Regulation of endothelial cell nitric oxide synthase mRNA expression by shear stress

Regulation of the endothelin system by shear stress in human endothelial cells

In this study, the effect of shear stress on the expression of genes of the human endothelin-1 system was examined. Primary cultures of human umbilical vein endothelial cells (HUVEC) were exposed to laminar shear stress of 1, 15 or 30 dyn cm-2 (i.e. 0.1, 1.5 or 3 N m-2) (venous and two different arterial levels of shear stress) in a cone-and-plate viscometer. Laminar shear stress transiently upregulates preproendothelin-1 (ppET-1) mRNA, reaching its maximum after 30 min (approx 1.7-fold increase). In contrast, long-term application of shear stress (24 h) causes downregulation of ppET-1 mRNA in a dose-dependent manner. Arterial levels of shear stress result in downregulation of endothelin-converting enzyme-1 isoform ECE-1a (predominating in HUVEC) to 36.2 +/- 8.5 %, and isoform ECE-1b mRNA to 72.3 +/- 1.9 % of static control level. The endothelin-1 (ET-1) release is downregulated by laminar shear stress in a dose-dependent manner. This downregulation of ppET-1 mRNA and ET-1 release is not affected by inhibition of protein kinase C (PKC), or tyrosine kinase. Inhibition of endothelial NO synthase (L-NAME, 500 microm) prevents downregulation of ppET-1 mRNA by shear stress. In contrast, increasing degrees of long-term shear stress upregulate endothelin receptor type B (ETB) mRNA by a NO- and PKC-, but not tyrosine kinase-dependent mechanism. In conclusion, our data suggest the downregulation of human endothelin synthesis, and an upregulation of the ETB receptor by long-term arterial laminar shear stress. These effects might contribute to the vasoprotective and anti-arteriosclerotic potential of arterial laminar shear stress.

Regulation of types I and III NOS in ovine uterine arteries by daily and acute estrogen exposure

Nitric oxide contributes to estrogen-mediated uterine vasodilation; however, the nitric oxide synthases (NOS) involved and their location within uterine arteries are incompletely documented. We investigated the effects of repetitive daily and acute estradiol-17beta (E(2)beta) exposure on uterine hemodynamics and NOS abundance and localization in uterine arteries from nonpregnant ovariectomized ewes receiving daily intravenous E(2)beta (1 microg/kg, n = 5) or no E(2)beta (n = 7) for 5 days to determine NOS abundance, cGMP contents, and NOS immunohistochemistry. Daily E(2)beta increased basal and E(2)beta-mediated rises in uterine blood flow (UBF) 36 and 43% (<0.01), respectively, calcium-dependent NOS activity 150% (P < 0.02) in endothelium-intact and -denuded ( approximately 40% of total NOS) arteries, and cGMP contents 39% (P < 0.05). Endothelial (eNOS) was detected in luminal endothelium, whereas neuronal NOS (nNOS) protein was only in the media. A second group of ewes received E(2)beta (1 microg/kg iv) for 4 days and acute intravenous E(2)beta (n = 8) or vehicle (n = 4) on day 5. UBF rose 5.5-fold (P < 0.001) 115 min after E(2)beta, at which time only endothelium-derived calcium-dependent NOS activity increased 30 +/- 13% (P < 0.05). Daily E(2)beta enhances basal and E(2)beta-mediated increases in UBF, which parallel increases in endothelium-derived eNOS and smooth muscle-derived nNOS. Acute E(2)beta, however, selectively increases endothelium-derived eNOS.

Effect of 40-kHz ultrasound on acute thrombotic ischemia in a rabbit femoral artery thrombosis model: enhancement of thrombolysis and improvement in capillary muscle perfusion

BACKGROUND

We have shown previously that 40-kHz ultrasound (US) at low intensity accelerates fibrinolysis in vitro with little heating and good tissue penetration. These studies have now been extended to examine the effects of 40-kHz US on thrombolysis and tissue perfusion in a rabbit model.

METHODS AND RESULTS

Treatment was administered with either US alone at 0.75 W/cm(2), streptokinase alone, or the combination of US and streptokinase. US or streptokinase resulted in minimal thrombolysis, but reperfusion was nearly complete with the combination after 120 minutes. US also reversed the ischemia in nonperfused muscle in the absence of arterial flow. Tissue perfusion decreased after thrombosis from 13. 7+/-0.2 to 6.6+/-0.8 U and then declined further to 4.5+/-0.4 U after 240 minutes. US improved perfusion to 10.6+/-0.5 and 12.1+/-0. 5 U after 30 and 60 minutes, respectively. This effect was reversible and declined to pretreatment values after US was discontinued. Similarly, tissue pH declined from normal to 7.05+/-0. 02 after thrombosis, but US improved pH to 7.34+/-0.03 after 60 minutes. US-induced improvement in tissue perfusion and pH also occurred after femoral artery ligation, indicating that thrombolysis did not cause these effects.

CONCLUSIONS

40-kHz US at low intensity markedly accelerates fibrinolysis and also improves tissue perfusion and reverses acidosis, effects that would be beneficial in treatment of acute thrombosis.

The response of adult human saphenous vein endothelial cells to combined pressurized pulsatile flow and cyclic strain, in vitro

Adult human saphenous vein endothelial cells (HVEC) were cultured in a compliant tubular device and evaluated by Northern hybridization for the effects of combined pressurized pulsatile flow and cyclic strain on the expression of mRNAs for endothelin-1 (ET-1), endothelial cell nitric oxide synthase (ecNOS), tissue plasminogen activator (tPA), and plasminogen activator inhibitor type 1 (PAI-1). The hemodynamic environment was designed to mimic shear stress conditions at the distal anastomosis of a saphenous vein graft, a common site of intimal proliferation. Steady-state mRNA levels in experimental tubes were expressed relative to that in controls. No changes were observed in ET-1 mRNA after 1 and 24 hr, but a 50% decrease in experimental cultures was observed after 48 hr in the vascular simulating device. Similar results were obtained for ecNOS mRNA, although a subgroup (4 of 11) showed a significant decrease (>50%) by 24 hr. For tPA mRNA, no change was observed after 1 hr, but a significant decrease (>60%) was measured after 24 hr and no message was detectable after 48 hr. Steady-state levels for PAI-1 mRNA remained unchanged through 48 hr of treatment. These results show that pressure, pulsatile flow, and cyclic strain, when applied in concert, differentially alter vasoactive and fibrinolytic functions in HVEC. Moreover, the dramatic decrease in steady-state levels of tPA mRNA is consistent with a shift toward an increased thrombotic state.

Alterations of nitric oxide synthase expression and activity during rat lung transplantation

Decreased nitric oxide (NO) production has been reported during lung transplantation in patients. To study the effects of ischemia and reperfusion on endogenous NO synthase (NOS) expression, both an ex vivo and an in vivo lung injury model for transplantation were used. Donor rat lungs were flushed with cold low-potassium dextran solution and subjected to either cold (4 degrees C for 12 h) or warm (21 degrees C for 4 h) ischemic preservation followed by reperfusion with an ex vivo model. A significant increase in inducible NOS and a decrease in endothelial NOS mRNA was found after reperfusion. These results were confirmed in a rat single-lung transplant model after warm preservation. Interestingly, protein contents of both inducible NOS and endothelial NOS increased in the transplanted lung after 2 h of reperfusion. However, the total activity of NOS in the transplanted lungs remained at very low levels. We conclude that ischemic lung preservation and reperfusion result in altered NOS gene and protein expression with inhibited NOS activity, which may contribute to the injury of lung transplants.

Signalling pathways in vascular endothelium activated by shear stress: relevance to atherosclerosis

Major advances in our understanding of how endothelial cells sense and respond to haemodynamic forces and, more specifically, to fluid shear stress have been achieved during the past 3 years. These include definition of potential shear stress receptors and multiple signalling pathways that mediate shear stress regulation of gene expression. A few studies have also pointed to the unique effects of complex shear stress on endothelial activation, thus leading to better understanding of the mechanisms that lead to the development of atherosclerosis.

Cyclic tension force activates nitric oxide production in cultured human periodontal ligament cells

BACKGROUND

Nitric oxide (NO) is involved in a number of physiological and pathophysiological processes. The aim of this study was to examine the ability of human periodontal ligament (PDL) cells to produce NO and whether mechanical forces could induce NO production in the PDL cells.

METHODS

Human PDL cells were seeded onto flexible bottoms of a culture plate and subjected to cyclic tension forces. NO production was evaluated by measuring concentration of NO2- and NO3- (NO2-/NO3-), the oxidized products of NO, in the culture medium. We employed reverse transcription polymerase chain reaction (RT-PCR) methods to detect NO synthase mRNA in the PDL cells. NO synthase immunoreactivity was also evaluated in both stimulated and unstimulated PDL cells.

RESULTS

In unstimulated PDL cell culture, NO2-/NO3- increased to 140% of the initial value in 12 hours. In contrast, NO2-/NO3- showed a 3-fold increase when the cells had been subjected to cyclic tension forces for 12 hours. The increase in NO production was blocked by NG-monomethyl-L-arginine (5 x 10(-4) M), an inhibitor of NO synthase. Endothelial NO synthase (ecNOS) mRNA was expressed in both stimulated and unstimulated PDL cells, whereas inducible NO synthase (iNOS) mRNA was detected in neither culturing condition. We found strong ecNOS but not iNOS immunoreactivity in the stimulated PDL cells.

CONCLUSIONS

These results suggest that human PDL cells produce NO by ecNOS and that the production is enhanced by stimulating the cells with cyclic tension forces. Mechanically stimulated PDL cells may modulate the function of periodontium by the upregulated NO production.

Pulsatile flow enhances endothelium-derived nitric oxide release in the peripheral vasculature

The effects of pulsatility in blood flow on endothelium-derived nitric oxide (EDNO) release in the peripheral vasculature were investigated. The basal and flow-stimulated EDNO release were compared between pulsatile and nonpulsatile systemic flows before and after the administration of NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA). Peripheral vascular resistance (PVR) was significantly lower in pulsatile flow than in nonpulsatile flow, but this difference disappeared after L-NMMA. The percent increase in PVR by L-NMMA was significantly larger in pulsatile flow. In reactive hyperemia in the hindlimb, the peak flow did not differ; however, both the repayment flow and the duration were significantly larger in pulsatile flow. Percent changes of these parameters by L-NMMA were significantly larger in pulsatile flow. These data indicated that pulsatility significantly enhances the basal and flow-stimulated EDNO release in the peripheral vasculature under in vivo conditions. We also studied the involvement of the Ca(2+)-dependent and Ca(2+)-independent pathways in flow-induced vasodilation using calmodulin inhibitor calmidazolium and tyrosine kinase inhibitor erbstatin A. PVR was significantly elevated by erbstatin A but not by calmidazolium, suggesting that flow-induced vasodilation was largely caused by tyrosine kinase inhibitor-sensitive activation of NO synthase.

Targeting of human eNOS promoter to the Hprt locus of mice leads to tissue-restricted transgene expression

Phenotypic heterogeneity of the endothelium arises from cell type-specific differences in gene expression. An understanding of the mechanisms that underlie differential gene expression would provide important insight into the molecular basis of vascular diversity. In standard transgenic assays, multiple copies of heterologous DNA cassettes are randomly integrated into the mouse genome, resulting in significant line-to-line variation in expression. To overcome these limitations, we have targeted a single copy of a transgene that contains 1,600 bp of the human endothelial nitric oxide synthase (eNOS) promoter coupled to the LacZ reporter gene to the X-linked hypoxanthine phosphoribosyltransferase (Hprt) locus of mice by homologous recombination. The transgene was inserted in either of the orientations relative to that of the Hprt gene. In mice derived from multiple embryonic stem (ES) cell clones, the expression pattern was limited to a subset of endothelial cells, cardiomyocytes, and vascular smooth muscle cells. These findings suggest that Hprt locus targeting is a feasible tool for studying endothelial cell-restricted gene regulation.

Endothelial cell regulation of nitric oxide production during hypoxia in coronary microvessels and epicardial arteries

Nitric oxide (NO) synthesized by endothelial cell nitric oxide synthase (eNOS) elicits vasodilation of resistance-sized coronary microvessels. Since coronary blood flow increases during hypoxia, we tested the hypotheses that: (1) hypoxia results in increased blood flow through increased NO production mediated by the upregulation of both eNOS mRNA and protein and (2) the regulation of NO production in response to hypoxia differs in microvascular endothelial cells and nonresistance, epicardial endothelial cells. Monocultures of vascular endothelium from resistance (approximately 100 micro) and nonresistance epicardial arteries were established and characterized. Nitric oxide was quantitated using a chemiluminescence method. Hypoxia (pO(2) = 10 mmHg) significantly increased NO production in both cell lines, with less NO produced in microvascular endothelium. Western blots demonstrated that hypoxia caused a time-dependent increase in eNOS protein in both lines, with an average 2.5-fold increase in nonresistance, epicardial endothelial cells compared to an average 1.7-fold increase in protein from microvascular endothelium. Total mRNA recovery increased 2.4 +/- 0.6-fold within 30 min of hypoxia in nonresistance, epicardial endothelial cells with no increase in microvascular endothelial cells. Although hypoxia increased NO production in both populations of endothelial cells, the increase in NO production and eNOS protein in microvascular endothelium was less compared to nonresistance, epicardial endothelial cells. Furthermore, there was no significant upregulation of total mRNA for eNOS in microvascular endothelium. The data indicate that increased NO production in microvascular endothelium during hypoxia may be through translational or posttranslational modifications of the enzyme, whereas transcriptional upregulation may account for the increased NO production in nonresistance, epicardial endothelial cells. Oxygen-sensitive response mechanisms that modulate NO production may be different in endothelium from different coronary artery vascular beds.

Transcriptional induction of endothelial nitric oxide gene by cyclosporine A. A role for activator protein-1

We have previously shown that the immunosuppressant cyclosporine A (CsA) increases the activity, the protein level, and the steady-state levels of the mRNA of the endothelial nitric-oxide synthase (eNOS) gene in bovine aortic endothelial cells (BAEC). We have now investigated the mechanisms responsible for these effects. Preincubation with an inhibitor of RNA polymerase II abolished CsA-induced eNOS up-regulation. Nuclear run-on experiments demonstrated a 1.6-fold increase in the induction of eNOS gene by CsA. In agreement with these results, transient transfections showed that CsA augmented the transactivation of the eNOS promoter. Electrophoretic mobility shift assays showed an increase in the activator protein-1 (AP-1) DNA binding activity in BAEC treated with CsA. An increase in the level of c-fos mRNA and in the nuclear content of c-Fos protein was detected in BAEC treated with CsA. Site-directed mutagenesis of the AP-1 cis-regulatory element in the context of the human eNOS promoter resulted in the abrogation of the induction mediated by CsA. Hence, up-regulation of eNOS mRNA by CsA is a transcriptional phenomenon involving the proximal AP-1 site in the 5'-regulatory region of the human eNOS gene. Furthermore, our data exemplify how immunosuppressive drugs may result in the regulation of specific genes involved in the homeostasis of endothelial function, such as eNOS.

Unidirectional and oscillatory shear stress differentially modulate NOS III gene expression

Atherosclerotic plaques preferentially develop in regions exposed to a low mean shear stress and cyclic reversal of flow direction (oscillatory flow). This contrasts with plaque-free zones where endothelial cells are exposed to unidirectional flow. Previous works from our laboratory using a unique experimental flow system demonstrated the existence of a differential regulation of endothelial nitric oxide synthase (NOS III) gene expression by unidirectional and oscillatory flow patterns. We further studied the possible mechanisms responsible for selective unresponsiveness of NOS III gene regulation to oscillatory flow. The results obtained demonstrate that (i) induction of the activity of the 1600-base-pair NOS III gene promoter by unidirectional and oscillatory shear stress is modulated by similar mechanisms that involve NF-kappaB activation, but do not involve Ras-dependent MAP kinase activation, and (ii) the lack of induction of NOS III gene regulation by oscillatory shear stress can be attributed to the activation of a yet unidentified negative cis-acting element present in the NOS III gene.

Pulmonary blood flow alters nitric oxide production in patients undergoing device closure of atrial septal defects

OBJECTIVE

To determine the effect of pulmonary blood flow (Qp) on nitric oxide (NO) production in patients with increased Qp due to an atrial septal defect (ASD).

BACKGROUND

Alterations in pulmonary vascular NO production have been implicated in the development of pulmonary hypertension secondary to increased Qp. In vitro, acute changes in flow or shear stress alter NO production. However, the effect of Qp on lung NO production in vivo is unclear.

METHODS

Nineteen patients (2.4-61 years of age, median 17) with secundum ASD undergoing device closure were studied. Before, and 30 min after ASD closure, exhaled NO and plasma nitrate concentration were measured by chemiluminescence (NOA 280, Sievers, Boulder, Colorado).

RESULTS

Before ASD closure, all patients had increased Qp (Qp: systemic blood flow [Qs] of 2.0 +/- 0.7) and normal mean pulmonary arterial pressure (13.4 +/- 3.1 mm Hg). Atrial septal defect device closure decreased Qp from 6.0 +/- 2.5 to 3.6 +/- 1.3 L/min/m2 (p < 0.05). Mean pulmonary arterial pressure was unchanged. Associated with the decrease in Qp, both exhaled NO (-22.1%, p < 0.05) and plasma nitrate concentrations (-17.9%, p < 0.05) decreased.

CONCLUSIONS

These data represent the first demonstration that acute changes in Qp alter pulmonary NO production in vivo in humans. Exhaled NO determinations may provide a noninvasive assessment of pulmonary vascular NO production in patients with congenital heart disease. Potential correlations between exhaled NO, pulmonary vascular reactivity and pulmonary hypertension warrant further study.

Blood pressure control in eNOS knock-out mice: comparison with other species under NO blockade

Changes in arterial blood pressure (ABP) lead to changes in vascular shear stress. This mechanical stimulus increases cytosolic Ca2+ in endothelial cells, which in turn activates the endothelial isoform of the nitric oxide synthase. The subsequently formed NO reaches the adjacent vascular smooth muscle cells, where it reduces vascular resistance in order to maintain ABP at its initial level. Thus, NO may play an important role as a physiological blood pressure buffer. Previous data on the importance of eNOS for blood pressure control are reviewed with special emphasis on the fact that endogenous nitric oxide can buffer blood pressure variability (BPV) in dogs, rats and mice. In previous studies where all isoforms of the nitric oxide synthase were blocked pharmacologically, increases in blood pressure and variability were observed. Thus, we set out to clarify which isoform of the nitric oxide synthase is responsible for this BPV controlling effect. Hence, blood pressure control was studied in knock-out mice lacking specifically the gene for endothelial nitric oxide synthase with their respective wild-type controls. One day after surgery, under resting conditions, blood pressure was increased by 47 mmHg (P < 0.05), heart rate was lower (-77 beats min-1, P < 0.05), and BPV doubled (P < 0.05). Based on these results, we conclude that chronic blood pressure levels are influenced by eNOS and that there is a blood pressure buffering effect of endogenous nitric oxide which is mediated by the endothelial isoform of the nitric oxide synthase.

Enhanced endothelial vasoreactivity in endurance-trained older men

Using external vascular ultrasound, we measured brachial artery diameter (Diam) at rest, after release of 4 min of limb ischemia, i. e., endothelium-dependent dilation (EDD), and after sublingual nitroglycerin, i.e., non-endothelium-dependent dilation (NonEDD), in 35 healthy men aged 61-83 yr: 12 endurance athletes (A) and 23 controls (C). As anticipated, treadmill exercise maximal oxygen consumption (VO(2 max)) was significantly higher in A than in C (40. 2 +/- 6.6 vs. 27.9 +/- 3.8 ml. kg(-1). min(-1); respectively, P < 0. 0001). With regard to arterial physiology, A had greater EDD (8.9 +/- 4.2 vs. 5.7 +/- 3.5%; P = 0.02) and a tendency for higher NonEDD (13.9 +/- 6.7 vs. 9.7 +/- 4.2%; P = 0.07) compared with C. By multiple linear regression analysis in the combined sample of older men, only baseline Diam (beta = -2.0, where beta is the regression coefficient; P = 0.005) and VO(2 max) (beta = 0.23; P = 0.003) were independent predictors of EDD; similarly, only Diam (beta = -4.0; P = 0.003) and VO(2 max) (beta = 0.27; P = 0.01) predicted NonEDD. Thus endurance-trained older men demonstrate both augmented EDD and NonEDD, consistent with a generalized enhanced vasodilator responsiveness, compared with their sedentary age peers.

Nitric-oxide synthase is a mechanical signal transducer that modulates talin and vinculin expression

Mechanical stimuli can cause changes in muscle mass and structure which indicate that mechanisms exist for transducing mechanical stimuli into signals that influence gene expression. Myotendinous junctions show adaptations to modified muscle loading which suggest that these are transcriptionally distinct domains in muscle fibers that may experience local regulation of expression of structural proteins that are concentrated at these sites. Vinculin and talin are cytoskeletal proteins that are highly enriched at myotendinous junctions that we hypothesize to be subject to local transcriptional regulation. Our findings show that mechanical stimulation of muscle cells in vivo and in vitro causes an increase in the expression of vinculin and talin that is mediated by nitric oxide. Furthermore, nitric oxide-stimulated increases in vinculin and talin expression occur through a protein kinase G-dependent pathway and therefore differ from other mechanisms through which nitric oxide has been shown previously to modulate transcription. Analysis of vinculin mRNA distribution in mechanically stimulated muscle fibers shows that the mRNA is highly concentrated at myotendinous junctions, which supports the hypothesis that myotendinous junctions are distinct domains in which the expression of cytoskeletal proteins is modulated by mechanical stimuli through a nitric oxide and protein kinase G-dependent pathway.

Vascular endothelial growth factor governs endothelial nitric-oxide synthase expression via a KDR/Flk-1 receptor and a protein kinase C signaling pathway

The mechanism by which vascular endothelial growth factor (VEGF) regulates endothelial nitric-oxide synthase (eNOS) expression is presently unclear. Here we report that VEGF treatment of bovine adrenal cortex endothelial cells resulted in a 5-fold increase in both eNOS protein and activity. Endothelial NOS expression was maximal following 2 days of constant VEGF exposure (500 pM) and declined to base-line levels by day 5. The elevated eNOS protein level was sustained over the time course if VEGF was co-incubated with L-N(G)-nitroarginine methyl ester, a competitive eNOS inhibitor. Addition of S-nitroso-N-acetylpenicillamine, a nitric oxide donor, prevented VEGF-induced eNOS up-regulation. These data suggest that nitric oxide participates in a negative feedback mechanism regulating eNOS expression. Various approaches were used to investigate the role of the two high affinity VEGF receptors in eNOS up-regulation. A KDR receptor-selective mutant increased eNOS expression, whereas an Flt-1 receptor-selective mutant did not. Furthermore, VEGF treatment increased eNOS expression in a KDR but not in an Flt-1 receptor-transfected porcine aorta endothelial cell line. SU1498, a selective inhibitor of the KDR receptor tyrosine kinase, blocked eNOS up-regulation, thus providing further evidence that the KDR receptor signals for eNOS up-regulation. Finally, treatment of adrenal cortex endothelial cells with VEGF or phorbol ester resulted in protein kinase C activation and elevated eNOS expression, whereas inhibition of protein kinase C with isoform-specific inhibitors abolished VEGF-induced eNOS up-regulation. Taken together, these data demonstrate that VEGF increases eNOS expression via activation of the KDR receptor tyrosine kinase and a downstream protein kinase C signaling pathway.

Oxidative stress as a regulator of gene expression in the vasculature

Oxidative stress and the production of intracellular reactive oxygen species (ROS) have been implicated in the pathogenesis of a variety of diseases. In excess, ROS and their byproducts that are capable of causing oxidative damage may be cytotoxic to cells. However, it is now well established that moderate amounts of ROS play a role in signal transduction processes such as cell growth and posttranslational modification of proteins. Oxidants, antioxidants, and other determinants of the intracellular reduction-oxidation (redox) state play an important role in the regulation of gene expression. Recent insights into the etiology and pathogenesis of atherosclerosis suggest that this disease may be viewed as an inflammatory disease linked to an abnormality in oxidation-mediated signals in the vasculature. In this review, we summarize the evidence supporting the notion that oxidative stress and the production of ROS function as physiological regulators of vascular gene expression mediated via specific redox-sensitive signal transduction pathways and transcriptional regulatory networks. Elucidating, at the molecular level, the regulatory processes involved in redox-sensitive vascular gene expression represents a foundation not only for understanding the pathogenesis of atherosclerosis and other inflammatory diseases but also for the development of novel therapeutic treatment strategies.

Hindlimb unweighting decreases ecNOS gene expression and endothelium-dependent dilation in rat soleus feed arteries

We tested the hypothesis that hindlimb unweighting (HLU) and the associated reduction in soleus muscle blood flow causes decreased expression of endothelial cell nitric oxide synthase (ecNOS) mRNA and protein and attenuated endothelium-dependent vasodilator responses in rat soleus feed arteries (SFA). Male Sprague-Dawley rats were exposed to HLU (n = 12) or cage control (Con; n = 12) conditions for 14 days. At the end of this period, SFA were isolated, removed, and cannulated with two glass micropipettes for examination of vasodilator responses or frozen for analysis of ecNOS mRNA and protein expression. RT-PCR of RNA from single SFA was used to measure ecNOS mRNA, and immunoblots on single SFAs were used to measure ecNOS protein content. Results revealed that both ecNOS mRNA and ecNOS protein expression were lower in SFA from HLU rats. Dilation to increased intraluminal flow was attenuated in SFA from HLU rats (Con: 88 +/- 8% vs. HLU: 53 +/- 8%) as was maximal vasodilation to acetylcholine (10(-9)-10(-4) M; Con: 88 +/- 5% vs. HLU: 73 +/- 5%). Sensitivity to the endothelium-independent vasodilator sodium nitroprusside (10(-10)-10(-4) M) was enhanced by HLU (EC(50): Con: 4.46 x 10(-7) M vs. HLU: 5.00 x 10(-8) M). Collectively, these data indicate that the chronic reduction in soleus blood flow associated with the reduced physical activity during HLU results in reduced expression of ecNOS mRNA and protein in SFA and attenuated endothelium-dependent vasodilation.

Mechanical force-induced signal transduction in lung cells

The lung is a unique organ in that it is exposed to physical forces derived from breathing, blood flow, and surface tension throughout life. Over the past decade, significant progress has been made at the cellular and molecular levels regarding the mechanisms by which physical forces affect lung morphogenesis, function, and metabolism. With the use of newly developed devices, mechanical forces have been applied to a variety of lung cells including fetal lung cells, adult alveolar epithelial cells, fibroblasts, airway epithelial and smooth muscle cells, pulmonary endothelial and smooth muscle cells, and mesothelial cells. These studies have led to new insights into how cells sense mechanical stimulation, transmit signals intra- and intercellularly, and regulate gene expression at the transcriptional and posttranscriptional levels. These advances have significantly increased our understanding of the process of mechanotransduction in lung cells. Further investigation in this exciting research field will facilitate our understanding of pulmonary physiology and pathophysiology at the cellular and molecular levels.

Dietary salt increases endothelial nitric oxide synthase and TGF-beta1 in rat aortic endothelium

The amount of NaCl in the diet plays an important role in modulating nitric oxide (NO) synthesis in vivo. In the glomerulus, dietary NaCl also regulates transforming growth factor-beta1 (TGF-beta1) production. We hypothesized that dietary NaCl intake regulated expression of the endothelial isoform of nitric oxide synthase (NOS3) and TGF-beta1 in the aorta. Administration of 8.0% NaCl diet to rats for 7 days did not affect blood pressure but increased steady-state mRNA and protein levels of NOS3 in the arterial wall compared with animals on 0.3% NaCl diet. Northern analysis demonstrated increased steady-state amounts of mRNA of TGF-beta1 in aortas of rats on 8.0% NaCl diet. By ELISA, both total and active TGF-beta1 were increased in these vessel segments. Endothelial denudation of aortic rings reduced active TGF-beta1 secretion to undetectable levels. Addition of a neutralizing antibody to TGF-beta to aortic ring segments attenuated NO production but not to that observed in animals on the 0.3% NaCl diet. The data showed that dietary NaCl intake modulated NOS3 and TGF-beta1 expression in the arterial wall; NOS3 expression was at least partially regulated by endothelial cell production of TGF-beta1.

Adrenal capillary endothelial cells stimulate aldosterone release through a protein that is distinct from endothelin

We tested the possibility that bovine adrenal capillary endothelial cells (ECs) stimulate aldosterone secretion from bovine zona glomerulosa (ZG) cells by the release of a transferable factor. In coincubations of ZG cells and ECs in serum-free medium, aldosterone release was stimulated approximately 17-fold, and the stimulation was related to the concentration of ECs. The maximal stimulation by ECs was 75% of the maximal response to ACTH. In contrast, adrenal pericytes and fibroblasts were without effect. ECs incubated alone without ZG cells did not produce aldosterone. Conditioned medium from ECs (EC-CM), but not adrenal fibroblasts, stimulated aldosterone release approximately 3-fold. The stimulation increased with the concentration of EC-CM and the duration of conditioning time. Steroidogenic activity in EC-CM was abolished by pronase treatment, indicating that the active factor was a protein. However, the activity in EC-CM was distinct from that of endothelin-1 (ET-1), an endothelial peptide that also stimulates aldosterone secretion, as it was not blocked by the ET(B) receptor antagonist PD-145065, it did not alter [125I]ET-1 binding to ZG cells, and its release occurred before the release of ET-1. Neither ECs nor EC-CM stimulated the production of cortisol from zona fasciculata cells. The activity of EC-CM was not blocked by an angiotensin II AT1 receptor antagonist or a bradykinin B2 receptor antagonist. EC-CM stimulated increased intracellular calcium in fura-2-loaded ZG cells, but did not increase the production of cAMP. Using gel filtration, this peptide had an approximate molecular mass of 3000 Da and migrated earlier than ET-1. This study demonstrates that ECs in vitro alter steroidogenesis through the release of a transferable substance and suggests the existence of an endothelium-derived steroidogenic factor that is produced by adrenal capillary ECs. This endothelium-derived steroidogenic factor may function in the adrenal gland as a paracrine regulator of aldosterone secretion.

Regular aerobic exercise augments endothelium-dependent vascular relaxation in normotensive as well as hypertensive subjects: role of endothelium-derived nitric oxide

BACKGROUND

Several nonpharmacological interventions, including exercise, are recommended in primary prevention of hypertension and other cardiovascular diseases in which the pathogenetic role of endothelial dysfunction has been suggested. We studied the effects of long-term aerobic exercise on endothelial function in patients with essential hypertension.

METHODS AND RESULTS

The forearm blood flow was measured by strain-gauge plethysmography. The responses of forearm vasculature to acetylcholine were smaller in the hypertensive patients than in the normotensive subjects. There was no significant difference in forearm vascular responses to isosorbide dinitrate in the normotensive and hypertensive subjects. We evaluated the effects of physical exercise for 12 weeks on forearm hemodynamics in untreated patients with mild essential hypertension who were divided randomly into an exercise group (n=10) and a control group (n=7). After 12 weeks, the forearm blood flow response to acetylcholine increased significantly, from 25.8+/-9.8 to 32.3+/-11.2 mL. min(-1). 100 mL tissue(-1) (P<0.05), in the exercise group but not in the control group. The increase in the forearm blood flow after isosorbide dinitrate was similar before and after 12 weeks of follow-up in both groups. The infusion of N(G)-monomethyl-L-arginine abolished the exercise-induced enhancement of forearm vasorelaxation evoked by acetylcholine in the exercising group. In normotensive subjects also, long-term aerobic exercise augmented acetylcholine-stimulated nitric oxide release.

CONCLUSIONS

These findings suggest that long-term physical exercise improves endothelium-dependent vasorelaxation through an increase in the release of nitric oxide in normotensive as well as hypertensive subjects.

Oxidant stress in the vasculature

Vascular disease and vasomotor responses are largely influenced by oxidant stress. Superoxide is generated via the cellular oxidase systems, xanthine oxidase, and NADH/NADPH oxidases. Once formed, superoxides participate in a number of reactions, yielding various free radicals such as hydrogen peroxide, peroxynitrite, oxidized low-density lipoprotein, or hypochlorous acid. Numerous cellular antioxidant systems exist to defend against oxidant stress; glutathione and the enzymes superoxide dismutase and glutathione peroxidase are critical for maintaining the redox balance of the cell. However, the redox state is disrupted by certain vascular diseases. It appears that oxidant stress both promotes and is induced by diseases such as hypertension, atherosclerosis, and restenosis as well as by certain risk factors for coronary artery disease including hyperlipidemia, diabetes, and cigarette smoking. Once oxidant stress is invoked, characteristic pathophysiologic features ensue, namely adverse vessel reactivity, vascular smooth muscle cell proliferation, macrophage adhesion, platelet activation, and lipid peroxidation.

The cGMP-specific phosphodiesterase inhibitor E4021 dilates the pulmonary circulation

We investigated the pulmonary vascular effects of E4021, a potent inhibitor of cGMP-specific phosphodiesterase, in control late-gestation fetal lambs, and in newborn lambs with persistent pulmonary hypertension (PPHN) after prenatal ligation of the ductus arteriosus. E4021 alone significantly relaxed fifth-generation pulmonary arteries isolated from control fetal lambs, an effect completely blocked after inhibition of nitric oxide synthase (NOS). In contrast, E4021 did not relax pulmonary arteries isolated from hypertensive lambs. Pretreatment with E4021 (10(-7) M) significantly enhanced relaxations to the NO donor S-nitrosyl-acetyl-penicilamine (SNAP) in arteries from both control and hypertensive lambs. In control, fully instrumented fetal lambs, infusions of E4021 (31 microgram/min) selectively dilated the pulmonary circulation, an effect again blocked after inhibition of NO synthase. Further studies were performed in newborn lambs with PPHN to study the vascular effects of E4021 alone, and in combination with inhaled NO. E4021 alone (1 to 100 microgram/kg/min) decreased pulmonary artery pressure (Ppa) in a dose-dependent fashion, and had minimal effect on systemic pressure. At the highest dose (100 microgram/kg/min), the dilation was selective for the pulmonary circulation. In subsequent protocols, E4021 (10 microgram/kg/min) significantly decreased Ppa and pulmonary vascular resistance (PVR), but these pulmonary vascular effects were not enhanced after NO inhalation at 0.5 or 5 ppm. We speculate that the lack of enhancement was due to the dramatic effects of E4021 alone. Potent, specific phosphodiesterase inhibitors such as E4021 may prove to be useful in the treatment of PPHN.

Nitric oxide regulates shear stress-induced early growth response-1. Expression via the extracellular signal-regulated kinase pathway in endothelial cells

Endothelial cells (ECs) subjected to shear stress constantly release nitric oxide (NO). The effect of NO on shear stress-induced endothelial responses was examined. ECs subjected to shear stress induced a transient and shear force-dependent increase in early growth response-1 (Egr-1) mRNA levels. Treatment of ECs with an NO donor, S-nitroso-N-acetylpenicillamine (SNAP) or 3-morpholinosydnonimine (SIN-1), inhibited this shear stress-induced Egr-1 expression. Conversely, an NO synthase inhibitor to ECs, N(G)-monomethyl-L-arginine, augmented this Egr-1 expression. NO modulation of Egr-1 expression was demonstrated by functional analysis of Egr-1 promoter activity using a chimera containing the Egr-1 promoter region (-698 bp) and reporter gene luciferase. In contrast to the enhanced promoter activity after N(G)-monomethyl-L-arginine treatment, shear stress-induced Egr-1 promoter activity was attenuated after ECs were treated with an NO donor. ECs cotransfected with a dominant negative mutant of Ras (RasN17), Raf-1 (Raf301), or a catalytically inactive mutant of extracellular signal-regulated kinase (ERK)-2 (mERK) inhibited shear stress-induced Egr-1 promoter activity. NO modulation of the signaling pathway was shown by its inhibitory effect on shear stress-induced ERK1/ERK2 phosphorylation and activity. This inhibitory effect was further substantiated by the inhibition of NO on both the shear stress-induced transcriptional activity of Elk-1 (an ERK substrate) and the promoter activity of a reporter construct containing serum response element. NO-treated ECs resulted in a reduction of binding of nuclear proteins to the Egr-1 binding sequences in the platelet-derived growth factor-A promoter region. These results indicate that shear stress-induced Egr-1 expression is modulated by NO via the ERK signaling pathway in ECs. Our findings support the importance of NO as a negative regulator in endothelial responses to hemodynamic forces.

Modulation by pathophysiological stimuli of the shear stress-induced up-regulation of endothelial nitric oxide synthase expression in endothelial cells

OBJECTIVE

Fluid shear stress (the frictional force resulting from blood flow) is a principal regulator of endothelial nitric oxide synthase (eNOS) expression. We examined the responses of eNOS messenger ribonucleic acid (mRNA) levels to dynamic shear stimuli in the presence of pathological risk modifiers.

METHODS

Confluent bovine aortic endothelial cells were subjected in vitro to shear stress (using a cone-plate viscometer) and to hydrostatic pressure (using a custom-built pressure chamber device). eNOS mRNA levels were quantitated by densitometric analysis of Northern blots.

RESULTS

In contrast to steady laminar shear stress, which elevated eNOS mRNA levels in a time- and dose-dependent manner (2.9- and 3.6-fold after 6 h at 4 and 20 dyn/cm2, respectively), steady hydrostatic pressure of 150 mm Hg decreased eNOS mRNA levels by 46%. eNOS mRNA up-regulation by shear stress was reversible after cessation of flow, although it was not influenced by previous shear exposure, and it was not mediated by a stable transferable factor. eNOS mRNA up-regulation by sinusoidal shear stress was frequency-dependent, with a moderate response at 1-Hz oscillating shear and no change at 0.3 Hz. Hypoxia (3% O2) suppressed eNOS mRNA expression by 78% under static conditions and by 72% under shear conditions but did not alter the fold induction by shear. Elevated glucose concentrations reduced eNOS mRNA levels in both resting and shear stress-exposed cells but did not reduce the fold induction by shear; the protein kinase C inhibitor calphostin C was without effect. Shear-induced up-regulation of eNOS mRNA was unaffected by changes in the medium partial pressure of CO2/pH, by the Na+/H+-exchanger inhibitor HOE694, or by aspirin. In contrast, the shear response was potentiated by homocysteine.

CONCLUSION

Both physical and chemical stimuli regulate eNOS mRNA levels in endothelial cells. Although eNOS mRNA expression is increased by shear stress, it is decreased by hydrostatic pressure, hypoxia, and elevated glucose levels. The effect of shear on eNOS mRNA expression involves a reversible, frequency-dependent process. These in vitro findings suggest possible contributions of the eNOS flow response to atherosclerosis, in the presence of systemic risk factors.

Opposing effects of reactive oxygen species and cholesterol on endothelial nitric oxide synthase and endothelial cell caveolae

Synthesis of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) is critical for normal vascular homeostasis. eNOS function is rapidly regulated by agonists and blood flow and chronically by factors that regulate mRNA stability and gene transcription. Recently, localization of eNOS to specialized plasma membrane invaginations termed caveolae has been proposed to be required for maximal eNOS activity. Because caveolae are highly enriched in cholesterol, and hypercholesterolemia is associated with increased NO production, we first studied the effects of cholesterol loading on eNOS localization and NO production in cultured bovine aortic endothelial cells (BAECs). Caveolae-enriched fractions were prepared by OptiPrep gradient density centrifugation. Treatment of BAECs with 30 microgram/mL cholesterol for 24 hours stimulated significant increases in total eNOS protein expression (1.50-fold), eNOS associated with caveolae-enriched membranes (2.23-fold), and calcium ionophore-stimulated NO production (1.56-fold). Because reactive oxygen species (ROS) contribute to endothelial dysfunction in hypercholesterolemia, we next studied the effects of ROS on eNOS localization and caveolae number. Treatment of BAECs for 24 hours with 1 micromol/L LY83583, a superoxide-generating napthoquinolinedione, decreased caveolae number measured by electron microscopy and prevented the cholesterol-mediated increases in eNOS expression. In vitro exposure of caveolae-enriched membranes to ROS (xanthine plus xanthine oxidase) dissociated caveolin more readily than eNOS from the membranes. These results show that cholesterol treatment increases eNOS expression, whereas ROS treatment decreases eNOS expression and the association of eNOS with caveolin in caveolae-enriched membranes. Our data suggest that oxidative stress modulates endothelial function by regulating caveolae formation, eNOS expression, and eNOS-caveolin interactions.

Adaptation to chronic hypoxia confers tolerance to subsequent myocardial ischemia by increased nitric oxide production

Chronic exposure to hypoxia from birth increased the tolerance of the rabbit heart to subsequent ischemia compared with age-matched normoxic controls. The nitric oxide donor GSNO increased recovery of post-ischemic function in normoxic hearts to values not different from hypoxic controls, but had no effect on hypoxic hearts. The nitric oxide synthase inhibitors L-NAME and L-NMA abolished the cardioprotective effect of hypoxia. Message and catalytic activity for constitutive nitric oxide synthase as well as nitrite, nitrate, and cGMP levels were elevated in hypoxic hearts. Inducible nitric oxide synthase was not detected in normoxic or chronically hypoxic hearts. Increased tolerance to ischemia in rabbit hearts adapted to chronic hypoxia is associated with increased expression of constitutive nitric oxide synthase.

Exercise improves flow-mediated vasodilatation of skeletal muscle arteries in rats with chronic heart failure. Role of nitric oxide, prostanoids, and oxidant stress

BACKGROUND

Flow-mediated dilatation (FMD) of the peripheral arteries may be impaired in chronic heart failure (CHF), and this could contribute to the increased peripheral resistance and exercise intolerance that occur with this disease. Physical exercise improves the FMD of large conduit arteries in CHF, but whether a similar impairment also occurs in smaller arteries is unknown. The mechanisms of the changes in FMD after CHF or exercise are also unknown.

METHODS AND RESULTS

FMD was assessed in isolated, perfused, and preconstricted gracilis muscle arteries from sham-operated rats or CHF rats (coronary artery ligation) who were either sedentary or exercised (30-minute swimming period twice a day for 10 weeks, starting 7 days after ligation). In animals with hemodynamic and echographic signs of CHF, FMD was abolished and converted into vasoconstriction (percent change in diameter after 370 microL/min flow: sham, 42+/-5%; CHF, -4+/-3%; P<0.05). Exercise partially restored FMD (18+/-3%; P<0.05 versus CHF). In sham rats, FMD was abolished by the nitric oxide-synthase inhibitor Nomega-nitro-L-arginine (L-NA) but unaffected by the cyclooxygenase inhibitor diclofenac or the free radical scavenger N-(2-mercaptopropionyl)-glycine (MPG). In arteries from sedentary CHF rats, FMD was not modified by L-NA, but it was partially restored by diclofenac or MPG. In exercised CHF rats, FMD was abolished by L-NA and only moderately improved by diclofenac or MPG. Likewise, endothelial nitric oxide synthase mRNA expression (determined by reverse transcription polymerase chain reaction at the level of the gracilis muscle) was reduced by CHF, and this was prevented by exercise.

CONCLUSIONS

CHF abolishes the FMD of small arteries by impairing the nitric oxide pathway, increasing oxidant stress, and releasing a prostanoid-contracting factor. Exercise partially restores FMD by increasing expression of endothelial nitric oxide synthase and preventing the production of vasoconstrictor prostanoids and free radicals. Such restoration of FMD might contribute to the increase in exercise capacity after physical exercise in CHF.

The 67-kDa laminin-binding protein is involved in shear stress-dependent endothelial nitric-oxide synthase expression

It has been suggested that the mechanical forces acting on endothelial cells may be sensed in part by cell-matrix connections. We therefore studied the role of different matrix proteins, in particular laminin I, on a shear stress-dependent endothelial response, namely nitric-oxide synthase (eNOS) expression. Primary porcine aortic endothelial cells were seeded onto glass plates either noncoated (NC cells) or precoated with fibronectin (FN cells), laminin (LN cells), or collagen I (CN cells). Western blots were used to detect differences in the final matrix composition of these cells. A shear stress of 16 dyn/cm2 was applied for 6 h. Only LN cells showed detectable amounts of laminin I in their underlying matrix when they reached confluence. They reacted with a 2-fold increase of eNOS expression (n = 16, p < 0.001) to the exposure of shear stress, which went along with enhanced eNOS protein and NO release. In contrast, neither FN cells (n = 9) nor NC cells (n = 13) showed a significant increase of eNOS expression under shear stress. The increase in CN cells was borderline (1.4-fold; n = 9, p < 0.05) and was not associated with an increase of eNOS protein. The shear-induced increase in eNOS expression of LN cells was abolished by the peptide YIGSR, which blocks the cellular binding to laminin I via a 67-kDa laminin-binding protein, whereas a control peptide (YIGSK) had no effect. The induction of eNOS expression by shear stress is stimulated by an interaction of endothelial cells with laminin which is, at least in part, mediated by a 67-kDa laminin-binding protein.

Enhanced blood pressure variability in eNOS knockout mice

It has been shown previously that endogenous nitric oxide can buffer arterial blood pressure variability in dogs and rats. In these former studies, all isoforms of the nitric oxide synthase were blocked pharmacologically and an increased blood pressure variability was observed. Thus the question as to which isoform of the nitric oxide synthase is responsible for the blood pressure buffering effect of endogenous nitric oxide remains unraveled. In the present study, we therefore compared blood pressure variability in knockout mice that lack specifically the gene for endothelial nitric oxide synthase with their respective wild-type controls. One day after carotid artery cannulation, blood pressure was recorded in these conscious mice. During resting conditions, blood pressure variability was markedly enhanced in knockout mice compared with wild-type mice (10.5+/-1.5 mm Hg2 vs 6.0+/-0.8 mm Hg2, P<0.05). Power spectral analysis revealed that this increase in blood pressure variability is manifested at low frequencies that range from 0.05 to 0.40 s-1 (Hz) (5.1+/-1.0 mm Hg2 vs 2.5+/-0.5 mm Hg2, P<0.05). On the basis of these results, we conclude that the blood pressure buffering effect of endogenous nitric oxide is mediated by the endothelial isoform of the nitric oxide synthase. In addition, endothelial nitric oxide is most effective in buffering blood pressure oscillations at frequencies that range from 0.05 to 0.40 s-1 (Hz) in conscious mice.

The exercise-induced oxidative stress paradox: the effects of physical exercise training

BACKGROUND

Although physical exercise training is highly recommended, physical exercise causes oxidative stress, which is potentially injurious. This study evaluates this 'exercise paradox' by evaluating the effect of physical exercise on exercise-induced lipid peroxidation.

METHODS

Measurement of lipid peroxidation (ie, expired ethane and pentane and plasma malondealdehyde) taken during cardiopulmonary exercise stress testing were compared between a group of 10 cardiac patients who underwent physical exercise training in a cardiac rehabilitation setting and a group of 10 nonexercising cardiac patients.

RESULTS

Our findings indicate that physical exercise training increased physical work capacity without a concomitant increase in expired markers of lipid peroxidation (ethane and pentane) and decreased malondealdehyde levels.

CONCLUSIONS

Because physical exercise-trained people can perform more intense physical work with less oxidative stress, we conclude that physical exercise training can reduce potential chronic health effects associated with daily activities by contributing to an overall reduction in exercise-induced free radical production.

Cardiac microvascular endothelial cells express alpha-smooth muscle actin and show low NOS III activity

We established a culture system of porcine coronary microvascular endothelial cells (MVEC) with high cellular yield and purity >98%. Endothelial origin was confirmed by immunostaining, immunoblotting and fluorescence-activated cell sorter (FACS) analysis using low-density lipoprotein uptake, CD31, von Willebrand factor, and the lectin Dolichos biflorus agglutinin. MVEC were positive for alpha-smooth muscle actin in culture and in myocardium, as confirmed by FACS. Of the primary MVEC, approximately 30% expressed nitric oxide synthase (NOS) III in numbers decreasing from the first passage (6 +/- 1%) to the second passage (4 +/- 1%; P < 0.001 vs. primary isolates), whereas approximately 100% of aortic endothelial cells (AEC) expressed NOS III. In AEC, NOS III activity (pmol citrulline. mg protein-1. min-1) was 80 +/- 10 and was nearly abolished in the absence of calcium (5 +/- 1, P < 0.001). In primary MVEC, however, NOS III activity in the presence and absence of calcium was 20 +/- 4 and 25 +/- 5, respectively. We conclude that cardiac MVEC, in contrast to AEC, contain alpha-smooth muscle actin, show low-grade NOS III activity, and provide a suitable in vitro system for the study of endothelial pathophysiology.

Influences of inflation rate and duration on vasodilatory effect by intermittent pneumatic compression in distant skeletal muscle

Previous study has demonstrated that application of intermittent pneumatic compression on legs can cause vasodilation in distant skeletal muscle at the microcirculation level. This study evaluated the influence of inflation rate and peak-pressure duration on the vasodilatory effects of intermittent pneumatic compression. The cremaster muscles of 50 male rats were exposed and divided into five groups of 10 each. A specially designed intermittent pneumatic-compression device was applied in a medial-lateral fashion to both legs of all rats for 60 minutes, with an inflation rate and peak-pressure duration of 0.5 and 5 seconds, respectively, in group A, 5 and 0 seconds in group B, 5 and 5 seconds in group C, 10 and 0 seconds in group D, and 10 and 5 seconds in group E. Diameters of arterial segments were measured in vessels of three size categories (10-20, 21-40, and 41-70 microm) for 120 minutes. The results showed that the greatest increase in diameter was produced by intermittent pneumatic compression with the shortest inflation rate (0.5 seconds). A moderate increase resulted from compression with an inflation rate of 5 seconds, and no effective vasodilation occurred during compression with the longest inflation rate (10 seconds). When the groups with different inflation rates but the same peak-pressure duration were compared, there was a significant difference between any two groups among groups A, C, and E and between groups B and D. When the groups with different peak-pressure durations but the same inflation rate were compared, compression with a peak-pressure duration of 5 seconds caused a generally similar degree of diameter change as did compression without inflation at peak pressure. The findings suggest that inflation rate plays an important role in the modulation of distant microcirculation induced by intermittent pneumatic compression whereas peak-pressure duration does not significantly influence the vasodilatory effects of the compression. This may be due to the fact that rapid inflation produces a significant increase in shear stress on the vascular wall, which stimulates vascular endothelium to release nitric oxide, causing systemic vasodilation.

A vascular bed-specific pathway

The endothelial nitric oxide synthase (eNOS) gene is induced by a variety of extracellular signals under both in vitro and in vivo conditions. To gain insight into the mechanisms underlying environmental regulation of eNos expression, transgenic mice were generated with the 1,600-bp 5' flanking region of the human eNos promoter coupled to the coding region of the LacZ gene. In multiple independent lines of mice, transgene expression was detected within the endothelium of the brain, heart, skeletal muscle, and aorta. beta-galactosidase activity was consistently absent in the vascular beds of the liver, kidney, and spleen. In stable transfection assays of murine endothelial progenitor cells, the 1,600-bp promoter region was selectively induced by conditioned media from cardiac myocytes, skeletal myocytes, and brain astrocytes. Cardiac myocyte-mediated induction was partly abrogated by neutralizing anti-platelet-derived growth factor (PDGF) antibodies. In addition, promoter activity was upregulated by PDGF-AB. Analysis of promoter deletions revealed that a PDGF response element lies between -744 and -1,600 relative to the start site of transcription, whereas a PDGF-independent cardiac myocyte response element is present within the first 166 bp of the 5' flanking region. Taken together, these results suggest that the eNos gene is regulated in the cardiac endothelium by both a PDGF-dependent and PDGF-independent microvascular bed-specific signaling pathway.

Inducible NO synthase inhibition attenuates shear stress-induced pulmonary vasodilation in the ovine fetus

Recent studies have suggested that type II (inducible) nitric oxide (NO) synthase (NOS II) is present in the fetal lung, but its physiological roles are uncertain. Whether NOS II activity contributes to the NO-mediated fall in pulmonary vascular resistance (PVR) during shear stress-induced pulmonary vasodilation is unknown. We studied the hemodynamic effects of two selective NOS II antagonists [aminoguanidine (AG) and S-ethylisothiourea (EIT)], a nonselective NOS antagonist [nitro-L-arginine (L-NNA)], and a nonselective vasoconstrictor (U-46619) on PVR during partial compression of the ductus arteriosus (DA) in 20 chronically prepared fetal lambs (mean age 132 +/- 2 days, term 147 days). At surgery, catheters were placed in the left pulmonary artery (LPA) for selective drug infusion, an ultrasonic flow transducer was placed on the LPA to measure blood flow, and an inflatable vascular occluder was placed loosely around the DA for compression. On alternate days, a brief intrapulmonary infusion of normal saline (control), AG, EIT, L-NNA, or U-46619 was infused in random order into the LPA. The DA was compressed to increase mean pulmonary arterial pressure (MPAP) 12-15 mmHg above baseline values and held constant for 30 min. In control studies, DA compression reduced PVR by 42% from baseline values (P < 0.01). L-NNA treatment completely blocked the fall in PVR during DA compression. AG and EIT attenuated the decrease in PVR by 30 and 19%, respectively (P < 0.05). Nonspecific elevation in PVR by U-46619 did not affect the fall in PVR during DA compression. Immunostaining for NOS II identified this isoform in airway epithelium and vascular smooth muscle in the late-gestation ovine fetal lung. We conclude that selective NOS II antagonists attenuate but do not block shear stress-induced vasodilation in the fetal lung. We speculate that stimulation of NOS II activity, perhaps from smooth muscle cells, contributes in part to the NO-mediated fall in PVR during shear stress-induced pulmonary vasodilation.

Upregulation of superoxide dismutase and nitric oxide synthase mediates the apoptosis-suppressive effects of shear stress on endothelial cells

Physiological levels of laminar shear stress completely abrogate apoptosis of human endothelial cells in response to a variety of stimuli and might therefore importantly contribute to endothelial integrity. We show here that the apoptosis-suppressive effects of shear stress are mediated by upregulation of Cu/Zn SOD and NO synthase. Shear stress-mediated inhibition of endothelial cell apoptosis in response to exogenous oxygen radicals, oxidized LDL, and tumor necrosis factor-alpha was associated with complete inhibition of caspase-3-like activity, the central effector arm executing the apoptotic cell death program in endothelial cells. Shear stress-dependent upregulation of Cu/Zn SOD and NO synthase blocks activation of the caspase cascade in response to apoptosis-inducing stimuli. These findings establish the upregulation of Cu/Zn SOD and NO synthase by shear stress as a central protective cellular mechanism to preserve the integrity of the endothelium after proapoptotic stimulation.

Novel optical methodologies in studying mechanical signal transduction in mammalian cells

For the last 3 decades evidence has been accumulating that some types of mammalian cells respond to their mechanically active environment by altering their morphology, growth rate, and metabolism. The study of such responses is very important in understanding, physiological and pathological conditions ranging from bone formation to atherosclerosis. Obtaining this knowledge has been the goal for an active research area in bioengineering termed cell mechanotransduction. The advancement of optical methodologies used in cell biology research has given the tools to elucidate cellular mechanisms that would otherwise be impossible to visualize. Combined with molecular biology techniques, they give engineers invaluable tools in understanding the chemical pathways involved in mechanotransduction. Herein we briefly review the current knowledge on mechanical signal transduction in mammalian cells, focusing on the application of novel optical techniques in the ongoing research.

Flow regulation of ecNOS and Cu/Zn SOD mRNA expression in porcine coronary arterioles

The purpose of this study was to test the hypothesis that increased flow through coronary arterioles increases endothelial cell nitric oxide synthase (ecNOS) and Cu/Zn superoxide dismutase (SOD) mRNA expression. Single porcine coronary arterioles (ID 100-160 micrometers; pressurized) were cannulated, perfused, and exposed to intraluminal flow sufficient to produce maximal flow-induced dilation of coronary arterioles (high flow; 7.52 +/- 0.22 microliter/min), low flow (0.84 +/- 0.05 microliter/min), or no flow for 2 or 4 h. Mean shear stress was calculated to be 5.7 +/- 1.0 dyn/cm2 for high-flow arterioles and 1. 6 +/- 1.0 dyn/cm2 for low-flow arterioles. At the end of the treatment period, mRNA was isolated from each vessel, and ecNOS and SOD mRNA expression was assessed using a semiquantitative RT-PCR. All data were standardized by coamplifying ecNOS or SOD with glyceraldehyde-3-phosphate dehydrogenase. The results indicate that ecNOS mRNA expression is increased in arterioles exposed to 2 or 4 h of high flow. In contrast, SOD mRNA expression was increased only after 4 h of high flow. Neither gene is induced by exposure to low flow. On the basis of these data, we concluded that ecNOS and SOD mRNA expression is regulated by flow in porcine coronary arterioles. In addition, we concluded that a threshold level of flow and shear stress must be sustained to elicit the upregulation of ecNOS and SOD mRNA expression.

Variable expression of endothelial NO synthase in three forms of rat pulmonary hypertension

Endothelial nitric oxide (NO) synthase (eNOS) mRNA and protein and NO production are increased in hypoxia-induced hypertensive rat lungs, but it is uncertain whether eNOS gene expression and activity are increased in other forms of rat pulmonary hypertension. To investigate these questions, we measured eNOS mRNA and protein, eNOS immunohistochemical localization, perfusate NO product levels, and NO-mediated suppression of resting vascular tone in chronically hypoxic (3-4 wk at barometric pressure of 410 mmHg), monocrotaline-treated (4 wk after 60 mg/kg), and fawn-hooded (6-9 mo old) rats. eNOS mRNA levels (Northern blot) were greater in hypoxic and monocrotaline-treated lungs (130 and 125% of control lungs, respectively; P < 0.05) but not in fawn-hooded lungs. Western blotting indicated that eNOS protein levels increased to 300 +/- 46% of control levels in hypoxic lungs (P < 0.05) but were decreased by 50 +/- 5 and 60 +/- 11%, respectively, in monocrotaline-treated and fawn-hooded lungs (P < 0.05). Immunostaining showed prominent eNOS expression in small neomuscularized arterioles in all groups, whereas perfusate NO product levels increased in chronically hypoxic lungs (3.4 +/- 1.4 microM; P < 0.05) but not in either monocrotaline-treated (0.7 +/- 0.3 microM) or fawn-hooded (0.45 +/- 0.1 microM) lungs vs. normotensive lungs (0.12 +/- 0.07 microM). All hypertensive lungs had increased baseline perfusion pressure in response to nitro-L-arginine but not to the inducible NOS inhibitor aminoguanidine. These results indicate that even though NO activity suppresses resting vascular tone in pulmonary hypertension, there are differences among the groups regarding eNOS gene expression and NO production. A better understanding of eNOS gene expression and activity in these models may provide insights into the regulation of this vasodilator system in various forms of human pulmonary hypertension.

Nitric oxide, nitric oxide synthase, and hypertensive vascular disease

In normotension the endothelium produces mainly nitric oxide (NO) and prostacyclin, and the vasodilator and growth inhibitory influence predominates. Hypertension, however, is associated with a shift towards enhanced constriction and vascular hypertrophy. These effects are associated with an apparent decrease in the production of bioactive NO and concomitant increase in the generation of oxygen-derived free radicals, such as superoxide anions (O(2)-). While the enzymatic source of endothelial O(2)- has been debated intensely over the past few years, it may well turn out that the endothelial NO synthase is itself an important producer of O(2)-. Because the redox state of endothelial cells and, for example, the activation of redox-sensitive transcription factors is regulated by the balance between NO and O(2)- production, endothelial NO synthase may well be the most crucial enzyme determining the anti- or prohypertensive and eventually proatherogenic state of the vascular wall.

Characterization of the human endothelial nitric-oxide synthase promoter

Understanding transcription initiation of the endothelial nitric-oxide synthase (eNOS) gene appears pivotal to gaining a comprehensive view of NO biology in the blood vessel wall. The present study therefore focused upon a detailed dissection of the functionally important cis-DNA elements and the multiprotein complexes implicated in the cooperative control of constitutive expression of the human eNOS gene in vascular endothelium. Two tightly clustered cis-regulatory regions were identified in the proximal enhancer of the TATA-less eNOS promoter using deletion analysis and linker-scanning mutagenesis: positive regulatory domains I (-104/-95 relative to transcription initiation) and II (-144/-115). Analysis of trans-factor binding and functional expression studies revealed a surprising degree of cooperativity and complexity. The nucleoprotein complexes that form upon these regions in endothelial cells contained Ets family members, Sp1, variants of Sp3, MAZ, and YY1. Functional domain studies in Drosophila Schneider cells and endothelial cells revealed examples of positive and negative protein-protein cooperativity involving Sp1, variants of Sp3, Ets-1, Elf-1, and MAZ. Therefore, multiprotein complexes are formed on the activator recognition sites within this 50-base pair region of the human eNOS promoter in vascular endothelium.