Nitric oxide modulation of endothelium-derived hyperpolarizing factor in agonist-induced depressor responses in anesthetized rats

Sex Differences in the Vasodilation Mediated by G Protein-Coupled Estrogen Receptor (GPER) in Hypertensive Rats

Background

The protective effect of estrogen on the vasculature cannot be explained only by its action through the receptors ERα and ERβ. G protein-coupled estrogen receptors (GPER)-which are widely distributed throughout the cardiovascular system-may also be involved in this response. However, little is known about GPER actions in hypertension. Therefore, in this study we evaluated the vascular response mediated by GPER using a specific agonist, G-1, in spontaneously hypertensive rats (SHR). We hypothesized that G-1 would induce a relaxing response in resistance mesenteric arteries from SHR of both sexes.

Methods

G-1 concentration-response curves (1 nM-10 μM) were performed in mesenteric arteries from SHR of both sexes (10-12-weeks-old, weighing 180-250 g). The effects of G-1 were evaluated before and after endothelial removal and incubation for 30 min with the inhibitors L-NAME (300 μM) and indomethacin (10 μM) alone or combined with clotrimazole (0.75 μM) or catalase (1,000 units/mL). GPER immunolocalization was also investigated, and vascular hydrogen peroxide (H₂O₂) and ROS were evaluated using dichlorofluorescein (DCF) and dihydroethidium (DHE) staining, respectively.

Results

GPER activation promoted a similar relaxing response in resistance mesenteric arteries of female and male hypertensive rats, but with the participation of different endothelial mediators. Males appear to be more dependent on the NO pathway, followed by the H₂O₂ pathway, and females on the endothelium and H₂O₂ pathway.

Conclusion

These findings show that the GPER agonist G-1 can induce a relaxing response in mesenteric arteries from hypertensive rats of both sexes in a similar way, albeit with differential participation of endothelial mediators. These results contribute to the understanding of GPER activation on resistance mesenteric arteries in essential hypertension.

Diabetes Attenuates the Contribution of Endogenous Nitric Oxide but Not Nitroxyl to Endothelium Dependent Relaxation of Rat Carotid Arteries

Endothelial dysfunction is a major risk factor for several of the vascular complications of diabetes, including ischemic stroke. Nitroxyl (HNO), the one electron reduced and protonated form of nitric oxide (NO•), is resistant to scavenging by superoxide, but the role of HNO in diabetes mellitus associated endothelial dysfunction in the carotid artery remains unknown. Aim: To assess how diabetes affects the role of endogenous NO• and HNO in endothelium-dependent relaxation in rat isolated carotid arteries. Methods: Male Sprague Dawley rats were fed a high-fat-diet (HFD) for 2 weeks prior to administration of low dose streptozotocin (STZ; 35 mg/kg i. p./day) for 2 days. The HFD was continued for a further 12 weeks. Sham rats were fed standard chow and administered with citrate vehicle. After 14 weeks total, rats were anesthetized and carotid arteries collected to assess responses to the endothelium-dependent vasodilator, acetylcholine (ACh) by myography. The combination of calcium-activated potassium channel blockers, TRAM-34 (1 μmol/L) and apamin (1 μmol/L) was used to assess the contribution of endothelium-dependent hyperpolarization to relaxation. The corresponding contribution of NOS-derived nitrogen oxide species to relaxation was assessed using the combination of the NO• synthase inhibitor, L-NAME (200 μmol/L) and the soluble guanylate cyclase inhibitor ODQ (10 μmol/L). Lastly, L-cysteine (3 mmol/L), a selective HNO scavenger, and hydroxocobalamin (HXC; 100 μmol/L), a NO• scavenger, were used to distinguish between NO• and HNO-mediated relaxation. Results: At study end, diabetic rats exhibited significantly retarded body weight gain and elevated blood glucose levels compared to sham rats. The sensitivity and the maximal relaxation response to ACh was significantly impaired in carotid arteries from diabetic rats, indicating endothelial dysfunction. The vasorelaxation evoked by ACh was abolished by L-NAME plus ODQ, but not affected by the apamin plus TRAM-34 combination, indicating that NOS-derived nitrogen oxide species are the predominant endothelium-derived vasodilators in sham and diabetic rat carotid arteries. The maximum relaxation to ACh was significantly decreased by L-cysteine in both sham and diabetic rats, whereas HXC attenuated ACh-induced relaxation only in sham rats, suggesting that diabetes impaired the contribution of NO•, whereas HNO-mediated vasorelaxation remained intact. Conclusion: Both NO• and HNO contribute to endothelium-dependent relaxation in carotid arteries. In diabetes, NO•-mediated relaxation is impaired, whereas HNO-mediated relaxation was preserved. The potential for preserved HNO activity under pathological conditions that are associated with oxidative stress indicates that HNO donors may represent a viable therapeutic approach to the treatment of vascular dysfunction.

Endothelium-dependent Hyperpolarization-Mediated Relaxation Pathway in Bovine Mesenteric Lymph Nodes

Endothelium-dependent relaxation mechanisms have been studied in phenylephrine-precontracted capsules of bovine mesenteric lymph nodes studied in vitro. Tetraethylammonium chloride and TRAM-34 in a solution with L-NAME and Indomethacin, which suppress the production NO and prostacyclin of endothelium, increased the tone of the lymph nodes. We believe that in bovine mesenteric lymph nodes, the dilation mechanism is mediated by hyperpolarization of the endothelium, which is associated with activation of large- and intermedium conductance Ca²⁺-activated potassium channels.

Total Flavone of Rhododendron Improves Cerebral Ischemia Injury by Activating Vascular TRPV4 to Induce Endothelium-Derived Hyperpolarizing Factor-Mediated Responses

Background

Total flavonoids of Rhododendron (TFR) is extracted from Rhododendron, a herbal medicine widely used in China. The main components are flavone compounds such as warfarin, rutin, quercetin, and hyperoside. We investigated the role of TRPV4 channel in the TFR induced endothelium-dependent hyperpolarizing factor- (EDHF-) mediated responses against ischemia/reperfusion injury (IR) in cerebral IR (CIR) rats.

Methods

The morphological changes of cerebral cortex, the relaxation of cerebral basal artery (CBA), and cell membrane potential recording were studied in CIR rats. The outward potassium current in smooth muscle cell was recorded by whole-cell patch clamp recording. The protein expression of TRPV4, SKca, and IKca was determined. Confocal laser was used to measure the Ca²⁺ fluorescence intensity.

Results

After treatment with TFR, the number of pyramidal cells in brain tissue increased and the number of empty or lightly stained cells decreased and these effects were eliminated by using HC-067047, Apamin, or TRAM-34. TFR induced and EDHF-mediated dilatation and hyperpolarization in CBA were also attenuated by using these inhibitors. The increased outward current density elicited by TFR in acutely isolated CBA smooth muscle cells was abolished by using TRAM-34 and Apamin. TFR upregulated the protein expression of TRPV4, SKca, and IKca that was also eliminated by these inhibitors. Laser scanning showed that the increased mean fluorescence intensity of Ca²⁺ by CIR was decreased by using TFR and that this effect was again eliminated by the above inhibitors.

Conclusions

We conclude that in the CBA of the CIR rats the protective effect of TFR on ischemic cerebrovascular injury may be related to the activation of the TRPV4 in both endothelium and smooth muscle by increasing its expression and activity. The activation of TRPV4 channel in the endothelium may be linked to the opening of endothelial IKca/SKca channels that induces EDHF-mediated relaxation and hyperpolarization in the smooth muscle cell. In addition, the activation of TRPV4 in the smooth muscle cell in CBA may be linked with the activation of BK_Ca channel through a TRPV4-dependent pathway, reduce Ca²⁺ concentration in the cell, and relaxes the vessel. These findings may form a new therapeutic target for protection of ischemic brain injury and facilitate the use of Chinese medicine in brain protection.

Microcirculatory dopplerography as a method to evaluate drugs endothelial protective properties in type 2 diabetic patients

Objective - to identify the most accurate way of drugs endothelial protective properties evaluation. Material and methods. Blood endothelin-1 (E) and acetylcholine-induced endothelial dependent vasodilation (EDV) were measured for 9 months in type 2 diabetic patients receiving either metformin (MET) (group 1) or MET and liraglutide (LIR) (group 2). Results. E was normal in group 1 at baseline and decreased only with glycaemia decline, in group 2 it was primarily increased and declined independently on glycaemia dynamics. In both groups E normalized in 6 months. EDV was impaired primarily in groups 1 and 2 and normalized only in group 2 in 9 months. Conclusions. LIR improves endothelial function, independently on glycaemia. Dopplerography in more accurate in drugs endothelial protective effects evaluation than circulating markers.

Sub-chronic lead exposure produces β1-adrenoceptor downregulation decreasing arterial pressure reactivity in rats

Lead is considered a causative factor for hypertension and other cardiovascular diseases.

AIMS

To investigate the effects of sub-chronic lead exposure on blood pressure reactivity and cardiac β₁-adrenoceptor activity and to evaluate whether the effects found in vitro are similar to those found in vivo.

MAIN METHODS

Male Wistar rats were randomly distributed into two groups: control rats (Ct) and rats administered drinking water containing 100ppm lead (Pb) for 30days.

KEY FINDINGS

Blood pressure in the Pb rats increased starting from the first week of treatment until the end of the study [systolic blood pressure, Ct: 122±4 vs. Pb: 143±3mmHg; diastolic blood pressure, Ct: 63±4 vs. Pb: 84±4mmHg]. The heart rate was also increased (Ct: 299±11 vs. Pb: 365±11bpm), but the pressure reactivity to phenylephrine was decreased. Losartan and hexamethonium exhibited a greater reduction in blood pressure of Pb rats than in the Ct rats. Isoproterenol increased the left ventricular systolic and end-diastolic pressure, and heart rate only in Ct rats, suggesting that lead induced β₁-adrenoceptor downregulation. Indomethacin reduced the blood pressure and heart rate in the Pb rats, suggesting the involvement of cyclooxygenase-derived products (which are associated with reduced nitric oxide bioavailability) in this process.

SIGNIFICANCE

These findings offer further evidence that the effects of sub-chronic lead exposure in vitro can be reproduced in vivo-even at low concentrations-thus triggering mechanisms for the development of hypertension. Therefore, lead should be considered an environmental risk factor for cardiovascular disease.

Contribution of Maladaptive Adipose Tissue Expansion to Development of Cardiovascular Disease

The overweight and obesity epidemic has led to an increase in the metabolic syndrome and associated cardiovascular disease (CVD). These abnormalities include insulin resistance, type 2 diabetes mellitus, vascular stiffness, hypertension, stroke, and coronary heart disease. Visceral white adipocyte tissue (WAT) expansion and associated fibrosis/stiffness of WAT promote insulin resistance and CVD through increases in proinflammatory adipokines, oxidative stress, activation of renin-angiotensin-aldosterone system, dysregulation of adipocyte apoptosis and autophagy, dysfunctional immune modulation, and adverse changes in the gut microbiome. The expansion of WAT is partly determined by activation of peroxisome proliferator-activated receptor gamma and mammalian target of rapamycin/ribosomal S6 kinase signaling pathways. Further, the chronic activation of these signaling pathways may not only induce adipocyte hypertrophy and fibrosis, but also contribute to systemic inflammation, and impairment of insulin metabolic signaling in fat, liver, and skeletal muscle tissue. Therefore, the interplay of adipocyte dysfunction, maladaptive immune and inflammatory responses, and associated metabolic disorders often coexist leading to systemic low-grade inflammation and insulin resistance that are associated with increased CVD in obese individuals. © 2017 American Physiological Society. Compr Physiol 7:253-262, 2017.