolites was increased in LOX-1 + FD animals, but did not completely compensate for the loss of NO. Currents of calcium-activated potassium channels with large conductance (BKCa channels) were measured by the voltage-clamp method. The BKCa current amplitudes were not altered in endothelial cells, but highly increased in vascular smooth muscle cells from resistance arteries of LOX-1-overexpressing mice on FD. BK(Ca) currents were activated by low-dose H2O2 and cytochrome P450 metabolites 11,12-EET and 14,15-EET as EDHF in control mice.

CONCLUSION

LOX-1 overexpression and FD caused functional changes in endothelial and vascular smooth muscle cells of small resistance arteries.

Activation of Rho-kinase in the brainstem enhances sympathetic drive in mice with heart failure

Rho-kinase is involved in the pathogenesis of hypertension and left ventricular remodelling after myocardial infarction (MI). In an earlier study, we had demonstrated that Rho-kinase in the brainstem contributes to hypertensive mechanisms via the sympathetic nervous system; however, it is not known whether Rho-kinase in the brainstem also contributes to sympathetic nerve activation after MI. Male Institute of Cancer Research mice (8-10 weeks old) were used for the study. Two days before coronary artery occlusion (MI group), the left ventricular function was estimated by echocardiography. Following this, Y-27632 (0.5 mM, 0.25 microL/h), a specific Rho-kinase inhibitor, or a vehicle was intracisternally infused in the mice using an osmotic mini-pump. Nine days after coronary artery occlusion, we evaluated the 24-hour urinary norepinephrine excretion (U-NE) as a marker of sympathetic nerve activity. Ten days after coronary artery occlusion, we measured organ weight and evaluated Rho-kinase activity in the brainstem by measuring the amount of phosphorylated ezrin/radixin/moesin proteins, one of the substrates of Rho-kinase. The control group underwent a sham operation. Rho-kinase activity, U-NE, and lungs and liver weight were significantly greater in the MI group compared with the control group. Left ventricular size increased and percent fractional shortening decreased in the MI group compared with the control group. Y-27632 significantly decreased Rho-kinase activity and attenuated the increase in U-NE after MI. These results demonstrate that Rho-kinase is activated in the brainstem after MI and that the activation of this pathway is involved in the resulting enhanced sympathetic drive.