Endothelium-derived contracting factor in carotid artery of hypertensive Dahl rats

Spontaneous vascular dysfunction in Dahl salt-sensitive male rats raised without a high-salt diet

Dahl salt-sensitive (SS) rats fed a high-salt diet, but not low-salt, exhibit vascular dysfunction. Several substrains of SS rats exist that differ in their blood pressure phenotypes and salt sensitivity. The goal of this study was to investigate whether the John-Rapp-derived SS rat (SS/Jr), which exhibits spontaneous hypertension on a low-salt diet, presents with hallmarks of vascular dysfunction observed in another experimental model of hypertension independent of dietary salt, the spontaneously hypertensive rat (SHR). Endothelium-intact aortic rings and mesenteric resistance arteries were isolated from low-salt fed adult male SS/Jr rats and SHRs, or their respective controls, for isometric wire myography. Vessels were challenged with cumulative concentrations of various vasoactive substances, in the absence or presence of nitric oxide synthase or cyclooxygenase inhibitors. Despite showing some differences in their responses to various vasoactive substances, both SS/Jr rats and SHRs exhibited key features of vascular dysfunction, including endothelial dysfunction and hyperresponsiveness to vasocontractile agonists. In conclusion, this study provides evidence to support the utility of the SS/Jr rat strain maintained on a low-salt diet as a valid experimental model for vascular dysfunction, a key feature of human hypertension.

The Obligatory Role of the Acetylcholine-Induced Endothelium-Dependent Contraction in Hypertension: Can Arachidonic Acid Resolve this Inflammation?

The endothelium produces many substances that can regulate vascular tone. Acetylcholine is a widely used pharmacological tool to assess endothelial function. In general, acetylcholine binds to G-protein coupled muscarinic receptors that mediate a transient elevation in intracellular, free calcium. This intracellular rise in calcium is responsible for triggering several cellular responses, including the synthesis of nitric oxide, endothelium- derived hyperpolarizing factor, and eicosanoids derived from arachidonic acid. Endothelial arachidonic acid metabolism is also an important signaling pathway for mediating inflammation. Therefore, in conditions with sustained and excessive inflammation such as hypertension, arachidonic acid serves as a substrate for the synthesis of several vasoconstrictive metabolites, predominantly via the cyclooxygenase and lipoxygenase enzymes. Cyclooxygenase and lipoxygenase products can then activate G-protein coupled receptors expressed on vascular smooth muscle cells to causes contractile responses. As a result, acetylcholine-induced contraction due to arachidonic acid is a commonly observed feature of endothelial dysfunction and vascular inflammation in hypertension. In this review, we will critically analyze the literature supporting this concept, as well as address the potential underlying mechanisms, including the possibility that arachidonic acid signaling is diverted away from the synthesis of pro-resolving metabolites in conditions such as hypertension.

A Single Resistance Exercise Session Improves Aortic Endothelial Function in Hypertensive Rats

BACKGROUND

Physical exercise is an important tool for the improvement of endothelial function.

OBJECTIVE

To assess the effects of acute dynamic resistance exercise on the endothelial function of spontaneously hypertensive rats (SHR).

METHODS

Ten minutes after exercise, the aorta was removed to evaluate the expression of endothelial nitric oxide synthase (eNOS), phosphorylated endothelial nitric oxide synthase (p-eNOS1177) and inducible nitric oxide synthase (iNOS) and to generate concentration-response curves to acetylcholine (ACh) and to phenylephrine (PHE). The PHE protocol was also performed with damaged endothelium and before and after NG-nitro-L-arginine methyl ester (L-NAME) and indomethacin administration. The maximal response (Emax) and the sensitivity (EC50) to these drugs were evaluated.

RESULTS

ACh-induced relaxation increased in the aortic rings of exercised (Ex) rats (Emax= -80 ± 4.6%, p < 0.05) when compared to those of controls (Ct) (Emax = -50 ± 6.8%). The Emax to PHE was decreased following exercise conditions (95 ± 7.9%, p < 0.05) when compared to control conditions (120 ± 4.2%). This response was abolished after L-NAME administration or endothelial damage. In the presence of indomethacin, the aortic rings' reactivity to PHE was decreased in both groups (EC50= Ex -5.9 ± 0.14 vs. Ct -6.6 ± 0.33 log µM, p < 0.05 / Emax = Ex 9.5 ± 2.9 vs. Ct 17 ± 6.2%, p < 0.05). Exercise did not alter the expression of eNOS and iNOS, but increased the level of p-eNOS.

CONCLUSION

A single resistance exercise session improves endothelial function in hypertensive rats. This response seems to be mediated by increased NO production through eNOS activation.

Macro- and microvascular endothelial dysfunction in diabetes

Endothelial cells, as well as their major products nitric oxide (NO) and prostacyclin, play a key role in the regulation of vascular homeostasis. Diabetes mellitus is an important risk factor for cardiovascular disease. Diabetes-induced endothelial dysfunction is a critical and initiating factor in the genesis of diabetic vascular complications. The present review focuses on both large blood vessels and the microvasculature. The endothelial dysfunction in diabetic macrovascular complications is characterized by reduced NO bioavailability, poorly compensated for by increased production of prostacyclin and/or endothelium-dependent hyperpolarizations, and increased production or action of endothelium-derived vasoconstrictors. The endothelial dysfunction of microvascular complications is primarily characterized by decreased release of NO, enhanced oxidative stress, increased production of inflammatory factors, abnormal angiogenesis, and impaired endothelial repair. In addition, non-coding RNAs (microRNAs) have emerged as participating in numerous cellular processes. Thus, this reviews pays special attention to microRNAs and their modulatory role in diabetes-induced vascular dysfunction. Some therapeutic strategies for preventing and restoring diabetic endothelial dysfunction are also highlighted.

Endothelial dysfunction and vascular disease - a 30th anniversary update

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

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Suppression of endoplasmic reticulum stress improves endothelium-dependent contractile responses in aorta of the spontaneously hypertensive rat

A contributing factor to increased peripheral resistance seen during hypertension is an increased production of endothelium-derived contractile factors (EDCFs). The main EDCFs are vasoconstrictor prostanoids, metabolites of arachidonic acid (AA) produced by Ca(2+)-dependent cytosolic phospholipase A2 (cPLA2) following phosphorylation (at Ser(505)) mediated by extracellular signal-regulated kinase (ERK1/2) and cyclooxygenase (COX) activations. Although endoplasmic reticulum (ER) stress has been shown to contribute to pathophysiological alterations in cardiovascular diseases, the relationship between ER stress and EDCF-mediated responses remains unclear. We tested the hypothesis that ER stress plays a role in EDCF-mediated responses via activation of the cPLA2/COX pathway in the aorta of the spontaneously hypertensive rat (SHR). Male SHR and Wistar-Kyoto rats (WKY) were treated with ER stress inhibitor, tauroursodeoxycholic acid or 4-phenlybutyric acid (TUDCA or PBA, respectively, 100 mg·kg(-1)·day(-1) ip) or PBS (control, 300 μl/day ip) for 1 wk. There was a decrease in systolic blood pressure in SHR treated with TUDCA or PBA compared with control SHR (176 ± 3 or 181 ± 5, respectively vs. 200 ± 2 mmHg). In the SHR, treatment with TUDCA or PBA normalized aortic (vs. control SHR) 1) contractions to acetylcholine (ACh), AA, and tert-butyl hydroperoxide, 2) ACh-stimulated releases of prostanoids (thromboxane A2, PGF2α, and prostacyclin), 3) expression of COX-1, 4) phosphorylation of cPLA2 and ERK1/2, and 5) production of H2O2. Our findings demonstrate a novel interplay between ER stress and EDCF-mediated responses in the aorta of the SHR. Moreover, ER stress inhibition normalizes such responses by suppressing the cPLA2/COX pathway.

Bone marrow transplantation improves endothelial function in hypertensive Dahl salt-sensitive rats

Bone marrow-derived endothelial progenitor cells (EPCs) constitute an important endogenous system in the maintenance of endothelial integrity and vascular homeostasis. Cardiovascular risk factors are associated with a reduced number and functional capacity of EPCs. Here we investigated the effect of transplantation of bone marrow-derived cells from Dahl salt-resistant rat into age-matched Dahl salt-sensitive (DS) rat on blood pressure, endothelial function, and circulating EPC number. The recipient DS rats were fed a normal (0.5% NaCl, NS) or high-salt (4% NaCl, HS) diet for 6 weeks after bone marrow transplantation (BMT). DS rats on a NS or a HS diet without BMT were used as controls. Hypertensive DS (HS-DS) rat (systolic blood pressure: 213 ± 4 mm Hg vs. 152 ± 4 mm Hg in NS, P < .05) manifested impaired endothelium-dependent relaxation to acetylcholine (EDR), increased gene expression of vascular oxidative stress and proinflamamtory cytokines, and decreased eNOS expression. BMT on HS-DS rat significantly improved EDR and eNOS expression, reduced oxidative stress without reduction in SBP (206 ± 6 mm Hg). Flow cytometry analysis showed that there was no difference in the number of circulating EPCs, demonstrated by expression of EPC markers CD34, cKit, and vascular endothelial growth factor, between hypertensive and normotensive rats. Surprisingly, BMT resulted in a 5- to 10-fold increase in the previously mentioned EPC markers in hypertensive, but not normotensive rat. These results suggest that DS rat has an impaired ability to increase bone marrow-derived EPCs in response to HS diet challenge, which may contribute to endothelial dysfunction.

Mismatch between peripheral and central demands in salt-sensitive hypertensive Dahl rats

Sympathetic nerve activity in essential hypertension, which accounts for 90% of all hypertension cases, is in general thought to be elevated regardless of whether there is salt sensitivity or insensitivity. The cause is thought to be an abnormality in the sympathetic center. On the other hand, neuronal nitric oxide synthase-expressing neurons that function to inhibit the sympathetic center are clearly activated in the salt-sensitive hypertensive Dahl rat model. How is this related to sympathetic hyperactivity and hypertension? Also, how is hypertension associated with peripheral vessel contractility and renal function? Human life is supported by the body's various essential functions. The circulatory system links all these functions into one system that cannot be separated. Blood pressure is the driving force of this circulatory system, and both the central and peripheral demands determine the output. We examined the 'mismatch' between these two sides and its association with hypertension.

Long-term blood pressure control: is there a set-point in the brain?

Mean arterial pressure fluctuates depending on physical or psychological activity, but should be stable at rest at around 100 mmHg throughout an entire life in human. The causes of hypertension and the blood pressure regulation mechanisms have been discussed for a long time, and many aspects have recently become more clear. Circulatory shock or short-term hypotension can be treated based on what is now known, but chronic hypertension is still difficult to treat thoroughly. The exact mechanisms for long-term blood pressure regulation have yet not been elucidated. Neuro–humoral interaction has been suggested as one of the mechanisms. Then, from the 1990s, paracrine hormones like nitric oxide or endothelins have been extensively researched in order to develop endothelial local control mechanisms for blood pressure, which have some relationships to long-term control. Although these new ideas and mechanisms are newly developed, no clear explanation for long-term control has yet been discussed, except for renal abnormality. Recently, a central set-point theory has begun to be discussed. This review will discuss the mechanisms for long-term blood pressure control, based on putative biological missions of circulatory function for life support.

The role of RhoA/Rho kinase pathway in endothelial dysfunction

Endothelial dysfunction is a key event in the development of vascular disease, and it precedes clinically obvious vascular pathology. Abnormal activation of the RhoA/Rho kinase (ROCK) pathway has been found to elevate vascular tone through unbalancing the production of vasodilating and vasoconstricting substances. Inhibition of the RhoA/ROCK pathway can prevent endothelial dysfunction in a variety of pathological conditions. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of the ROCK pathway and its roles in endothelial dysfunction.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction. Their use is attractive, as they can address arterial blood pressure and vascular tone simultaneously. The severity of endothelial dysfunction correlates with the development of coronary artery disease and predicts future cardiovascular events. Thus, endothelial dysfunction needs to be considered as a strategic target in the treatment of hypertension.

Endothelial dysfunction and vascular disease

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

Endothelial dysfunction: a multifaceted disorder (The Wiggers Award Lecture)

Endothelial cells synthesize and release various factors that regulate angiogenesis, inflammatory responses, hemostasis, as well as vascular tone and permeability. Endothelial dysfunction has been associated with a number of pathophysiological processes. Oxidative stress appears to be a common denominator underlying endothelial dysfunction in cardiovascular diseases. However, depending on the pathology, the vascular bed studied, the stimulant, and additional factors such as age, sex, salt intake, cholesterolemia, glycemia, and hyperhomocysteinemia, the mechanisms underlying the endothelial dysfunction can be markedly different. A reduced bioavailability of nitric oxide (NO), an alteration in the production of prostanoids, including prostacyclin, thromboxane A2, and/or isoprostanes, an impairment of endothelium-dependent hyperpolarization, as well as an increased release of endothelin-1, can individually or in association contribute to endothelial dysfunction. Therapeutic interventions do not necessarily restore a proper endothelial function and, when they do, may improve only part of these variables.

Endothelium-dependent contractions occur in the aorta of wild-type and COX2-/- knockout but not COX1-/- knockout mice

The present experiments were designed to determine whether or not endothelium-dependent contractions can be evoked in the aorta of the mouse, and if so, whether or not deleting the COX1 gene affects the response. Sex differences in the response were also examined. Rings of murine aorta were suspended in a Halpern-Mulvany myograph for recording of isometric force. In the aorta of the male wild type C57BL/b6 mice (36-40 weeks old), both acetylcholine and the calcium ionophore caused endothelium-dependent increases in force in the presence of L-NAME, and these were inhibited by valeryl salicylate (a selective COX1 inhibitor) and S18886 (a selective antagonist of TP receptors). Such endothelium-dependent contraction was absent in the aorta of COX1 knockout mice and present in that of COX2 knockout mice. Similar results were obtained in aortas of female wild-type, COX2 and COX1 knockout mice. These experiments reveal the existence of EDCF-mediated contractions in arteries of the mouse. These contractions, as in the aorta of the spontaneously hypertensive rat, are caused by endogenous agonists(s) of TP receptors produced by cyclooxygenase 1, because they are observed in the aortas of COX2 knockout mice but not in aortas of COX1 knockout mice. The present study provides direct evidence that COX1 is indeed the isoform of cyclooxygenase responsible for the production of EDCF.

Hydrogen peroxide is an endothelium-dependent contracting factor in rat renal artery

In addition to endothelium-derived relaxing factor and hyperpolarizing factor, vascular endothelium also modulates smooth muscle tone by releasing endothelium-derived contracting factor(s) (EDCF), but the identity of EDCF remains obscure. We studied here the involvement of hydrogen peroxide (H2O2) in endothelium-dependent contraction (EDC) of rat renal artery to acetylcholine (ACh). ACh (10(-6), 10(-5), and 10(-4) M) induced a transient contraction of rat renal artery with intact endothelium in a concentration-related manner, but not in the artery with endothelium removed. In phenylephrine-precontracted renal arteries, ACh induced an endothelium-dependent relaxation response at lower concentrations (10(-8)-10(-6) M), and a relaxation followed by a contraction at higher concentrations (10(-5) M). Inhibition of nitric oxide synthase by N(omega)-nitro-L-arginine (10(-4) M) enhanced the EDC to ACh. Catalase (1000 U ml(-1)) reduced the EDC to ACh. H2O2 (10(-6), 10(-5), and 10(-4) M) induced a similar transient contraction of the renal arteries as ACh, but in an endothelium-independent manner. Inhibition of NAD(P)H oxidase and cyclooxygenase by diphenylliodonium chloride and diclofenac greatly attenuated ACh-induced EDC, while inhibition of xanthine oxidase (allopurinol) and cytochrome P450 monooxygenase (17-octadecynoic acid) did not affect the contraction. Antagonist of thromboxane A2 and prostaglandin H2 receptors (SQ 29548) and thromboxane A2 synthase inhibitor (furegrelate) attenuated the contraction to ACh and to H2O2. In isolated endothelial cells, ACh (10(-5) M) induced a transient H2O2 production detected with a fluorescence dye sensitive to H2O2 (2',7'-dichlorofluorescein diacetate). The peak concentration of H2O2 was 5.1 x 10(-4) M at 3 min and was prevented by catalase. Taken together, these results show that ACh triggers H2O2 production through NAD(P)H oxidase activation in the endothelial cells, and that ACh and H2O2 share the same signaling pathway in causing smooth muscle contraction. Therefore, H2O2 is most likely the EDCF in rat renal artery in response to ACh stimulation.

Acetylcholine causes endothelium-dependent contraction of mouse arteries

The goal of this study was to determine whether acetylcholine evokes endothelium-dependent contraction in mouse arteries and to define the mechanisms involved in regulating this response. Arterial rings isolated from wild-type (WT) and endothelial nitric oxide (NO) synthase knockout (eNOS−/−) mice were suspended for isometric tension recording. In abdominal aorta from WT mice contracted with phenylephrine, acetylcholine caused a relaxation that reversed at the concentration of 0.3–3 μM. After inhibition of NO synthase [with Nω-nitro-l-arginine methyl ester (l-NAME), 1 mM], acetylcholine (0.1–10 μM) caused contraction under basal conditions or during constriction to phenylephrine, which was abolished by endothelial denudation. This contraction was inhibited by the cyclooxygenase inhibitor indomethacin (1 μM) or by a thromboxane A2 (TxA2) and/or prostaglandin H2 receptor antagonist SQ-29548 (1 μM) and was associated with endothelium-dependent generation of the TxA2 metabolite TxB2. Also, SQ-29548 (1 μM) abolished the reversal in relaxation evoked by 0.3–3 μM acetylcholine and subsequently enhanced the relaxation to the agonist. The magnitude of the endothelium-dependent contraction to acetylcholine (0.1–10 μM) was similar in aortas from WT mice treated in vitro with l-NAME and from eNOS−/− mice. In addition, we found that acetylcholine (10 μM) also caused endothelium-dependent contraction in carotid and femoral arteries of eNOS−/− mice. These results suggest that acetylcholine initiates two competing responses in mouse arteries: endothelium-dependent relaxation mediated predominantly by NO and endothelium-dependent contraction mediated most likely by TxA2.

Hypertension increases the participation of vasoconstrictor prostanoids from cyclooxygenase-2 in phenylephrine responses

OBJECTIVE

The present study was designed to analyse whether hypertension alters the involvement of cyclooxygenase-2-derived mediators in phenylephrine-induced vasoconstrictor responses.

METHODS

Vascular reactivity experiments were performed in aortic segments from normotensive, Wistar-Kyoto, and spontaneously hypertensive rats (SHR); protein expression was measured by western blot and/or immunohistochemistry, and prostaglandin F2alpha (PGF2alpha), 8-isoprostane and prostacyclin release were determined by enzyme immunoassay commercial kits.

RESULTS

The protein synthesis inhibitor dexamethasone (1 micromol/l), the non-selective cyclooxygenase inhibitor indomethacin (10 micromol/l), the selective cyclooxygenase-2 inhibitor NS 398 (1 micromol/l), and the thromboxane A2/prostaglandin H2 (TP) receptor antagonist SQ 29,548 (1 micromol/l), reduced the concentration-response curves to phenylephrine more in segments from hypertensive than from normotensive rats; however, the thromboxane A2 (TxA2) synthase inhibitors furegrelate (10 micromol/l) and OKY 046 (1 and 10 micromol/l) had no effect in either strain. Removing endothelium or adding dexamethasone almost abolished the NS 398 effect. Cyclooxygenase-2 protein expression, which was reduced by dexamethasone, was higher in aorta from hypertensive animals. In both strains cyclooxygenase-2 was localized mainly in endothelial cells and adventitial fibroblasts. 13,14-Dihydro-15-keto-PGF2alpha, 6-keto-PGF1alpha and 8-isoprostane levels were greater in the medium from hypertensive than from normotensive rats; NS 398 decreased levels of the three metabolites studied only in the medium from SHR.

CONCLUSIONS

PGF2alpha and 8-isoprostane seem to be involved in the response to phenylephrine in rat aorta; this involvement is greater in hypertensive rats, probably due to a higher endothelial induction of cyclooxygenase-2.

Endothelium-dependent contractions in hypertension

1. Endothelial cells, under given circumstances, can initiate contraction (constriction) of the vascular smooth muscle cells that surround them. Such endothelium-dependent, acute increases in contractile tone can be due to the withdrawal of the production of nitric oxide, to the production of vasoconstrictor peptides (angiotensin II, endothelin-1), to the formation of oxygen-derived free radicals (superoxide anions) and/or the release of vasoconstrictor metabolites of arachidonic acid. The latter have been termed endothelium-derived contracting factor (EDCF) as they can contribute to moment-to-moment changes in contractile activity of the underlying vascular smooth muscle cells. 2. To judge from animal experiments, EDCF-mediated responses are exacerbated by aging, spontaneous hypertension and diabetes. 3. To judge from human studies, they contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients. 4. Since EDCF causes vasoconstriction by activation of the TP-receptors on the vascular smooth muscle cells, selective antagonists at these receptors prevent endothelium-dependent contractions, and curtail the endothelial dysfunction in hypertension and diabetes.

Effects of thiol antioxidant on reduced nicotinamide adenine dinucleotide phosphate oxidase in hypertensive Dahl salt-sensitive rats

Recent studies implicate of reactive oxygen species (ROS) in hypertension; however, whether reactive oxygen species promote hypertensive derangements is not fully clear. We thus investigated the effects of an antioxidant, N-acetyl-L-cysteine, on hypertensive Dahl salt-sensitive rats. High-salt intake for 4 weeks markedly elevated systolic arterial pressure, urinary excretion of protein, 8-isoprostane, and H(2)O(2), and the enzyme activity of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase along with the elevated expression of its subunits gp91phox and p47phox at the levels of mRNA and protein. Supplement with N-acetyl-L-cysteine reduced the increase in systolic arterial pressure and counteracted the elevation of urinary excretion of protein, 8-isoprostane, and H(2)O(2), and the increases in NADPH oxidase activity/expression in high-salt-loaded Dahl salt-sensitive rats. N-acetyl-L-cysteine supplement ameliorated plasma and urinary levels of thromboxane B(2) (an end metabolite of thromboxane A(2)), associated with improvement of both the abnormal contraction and the impaired nitric oxide-dependent relaxation in renal arteries. These results revealed that oxidative stress mediates hypertensive changes in Dahl salt-sensitive rats, because thiol antioxidant N-acetyl-L-cysteine attenuated the augmentation of local ROS production by diminishing the elevation of NADPH oxidase expression and ameliorated renal/vascular hypertensive changes.

Response of the left anterior descending coronary artery to acetylcholine in patients with chest pain and angiographically normal coronary arteries

Because atherosclerotic plaque burden affects the likelihood of plaque rupture, it is important to determine the presence and extent of atherosclerotic plaque. We hypothesized that endothelial dysfunction becomes more prominent with development of atherosclerotic plaque; therefore, we examined the relation between coronary endothelial dysfunction and the presence of atherosclerotic plaque. In 36 patients with normal coronary arteries, acetylcholine (ACh; 3 and 30 microg/min) and nitroglycerin were infused into the left coronary ostium, and the diameter of the left anterior descending (LAD) coronary artery was quantitatively measured in response to each drug. The plaque burden was measured in the same segment using intravascular ultrasonography. The plaque burden was 31.2 +/- 2.1% and correlated inversely with changes in coronary diameter induced by 3 microg/min of ACh (r = -0.754, p <0.0001), 30 microg/min of ACh (r = -0.552, p = 0.0005), and nitroglycerin (r = -0.531, p = 0.0009). Multivariate regression analysis showed that the change in coronary diameter induced by 3 microg/min of ACh was associated with plaque burden, independent of the effects of nitroglycerin-induced dilation. Receiver-operating characteristics analysis demonstrated that a cut-off value for the change in coronary diameter induced by 3 microg/min of ACh for predicting a plaque burden of >30% was 0%, with a sensitivity of 0.82 and a specificity of 0.95. These findings suggest that coronary endothelial dysfunction is correlated with atherosclerotic plaque burden, indicating that atherosclerotic plaque may be detected based on coronary endothelial function as assessed by low-dose ACh infusion.

Vitamin C lowers blood pressure and alters vascular responsiveness in salt-induced hypertension

The present study was undertaken to investigate the effect of vitamin C treatment on blood pressure and vascular reactivity in salt-induced hypertension. Male Sprague-Dawley rats were fed a normal rat diet, a high-sodium (8% NaCl) diet, a normal rat diet plus vitamin C treament (100 mg x kg(-1) x day(-1)), or a high-sodium diet plus vitamin C treatment for 6 weeks. Salt loading significantly increased blood pressure, which was attenuated by vitamin C treatment. Aortic rings from the different groups were suspended for isometric-tension recording. The contractile response to noradrenaline was significantly increased in the salt-loaded rats. Vitamin C reduced the sensitivity of aortic rings to noradrenaline in rats on normal and high-sodium diets. In noradrenaline-precontracted rings, the relaxation response to acetylcholine, which was attenuated in the salt-loaded rats, was restored by vitamin C treatment. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) abolished the enhanced response to acetylcholine caused by vitamin C. The results suggest that the antihypertensive effect of vitamin C is associated with a reduction in vascular sensitivity to noradrenaline and enhancement of endothelium-dependent relaxation due to increased nitric oxide bioavailability.

Alpha-lactorphin and beta-lactorphin improve arterial function in spontaneously hypertensive rats

alpha-lactorphin (Tyr-Gly-Leu-Phe) lowers blood pressure in conscious adult SHR. This tetrapeptide is originally released from milk protein alpha-lactalbumin by enzymatic hydrolysis. In order to evaluate the antihypertensive mechanisms of alpha-lactorphin, the effects of the tetrapeptide on vascular function were investigated in (30-35 weeks old) spontaneously hypertensive rats (SHR) with established hypertension and age-matched normotensive Wistar-Kyoto (WKY) rats in vitro. In addition, we studied the vascular effects of another structurally related tetrapeptide, beta-lactorphin (Tyr-Leu-Leu-Phe), which originates from milk protein beta-lactoglobulin. Endothelium-dependent relaxation to acetylcholine (ACh) was reduced in mesenteric arterial preparations of SHR as compared to those of WKY. In SHR, the ACh-induced relaxation was augmented by alpha-lactorphin or beta-lactorphin. The role of nitric oxide (NO) is suggested, since this improvement was abolished by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Simultaneous potassium channel inhibitor tetraethylammonium (TEA) elicited no additional effect on the ACh-induced relaxation. The cyclooxygenase inhibitor diclofenac did not attenuate the augmented ACh relaxation induced by alpha-lactorphin or beta-lactorphin, suggesting that endothelial vasodilatory prostanoids were not involved in the effect of the tetrapeptides. Endothelium-independent relaxation to the NO donor sodium nitroprusside (SNP) was augmented in mesenteric arterial preparations of SHR by simultaneous beta-lactorphin. The tetrapeptides did not alter vascular responses in mesenteric arteries from WKY. In conclusion, both alpha-lactorphin and beta-lactorphin improved vascular relaxation in adult SHR in vitro. The beneficial effect of alpha-lactorphin was directed towards endothelial function, whereas beta-lactorphin also enhanced endothelium-independent relaxation.

Sex-specific acute effect of estrogen on endothelium-derived contracting factor in the renal artery of hypertensive Dahl rats

OBJECTIVE

To determine whether estrogen rapidly affects endothelium-derived contracting factor (EDCF) in the renal artery of hypertensive Dahl rats, and whether factors other than nitric oxide (NO) contribute to the effect of estrogen.

DESIGN

Acute effects of estrogen on the acetylcholine-induced vasomotor responses and on prostaglandin H2/thromboxane A2 mimetic, U46619,-induced contraction were examined in isolated arterial rings.

METHODS AND RESULTS

Dahl salt-sensitive male and female rats were fed an 8% NaCl diet for 4 weeks. The blood pressure increased more rapidly and to a greater extent in males than in females. Renal arterial rings were prepared for isometric tension recording. 17beta-Estradiol, but not the biologically less active stereoisomer, 17alpha-estradiol, improved the relaxation response to acetylcholine in renal arteries from females. Estrogen also rapidly decreased the contraction evoked by acetylcholine (10(-6) to approximately 10(-4) mol/l) in renal arteries from females and it was effective at a physiological concentration (10(-9) mol/l) in the presence of Nomega-nitro-l-arginine methyl ester (an NO synthase inhibitor). The estrogen receptor antagonist, ICI 182,780, abolished the effect of estrogen, whereas the cytochrome P450 inhibitor, miconazole, had no effect. The contraction induced by U46619 was also suppressed by estrogen, without any contribution from NO. Estrogen had no effect on either relaxation or contraction responses in renal arteries from males.

CONCLUSION

17beta-Estradiol antagonizes increases in vascular tone in hypertensive females by enhancing NO-dependent relaxation, and by suppressing EDCF-mediated mechanisms in an NO-independent manner.

Heart, aging, and hypertension

Hypertension and aging adversely affect cardiovascular system and the heart is invariably involved. Manifestations of hypertensive heart disease and of the aging heart appear similar; ventricular hypertrophy, myocardial fibrosis, and impairments in ventricular function and coronary hemodynamics characterize both conditions. However, a great deal of evidence suggests that different underlying pathophysiological mechanisms may be involved. This report discusses most recent clinical and experimental findings and focuses on the alterations in nonmyocytic elements that are a part of heart involvement. Particular attention was given to factors that are responsible for exaggerated myocardial deposition of collagen that, by itself, may be responsible for ventricular dysfunction and impaired coronary hemodynamics in hypertensive and aging hearts. Newly developed therapeutical strategies, based on the most recent experimental and clinical studies, are also discussed.

L-Arginine improves endothelial function in renal artery of hypertensive Dahl rats

OBJECTIVES

To clarify whether endothelium-derived contracting factor (EDCF) is developed in renal artery of hypertensive Dahl rats and whether prolonged oral L-arginine treatments prevent development of EDCF and hypertension.

DESIGN

The effect of prolonged salt treatment with or without L-arginine on the renal artery was examined.

METHODS AND RESULTS

Dahl salt-sensitive and -resistant rats were fed a 0.4 or an 8% NaCl diet for 4 weeks. High sodium intake increased arterial pressure in Dahl salt-sensitive rats. The rings of renal arteries were suspended for isometric tension recording. Only in the hypertensive rats, more than 1 micromol/l acetylcholine induced an endothelium-dependent contraction response. The contraction was completely inhibited by indomethacin or ONO-3708 [prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist], and partially inhibited by OKY-046 (TXA2 synthetase inhibitor). Acetylcholine-induced relaxation was significantly depressed in hypertensive rats, which was partially improved by SQ29548 (PGH2/TXA2 receptor antagonist). Oral L-arginine, but not ONO-8809 (orally active PGH2/TXA2 receptor antagonist) treatment, inhibited the contraction and amended the relaxation. The endothelium-independent contraction to TXA2 receptor agonist U46619 and relaxation to nitroprusside were not altered by L-arginine treatment The L-Arginine treatment reduced blood pressure and sodium retention with increases in urinary NO2-/NO3- and cGMP excretion. Hydralazine treatment also inhibited development of EDCF.

CONCLUSIONS

The present results suggest that impaired endothelium-dependent relaxation to acetylcholine is caused in part by induction of EDCF synthesis/release in renal arteries of hypertensive Dahl rats. L-arginine can attenuate sodium retention and development of hypertension, which lead to a decrease in EDCF synthesis in renal arteries.

Impaired relaxation to acetylcholine in 2K-1C hypertensive rat aortas involves changes in membrane hyperpolarization instead of an abnormal contribution of endothelial factors

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33+/-3.36%; pD(2): 7.050+/-0.03] than in 2K (ME: 95.26+/-1.59%; pD(2): 7.31+/-0.07). This response was abolished by N(G)-nitro-L-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21+/-9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61+/-8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50+/-5.64% vs. 41.60+/-4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the pD(2) values (7.72+/-0.20 vs. 8.59+/-0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (-41.57+/-1.19 vs. -51.00+/-1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00+/-0.66 vs. 13.27+/-1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32+/-0.06 to 1.90+/-0.21 g) than 2K (from 1.49+/-0.07 to 2.83+/-0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85+/-0.18 g) and were lower in 2K (2.18+/-0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.