Physiological Regulation Of Vascular Tone Research Articles

From ABCD to E for endothelin in resistant hypertension

The potent vasoconstrictor peptide endothelin-1 has long been recognized as a physiological regulator of vascular tone. However, pharmacological blockade of the endothelin-1 pathway has few proven indications thus far. A recent clinical trial for resistant hypertension published in The Lancet may yet herald a new era for endothelin receptor antagonists into the clinical mainstream.

Cyclic GMP-Dependent Regulation of Vascular Tone and Blood Pressure Involves Cysteine-Rich LIM-Only Protein 4 (CRP4).

The cysteine-rich LIM-only protein 4 (CRP4), a LIM-domain and zinc finger containing adapter protein, has been implicated as a downstream effector of the second messenger 3′,5′-cyclic guanosine monophosphate (cGMP) pathway in multiple cell types, including vascular smooth muscle cells (VSMCs). VSMCs and nitric oxide (NO)-induced cGMP signaling through cGMP-dependent protein kinase type I (cGKI) play fundamental roles in the physiological regulation of vascular tone and arterial blood pressure (BP). However, it remains unclear whether the vasorelaxant actions attributed to the NO/cGMP axis require CRP4. This study uses mice with a targeted deletion of the CRP4 gene (CRP4 KO) to elucidate whether cGMP-elevating agents, which are well known for their vasorelaxant properties, affect vessel tone, and thus, BP through CRP4. Cinaciguat, a NO- and heme-independent activator of the NO-sensitive (soluble) guanylyl cyclase (NO-GC) and NO-releasing agents, relaxed both CRP4-proficient and -deficient aortic ring segments pre-contracted with prostaglandin F2α. However, the magnitude of relaxation was slightly, but significantly, increased in vessels lacking CRP4. Accordingly, CRP4 KO mice presented with hypotonia at baseline, as well as a greater drop in systolic BP in response to the acute administration of cinaciguat, sodium nitroprusside, and carbachol. Mechanistically, loss of CRP4 in VSMCs reduced the Ca2+-sensitivity of the contractile apparatus, possibly involving regulatory proteins, such as myosin phosphatase targeting subunit 1 (MYPT1) and the regulatory light chain of myosin (RLC). In conclusion, the present findings confirm that the adapter protein CRP4 interacts with the NO-GC/cGMP/cGKI pathway in the vasculature. CRP4 seems to be part of a negative feedback loop that eventually fine-tunes the NO-GC/cGMP axis in VSMCs to increase myofilament Ca2+ desensitization and thereby the maximal vasorelaxant effects attained by (selected) cGMP-elevating agents.

Acute glucose influx-induced mitochondrial hyperpolarization inactivates myosin phosphatase as a novel mechanism of vascular smooth muscle contraction

It is well-established that long-term exposure of the vasculature to metabolic disturbances leads to abnormal vascular tone, while the physiological regulation of vascular tone upon acute metabolic challenge remains unknown. Here, we found that acute glucose challenge induced transient increases in blood pressure and vascular constriction in humans and mice. Ex vivo study in isolated thoracic aortas from mice showed that glucose-induced vascular constriction is dependent on glucose oxidation in vascular smooth muscle cells. Specifically, mitochondrial membrane potential (ΔΨm), an essential component in glucose oxidation, was increased along with glucose influx and positively regulated vascular smooth muscle tone. Mechanistically, mitochondrial hyperpolarization inhibited the activity of myosin light chain phosphatase (MLCP) in a Ca2+-independent manner through activation of Rho-associated kinase, leading to cell contraction. However, ΔΨm regulated smooth muscle tone independently of the small G protein RhoA, a major regulator of Rho-associated kinase signaling. Furthermore, myosin phosphatase target subunit 1 (MYPT1) was found to be a key molecule in mediating MLCP activity regulated by ΔΨm. ΔΨm positively phosphorylated MYPT1, and either knockdown or knockout of MYPT1 abolished the effects of glucose in stimulating smooth muscle contraction. In addition, smooth muscle-specific Mypt1 knockout mice displayed blunted response to glucose challenge in blood pressure and vascular constriction and impaired clearance rate of circulating metabolites. These results suggested that glucose influx stimulates vascular smooth muscle contraction via mitochondrial hyperpolarization-inactivated myosin phosphatase, which represents a novel mechanism underlying vascular constriction and circulating metabolite clearance.

Nitric oxide in patients with chronic chagas disease

Among the main causes of death around the world, we can highlight those caused by cardiovascular diseases, which have been growing significantly. The knowledge of the pathophysiology of cardiovascular diseases evidences the involvement of inflammatory processes, acute or chronic, with action of pro-inflammatory and vasoactive factors. One of these factors is nitric oxide (NO), a potent vasodilator that acts on the physiological regulation of vascular tone and has its serum levels altered in the presence of cardiovascular event, representing a physiological compensatory mechanism, to be included in Chagas disease. Method: Peripheral blood samples from 2 patients (men, mean age 65 years) with positive Chagas; disease serology (cardiac form, chronic phase) were collected at the cardiology outpatient service of the Hospital Electro Bonini (UNAERP). Two healthy volunteer participants were used as a negative control. NO (NO 2- / NO 3-) levels were determined by a quantitative detection kit for nitrate and nitrite concentrations using colorimetric assay. Absorbance was read at 540 nm. Partial Results: The median NO activity was 1.4 umol/L in chagasic patients and 1.0 umol/L in healthy participants (p <0.001). Discussion and conclusion of the results: The cardiac form of Chagas Disease, a condition caused by the chronic infection of the protozoan Trypanossoma cruzi and marked by chronic inflammation and progressive myocardial cell damage, has progressed with new endemic areas throughout the world, although its incidence has decreased last years. The parasite compromises the energetic synthesis of cardiac myocytes without altering the mitochondrial ultrastructure. It is reported that the parasite can control the central structure of the organelle in order to obtain substrate for its proliferation. Therefore, it has become relevant to investigate the relationship of serum NO concentration with cardiovascular diseases, due to the importance of vasoactive factor and the subject for public health. Developing knowledge that allows better understanding of oxidative stress in the presence of T. cruzi infection and associating them with inflammatory mechanisms culminates in the elucidation of this chronic pathology.

Acid stress reduces the function of Na+-K+-ATPase in superior mesenteric artery of Capra hircus

Context: Extracellular hydrogen ion concentration (pH o ) is an important physiological regulator of vascular tone, maintained within 7.35–7.45 and any change in it leads to complex health problem including maintenance of normal blood pressure. Aims: This study aims to examine the altered function of Na + -K + pump and inward rectifier potassium channels (K ir ) channels in extracellular acidosis in goat superior mesenteric artery (GSMA). Subjects and Methods: Isolated GSMA rings were mounted in an automatic organ bath containing 20-ml modified Krebs–Henseleit solution at pH 7.4/6.8/6.0 and KCl-induced contraction was elicited either in the absence or presence of ouabain, barium (Ba 2+ ), and combination of ouabain and Ba 2+ . Rings were dilated with potassium chloride either in the absence or presence of ouabain, Ba 2+ and combination of ouabain and Ba 2+ while maintaining at acidic pH. The responses were recorded isometrically by highly sensitive isometric force transducer connected to Powerlab and analyzed using LabChart 7.1.3 software. Statistical Analysis Used: Data were analyzed in GraphPad Prism 5 software. Results: K + vasorelaxation response in K + -free solution precontracted rings the percent maximal response (93.57 ± 2.57%, 62.60 ± 3.56%, and 53.38 ± 5.41%) was decreased with decrease pH o (7.4, 6.8 and 6.0). Ouabain, Ba 2+ , and ouabain and Ba 2+ inhibited the maximal vasorelaxation of potassium chloride (26.20 ± 3.48%, 17.39 ± 0.54%, 31.92 ± 1.10%) at pH o 7.4, (42.74 ± 2.48%, 16.12 ± 3.49%, 22.32 ± 1.63%) at pH o 6.8, and (53.87 ± 2.18%, 25.24 ± 2.90%, 39.71 ± 0.14%) at pH o 6.0, respectively. Conclusions: Attenuated vasodilation in acidosis is due to reduced function or expression of ouabain-sensitive sodium–potassium ATPase (Na + -K + -ATPase) and K ir channels. In clinical acidosis, agents augmenting the activity of Na + -K + -ATPase and K + -Channel could improve hypertensive crisis. Abbreviations used: Ba 2+ : Barium; E max : Percent maximal response; E Bmax : Percent maximal response in presence of antagonist; K ATP : Adenosine triphosphate-sensitive potassium channel; K ir : Inward rectifier potassium channels; K Ca : Calcium-activated potassium channels; Na + -K + -ATPase: Sodium–potassium ATPase; NO: Nitric oxide; pH i : Intracellular hydrogen ion concentration; pH o : Extracellular hydrogen ion concentration; VSMCs: Vascular smooth muscle cells.

Regulation of vascular tone and arterial blood pressure: role of chloride transport in vascular smooth muscle.

Recent studies suggest that primary changes in vascular resistance can cause sustained changes in arterial blood pressure. In this review, we summarize current knowledge about Cl(-) homeostasis in vascular smooth muscle cells. Within vascular smooth muscle cells, Cl(-) is accumulated above the electrochemical equilibrium, causing Cl(-) efflux, membrane depolarization, and increased contractile force when Cl(-) channels are opened. At least two different transport mechanisms contribute to raise [Cl(-)] i in vascular smooth muscle cells, anion exchange, and cation-chloride cotransport. Recent work suggests that TMEM16A-associated Ca(2+)-activated Cl(-) currents mediate Cl(-) efflux in vascular smooth muscle cells leading to vasoconstriction. Additional proteins associated with Cl(-) flux in vascular smooth muscle are bestrophins, which modulate vasomotion, the volume-activated LRRC8, and the cystic fibrosis transmembrane conductance regulator (CFTR). Cl(-) transporters and Cl(-) channels in vascular smooth muscle cells (VSMCs) significantly contribute to the physiological regulation of vascular tone and arterial blood pressure.

Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle.

Vascular smooth muscle tone is controlled by a balance between the cellular signaling pathways that mediate the generation of force (vasoconstriction) and release of force (vasodilation). The initiation of force is associated with increases in intracellular calcium concentrations, activation of myosin light-chain kinase, increases in the phosphorylation of the regulatory myosin light chains, and actin-myosin crossbridge cycling. There are, however, several signaling pathways modulating Ca(2+) mobilization and Ca(2+) sensitivity of the contractile machinery that secondarily regulate the contractile response of vascular smooth muscle to receptor agonists. Among these regulatory mechanisms involved in the physiological regulation of vascular tone are the cyclic nucleotides (cAMP and cGMP), which are considered the main messengers that mediate vasodilation under physiological conditions. At least four distinct mechanisms are currently thought to be involved in the vasodilator effect of cyclic nucleotides and their dependent protein kinases: (1) the decrease in cytosolic calcium concentration ([Ca(2+)]c), (2) the hyperpolarization of the smooth muscle cell membrane potential, (3) the reduction in the sensitivity of the contractile machinery by decreasing the [Ca(2+)]c sensitivity of myosin light-chain phosphorylation, and (4) the reduction in the sensitivity of the contractile machinery by uncoupling contraction from myosin light-chain phosphorylation. This review focuses on each of these mechanisms involved in cyclic nucleotide-dependent relaxation of vascular smooth muscle under physiological conditions.

DORADO: Opportunity Postponed

Treatment-resistant hypertension (TRH) describes a situation where blood pressure (BP) remains above target in spite of the concurrent use of 3 antihypertensive agents of different classes, with 1 of the agents a diuretic, and all ideally given at an optimized dose. TRH is a common clinical problem, perhaps occurring in 20% to 30% of participants in hypertension trials, and is likely to become increasingly common in the future because BP targets are reducing, and older age and obesity are 2 of the strongest risk factors for its occurrence.1 A number of interventions have been shown to reduce BP substantially in patients with TRH, and, with its growing prevalence and the excellent cost-effectiveness of current first-line treatments, it is increasingly becoming a valuable indication in its own right for newly licensed medicines. One such intervention that has shown promise in this indication is the use of endothelin receptor antagonists (ETRAs). In a major study (DORADO) published last year,2 the ETRA darusentan, at doses of 50, 100, and 300 mg daily, was studied in 379 patients with TRH using a randomized, double-blind, placebo-controlled design. Comorbidities in these patients included type 2 diabetes mellitus and chronic kidney disease. Reduction in the coprimary end points of seated systolic and diastolic BPs at week 14 of treatment were 17/10, 18/10, and 18/11 mm Hg with increasing doses of darusentan but significantly less with placebo at only 9/5 …

Focus on carbon monoxide: a modulator of neutrophil oxidants and elastase spatial localization?

GASEOUS SIGNAL MEDIATORS include nitric oxide (NO), hydrogen sulfide, and carbon monoxide (CO) (3, 20, 35). Both NO and hydrogen sulfide play important roles in inflammation, with the existing evidence supporting them as components of the normal biochemical milieu that stabilize the vasculature against leukocyte adhesion, extravasation, and vascular permeability (25, 35). Unlike G protein-coupled receptors, gasotransmitters are membrane-permeant gases that modulate several forms of cell signaling by chemically binding numerous intracellular targets (25, 26, 35, 36). CO is formed in several tissues through the action of two types of hemoxygenases (HOs): an inducible form HO-1 and constituitive forms HO-2 and -3 (HO-3 is involved in O2 sensing) (19). HO-1 is the 32-kDa form of HO, synthesized in response to heat stress (hence, heat shock protein32), oxidants, cytokines, and environmental stress (e.g., metals). HOs catabolize heme to bilivervidin (rapidly converted to bilirubin by biliverdin reductase), Fe 2 , and CO. While biliverdin and bilirubin formed by HO-1 and -2 are major antioxidants, with potency comparable with glutathione, many studies suggest that the induction of HO-1 expression in inflammation is adaptive through CO-mediated effects. CO is a potent physiological regulator of vascular tone, like NO, and exhibits some similar properties. For example, CO

Raloxifene protects endothelial cell function against oxidative stress

Maintaining a delicate balance between the generation of nitric oxide (NO) and removal of reactive oxygen species (ROS) within the vascular wall is crucial to the physiological regulation of vascular tone. Increased production of ROS reduces the effect and/or bioavailability of NO, leading to an impaired endothelial function. This study tested the hypothesis that raloxifene, a selective oestrogen receptor modulator, can prevent endothelial dysfunction under oxidative stress. Changes in isometric tension were measured in rat aortic rings. The content of cyclic GMP in aortic tissue was determined by radioimmunoassay. Phosphorylation of endothelial NOS (eNOS) and Akt was assayed by Western blot analysis. In rings with endothelium, ACh-induced relaxations were attenuated by a ROS-generating reaction (hypoxanthine plus xanthine oxidase, HXXO). The impaired relaxations were ameliorated by acute treatment with raloxifene. HXXO suppressed the ACh-stimulated increase in cyclic GMP levels; this effect was antagonized by raloxifene. The improved endothelial function by raloxifene was abolished by ICI 182,780, and by wortmannin or LY294002. Raloxifene also protected endothelial cell function against H2O2. Raloxifene increased the phosphorylation of eNOS at Ser-1177 and Akt at Ser-473; this effect was blocked by ICI 182,780. Finally, raloxifene was not directly involved in scavenging ROS, and neither inhibited the activity of xanthine oxidase nor stimulated that of superoxide dismutase. Raloxifene is effective against oxidative stress-induced endothelial dysfunction in vitro through an ICI 182,780-sensitive mechanism that involves the increased phosphorylation and activity of Akt and eNOS in rat aortae.

Role of Sphingosine-1-Phosphate Phosphohydrolase 1 in the Regulation of Resistance Artery Tone

Sphingosine-1-phosphate (S1P), which mediates pleiotropic actions within the vascular system, is a prominent regulator of microvascular tone. By virtue of its S1P-degrading function, we hypothesized that S1P-phosphohydrolase 1 (SPP1) is an important regulator of tone in resistance arteries. Hamster gracilis muscle resistance arteries express mRNA encoding SPP1. Overexpression of SPP1 (via transfection of a SPP1(wt)) reduced resting tone, Ca2+ sensitivity, and myogenic vasoconstriction, whereas reduced SPP1 expression (antisense oligonucleotides) yielded the opposite effects. Expression of a phosphatase-dead mutant of SPP1 (SPP1(H208A)) had no effect on any parameter tested, suggesting that catalytic activity of SPP1 is critical. The enhanced myogenic tone that follows overexpression of S1P-generating enzyme sphingosine kinase 1 (Sk1(wt)) was functionally antagonized by coexpression with SPP1(wt) but not SPP1(H208A). SPP1 modulated vasoconstriction in response to 1 to 100 nmol/L exogenous S1P, a concentration range that was characterized as S1P2-dependent, based on the effect of S1P(2) inhibition by antisense oligonucleotides and 1 mumol/L JTE013. Inhibition of the cystic fibrosis transmembrane regulator (CFTR) (1) restored S1P responses that were attenuated by SPP1(wt) overexpression; (2) enhanced myogenic vasoconstriction; but (3) had no effect on noradrenaline responses. We conclude that SPP1 is an endogenous regulator of resistance artery tone that functionally antagonizes the vascular effects of both Sk1(wt) and S1P2 receptor activation. SPP1 accesses extracellular S1P pools in a manner dependent on a functional CFTR transport protein. Our study assigns important roles to both SPP1 and CFTR in the physiological regulation of vascular tone, which influences both tissue perfusion and systemic blood pressure.

Thrombospondin-1 antagonizes nitric oxide-stimulated vascular smooth muscle cell responses

Endothelial-derived nitric oxide (NO), by increasing cGMP, is a major physiological regulator of vascular tone and of vascular smooth muscle cell (VSMC) adhesion, chemotaxis, and proliferation. Thrombospondin-1 is a potent antagonist of NO/cGMP signaling in endothelial cells. Because endothelial and VSMC typically exhibit opposing responses to thrombospondin-1, we examined thrombospondin-1 effects on NO signaling in VSMC. Effects of exogenous thrombospondin-1 on human VSMC adhesion, chemotaxis, proliferation, and cGMP signaling were examined. Endogenous thrombospondin-1 function was characterized by comparing NO signaling in VSMC from wild type and thrombospondin-1 null mice. Picomolar concentrations of exogenous thrombospondin-1 prevented adhesive, chemotactic, and proliferative responses of human aortic VSMC stimulated by low dose NO. A recombinant CD36-binding domain of thrombospondin-1 or antibody ligation of CD36 similarly inhibited NO-stimulated VSMC responses. Thrombospondin-1 and CD36 ligation inhibited NO responses in VSMC by preventing cGMP accumulation. Thrombospondin-1 null VSMC responses to NO and cGMP signaling were enhanced relative to wild type murine VSMC. In the presence of NO, thrombospondin-1 is converted from a weak stimulator to a potent inhibitor of VSMC responses. Both exogenous and endogenous thrombospondin-1 inhibit NO signaling in VSMC. This activity is mediated by the type 1 repeats and utilizes the same CD36-dependent cGMP signaling pathway in endothelial and VSMC.

Detection of specific nitrotyrosine-modified proteins as a marker of oxidative stress in cardiovascular disease

the oxidative modification of proteins is a natural consequence of aerobic life and is also recognized to play a crucial role in the pathological response of cells to increased oxidative stress. Several oxidative modifications of a protein can occur as a result of oxidative stress. These can range

Le système rénine-angiotensine : données actuelles

The renin-angiotensin system (RAS) is a major physiological regulator of vascular tone and is implicated in cardiovascular pathophysiology. More recently, basic research has however continuously extended our understanding of the complexicity of the systemic and tissular RASs. The peptid hormone, angiotensin II, acts primarily via type I (AT1) and type II (AT2) angiotensin receptors. Most, if not all, of the peripheral and central actions of angiotensin II, including vasoconstriction, renal salt and water retention, facilitation of sympathetic transmission, modification of vascular and cardiac structure, oxydative stress stimulation and proinflammatory action were all thought to be mediated by the angiotensin type 1 receptor, AT1. Angiotensin II/III exerts actions through the AT2 receptor, which are directly opposed to those mediated by the AT1 receptor. Most notably, proteolytic fragments of angiotensin II also have biological activity via ther own receptors: angiotensin-(1-7)/AT1-7 and angiotensin IV/AT4. They are vasodilators in many arterial beds. The identification of these angiotensins opens the way to develop new therapeutics.

Oxytocin does not directly affect vascular tone in vessels from nonpregnant and pregnant rats

Recent evidence suggests oxytocin (OT) may regulate vascular tone. OT and its receptor (OTR) have been identified in the rat heart and great vessels. Expression of OT and OTR is increased in some tissues during pregnancy. We hypothesized that the OT/OTR system may be a physiological regulator of vascular tone and mediate the decreased vascular resistance noted during pregnancy. Using a wire myograph system, we measured changes in vascular tone in response to OT in small mesenteric arteries, uterine arcuate arteries, and thoracic aorta from nonpregnant and pregnant rats. Additionally, we used reverse transcriptase-polymerase chain reaction (RT-PCR) to measure mRNA for OTR in these vascular tissues. Although OTR mRNA was identified by RT-PCR, OT did not elicit a vasodilatory effect in any of the vessels studied. High concentrations of OT (>10(-8) M) caused vasoconstriction that was eliminated by a specific vasopressin V(1a) receptor antagonist. Although it may have an indirect effect in regulation of peripheral resistance, we conclude that OT is unlikely to play a direct role in the physiological regulation of vascular tone.

Functional roles of KATP channels in vascular smooth muscle.

1. ATP-sensitive potassium channels (K(ATP)) are present in vascular smooth muscle cells and play important roles in the vascular responses to a variety of pharmacological and endogenous vasodilators. 2. The K(ATP) channels are composed of four inwardly rectifying K+ channel subunits and four regulatory sulphonylurea receptors. The K(ATP) channels are inhibited by intracellular ATP and by sulphonylurea agents. 3. Pharmacological vasodilators such as cromakalim, pinacidil and diazoxide directly activate K(ATP) channels. The associated membrane hyperpolarization closes voltage-dependent Ca2+ channels, which leads to a reduction in intracellular Ca2+ and vasodilation. 4. Endogenous vasodilators such as calcitonin gene-related peptide, vasoactive intestinal polypeptide, prostacylin and adenosine activate K(ATP) by stimulating the formation of cAMP and increasing the activity of protein kinase A. Part of the mechanism of contraction of endogenous vasoconstrictors is due to inhibition of K(ATP) channels. 5. The K(ATP) channels appear to be tonically active in some vascular beds and contribute to the physiological regulation of vascular tone and blood flow. These channels also are activated under pathophysiological conditions, such as hypoxia, ischaemia, acidosis and septic shock, and, in these disease states, may play an important role in the regulation of tissue perfusion.

Reciprocal regulation of endothelin-1 and nitric oxide: Relevance in the physiology and pathology of the cardiovascular system

The endothelium plays a crucial role in the regulation of cardiovascular structure and function by releasing several mediators in response to biochemical and physical stimuli. These mediators are grouped into two classes: (1) endothelium-derived constricting factors (EDCFs) and (2) endothelium-derived relaxing factors (EDRFs), the roles of which are considered to be detrimental and beneficial, respectively. Endothelin-1 (ET-1) and nitric oxide (NO) are the prototypes of EDCFs and EDRFs, respectively, and their effects on the cardiovascular system have been studied in depth. Numerous conditions characterized by an impaired availability of NO have been found to be associated with enhanced synthesis of ET-1, and vice versa, thereby suggesting that these two factors have a reciprocal regulation. Experimental studies have provided evidence that ET-1 may exert a bidirectional effect by either enhancing NO production via ETB receptors located in endothelial cells or blunting it via ETA receptors prevalently located in the vascular smooth muscle cells. Conversely, NO was found to inhibit ET-1 synthesis in different cell types. In vitro and in vivo studies have started to unravel the molecular mechanisms involved in this complex interaction. It has been clarified that several factors affect in opposite directions the transcription of preproET-1 and NO-synthase genes, nuclear factor-KB and peroxisome proliferator-activated receptors playing a key role in these regulatory mechanisms. ET-1 and NO interplay seems to have a great relevance in the physiological regulation of vascular tone and blood pressure, as well as in vascular remodeling. Moreover, an imbalance between ET-1 and NO systems may underly the mechanisms involved in the pathogenesis of systemic and pulmonary hypertension and atherosclerosis.

Endogenous nitric oxide as a physiological regulator of vascular tone in cat skeletal muscle during haemorrhage.

The problem whether endogenous nitric oxide (NO) may serve as a true physiological regulator of vascular tone in vivo was approached by testing its role during graded acute haemorrhage with the aid of the nitric oxide synthase (NOS) inhibitor L-NAME. The study was performed on the vascular bed of cat skeletal muscle with a technique permitting quantitative recordings of vascular resistance in the whole vascular bed (RT) and in its consecutive sections, the proximal arterial resistance ('feeder') vessels (> 25 microns; Ra,prox), the small arterioles (< 25 microns) and the veins. NO blockade by close-arterial L-NAME infusion in the control situation increased RT from 16.3 to 33.0 PRU (+102%), because of a selective increase in Ra,prox by 16.7 PRU. A 35% blood loss per se raised RT from 13.6 to 21.7 PRU. Superimposed NO blockade in this state caused a much stronger vasoconstriction than in the control situation, increasing RT to 60.9 PRU (+181%) and Ra,prox by 40.5 PRU, which indicated an approximately 2.4-fold increase (P < 0.001) in the NO dilator influence in the Ra,prox section above control. The effect was independent of autonomic nerves. The increased NO dilator influence during haemorrhage most likely was caused by an increased production of endothelium-derived nitric oxide (EDNO), The constrictor response to L-NAME was graded in relation to the blood loss (17.5 vs. 35%). The results indicate that EDNO functions as a physiological regulator of vascular tone in the arterial 'feeder' vessels during haemorrhage, serving to counterbalance to a significant extent the concomitant adrenergic constriction, and thereby preventing critical reduction of blood flow and untoward heterogeneous flow distribution within the tissue.

Effects of adenosine tetraphosphate (ATPP) on vascular tone in the isolated rat aorta.

Effects of a platelet-released, naturally occurring nucleotide, adenosine 5'-tetraphosphate (ATPP) on vascular tone were analyzed in the isolated rat aorta. Under resting tension ATPP (1 approximately 100 microM) elicited concentration-dependent contractions in endothelium-intact aortic rings in contrast to the concentration-dependent relaxation with ATP. In endothelium-denuded aortic rings, ATPP induced contraction, as ATP did, but with a greater potency. alpha, beta-methylene ATP (APCPP 50 microM), a P2x-purinoceptor antagonist, significantly inhibited ATPP- as well as ATP-induced contractions in the endothelium-denuded preparations suggesting that ATPP acts via P2x-purinoceptors. ATPP (10 approximately 100 microM) relaxed precontracted aortic rings with an intact endothelium in a concentration-dependent manner. This effect of ATPP was 3.7 fold less potent than that of ATP. However, after P2x-purinoceptor blockade, the effect became identical between the two nucleotides. Reactive blue 2, a selective antagonist of P2x-purinoceptors, significantly attenuated the ATPP-induced relaxation with no change in the ATP-induced relaxation. These results indicated that the rat aortic endothelium contains heterogeneous populations of P2-purinoceptors (possibly P2y and nucleotide receptors). Since ATPP shows dual effects depending upon the vascular tension, it may play a significant role in the physiological regulation of vascular tone.

Lack of role for nitric oxide (NO) in the selective destabilization of endothelial NO synthase mRNA by tumor necrosis factor-alpha.

The constitutive expression of endothelial nitric oxide (NO) synthase (cNOS) is essential for the physiological regulation of vascular tone and structure. The mechanism of downregulation of steady state cNOS mRNA in human umbilical vein endothelial cells exposed to tumor necrosis factor-alpha (TNF-alpha) was investigated by using Northern blot analysis of total cellular RNA. TNF-alpha produced a dose- and time-dependent decrease in cNOS mRNA expression that was near maximal at 10 U/mL and 6 hours of exposure, respectively. In contrast, steady state expression of endothelin-1 and plasminogen activator inhibitor-1 (PAI-1) mRNA was upregulated by TNF-alpha. The pharmacological generation of NO using sodium nitroprusside (10 mumol/L) and S-nitroso-acetylpenicillamine (100 to 400 mumol/L) had no effect on cNOS mRNA levels, and TNF-alpha-induced downregulation of cNOS was not prevented by coincubation with the inhibitors of NO synthesis N omega-nitro-L-arginine methyl ester (1 mmol/L) and NG-monomethyl L-arginine (10 mmol/L). Under control conditions, cNOS and PAI-1 mRNA were stable after treatment with actinomycin D for periods greater than 24 hours, whereas endothelin-1 message was rapidly degraded (half-life, < 1 hour). Pretreatment with TNF-alpha (30 U/mL) selectively reduced that half-life of cNOS mRNA to less than 12 hours without altering the stability of PAI-1 message. TNF-alpha-induced destabilization of cNOS mRNA could be partially prevented by coincubation with cycloheximide (1 mumol/L) but was not reproduced by addition of sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)