Background-Indirect evidence implicates endothelial dysfunction in the pathogenesis of vascular diseases associated with obstructive sleep apnea (OSA). We investigated directly whether dysfunction and inflammation occur in vivo in the vascular endothelium of patients with OSA. The effects of continuous positive airway pressure (CPAP) therapy on endothelial function and repair capacity were assessed. Methods and Results-Thirty-two patients with newly diagnosed OSA and 15 control subjects were studied. Proteins that regulate basal endothelial nitric oxide (NO) production (endothelial NO synthase [eNOS] and phosphorylated eNOS) and inflammation (cyclooxygenase-2 and inducible NOS) and markers of oxidative stress (nitrotyrosine) were quantified by immunofluorescence in freshly harvested venous endothelial cells before and after 4 weeks of CPAP therapy. Vascular reactivity was measured by flow-mediated dilation. Circulating endothelial progenitor cell levels were quantified to assess endothelial repair capacity. Baseline endothelial expression of eNOS and phosphorylated eNOS was reduced by 59% and 94%, respectively, in patients with OSA compared with control subjects. Expression of both nitrotyrosine and cyclooxygenase-2 was 5-fold greater in patients with OSA than in control subjects, whereas inducible NOS expression was 56% greater. Expression of eNOS and phosphorylated eNOS significantly increased, whereas expression of nitrotyrosine, cyclooxygenase-2, and inducible NOS significantly decreased in patients who adhered to CPAP Ն4 hours daily. Baseline flow-mediated dilation and endothelial progenitor cell levels were lower in patients than in control subjects, and both significantly increased in patients who adhered to CPAP Ն4 hours daily. Conclusions-OSA directly affects the vascular endothelium by promoting inflammation and oxidative stress while decreasing NO availability and repair capacity. Effective CPAP therapy is associated with the reversal of these alterations.

Because animal studies have demonstrated that mechanical ventilation at high volume and pressure can be deleterious to the lungs, limitation of airway pressure, allowing hypercapnia if necessary, is already used for ventilation of acute respiratory distress syndrome (ARDS). Whether a systematic and more drastic reduction is necessary is debatable. A multicenter randomized study was undertaken to compare a strategy aimed at limiting the end-inspiratory plateau pressure to 25 cm H2O, using tidal volume (VT) below 10 ml/kg of body weight, versus a more conventional ventilatory approach (with regard to current practice) using VT at 10 ml/kg or above and close to normal PaCO2. Both arms used a similar level of positive end-expiratory pressure. A total of 116 patients with ARDS and no organ failure other than the lung were enrolled over 32 mo in 25 centers. The two groups were similar at inclusion. Patients in the two arms were ventilated with different VT (7.1 +/- 1.3 versus 10.3 +/- 1.7 ml/kg at Day 1, p < 0.001) and plateau pressures (25.7 +/- 5. 0 versus 31.7 +/- 6.6 cm H2O at Day 1, p < 0.001), resulting in different PaCO2 (59.5 +/- 15.0 versus 41.3 +/- 7.6 mm Hg, p < 0.001) and pH (7.28 +/- 0.09 versus 7.4 +/- 0.09, p < 0.001), but a similar level of oxygenation. The new approach did not reduce mortality at Day 60 (46.6% versus 37.9% in control subjects, p = 0.38), the duration of mechanical ventilation (23.1 +/- 20.2 versus 21.4 +/- 16. 3 d, p = 0.85), the incidence of pneumothorax (14% versus 12%, p = 0. 78), or the secondary occurrence of multiple organ failure (41% versus 41%, p = 1). We conclude that no benefit could be observed with reduced VT titrated to reach plateau pressures around 25 cm H2O compared with a more conventional approach in which normocapnia was achieved with plateau pressures already below 35 cm H2O.

No abstract

Vasopressin is a potent vasopressor for improving organ perfusion during septic shock. The rationale for the use of vasopressin is its relative deficiency of plasma levels and hypersensitivity to its vasopressor effects during septic shock. Growing evidence suggests that low-dose (<0.04 U/min) vasopressin is safe and effective for the treatment of vasodilatory shock. Although it is being used more frequently, there are no randomized clinical trials comparing vasopressin as a first-line agent to commonly used vasopressors. However, vasopressin causes arterial smooth muscle cell contraction through a non-catecholamine receptor pathway, thus it represents an attractive adjunct to the management of septic shock, especially when catecholamines are ineffective.

Abstract-Alveolar epithelial ␤-adrenergic receptor (␤AR) activation accelerates active Na ϩ transport in lung epithelial cells in vitro and speeds alveolar edema resolution in human lung tissue and normal and injured animal lungs. Whether these receptors are essential for alveolar fluid clearance (AFC) or if other mechanisms are sufficient to regulate active transport is unknown. In this study, we report that mice with no ␤ 1 -or ␤ 2 -adrenergic receptors (␤ 1 AR Ϫ/Ϫ /␤ 2 AR Ϫ/Ϫ ) have reduced distal lung Na,K-ATPase function and diminished basal and amiloride-sensitive AFC. Total lung water content in these animals was not different from wild-type controls, suggesting that ␤AR signaling may not be required for alveolar fluid homeostasis in uninjured lungs. Comparison of isoproterenol-sensitive AFC in mice with ␤ 1 -but not ␤ 2 -adrenergic receptors to ␤ 1 AR Ϫ/Ϫ /␤ 2 AR Ϫ/Ϫ mice indicates that the ␤ 2 AR mediates the bulk of ␤-adrenergic-sensitive alveolar active Na ϩ transport. To test the necessity of ␤AR signaling in acute lung injury, Key Words: alveolar fluid clearance Ⅲ pulmonary edema Ⅲ ␤ 2 -adrenergic receptor Ⅲ adenovirus Ⅲ Na ϩ channel T he combined action of alveolar epithelial Na ϩ channels (ENaCs), the cystic fibrosis transmembrane conductance regulator (CFTR), Na,K-ATPases, and K ϩ channels creates the transepithelial Na ϩ gradient needed for the transit of excess fluid from the alveolar airspace. 1,2 The importance of these proteins to this energy-dependent (ie, active) process is evidenced by data showing that their inhibition reduces the lung's ability to clear excess alveolar fluid [3][4][5][6][7] and that their upregulation confers protection from acute injury. 4,8,9 Despite these extensive investigations, the mechanisms by which these proteins are upregulated in response to excess alveolar fluid (pulmonary edema) are not well resolved.One possible pathway for upregulation of alveolar-active Na ϩ transport is ␤-adrenergic receptor activation. Stimulation of alveolar epithelial ␤ARs by endogenous or exogenous catecholamines accelerates active Na ϩ transport in lung epithelial cells in vitro and in experimental in vivo systems by increasing the expression and/or function of epithelial transport proteins. 10 -12 Thus, this G protein-dependent pathway represents a mechanism by which the lung can alter its physiology to adapt to and protect itself from excess alveolar fluid. What is not known is if ␤AR signaling is essential for the regulation of alveolar active Na ϩ transport or whether other mechanisms (eg, intracellular osmo-, redox-, or chemosensitive regulators) can enhance alveolar active transport to clear pulmonary edema.The present study was structured to define what contribution alveolar epithelial ␤ARs make to active Na ϩ transport in the alveolar epithelium of normal mice and mice with acute lung injury caused by exposure to hyperoxia. Herein, we show that distal lung transport protein function and the lung's ability to clear excess alveolar fluid is highly dependent on Materials an...

Abstract-␤-Adrenergic agonists accelerate the clearance of alveolar fluid by increasing the expression and activity of epithelial solute transport proteins such as amiloride-sensitive epithelial Na ϩ channels (ENaC) and Na,K-ATPases. Here we report that adenoviral-mediated overexpression of a human ␤ 2 -adrenergic receptor (␤ 2 AR) cDNA increases ␤ 2 AR mRNA, membrane-bound receptor protein expression, and receptor function (procaterol-induced cAMP production) in human lung epithelial cells (A549). Receptor overexpression was associated with increased catecholamine (procaterol)-responsive active Na ϩ transport and increased abundance of Na,K-ATPases in the basolateral cell membrane. ␤ 2 AR gene transfer to the alveolar epithelium of normal rats improved membrane-bound ␤ 2 AR expression and function and increased levels of ENaC (␣ subunit) abundance and Na,K-ATPases activity in apical and basolateral cell membrane fractions isolated from the peripheral lung, respectively. Alveolar fluid clearance (AFC), an index of active Na ϩ transport, in ␤ 2 AR overexpressing rats was up to 100% greater than sham-infected controls and rats infected with an adenovirus that expresses no cDNA. The addition of the ␤ 2 AR-specific agonist procaterol to ␤ 2 AR overexpressing lungs did not increase AFC further. AFC in ␤ 2 AR overexpressing lungs from adrenalectomized or propranolol-treated rats revealed clearance rates that were the same or less than normal, untreated, sham-infected controls. These experiments indicate that alveolar ␤ 2 AR overexpression improves ␤ 2 AR function and maximally upregulates ␤-agonist-responsive active Na ϩ transport by improving responsiveness to endogenous catecholamines. These studies suggest that upregulation of ␤ 2 AR function may someday prove useful for the treatment of pulmonary edema.

Adenosine is a purine nucleoside that regulates cell function through G protein-coupled receptors that activate or inhibit adenylyl cyclase. Based on the understanding that cAMP regulates alveolar epithelial active Na ؉ transport, we hypothesized that adenosine and its receptors have the potential to regulate alveolar ion transport and airspace fluid content. Herein, we report that type 1 (A1R), 2a (A2aR), 2b (A2bR), and 3 (A3R) adenosine receptors are present in rat and mouse lungs and alveolar type 1 and 2 epithelial cells (AT1 and AT2). Rat AT2 cells generated and produced cAMP in response to adenosine, and micromolar concentrations of adenosine were measured in bronchoalveolar lavage fluid from mice. Ussing chamber studies of rat AT2 cells indicated that adenosine affects ion transport through engagement of A1R, A2aR, and/or A3R through a mechanism that increases CFTR and amiloride-sensitive channel function. Intratracheal instillation of low concentrations of adenosine (<10 ؊8 M) or either A2aR-or A3R-specific agonists increased alveolar fluid clearance (AFC), whereas physiologic concentrations of adenosine (>10 ؊6 M) reduced AFC in mice and rats via an A1R-dependent pathway. Instillation of a CFTR inhibitor (CFTRinh-172) attenuated adenosine-mediated down-regulation of AFC, suggesting that adenosine causes Cl ؊ efflux by means of CFTR. These studies report a role for adenosine in regulation of alveolar ion transport and fluid clearance. These findings suggest that physiologic concentrations of adenosine allow the alveolar epithelium to counterbalance active Na ؉ absorption with Cl ؊ efflux through engagement of the A1R and raise the possibility that adenosine receptor ligands can be used to treat pulmonary edema.active sodium transport ͉ adenosine receptors ͉ cystic fibrosis transmembrane conductance regulator P ulmonary edema is due to increased fluid flux into the airspace and impairment of the active Na ϩ transport that clears it (1-4). A variety of approaches to improve alveolar epithelial cell active Na ϩ transport for purposes of accelerating alveolar fluid clearance (AFC) have been explored in experimental systems. Of particular interest are receptor-ligand interactions that increase cAMP production in alveolar epithelial cells. Adenosine is a purine nucleoside that signals through four distinct G protein-coupled receptors, type 1 (A 1 R), type 2a (A 2a R), type 2b (A 2b R), and type 3 (A 3 R). In most cell systems, the A 1 R and A 3 R receptors inhibit adenylyl cyclase and/or lead to signaling through inositol-3-phosphate and phospholipase C. Engagement of type 2 receptors activates adenylyl cyclase by means of Gs␣ and increases cAMP levels. The ability of adenosine receptors (ARs) to couple to adenylyl cyclase led us to hypothesize that ARs might participate in regulation of alveolar epithelial active Na ϩ transport. We approached this hypothesis in rats and mice by testing whether adenosine and its receptors are present in the distal airspace and whether they affect AFC in vivo and vectorial Na ϩ...

Pulmonary edema is cleared via active Na(+) transport by alveolar epithelial Na(+)/K(+)-ATPases and Na(+) channels. Rats exposed to acute hyperoxia have a high mortality rate, decreased Na(+)/K(+)-ATPase function, and decreased alveolar fluid clearance (AFC). We hypothesized that Na(+)/K(+)-ATPase subunit gene overexpression could improve AFC in rats exposed to hyperoxia. We delivered 4 x 10(9) PFU of recombinant adenoviruses containing rat alpha(1) and beta(1) Na(+)/K(+)-ATPase subunit cDNAs (adalpha(1) and adbeta(1), respectively) to rat lungs 7 days prior to exposure to 100% O(2) for 64 hr. As compared with controls and ad alpha(1), AFC in the adbeta(1) rats was increased by >300%. Permeability for large solutes was less in the ad beta(1) than in the other hyperoxia groups. Glutathione oxidation, but not superoxide dismutase activity, was increased only in the adbeta(1) group. Survival through 14 days of hyperoxia was 100% in the adbeta(1) group but was not different from hyperoxic controls in animals given adalpha(1). Our data show that overexpression of a beta(1) Na(+)/K(+)-ATPase subunit augments AFC and improves survival in this model of acute lung injury via antioxidant-independent mechanisms. Conceivably, restoration of AFC via gene transfer of Na(+)/K(+)-ATPase subunit genes may prove useful for the treatment of acute lung injury and pulmonary edema.