N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation in the rabbit renal artery: effect of hypercholesterolemia

Endothelial KCa 1.1 and KCa 3.1 channels mediate rat intrarenal artery endothelium-derived hyperpolarization response

AIM

Endothelium-derived hyperpolarization (EDH)-mediated response plays an essential role in the control of kidney preglomerular circulation, but the identity of the K⁺ channels involved in this response is still controversial. We hypothesized that large- (K_Ca 1.1), intermediate- (K_Ca 3.1) and small (K_Ca 2.3) -conductance Ca²⁺ -activated K⁺ (K_Ca ) channels are expressed in the endothelium of the preglomerular circulation and participate in the EDH-mediated response.

METHODS

We study the functional expression of different K⁺ channels in non-cultured, freshly isolated native endothelial cells (ECs) of rat intrarenal arteries using immunofluorescence and the patch-clamp technique. We correlate this with vasorelaxant responses ex vivo using wire myography.

RESULTS

Immunofluorescence revealed the expression of K_Ca 1.1, K_Ca 3.1 and K_Ca 2.3 channels in ECs. Under voltage-clamp conditions, acetylcholine induced a marked increase in the outward currents in these cells, sensitive to the blockade of K_Ca 1.1, K_Ca 3.1 and K_Ca 2.3 channels respectively. Isometric myography experiments, under conditions of endothelial nitric oxide synthase and cyclooxygenase inhibition, showed that blockade either of K_Ca 1.1 or K_Ca 3.1 channels was able to reduce the endothelium-derived vasorelaxation of isolated interlobar arteries, while their combined blockade completely abolished it. In contrast, blockade of K_Ca 2.3 channels did not reduce this vasorelaxant response, despite being functionally expressed in the endothelial cells.

CONCLUSION

This study shows that K_Ca 1.1 and K_Ca 3.1 channels are functionally expressed at the renal vascular endothelium and play a central role in the EDH-mediated relaxation of kidney preglomerular arteries, which is important in the control of renal blood flow and glomerular filtration rate.

Light-intensity and high-intensity interval training improve cardiometabolic health in rats

Physical activity has the potential to reduce cardiometabolic risk factors but evaluation of different intensities of physical activity and the mechanisms behind their health effects still need to be fully established. This study examined the effects of sedentary behaviour, light-intensity training, and high-intensity interval training on biometric indices, glucose and lipid metabolism, inflammatory and oxidative stress markers, and vascular and cardiac function in adult rats. Rats (12 weeks old) were randomly assigned to 1 of 4 groups: control (CTL; no exercise), sedentary (SED; no exercise and housed in small cages to reduce activity), light-intensity trained (LIT; four 30-min exercise bouts/day at 8 m/min separated by 2-h rest period, 5 days/week), and high-intensity interval trained (HIIT, four 2.5-min work bouts/day at 50 m/min separated by 3-min rest periods, 5 days/week). After 12 weeks of intervention, SED had greater visceral fat accumulation (p < 0.01) and slower cardiac conduction (p = 0.04) compared with the CTL group. LIT and HIIT demonstrated beneficial changes in body weight, visceral and epididymal fat weight, glucose regulation, low-density lipoprotein cholesterol, total cholesterol, and mesenteric vessel contractile response compared with the CTL group (p < 0.05). LIT had significant improvements in insulin sensitivity and cardiac conduction compared with the CTL and SED groups whilst HIIT had significant improvements in systolic blood pressure and endothelium-independent vasodilation to aorta and mesenteric artery compared with the CTL group (p < 0.05). LIT and HIIT induce health benefits by improving traditional cardiometabolic risk factors. LIT improves cardiac health while HIIT promotes improvements in vascular health.

Differential contribution of endothelium-derived relaxing factors to vascular reactivity in conduit and resistance arteries from normotensive and hypertensive rats

The endothelium contributes to the maintenance of vasodilator tone by releasing nitric oxide (NO), prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF). In hypertension, endothelium-dependent relaxation is attenuated (a phenomenon referred to as endothelial dysfunction) and contributes to the increased peripheral resistance. However, which vasodilator among NO, PGI2, and EDHF is impaired in hypertension remains largely unknown. The present study was designed to study the exact contribution of NO, PGI2, and EDHF to vascular reactivity in conduit and resistance artery, under physiological and pathological conditions. The aorta and the second-order mesenteric artery from spontaneous hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were used to measure the vasorelaxation with myograph technology, in the presence or absence of different inhibitors. The results showed that the endothelium-dependent vasodilatation in the conduit artery was mediated mainly by NO, whereas the resistant artery by NO, PGI2, and EDHF together. In hypertension, both NO-mediated relaxation in the conduit artery and NO-, PGI2-, and EDHF-mediated dilation in the resistant artery were markedly impaired. Furthermore, the endothelium-dependent and the endothelium-independent vasorelaxation in conduit artery was attenuated more pronouncedly than that in the resistant artery from hypertensive rats, suggesting that the conduit artery is more vulnerable to hypertensive condition. In conclusion, vasodilators including NO, PGI2, and EDHF contribute distinctively to endothelium-dependent relaxation in conduit and resistance artery under physiological and pathological conditions.

Correlation between Echo-Tracking Parameters and In Vitro Measurements of Arterial Contraction and Relaxation in Rats Fed a High-Cholesterol Diet

BACKGROUND

Echo-tracking (ET) is a new technique that allows the assessment of arterial function and stiffness. This study aimed to ascertain the utility of the echo-tracking (ET) technique to assess vascular stiffness in rats with hypercholesterolemia and atherosclerosis.

MATERIAL AND METHODS

ET was used to measure the arterial stiffness of the aorta in cholesterol-fed Sprague-Dawley rats (group T1, n=10, for 4 weeks; group T2, n=10, for 12 weeks) and normal control rats (group C1, n=10; group C2, n=10). In vitro isometric tension experiments were used to measure the maximum contractile tension (MCT) and maximum relaxation percentage (MRR%) of aortic rings. Indicators of arterial stiffness and aortic MCT and MRR% were compared between groups using linear regression analysis. Light microscopic evaluation was used to demonstrate atherosclerotic changes in the aorta.

RESULTS

The rat models were successfully induced; pathological examination of the aortas showed significant atherosclerosis in group T2, but not in groups C1, C2, or T1. The arterial stiffness parameters obtained using ET and aortic rings in vitro showed significant impairments in T1 and T2 rats compared with C1 and C2 controls (all P<0.05 vs. controls). In addition, these impairments were greater in the T2 group than in the T1 group (all P<0.05). Finally, MRR% correlated with the distensibility coefficient (r=0.396, P=0.012), arterial compliance (r=0.317, P=0.047), stiffness parameter b (r=-0.406, P=0.009) and one-point pulse wave β (r=-0.434, P=0.005).

CONCLUSIONS

These results suggest that ET could be used to evaluate the changes in arterial wall elasticity associated with atherosclerosis and hypercholesterolemia.

Improvement of thoracic aortic vasoreactivity by continuous and intermittent exercise in high-fat diet-induced obese rats

The aim of the present study was to explore the effects of continuous and intermittent exercise on the thoracic aortic vasoreactivity and free radical metabolism in rats fed with a high-fat diet (HD). Sprague-Dawley (SD) rats were randomly divided into four groups (n=8, each group): Conventional diet (CD), HD, HD with continuous exercise (HCE) and HD with intermittent exercise (HIE). HCE rats swam once/day for 90 min; HIE rats performed swimming exercises 3 times/day, 30 min each time with an interval of 4 h. In these two groups, the exercise was conducted 5 days a week for 8 weeks. Rats in the CD and HD groups were fed without swimming training. At the end of the exercise, all the rats were sacrificed and the blood, thoracic aorta and myocardium were collected immediately. The thoracic aortic vasoreactivity, the plasma total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), superoxide dismutase (SOD), malondialdehyde (MDA) and vascular endothelial nitric oxide synthase (eNOS) gene expression were measured. Compared to the control group, in the HD group the enhanced contractile response of the thoracic aortic rings to noradrenaline (NA) was observed (P<0.01). The levels of TC and LDL (P<0.01) were also increased in serum while the HDL level was reduced without statistical significance. In addition, the MDA content was upregulated in the myocardium, but the SOD level decreased (P<0.01). Furthermore, the expression of vascular eNOS mRNA was reduced (P<0.01). However, following the exercise the contraction of the thoracic aorta vascular rings to NA was reduced in the HCE and HIE groups (P<0.01), and the decreased contractile response was more evident in the HIE group compared to the HCE group (P<0.01). Additionally, in the HCE group the level of TG (P<0.01) was decreased, while the HDL (P<0.01) level was increased. Although the reduction of the TC and LDL level was also observed there was no significant difference compared to the HD group. In the HIE group, the TG, TC and LDL were downregulated while the HDL was enhanced (P<0.01). The TC and LDL levels were decreased more than those of the HCE group; however, there was no significant difference in the TG and HDL levels between these two groups; additionally, in these two exercise groups, the MDA level was decreased in the myocardium (P<0.01) while the SOD level was increased (P<0.01). Furthermore, the expression of eNOS was upregulated (P<0.01), but the increase was much more in the HIE group than that in the HCE group. In conclusion, exercise may attenuate the aggravated contraction induced by NA and improve the activity of the thoracic aorta in obese rats, which may be associated with enhanced antioxidant enzyme activity and reduced free radical generating. Additionally, intermittent exercise is better than the continuous exercise in improving the thoracic aorta vasoreactivity.

Assessments of arterial stiffness and endothelial function using pulse wave analysis

Conventionally, the assessments of endothelial function and arterial stiffness require different sets of equipment, making the inclusion of both tests impractical for clinical and epidemiological studies. Pulse wave analysis (PWA) provides useful information regarding the mechanical properties of the arterial tree and can also be used to assess endothelial function. PWA is a simple, valid, reliable, and inexpensive technique, offering great clinical and epidemiological potential. The current paper will outline how to measure arterial stiffness and endothelial function using this technique and include discussion of validity and reliability.

Endothelium-derived hyperpolarizing factor and vascular function

Endothelial function refers to a multitude of physiological processes that maintain healthy homeostasis of the vascular wall. Exposure of the endothelium to cardiac risk factors results in endothelial dysfunction and is associated with an alteration in the balance of vasoactive substances produced by endothelial cells. These include a reduction in nitric oxide (NO), an increase in generation of potential vasoconstrictor substances and a potential compensatory increase in other mediators of vasodilation. The latter has been surmised from data demonstrating persistent endothelium-dependent vasodilatation despite complete inhibition of NO and prostaglandins. This remaining non-NO, non-prostaglandin mediated endothelium-dependent vasodilator response has been attributed to endothelium-derived hyperpolarizing factor/s (EDHF). Endothelial hyperpolarization is likely due to several factors that appear to be site and species specific. Experimental studies suggest that the contribution of the EDHFs increase as the vessel size decreases, with a predominance of EDHF activity in the resistance vessels, and a compensatory up-regulation of hyperpolarization in states characterized by reduced NO availability. Since endothelial dysfunction is a precursor for atherosclerosis development and its magnitude is a reflection of future risk, then the mechanisms underlying endothelial dysfunction need to be fully understood, so that adequate therapeutic interventions can be designed.

Endothelium-derived hyperpolarizing factor determines resting and stimulated forearm vasodilator tone in health and in disease

BACKGROUND

We assessed the contribution of endothelium-derived hyperpolarizing factors to resting and agonist-stimulated vasodilator tone in health and disease. Tetraethylammonium chloride (TEA) was used to inhibit K(+)(Ca) channel activation and fluconazole was used to inhibit cytochrome P450 2C9-mediated epoxyeicosatrienoic acid synthesis. We hypothesized that endothelium-derived hyperpolarizing factors contribute to resting vascular tone by K(+)(Ca) channel activation and epoxyeicosatrienoic acid release and that endothelium-derived hyperpolarizing factors compensate for reduced nitric oxide bioavailability at rest and with endothelium-dependent vasodilators.

METHODS AND RESULTS

In 103 healthy subjects and 71 nonhypertensive subjects with multiple risk factors, we measured resting forearm blood flow (FBF) using venous occlusion plethysmography before and after intra-arterial infusions of N(G)-monomethyl-l-arginine (L-NMMA), TEA, fluconazole, and their combination. The effects of these antagonists on resting FBF and on bradykinin- and acetylcholine-mediated vasodilation were studied. Resting FBF decreased with TEA and L-NMMA in all subjects (P<0.001); however, the vasoconstrictor response to L-NMMA was greater (P=0.04) and to TEA was lower (P=0.04) in healthy subjects compared with those with risk factors. Fluconazole decreased resting FBF in all subjects, and the addition of TEA further reduced FBF after fluconazole, suggesting that cytochrome P450 metabolites and other hyperpolarizing factor(s) activate K(+)(Ca) channels. Both L-NMMA and TEA attenuated bradykinin-mediated vasodilation in healthy and hypercholesterolemic subjects (P<0.001). In contrast, acetylcholine-mediated vasodilation remained unchanged with TEA in healthy subjects but was significantly attenuated in hypercholesterolemia (P<0.04).

CONCLUSIONS

First, by activating TEA-inhibitable K(+)(Ca) channels, endothelium-derived hyperpolarizing factors, together with nitric oxide, contribute to resting microvascular dilator tone. The contribution of K(+)(Ca) channel activation compared with nitric oxide is greater in those with multiple risk factors compared with healthy subjects. Second, activation of K(+)(Ca) channels is only partly through epoxyeicosatrienoic acid release, indicating the presence of other hyperpolarizing mechanisms. Third, bradykinin, but not acetylcholine, stimulates K(+)(Ca) channel-mediated vasodilation in healthy subjects, whereas in hypercholesterolemia, K(+)(Ca) channel-mediated vasodilation compensates for the reduced nitric oxide activity. Thus, enhanced endothelium-derived hyperpolarizing factor activity in conditions of nitric oxide deficiency contributes to maintenance of resting and agonist-stimulated vasodilation. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00166166.

Identification of 13-hydroxy-14,15-epoxyeicosatrienoic acid as an acid-stable endothelium-derived hyperpolarizing factor in rabbit arteries

Arachidonic acid (AA) is metabolized by endothelial 15-lipoxygenase (15-LO) to several vasodilatory eicosanoids such as 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) and its proposed unstable precursor 15-hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA). In the present study, the acid-stable 13-hydroxy-trans-14,15-epoxy-eicosatrienoic acid (13-H-14,15-EETA) was identified and its vascular activities characterized. Rabbit aorta, mesenteric arteries, and the combination of 15-LO and cytochrome P450 2J2 converted AA to two distinct HEETA metabolites. The HEETA metabolites were resistant to acidic hydrolysis but were hydrolyzed by recombinant sEH to a more polar metabolite identified by mass spectrometry as 13,14,15-THETA. Mass spectrometric analyses and HPLC comigration identified the HEETAs as threo- and erythro-diastereomers of 13-H-trans-14,15-EETA. Erythro- and threo-diastereomers of 13-H-trans-14,15-EETA relaxed endothelium-denuded rabbit small mesenteric arteries with maximum relaxations of 22.6 +/- 6.0% and 8.6 +/- 4.3%, respectively. Apamin (10(-7) m) inhibited the relaxations to the erythro-isomer (maximum relaxation = 1.2 +/- 5.6%) and increasing [K(+)](o) from 4.6 to 30 mm blocked relaxations to both isomers. In cell-attached patches of mesenteric arterial smooth muscle cells (SMCs), erythro-13-H-trans-14,15-EETA (1-3 x 10(-6) m) increased mean open time of small conductance K(+) channels (13-14 pS) from 0.0007 +/- 0.0007 to 0.0053 +/- 0.0042. This activation was inhibited by apamin. The erythro, but not the threo, isomer blocked angiotensin II-stimulated aortic SMC migration. These studies demonstrate that 13-H-14,15-EETAs induces vascular relaxation via K(+) channel activation to cause SMC hyperpolarization. Thus, 13-H-14,15-EETA represents a new endothelial factor.

Effects of Thiopental on Endothelium-Dependent Relaxation in Porcine Coronary Arteries

This study investigated the effects of thiopental on endothelium-dependent relaxation (EDR), and especially the effects on nitric oxide-and prostacyclin-independent EDR. Fresh porcine coronary artery rings (4 mm long), were consecutively tested with and without 20 μg/ml thiopental in Krebs–Henseleit solution. Indomethacin (10 μmol/1) was used in all experiments to eliminate prostacyclin effects. Prostaglandin F2α (10 μmol/l) was used to induce contractions and bradykinin (10−10−10−5 M) was used to induce EDR. Experiments were also carried out using 300 μmol/1 N-nitro-l-arginine to block nitric oxide production and to assess the influence of thiopental on nitric oxide-and prostacyclin-independent EDR. Thiopental induced statistically significant increases in EDR at concentrations of 10−6−10−5 M bradykinin. Following nitric oxide production block, thiopental significantly reduced the relaxation response at concentrations of 10−8−10−5 M bradykinin. At a clinically relevant concentration of 20 μg/ml thiopental, a significant increase in EDR and a significant reduction in nitric oxide-and prostacyclin-independent relaxation was observed in porcine epicardial coronary arteries.

Role of arachidonic acid lipoxygenase metabolites in the regulation of vascular tone

Stimulation of vascular endothelial cells with agonists such as acetylcholine (ACh) or bradykinin or with shear stress activates phospholipases and releases arachidonic acid (AA). AA is metabolized by cyclooxygenases, cytochrome P-450s, and lipoxygenases (LOs) to vasoactive products. In some arteries, a substantial component of the vasodilator response is dependent on LO metabolites of AA. Nitric oxide (NO)- and prostaglandin (PG)-independent vasodilatory responses to ACh and AA are reduced by inhibitors of LO and by antisense oligonucleotides specifically against 15-LO-1. Vasoactive 15-LO metabolites derived from the vascular endothelium include 15-hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-HEETA) that is hydrolyzed by soluble epoxide hydrolase to 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA). HEETA and THETA are endothelium-derived hyperpolarizing factors that induce vascular relaxations by activation of smooth muscle apamin-sensitive, calcium-activated, small-conductance K(+) channels causing hyperpolarization. In other arteries, the 12-LO metabolite 12-hydroxyeicosatetraenoic acid is synthesized by the vascular endothelium and relaxes smooth muscle by large-conductance, calcium-activated K(+) channel activation. Thus formation of vasodilator eicosanoids derived from LO pathways contributes to the regulation of vascular tone, local blood flow, and blood pressure.

Endothelial Ca+-activated K+ channels in normal and impaired EDHF-dilator responses--relevance to cardiovascular pathologies and drug discovery

The arterial endothelium critically contributes to blood pressure control by releasing vasodilating autacoids such as nitric oxide, prostacyclin and a third factor or pathway termed 'endothelium-derived hyperpolarizing factor' (EDHF). The nature of EDHF and EDHF-signalling pathways is not fully understood yet. However, endothelial hyperpolarization mediated by the Ca(2+)-activated K(+) channels (K(Ca)) has been suggested to play a critical role in initializing EDHF-dilator responses in conduit and resistance-sized arteries of many species including humans. Endothelial K(Ca) currents are mediated by the two K(Ca) subtypes, intermediate-conductance K(Ca) (KCa3.1) (also known as, a.k.a. IK(Ca)) and small-conductance K(Ca) type 3 (KCa2.3) (a.k.a. SK(Ca)). In this review, we summarize current knowledge about endothelial KCa3.1 and KCa2.3 channels, their molecular and pharmacological properties and their specific roles in endothelial function and, particularly, in the EDHF-dilator response. In addition we focus on recent experimental evidences derived from KCa3.1- and/or KCa2.3-deficient mice that exhibit severe defects in EDHF signalling and elevated blood pressures, thus highlighting the importance of the KCa3.1/KCa2.3-EDHF-dilator system for blood pressure control. Moreover, we outline differential and overlapping roles of KCa3.1 and KCa2.3 for EDHF signalling as well as for nitric oxide synthesis and discuss recent evidence for a heterogeneous (sub) cellular distribution of KCa3.1 (at endothelial projections towards the smooth muscle) and KCa2.3 (at inter-endothelial borders and caveolae), which may explain their distinct roles for endothelial function. Finally, we summarize the interrelations of altered KCa3.1/KCa2.3 and EDHF system impairments with cardiovascular disease states such as hypertension, diabetes, dyslipidemia and atherosclerosis and discuss the therapeutic potential of KCa3.1/KCa2.3 openers as novel types of blood pressure-lowering drugs.

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.

Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?

The three subtypes of calcium-activated potassium channels (K(Ca)) of large, intermediate and small conductance (BK(Ca), IK(Ca) and SK(Ca)) are present in the vascular wall. In healthy arteries, BK(Ca) channels are preferentially expressed in vascular smooth muscle cells, while IK(Ca) and SK(Ca) are preferentially located in endothelial cells. The activation of endothelial IK(Ca) and SK(Ca) contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na(+)/K(+)-ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H(2)O(2)) hyperpolarize and relax the underlying smooth muscle cells by activating BK(Ca). In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BK(Ca). Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle K(Ca) could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IK(Ca) may prevent restenosis and that of BK(Ca) channels sepsis-dependent hypotension.

Endothelium-derived hyperpolarizing factor mediated relaxations in pig coronary arteries do not involve Gi/o proteins

AIM

Endothelium-dependent relaxations to certain neurohumoral substances are mediated by pertussis toxin-sensitive Gi/o protein. Our experiments were designed to determine the role, if any, of pertussis toxin-sensitive G-proteins in relaxations attributed to endothelium-derived hyperpolarizing factor (EDHF).

METHODS

Pig coronary arterial rings with endothelia were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution maintained at 37 degrees and continuously aerated with 95%O2 and 5% CO2. Isometric tension was measured during contractions to prostaglandin F2alpha in the presence of indomethacin and N(omega)- nitro-L-arginine methyl ester (L-NAME).

RESULTS

Thrombin, the thrombin receptor- activating peptide SFLLRN, bradykinin, substance P, and calcimycin produced dose-dependent relaxations. These relaxations were not inhibited by prior incubation with pertussis toxin, but were abolished upon the addition of charybdotoxin plus apamin. Relaxations to the alpha2-adrenergic agonist UK14304 and those to serotonin were abolished in the presence of indomethacin and L-NAME.

CONCLUSION

Unlike nitric oxide-mediated relaxations, EDHF-mediated relaxations of pig coronary arteries do not involve pertussis toxin-sensitive pathways and are Gi/o protein independent.

Effects of a Western diet versus high glucose on endothelium-dependent relaxation in murine micro- and macro-vasculature

Vascular contractility and endothelium-dependent vasodilatation were studied in mesenteric, aorta and coronary vasculature from male and female LDL receptor deficient (LDLR(-/-)) and wild type C57BL/6 mice fed either a high-fat Western Diet (WD) or regular animal chow (RD). Endothelium-dependent vasodilatation was also studied in small mesenteric arteries and aorta from C57BL/6 mice following a 20 h exposure in vitro to 30 mM glucose. Compared with RD-fed animals, WD-fed LDLR-/- animals had increased body weights, elevated triglycerides and total cholesterol, but not glucose. Control C57BL6 animals had elevated body weight without increased cholesterol, triglyceride or glucose levels. The contractile sensitivity to cirazoline (pD(2)) of small mesenteric arteries was the same for RD-fed LDLR-/- and RD-fed C57BL6 mice, but was reduced in WD-fed male LDLR-/- and WD-fed female C57BL/6 mice. Maximum mesenteric contractile values for cirazoline (Emax) were unchanged; however, the Emax for phenylephrine in the aorta from WD-fed male C57BL/6 (but not LDLR-/- or female C57BL/6) mice was reduced. The Emax for acetylcholine-mediated endothelium-dependent vasodilatation in micro- and macro vessels (small mesenteric artery, coronary artery and aorta) from WD-fed LDLR-/- and C57BL/6 mice was unaltered, in contrast to the reduction in Emax for glucose-exposed tissues. Furthermore, the component of acetylcholine-mediated vasodilatation resistant to the combination of inhibitors of nitric oxide synthase, cyclooxygenase and guanylyl cyclase (nitro L-arginine methyl ester - 100 microM; indomethacin 10 microM and 1H-[1,2,4]-oxadiazolo[4,3,-a]quinoxalin-1-one, ODQ - 10 microM, respectively) was generally greater in WD-fed mice. Thus, vasculature from WD-fed mice with short-term dyslipidaemia do not exhibit reduced endothelium-dependent vasodilatation, but the WD is associated with changes in the overall endothelial-dependent relaxation and contractile responses thus suggesting an impact of diet rather than dyslipidaemia on cellular signalling pathways in vascular tissue. In contrast, acute hyperglycaemia resulted in endothelial dysfunction in both small mesenteric arteries and thoracic aorta.

Type 1 diabetes and hypercholesterolaemia reveal the contribution of endothelium-derived hyperpolarizing factor to endothelium-dependent relaxation of the rat aorta

1. The present study evaluated the effect of diabetes, hypercholesterolaemia and their combination on the contribution of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) to relaxation of rat isolated aortic rings and the potential contribution of oxidant stress to the disturbance of endothelial function. 2. Thoracic aortic rings from control, diabetic, hypercholesterolaemic and diabetic plus hypercholesterolaemic rats were suspended in organ baths for tension recording. Generation of superoxide by the aorta was measured using lucigenin-enhanced chemiluminescence. 3. The maximal response to acetylcholine (ACh) was significantly reduced in diabetic or hypercholesterolaemic rats compared with control rats. In rats with diabetes plus hypercholesterolaemia, both the sensitivity and maximal response to ACh was impaired. In control rats, the response to ACh was abolished by the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA) or inhibition of soluble guanylate cyclase with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). In contrast, in rats with diabetes, hypercholesterolaemia or both, relaxation to ACh was resistant to inhibition by L-NNA or ODQ, but abolished by additional inhibition of K(Ca) channels with charybdotoxin plus apamin. 4. The generation of superoxide was not significantly enhanced in aortic rings from either diabetic or hypercholesterolaemic rats, but was significantly increased in aortic rings from rats with diabetes plus hypercholesterolaemia. 5. These results suggest that when diabetes and hypercholesterolaemia impair endothelium-dependent relaxation, due to a diminished contribution from NO, a compensatory contribution of EDHF to endothelium-dependent relaxation of the aorta is revealed. The attenuation of NO-mediated relaxation, at least in the presence of both diabetes and hypercholesterolaemia, is associated with enhanced superoxide generation.

ROS-sensitive cytochrome P450 activity maintains endothelial dilatation in ageing but is transitory in dyslipidaemic mice

Risk factors for cardiovascular diseases (CVD) have been proposed to accelerate the vascular endothelial dysfunction that develops during the normal ageing process. The objective of this work was to study the impact of dyslipidaemia (DL) on the dilatory efficacy of the non-NO/non-PGI2 endothelium-derived hyperpolarising factor (EDHF) through maturation and ageing. We isolated and pressurised (80 mmHg) gracilis arterial segments from 3, 12 and 20-month-old (m/o) DL mice expressing the human apolipoprotein B-100 and wild-type (WT) C57BL/6 mice. EDHF-dependent dilatations to acetylcholine (ACh) were measured in the presence of L-NNA (100 microM, NOS inhibitor) and indomethacin (INDO; 10 microM, COX inhibitor). Data are expressed as mean+/-s.e.m.EDHF-mediated maximal dilatation of arteries isolated from WT mice declined by 44% with ageing, from 86+/-3% at 3 months to 66+/-8% at 12 and 48+/-4% at 20 months of age (P<0.05). This decline was magnified by DL to 73%, characterised by an early increased efficacy at 3 m/o (95+/-2%, P<0.05) and a worsening of the dysfunction at 20 m/o (26+/-2%, P<0.05). 17-Octadecynoic acid (17-ODYA), a cytochrome P450/epoxygenase inhibitor, reduced by 56% (P<0.05) ACh-induced EDHF-dependent dilatation of arteries isolated from 3 m/o DL--but not WT--mice, an effect of 17-ODYA disappearing in older DL mice. 17-ODYA, however, reduced (P<0.05) ACh-induced EDHF-dependent dilatation in arteries isolated from 12 m/o WT mice by 35% and from 20 m/o WT mice by 31% (P<0.05). Reactive oxygen species production was increased in arteries isolated from 12 m/o DL mice. The antioxidant N-acetyl-L-cystein (NAC) restored the 17-ODYA-sensitive responses in arteries isolated from 12 - but not 20 - m/o DL mice (84+/-3% from an E(max) of 57+/-8%; P<0.05). NAC did not affect the dilatation of arteries isolated from WT mice. Our data suggest that the decline in EDHF-dependent dilatation is hastened by DL despite the early expression of a 17-ODYA-sensitive pathway increasing the efficacy of the non-NO/non-PGI2 endothelium-dependent dilatation. Acute free radical production contributes to the endothelial dysfunction in the presence of DL only, by abrogating this latter pathway. This 17-ODYA-sensitive pathway, however, appears in 12 m/o WT mice and remains active at 20 m/o.

Endothelium-dependent hyperpolarizations: past beliefs and present facts

Endothelium-dependent relaxations are attributed to the release of various factors, such as nitric oxide, carbon monoxide, reactive oxygen species, adenosine, peptides and arachidonic acid metabolites derived from the cyclooxygenases, lipoxygenases, and cytochrome P450 monooxygenases pathways. The hyperpolarization of the smooth muscle cell can contribute to or be an integral part of the mechanisms underlying the relaxations elicited by virtually all these endothelial mediators. These endothelium-derived factors can activate different families of K(+) channels of the vascular smooth muscle. Other events associated with the hyperpolarization of both the endothelial and the vascular smooth muscle cells (endothelium-derived hyperpolarizing factor (EDHF)-mediated responses) contribute also to endothelium-dependent relaxations. These responses involve an increase in the intracellular Ca(2+) concentration of the endothelial cells followed by the opening of Ca(2+)-activated K(+) channels of small and intermediate conductance and the subsequent hyperpolarization of these cells. Then, the endothelium-dependent hyperpolarization of the underlying smooth muscle cells can be evoked by direct electrical coupling through myoendothelial junctions and/or the accumulation of K(+) ions in the intercellular space between the two cell types. These various mechanisms are not necessarily mutually exclusive and, depending on the vascular bed and the experimental conditions, can occur simultaneously or sequentially, or also may act synergistically.

Comparison of endothelial function in the carotid artery between normal and short-term hypercholesterolemic rabbits

The present study was undertaken to investigate and compare the vascular function in carotid arteries isolated from normal short-term hypercholesterolemic rabbits. Rabbits were fed normal or 0.5% cholesterol chow for 5 weeks. The tension of isolated carotid artery rings was measured isometrically. Serum lipid levels were measured and morphometric analysis was performed. And content of nitrate/nitrite in the carotid artery was also determined. In the carotid artery precontracted by phenylephrine, the cholesterol chow diet administered for 5 weeks decreased acetylcholine-induced relaxation at only middle concentrations, though it significantly increased the content of nitrate/nitrite, the sum of stable nitric oxide metabolites, in the carotid artery. Cholesterol chow for 5 weeks had no influence on sodium nitroprusside-induced relaxation in the carotid artery. The N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine was significantly decreased in rabbits receiving the cholesterol chow as compared to rabbits receiving the control diet. The resistant part of acetylcholine-induced relaxation was significantly inhibited when the carotid artery was treated with glibenclamide, a selective inhibitor of ATP-sensitive K(+) channels, 4-aminopyridine, an inhibitor of voltage-dependent K(+) channels, or charybdotoxin, an inhibitor of large and intermediate conductance Ca(2+)-activated K(+) channels, and it was significantly inhibited by tetraethylammonium, a non-selective inhibitor of Ca(2+)-activated K(+) channels and N,N-di-ethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a nonselective cytochrome P-450 monooxygenase (CYP) inhibitor, or ketoconazole, a selective CYP3A inhibitor in only normal rabbits. These results suggest that short-term hypercholesterolemia decreased EDHF-induced relaxation mediated through K(+) channels in rabbit carotid artery and that it may be due partially to the inhibition of CYP3A system in the carotid artery at an early stage of hypercholesterolemia.

Aging associated with mild dyslipidemia reveals that COX-2 preserves dilation despite endothelial dysfunction

The endothelial function declines with age, and dyslipidemia (DL) has been shown to hasten this process by favoring the generation of reactive oxygen species (ROS). Cyclooxygenase-2 (COX-2) can be induced by ROS, but its contribution to the regulation of the endothelial function is unknown. Since COX-2 inhibitors may be deleterious to the cardiovascular system, we hypothesized that DL leads to ROS-dependent endothelial damage and a protective upregulation of COX-2. Dilations to acetylcholine (ACh) of renal arteries isolated from 3-, 6-, and 12-mo-old wild-type (WT) and DL mice expressing the human ApoB-100 were recorded with or without COX inhibitors and the antioxidant N-acetyl-l-cystein (NAC). Nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) were inhibited using N(omega)-nitro-l-arginine (l-NNA) and a depolarizing solution, respectively. In WT mice, the dilation to ACh declined at 12 mo but was insensitive to COX-1/2 inhibition alone or with NAC. DL led to an early endothelial dysfunction at 6 mo, normalized, however, by NAC. At 12 mo, vascular sensitivity to ACh was further reduced by DL. At this age, selective COX-2 inhibition reduced the dilation, whereas addition of NAC improved it. In 3- and 6-mo-old WT mice, l-NNA significantly reduced the dilation, whereas it limited the dilation only in 3-mo-old DL mice. EDHF-dependent dilation remains identical in both groups. These data suggest that COX-2 activity confers endothelium-dependent vasodilatory function in aged DL mice in the face of a pro-oxidative environment. Upregulation of this pathway compensates for the early loss of the contribution of NO in DL mice.

Effects of local gene transfer of VEGF on neointima formation after balloon injury in hypercholesterolemic rabbits

Enhancement of the generation of nitric oxide (NO) and vascular endothelial growth factor (VEGF) are suggested to prevent restenosis after angioplasty. Accordingly, we tested whether the local delivery of L-arginine (L-Arg), a substrate for NO generation and the VEGF gene, alone or in combination, can influence neointima formation in hypercholesterolemic rabbits. Balloon injury of the iliac arteries was performed in 24 New Zealand White rabbits fed a 1% cholesterol diet for 3 weeks followed by a local infusion of: (1) pSG5VEGF165 plasmid alone (1000 microg); (2) pSG5VEGF165 (1000 microg) with L-Arg (800mg); (3) L-Arg (800mg) alone; and (4) L-Arg (800 mg) with naked pSVbeta-gal plasmid (1000 microg). The animals were kept on the hypercholesterolemic diets for a further 28 days, when vessels were taken for morphometric analysis and immunocytochemistry. Endogenous rabbit VEGF concentration in the plasma increased significantly at 7 days after injury (17.06 +/- 1.57 vs 23.01 +/- 1.9 pg/ml; p < 0.02) and remained elevated for up to 28 days (28.46 +/- 5.24; p < 0.01). Injured arteries exhibited strong immunocytochemical staining for rabbit VEGF. Rabbits that received a VEGF gene transfer revealed more prominent neointima formation, whereas treatment with L-Arg was associated with significantly less intimal thickness (p < 0.05). Local transfer of the VEGF gene does not inhibit neointima formation in hypercholesterolemic rabbits. Our results suggest that VEGF gene therapy applied locally in atherosclerotic arteries may not be beneficial.

Sympathectomy Causes Aggravated Lesions and Dedifferentiation in Large Rabbit Atherosclerotic Arteries without Involving Nitric Oxide

Previously [Histochem J 1997;29:279-286], we found that sympathectomy induced neointima formation in ear but not cerebral arteries of genetically hyperlipidemic rabbits. To clarify the influence of sympathetic nerves in atherosclerosis, and whether their influence involves vascular NO activity, we studied groups of normocholesterolemic intact (NI) and sympathectomized (NS), and hypercholesterolemic intact (HI) and sympathectomized (HS) rabbits (diet/6-hydroxydopamine for 79 days). Segments of basilar (BA) and femoral (FA) arteries were studied histochemically, to evaluate differentiation (anti-desmin, anti-vimentin, anti-h-caldesmon, and nuclear dye), by confocal microscopy, and by in vitro myography. In BAs, staining of NI and NS groups was similar. In hypercholesterolemic groups, a small neointima developed, more frequently in HS segments where smooth muscle cells (SMCs) positive for all antibodies appeared to be migrating into the neointima. In FAs, SMCs stained for the three antibodies in the NI group, but we observed desmin- and h-caldesmon-negative, vimentin-positive cells in some external medial layers of the NS, HI and HS groups, identical to adventitial fibroblasts. Large neointimas of the HS group contained vimentin-positive and largely desmin- and h-caldesmon-negative cells. Relaxation of BA or FA segments to acetylcholine was not decreased by sympathectomy. Sympathectomy increased the contraction of resting FAs to nitro-L-arginine (p = 0.0379). Thus, sympathectomy aggravates the tendency for FA SMCs to migrate and dedifferentiate, increasing atherosclerotic lesions, without decreasing NO activity, but has only minor effects on BAs.

Role of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) in the regulation of blood pressure by leptin in lean and obese rats

We investigated the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in hemodynamic action of leptin. The effect of leptin (1 mg/kg i.p.) on systolic blood pressure (SBP) was examined in lean rats and in rats made obese by feeding highly palatable diet for either 1 or 3 months. Separate groups received NO synthase inhibitor, L-NAME, or EDHF inhibitors, the mixture of apamin+charybdotoxin or sulfaphenazole, before leptin administration. Leptin increased NO production, as evidenced by increase in plasma and urinary NO metabolites and cyclic GMP. This effect was impaired in both obese groups. In lean rats either leptin or EDHF inhibitors had no effect on blood pressure. L-NAME increased blood pressure in lean animals and this effect was prevented by leptin. However, when leptin was administered to animals pretreated with both L-NAME and EDHF inhibitors, blood pressure increased even more than after L-NAME alone. In the 1-month obese group leptin had no effect on SBP, however, pressor effect of leptin was observed in animals pretreated with EDHF inhibitors. In the 3-month obese group leptin alone increased SBP, and EDHF inhibitors did not augment its pressor effect. The results suggest that leptin may stimulate EDHF when NO becomes deficient, e.g. after NOS blockade or in short-term obesity. Although the effect of leptin on NO production is impaired in the 1-month obese group, BP does not increase, probably because EDHF compensates for NO deficiency. In contrast, leptin increases BP in 3-month obesity because its effect on EDHF is also attenuated.

Two distinct pathways account for EDHF-dependent dilatation in the gracilis artery of dyslipidaemic hApoB+/+ mice

1 A universal endothelium-derived hyperpolarising factor (EDHF--non-NO/non-PGI(2)) has not been identified. EDHF, however, is essential for the physiological control of resistance artery tone. The impact of dyslipidaemia (DL), a risk factor for cardiovascular diseases, on the nature and the efficacy of EDHF has not been evaluated yet. 2 Pressurised (80 mmHg) gracilis arterial segments isolated from mice expressing the human apoB-100 and C57Bl/6 wild-type (WT) mice were used. EDHF-dependent dilatations to acetylcholine (ACh) were measured in the presence of L-NNA (100 microM, NOS inhibitor) and indomethacin (10 microM, COX inhibitor). 3 Maximal EDHF-induced dilatations were increased in DL when compared to WT (95+/-2 versus 86+/-4% in WT; P<0.05). Combination of apamin and charybdotoxin strongly reduced (P<0.05) ACh-induced dilatation in WT (22+/-4%) and DL (25+/-5%). 4 Combined addition of barium (Ba(2+)) and ouabain abolished EDHF-induced dilatations in WT arteries (13+/-3%; P<0.05). In vessels isolated from DL mice, however, only the addition of 14,15-EEZE (a 14,15-EET antagonist) to Ba(2+) and ouabain prevented EDHF-induced dilatations (5+/-3% compared to 54+/-11% in the presence of combined Ba(2+) and ouabain; P<0.05). 5 Our data suggest that EDHF-mediated dilatation depends on the opening of endothelial SK(Ca) and IK(Ca) channels. This is associated with the opening of K(ir) channels and activation of the Na(+)/K(+)-ATPase pump on smooth muscle cells leading to dilatation. In arteries from DL mice, a cytochrome P450 metabolite likely to be 14,15-EET equally contributes to the dilatory action of ACh. The early increased efficacy of EDHF in arteries isolated from DL mice may originate from the duplication of the EDHF pathways.

Alteration in endothelial function and modulation by treatment with pioglitazone in rabbit renal artery from short-term hypercholesterolemia

The present study was undertaken to investigate endothelial function and epoxyeicosatrienoic acids (EETs), which is a cytochrome P-450 monooxygenase (CYP) metabolite and one of the candidates as an endothelium-derived hyperpolarizing factor (EDHF) in the renal artery isolated from short-term hypercholesterolemic rabbits, and also to characterize the effects of pioglitazone on it. Rabbits were fed normal, 0.5% cholesterol chow, or 0.5% cholesterol chow plus 300 ppm pioglitazone for 5 weeks. The tension of isolated renal artery rings was measured isometrically. Serum lipid levels were measured and morphometric analysis was performed. EET contents in the renal artery were also determined. The cholesterol chow diet for 5 weeks increased serum lipid levels, and pioglitazone had no influence on it. In the phenylephrine precontracted renal artery, the cholesterol chow did not affect acetylcholine-induced relaxation. The N(G)-nitro-l-arginine- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine was significantly enhanced in rabbits receiving the cholesterol chow as compared to rabbits receiving the control diet, and pioglitazone normalized it. The resistant part of acetylcholine-induced relaxation was significantly inhibited when the renal artery was treated with charybdotoxin, an inhibitor of large- and intermediate-conductance Ca(2+)-activated K(+) channels, or N,N-di-ethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a nonselective CYP inhibitor, and it was significantly inhibited by sulfaphenazole, a selective CYP2C9 inhibitor in rabbits receiving only the cholesterol chow. In KCl-precontracted renal artery, the cholesterol chow inhibited acetylcholine-induced relaxation and pioglitazone normalized it. The cholesterol chow increased the production of EETs and reduced nitrate/nitrite contents in the renal artery, and pioglitazone strongly suppressed them. These results suggest that the EETs may be one of the EDHFs in the rabbit renal artery and beneficial effects of pioglitazone on alterations in endothelial function induced by cholesterol feeding are due, in part, to the protective action on the nitric oxide system and/or the suppression of increased production of EETs.

Calcium-activated potassium channels and NO regulate human peripheral conduit artery mechanics

The role of NO in the regulation of the mechanical properties of conduit arteries is controversial in humans, and the involvement of an endothelium-derived hyperpolarizing factor (EDHF), acting through calcium-activated potassium (KCa) channels, has never been investigated at this level in vivo. We assessed in healthy volunteers, after oral administration of aspirin (500 mg), the effect of local infusion of NG-monomethyl-L-arginine (L-NMMA; 8 mumol/min for 8 minutes), an NO synthase inhibitor, tetraethylammonium chloride (TEA; 9 mumol/min for 8 minutes), a KCa channels inhibitor, and the combination of both on radial artery internal diameter, wall thickness (echo tracking), blood flow (Doppler), and pressure. The incremental elastic modulus and compliance were fitted as functions of midwall stress. L-NMMA decreased modulus and increased compliance at high levels of midwall stress (all P<0.05) without affecting radial diameter. TEA reduced radial diameter from 2.68+/-0.07 to 2.50+/-0.08 10(-3) m, increased the modulus, and decreased the compliance at all levels of stress (all P<0.05). Combination of both inhibitors synergistically enhanced the increase in modulus, the decrease in diameter (from 2.71+/-0.10 to 2.42+/-0.09 10(-3) m), and compliance compared with TEA alone (all P<0.05). These results confirm that inhibition of NO synthesis is associated with a paradoxical isometric smooth muscle relaxation of the radial artery. They demonstrate the involvement of KCa channels in the regulation of the mechanical properties of peripheral conduit arteries, supporting a role for EDHF at this level in vivo. Moreover, the synergistic effect of l-NMMA and TEA shows that KCa channels compensate for the loss of NO synthesis to maintain peripheral conduit artery diameter and mechanics.

Influence of Diabetes Mellitus, Hypercholesterolemia, and Their Combination on EDHF-Mediated Responses in Mice

The endothelium synthesizes and releases several vasodilator substances, including vasodilator prostaglandins, NO, and EDHF. NO-mediated relaxations are reduced by various risk factors, such as diabetes mellitus and hypercholesterolemia. However, it remains to be elucidated whether EDHF-mediated relaxations also are reduced by those factors and their combination. In this study, we addressed this point in mice. We used small mesenteric arteries from control, diabetic (streptozotocin-induced), apolipoprotein-E-deficient (ApoE-/-), and diabetic ApoE-/- mice. In control mice, endothelium-dependent relaxations to acetylcholine were largely mediated by EDHF. This EDHF-mediated component was slightly reduced in diabetic mice, preserved in ApoE-/- mice, and markedly reduced in diabetic ApoE-/- mice with an increase in NO-mediated component and a negative contribution of indomethacin-sensitive endothelium-derived contracting factor (EDCF). Endothelium-independent relaxations to sodium nitroprusside or NS1619, a direct opener of calcium-activated K channels, were attenuated in ApoE-/- and diabetic ApoE-/- mice. Endothelium-dependent hyperpolarizations were significantly reduced in diabetic mice, preserved in ApoE-/- mice, and again markedly reduced in diabetic ApoE-/- mice. These results indicate that hypercholesterolemia alone minimally affects the EDHF-mediated relaxations, and diabetes mellitus significantly attenuated the responses, whereas their combination markedly attenuates the responses with a compensatory involvement of NO and a negative contribution of EDCF.

Enhanced endothelium derived hyperpolarising factor activity in resistance arteries from normal pressure glaucoma patients: implications for vascular function in the eye

BACKGROUND/AIMS

Endothelial cell dysfunction in the ocular circulation may contribute to normal pressure glaucoma (NPG). This study aimed to investigate the contributions made by endothelium derived relaxing factors to relaxation of (1) subcutaneous resistance arteries from patients with NPG, and (2) porcine ciliary arteries.

METHODS

Human gluteal resistance arteries were isolated from seven patients with NPG and matched controls. Human and porcine arteries produced endothelium dependent relaxation when exposed to acetylcholine (ACh) (10(-9)-3 x 10(-5)M) or bradykinin (10(-10)-3 x 10(-6)M). Pharmacological agents were used to inhibit the nitric oxide pathway (l-arginine analogues, soluble guanylate cyclase inhibitor), endothelium derived hyperpolarising factor (EDHF) activity (potassium channel antagonists), and prostaglandin synthesis (cyclo-oxygenase inhibitors).

RESULTS

In all arteries, endothelium dependent relaxation was attenuated by nitric oxide (NO) inhibition or potassium channel blockade, but not by cyclo-oxygenase inhibition. Inhibition of ACh mediated relaxation by potassium channel antagonists was greater (p<0.05) in patients with NPG (Emax, 55.4% (SD 8.16%) relaxation, n = 4) than controls (Emax, 81.8% (6.0%), n = 5). In contrast, combined inhibition of NO synthase (NOS) and cyclo-oxygenase produced similar inhibition of ACh mediated relaxation in both groups.

CONCLUSIONS

The enhanced contribution of EDHF to ACh mediated relaxation in systemic resistance arteries from NPG patients may contribute to the maintained endothelium mediated relaxation in these vessels. EDHF also contributes significantly to bradykinin mediated relaxation in porcine ocular ciliary arteries. Therefore, similar changes in the balance of relaxing factors in the ocular circulation could influence the response of the eye to vascular endothelial dysfunction in NPG.

Rapid and simple determination of epoxyeicosatrienoic acids in rabbit renal artery by reversed-phase HPLC with fluorescence detection

A liquid chromatographic method with fluorescence detection coupled with a solid-phase extraction was applied to the rapid determination of epoxyeicosatrienoic acids (EETs) in the rabbit renal artery. The EETs were extracted with an acetonitrile from renal artery homogenate and concentrated by a solid-phase extraction method. The concentrated EETs were reacted directly with a 6, 7-dimethoxy-1-methyl-2 (1H)-quinoxalinone-3-propionyl-carboxylic acid (DMEQ) hydrazide and separated by a reversed-phase HPLC with eluting a combination of a step-wise and a gradient of a mixture of methanol and water. The content of EETs in the renal arteries was significantly greater in the 0.5% cholesterol fed rabbits than in control rabbits. It is suggested that hyperchlesterolemia increases the production of EETs in the rabbit renal artery.

Soluble epoxide hydrolase is a main effector of angiotensin II-induced hypertension

The soluble epoxide hydrolase (sEH) metabolizes vasodilatory epoxyeicosatrienoic acids (EETs) to their di-hydroxy derivatives. We hypothesized that the metabolism of EETs by the sEH contributes to angiotensin II-induced hypertension and tested the effects of a water-soluble sEH inhibitor, 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) on blood pressure. AUDA (130 microg/mL in drinking water) did not affect blood pressure in normotensive animals but markedly lowered it in mice with angiotensin II-induced hypertension (1 mg/kg per day). The effect of AUDA was accompanied by an increase in urinary salt and water excretion. Intravenous application of AUDA (8 mg/kg) acutely lowered blood pressure and heart rate in animals with angiotensin II-induced hypertension but failed to affect blood pressure in animals with phenylephrine-induced hypertension (29 mg/kg per day). AUDA (0.1 micromol/L) selectively lowered vascular resistance in an isolated perfused kidney preparation from angiotensin II-pretreated mice but not from control mice. In the perfused hind limb and in isolated carotid arteries from angiotensin II-treated mice, AUDA was without effect. The omega-hydroxylase inhibitor N-methylsulfonyl-12,12-dibromododec-11-enamide, which attenuates formation of the potent vasoconstrictor 20-hydroxyeicosatetraenoic acid, decreased tone in carotid arteries from angiotensin II-treated but not from control mice. These data demonstrate that the decrease in blood pressure observed after sEH inhibition in angiotensin II-induced hypertension can be attributed to an initial reduction in heart rate followed by pressure diuresis resulting from increased perfusion of the kidney. Direct vasodilatation of resistance arteries in skeletal muscles does not appear to contribute to the antihypertensive effects of sEH inhibition in mice.

Loss of endothelial KATP channel-dependent, NO-mediated dilation of endocardial resistance coronary arteries in pigs with left ventricular hypertrophy

The influence of left ventricular hypertrophy (LVH) on the endothelial function of resistance endocardial arteries is not well established. The aim of this study was to characterise the mechanisms responsible for UK-14,304 (alpha(2)-adrenoreceptor agonist)-induced endothelium-dependent dilation in pig endocardial arteries isolated from hearts with or without LVH. LVH was induced by aortic banding 2 months before determining endothelial function. Following euthanasia, hearts were harvested and endocardial resistance arteries were isolated and pressurised to 100 mmHg in no-flow conditions. Vessels were preconstricted with acetylcholine (ACh) or high external K(+) (40 mmol l(-1) KCl). Results are expressed as mean+/-s.e.m. UK-14,304 induced a maximal dilation representing 79+/-6% (n=8) of the maximal diameter. NO synthase (l-NNA, 10 micromol l(-1), n=7) or guanylate cyclase (ODQ, 10 micromol l(-1), n=4) inhibition reduced (P<0.05) UK-14,304-dependent dilation to 35+/-6 and 18+/-7%, respectively. Apamin and charybdotoxin reduced (P<0.05) to 39+/-8% (n=4) the dilation induced by UK-14,304. In depolarised conditions, however, this dilation was prevented (P<0.05). UK-14,304-induced dilation was reduced (P<0.05) by glibenclamide (Glib, 1 micromol l(-1)), a K(ATP) channel blocker, either alone (35+/-10%, n=5) or in combination with l-NNA (34+/-9%, n=4). In LVH, UK-14,304-induced maximal dilation was markedly reduced (25+/-4%, P<0.05) compared to control; it was insensitive to l-NNA (21+/-5%) but prevented either by the combination of l-NNA, apamin and charybdotoxin, or by 40 mmol l(-1) KCl. Activation of endothelial alpha(2)-adrenoreceptor induces an endothelium-dependent dilation of pig endocardial resistance arteries. This dilation is in part dependent on NO, the release of which appears to be dependent on the activation of endothelial K(ATP) channels. This mechanism is blunted in LVH, leading to a profound reduction in UK-14,304-dependent dilation.

Characterization of endothelium-dependent relaxation and modulation by treatment with pioglitazone in the hypercholesterolemic rabbit renal artery

The present study was undertaken to investigate vascular function in hypercholesterolemic rabbits and also to characterize the effects of pioglitazone on it. Rabbits were fed normal, 0.5% cholesterol chow, or 0.5% cholesterol chow plus 300 ppm pioglitazone for 5 or 10 weeks. The tension of isolated renal artery rings was measured isometrically, and morphometric analysis was performed. The cholesterol chow diet administered for 5 weeks did not affect acetylcholine-induced relaxation in the renal artery but that for 10 weeks decreased it. The N(G)-nitro-L-arginine (L-NOARG)- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine in the renal artery was enhanced in rabbits receiving the cholesterol chow for 5 or 10 weeks, as compared to rabbits receiving the control diet, and the percentage of plaque area formation was increased in the renal artery by the cholesterol chow for 10 weeks. Pioglitazone normalized them without lowering serum lipid levels. The resistant parts of acetylcholine-induced relaxation was significantly inhibited when the renal artery was treated with charybdotoxin, an inhibitor of large and intermediate conductance Ca(2+)-activated K(+) channels, or N,N-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a cytochrome P-450 monooxygenase inhibitor. Results indicate that hypercholesterolemia enhances endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in the rabbit renal artery and pioglitazon normalizes it without lowering serum lipid levels, and suggest that the maintenance of endothelial function by pioglitazon is related to the mechanisms for its anti-atheromatous activity.

Effects of a topical enamel matrix derivative on skin wound healing

Enamel matrix derivative, obtained from developing porcine teeth, is composed mainly of amelogenin proteins and used topically in periodontal surgery for advanced periodontitis to regenerate lost connective tissues. The primary objective of this study was to investigate the effects of enamel matrix derivative on skin wound healing. Secondly, in vitro effects of enamel matrix derivative on dermal fibroblasts and microvascular endothelial cells were examined. Full-thickness, circular 2-cm skin wounds in white 16-week-old rabbits were treated thrice weekly with enamel matrix derivative (30 mg/ml) in the vehicle propylene glycol alginate or with vehicle alone. Enamel matrix derivative treatment increased the amount of granulation tissue and accelerated time to complete epithelialization by 3 days (p < 0.001) compared to vehicle treatment. In cultured fibroblasts, vascular endothelial growth factor levels in conditioned media were increased more than fivefold (p < 0.001) with enamel matrix derivative treatment (0.1mg/ml) over control, measured by specific enzyme-linked immunosorbent assay. Enamel matrix derivative also increased release of matrix metalloproteinase-2 more than threefold from fibroblasts (p < 0.001) and from endothelial cells (p < 0.001). Thus, enamel matrix derivative significantly accelerated wound closure in rabbits, possibly by increasing levels of growth factors and proteinases important for granulation tissue formation and remodeling.

Endothelium mediated vasorelaxant response of garlic in isolated rat aorta: role of nitric oxide

The vasorelaxant effect of garlic (Alium sativum L.) has been suggested to be partially mediated through endothelium. The present study was designed to evaluate the role of various endothelium-mediated mechanisms in vasorelaxant response of garlic on isolated aortic rings of rats. In tissues precontracted with phenylephrine (PE) 10(-6)M, concentration-response curve for different concentrations of garlic (1, 5, 10, 20 and 50 microg/ml) was examined. In all the preparations garlic showed a concentration-dependent vasorelaxant response. There was a significant attenuation of vasorelaxation in tissues pretreated with K(+) channel blocker, glybenclamide (10(-6)M). Indomethacin (10(-5)M) enhanced the relaxant response of garlic. N(G)-Monomethyl-L-arginine (L-NMMA) 30 microM, a potent inhibitor of nitric oxide synthase, did not produce any significant effect on the response of garlic. However, cGMP blocker methylene blue (10(-5)M) showed a strong vasoconstriction and inhibited the vasorelaxant response of garlic. The results indicate that endothelium modulated vasorelaxation of garlic is partly mediated through EDHFs and cycloxygenase pathways. However, relaxing factor(s) other than NO, mediated through cGMP has a major role in the vasorelaxant response of garlic.

Aged spontaneously hypertensive rats exhibit a selective loss of EDHF-mediated relaxation in the renal artery

Endothelium-dependent relaxation is frequently attenuated in hypertension. We hypothesized that the contribution of the endothelium-derived hyperpolarizing factor (EDHF) to the acetylcholine (ACh)-induced, endothelium-dependent relaxation is attenuated with aging in the renal artery of spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) rats. ACh-induced, NO-mediated relaxation was identical in young (8-week-old) WKY and SHR, whereas EDHF-mediated relaxations (assessed in the presence of Nomega-nitro-l-arginine and diclofenac) were much more pronounced in SHR than WKY. KCl-induced relaxations were more pronounced in vessels from young WKY rats than from young SHR. The cytochrome P450 inhibitor sulfaphenazole significantly inhibited EDHF-mediated relaxation in vessels from young SHR but not WKY. Vessels from old (22 months) SHR exhibited a slightly reduced NO-mediated relaxation but a complete loss of EDHF-mediated responses. In contrast, aging did not affect EDHF-mediated responses in WKY. Moreover, ACh-induced hyperpolarization and resting membrane potential were decreased in old SHR but not in WKY. KCl-induced relaxation increased with age in WKY, whereas no response to KCl was recorded in arteries from aged SHR. In vessels from old WKY but not old SHR, mRNA expression of the Na-K-ATPase subunit alpha2 was increased by 2-fold compared with young animals. These data indicate that the increase in EDHF responses in renal arteries from aged WKY can be attributed to the release of K+ ions from the endothelium, whereas increased EDHF responses in renal arteries from young SHR can be attributed to a sulfaphenazole-sensitive cytochrome P450-dependent EDHF.

Ca2+-activated K+ channels mediate relaxation of forearm veins in chronic renal failure

BACKGROUND

In arteries, agonists such as acetylcholine release an endothelium-derived hyperpolarizing factor (EDHF) that is neither nitric oxide nor prostacyclin.

OBJECTIVES

To examine the responses to acetylcholine in segments of forearm veins from patients with chronic renal failure who either had never received dialysis or had undergone long-term dialysis, and to determine the contribution of nitric oxide and EDHF to endothelium-dependent relaxation in veins from patients with chronic renal failure.

METHODS

Isometric tension was recorded in rings of forearm vein from 34 non-dialysed patients, 27 dialysed patients and 14 multiorgan donors (controls).

RESULTS

Relaxation in response to acetylcholine was reduced in veins of non-dialysed and dialysed patients. The inhibitors of nitric oxide synthase NG-monomethyl-l-arginine (l-NMMA) and NG,NG-dimethyl-l-arginine (ADMA) reduced by 50% the maximum relaxation in response to acetylcholine in veins from controls and non-dialysed patients; the remaining relaxation was inhibited by 20 mmol/l KCl or by the K+ channel blockers tetraethylammonium chloride, iberiotoxin, charybdotoxin and the combination of barium plus ouabain, but not by apamin or glibenclamide. Relaxation in veins from dialysed patients was inhibited by K+ channel blockade but not by l-NMMA or ADMA.

CONCLUSIONS

The results demonstrate that the endothelium-dependent relaxation in forearm veins from controls and non-dialysed patients is mediated by release of nitric oxide and EDHF. In contrast, the relaxation in veins from dialysed patients is mediated mainly by EDHF. EDHF-induced relaxation involves activation of large-conductance Ca2+-activated K+ channels.

Preservation of endothelium-dependent and Nomega-nitro-L-arginine methyl ester- and indomethacin-resistant arterial relaxation in high-cholesterol-diet fed rabbits by treatment with fluvastatin, an HMG-CoA reductase inhibitor

This study was designed to test the hypothesis that fluvastatin preserves endothelium-dependent and nitric oxide (NO)-independent relaxations in arterial preparations from rabbits fed a high-cholesterol diet in the absence of any cholesterol-lowering action. Rabbits were fed a 0.5% high-cholesterol diet for 12 weeks and then fed the high-cholesterol diet with/without fluvastatin 2 mg/kg/d for an additional 8 weeks. Plasma total and LDL-cholesterol concentrations were not affected by fluvastatin treatment. Endothelium-dependent and NO-mediated relaxation elicited by acetylcholine and A23187 in both the thoracic aorta and femoral artery was impaired in the high-cholesterol group but not in the fluvastatin-treated group. Endothelium-independent relaxation elicited by sodium nitroprusside was similar among the 3 groups. Preincubation of thoracic aortas from each of the 3 groups with Nomega-nitro-L-arginine methyl ester (L-NAME) and indomethacin completely abolished the relaxant response to acetylcholine. In contrast, the maximal response to acetylcholine (1 microM) in femoral artery was only partially reversed in the presence of L-NAME and indomethacin. Fluvastatin treatment preserved the acetylcholine-induced L-NAME and indomethacin-resistant relaxation impaired in the femoral artery from the high-cholesterol diet group. These results suggest that fluvastatin treatment preserves endothelium-dependent, NO-independent function as well as NO-dependent function in absence of its lipid lowering-action.

Altered endothelial Ca2+ regulation after ischemia/reperfusion produces potentiated endothelium-derived hyperpolarizing factor-mediated dilations

BACKGROUND AND PURPOSE

Endothelium-derived hyperpolarizing factor (EDHF)-mediated dilations are potentiated after several pathologies, including ischemia/reperfusion (I/R). However, no study to date has addressed the mechanism by which this potentiation occurs. This study tested the hypothesis that potentiated EDHF-mediated dilations are due to altered endothelial Ca2+ handling after I/R.

METHODS

Rat middle cerebral arteries (MCAs) were isolated after 2 hours of MCA occlusion and 24 hours of reperfusion (or sham surgery). This model has been previously demonstrated to produce potentiated EDHF-mediated dilations. MCAs were studied in a pressurized/perfused vessel chamber equipped for the simultaneous measurement of endothelial Ca2+ (with fura 2) and artery diameter. Measures were made after luminal administration of UTP (P2Y2 purinoceptor agonist), 2 MeS-ATP (P2Y1 purinoceptor agonist), and Br-A23187 (receptor-independent Ca2+ ionophore) for sham and I/R MCAs.

RESULTS

I/R resulted in significantly potentiated UTP-mediated dilations (through a P2Y2 purinoceptor) and endothelial Ca2+ responses in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME) and indomethacin. Endothelial Ca2+ and diameter responses were also significantly potentiated with 2 MeS-ATP (through a P2Y1 purinoceptor) when L-NAME and indomethacin were absent. Br-A23187, a receptor-independent Ca2+ ionophore, produced significantly potentiated endothelial Ca2+ responses after I/R in the presence of L-NAME/indomethacin. Evaluation of artery diameter as a function of endothelial Ca2+ demonstrated no differences between sham and I/R groups.

CONCLUSIONS

These findings demonstrate that I/R results in augmented endothelial Ca2+ responses that appear to be downstream of the receptor level. Moreover, these data suggest that this augmented Ca2+ response contributes to the potentiated EDHF-mediated dilations after I/R.

Organ culture: a new model for vascular endothelium dysfunction

BACKGROUND

Endothelium dysfunction is believed to play a role in the development of cardiovascular disease. The aim of the present study was to evaluate the suitability of organ culture as a model for endothelium dysfunction.

METHODS

The isometric tension was recorded in isolated segments of the rat mesenteric artery branch, before and after organ culture for 20 h. Vasodilatation was expressed as % of preconstriction with U46619. The acetylcholine (ACh) induced nitric oxide (NO) mediated dilatation was studied in the presence of 10 microM indomethacin, 50 nM charybdotoxin and 1 microM apamin. Endothelium-derived hyperpolarising factor (EDHF) was studied in the presence of 0.1 mM L-NOARG and indomethacin. Prostaglandins were studied in the presence of L-NOARG, charybdotoxin and apamin.

RESULTS

The ACh-induced NO and prostaglandin-mediated dilatations decreased significantly during organ culture (NO: 84% in control and 36% in cultured; prostaglandins: 48% in control and 16% in cultured). Notably, the total ACh-dilatation was not changed. This might be explained by the finding that EDHF alone stimulated a full dilatation even after organ culture (83% in control and 80% in cultured). EDHF may thereby compensate for the loss in NO and prostaglandin-mediated dilatation. Dilatations induced by forskolin or sodium nitroprusside did not change after organ culture, indicating intact smooth muscle cell function.

CONCLUSIONS

Organ culture induces a loss in NO and prostaglandin-mediated dilatation, which is compensated for by EDHF. This shift in mediator profile resembles that in endothelium dysfunction. Organ culture provides an easily accessible model where the molecular changes that take place, when endothelium dysfunction is developed, can be examined over time.

Role of endothelium in adenosine receptor-mediated vasorelaxation in hypertensive rats

The present study was designed to investigate the role of endothelium derived relaxing factor nitric oxide (NO) in adenosine A2 receptor mediated vasorelaxation in normotensive (WKY) and hypertensive (SHR) rat aortic ring preparations. Adenosine analogues, 2-chloroadenosine (CAD) and 5-ethylcarboxamidoadenosine (NECA) produced concentration-dependent (10(-9)-10(-4) M) relaxation in phenylephrine (1 x 10(-6) M) precontracted vascular rings, which was significantly shifted to the right in SHR compared to WKY rats. Endothelium removal attenuated CAD and NECA relaxation responses in both SHR and WKY and abolished the difference in relaxation between SHR and WKY vascular tissues. The relaxation response to CAD was antagonised by adenosine A2 receptor antagonist, 8-sulfophenyltheophylline (8-SPT, 50 x 10(-6) M). The antagonism by 8-SPT was lower in SHR as compared to WKY tissues. L-monomethylarginine (L-LMMA) (30 x 10(-6) M) significantly shifted the CAD relaxation to the right, which was reversed by the addition of L-arginine (100 x 10(-6) M) in both SHR and WKY rats. However, the rightward shift by L-NMMA was smaller in SHR compared to WKY vascular tissues. Vasorelaxation response to acetylcholine (1 x 10(-6) M) was significantly inhibited (50%) in SHR rings compared to WKY. The relaxation produced by sodium nitroprusside (10(-9)-10(-5) M) in endothelium-intact and -denuded aortic rings showed no difference between SHR and WKY. Isoproterenol produced concentration-dependent (10-9-10-5 M) relaxation, which was shifted to the right in SHR compared to WKY rings with an intact endothelium, while the removal of endothelium abolished the difference in the response between SHR and WKY. The results suggest: (i) adenosine A2 receptors mediate vasorelaxation in part through endothelium possibly by releasing nitric oxide (NO); (ii) the impairment of endothelium may be one of the factors for the attenuation of adenosine receptor and receptor-mediated responses in SHR.

Endothelial dysfunction induced by oxidized low-density lipoproteins in isolated mouse aorta: a comparison with apolipoprotein-E deficient mice

We characterized the acute effects of oxidized low-density lipoproteins (oxidized-LDL) on vascular reactivity in isolated aorta from wild-type C57BL/6J mice, and compared these with the chronic alterations in vascular function observed in apolipoprotein-E gene knockout [ApoE(-/-)] mice fed a high-fat diet, which results in hyperlipidemia and atherosclerosis. In the abdominal (but not thoracic) aorta, oxidized-LDL (100 microg/ml) reduced relaxations induced by acetylcholine (10(-9) M-10(-5) M), which are mediated entirely by nitric oxide (NO). The relaxations induced by the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 10(-8) M-10(-4) M), the cyclic GMP analogue 8-bromo cyclic GMP (100 microM) and the nonspecific vasodilator papaverine (100 microM) were not changed by oxidized-LDL. Native LDL had no effect on vasorelaxations. The attenuation of endothelium-dependent relaxations caused by oxidized-LDL mimicked the endothelial dysfunction found in ApoE(-/-) mice. These results are consistent with the suggestion that oxidized-LDL has an important role in the pathogenesis of endothelial NO dysfunction associated with hyperlipidemia and atherosclerosis in these mice.

Endothelium-derived hyperpolarizing factor and potassium use different mechanisms to induce relaxation of human subcutaneous resistance arteries

This investigation examined the hypothesis that release of K(+) accounts for EDHF activity by comparing relaxant responses produced by ACh and KCl in human subcutaneous resistance arteries. Resistance arteries (internal diameter 244+/-12 microm, n=48) from human subcutaneous fat biopsies were suspended in a wire myograph. Cumulative concentration-response curves were obtained for ACh (10(-9) - 3x10(-5) M) and KCl (2.5 - 25 mM) following contraction with noradrenaline (NA; 0.1 - 3 microM). ACh (E(max) 99.07+/-9.61%; -LogIC(50) 7.03+/-0.22; n=9) and KCl (E(max) 74.14+/-5.61%; -LogIC(50) 2.12+/-0.07; n=10)-induced relaxations were attenuated (P<0.0001) by removal of the endothelium (E(max) 8.21+/-5.39% and 11.56+/-8.49%, respectively; n=6 - 7). Indomethacin (10 microM) did not alter ACh-induced relaxation whereas L-NOARG (100 microM) reduced this response (E(max) 61.7+/-3.4%, P<0.0001; n=6). The combination of ChTx (50 nM) and apamin (30 nM) attenuated the L-NOARG-insensitive component of ACh-induced relaxation (E(max): 15.2+/-10.5%, P<0.002, n=6) although these arteries retained the ability to relax in response to 100 microM SIN-1 (E(max) 127.6+/-13.0%, n=3). Exposure to BaCl(2) (30 microM) and Ouabain (1 mM) did not attenuate the L-NOARG resistant component of ACh-mediated relaxation (E(max), 76.09+/-8.92, P=0.16; n=5). KCl-mediated relaxation was unaffected by L-NOARG+indomethacin (E(max); 68.1+/-5.6%, P=0.33; n=5) or the combination of L-NOARG/indomethacin/ChTx/apamin (E(max); 86.61+/-14.02%, P=0.35; n=6). In contrast, the combination of L-NOARG, indomethacin, ouabain and BaCl(2) abolished this response (E(max), 5.67+/-2.59%, P<0.0001, n=6). The characteristics of KCl-mediated relaxation differed from those of the nitric oxide/prostaglandin-independent component of the response to ACh, and were endothelium-dependent, indicating that K(+) does not act as an EDHF in human subcutaneous resistance arteries.

Short term hypercholesterolemia alters N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation by acetylcholine in rabbit renal artery

The tension of isolated rings was measured isometrically to compare the N(G)-nitro-L-arginine- and indomethacin-resistant relaxation by acetylcholine (ACh) in the renal artery from normal rabbits and short term hypercholesterolemia rabbits (0.5% cholesterol chow for 5 weeks). ACh-induced relaxation in the renal artery precontracted with phenylephrine was not influenced by cholesterol-enriched chow. However, in comparison with artery from normal rabbits, the N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation by ACh was significantly enhanced by the chow. The resistant part of ACh-induced relaxation was significantly inhibited when the artery was treated with tetraethylammonium or SKF 525a. Results suggest that short term hypercholesterolemia modulates endothelium-derived hyperpolarizing factor-mediated relaxation in rabbit renal artery.