The adenosine 2A receptor agonist GW328267C improves lung function after acute lung injury in rats.

There is a significant unmet need for treatments of patients with acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). The primary mechanism that leads to resolution of alveolar and pulmonary edema is active vectorial Na(+) and Cl(-) transport across the alveolar epithelium. Several studies have suggested a role for adenosine receptors in regulating this fluid transport in the lung. Furthermore, these studies point to the A(2A) subtype of adenosine receptor (A(2A)R) as playing a role to enhance fluid transport, suggesting that activation of the A(2A)R may enhance alveolar fluid clearance (AFC). The current studies test the potential therapeutic value of the A(2A)R agonist GW328267C to accelerate resolution of alveolar edema and ALI/ARDS in rats. GW328267C, at concentrations of 10(-5) M to 10(-3) M, instilled into the airspaces, increased AFC in control animals. GW328267C did not increase AFC beyond that produced by maximal ß-adrenergic stimulation. The effect of GW328267C was inhibited by amiloride but was not affected by cystic fibrosis transmembrane conductance regulator inhibition. The drug was tested in three models of ALI, HCl instillation 1 h, LPS instillation 16 h, and live Escherichia coli instillation 2 h before GW328267C instillation. After either type of injury, GW328267C (10(-4) M) decreased pulmonary edema formation and restored AFC, measured 1 h after GW328267C instillation. These findings show that GW328267C has beneficial effects in experimental models of ALI and may be a useful agent for treating patients with ALI or prophylactically to prevent ALI.

Phosphatidylinositol 4,5-bisphosphate stimulates alveolar epithelial fluid clearance in male and female adult rats.

Cell membrane phospholipids, like phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)], can regulate epithelial Na channel (ENaC) activity. Gender differences in lung ENaC expression have also been demonstrated. However, the effects in vivo on alveolar fluid clearance are uncertain. Thus PI(4,5)P(2) effects on alveolar fluid clearance were studied in male and female rats. An isosmolar 5% albumin solution was intrapulmonary instilled; alveolar fluid clearance was studied for 1 h. Female rats had a 37 ± 19% higher baseline alveolar fluid clearance than male rats. Bilateral ovariectomy attenuated this gender difference. Compared with controls, PI(4,5)P(2) instillation (300 µM) increased alveolar fluid clearance by ∼93% in both genders. Amiloride or the specific αENaC small-interfering RNA inhibited baseline and PI(4,5)P(2)-stimulated alveolar fluid clearance in both genders, indicating a dependence on amiloride-sensitive pathways. The fraction of amiloride inhibition was greater in PI(4,5)P(2)-instilled rats (male: 64 ± 10%; female: 70 ± 11%) than in controls (male: 30 ± 6%; female: 44 ± 8%). PI(4,5)P(2) instillation lacked additional alveolar fluid clearance stimulation above that of terbutaline, nor did propranolol inhibit alveolar fluid clearance after PI(4,5)P(2) instillation, indicating that PI(4,5)P(2) stimulation was not secondary to endogenous ß-adrenoceptor activation. PI(4,5)P(2) amine instillation resulted in an intermediate alveolar fluid clearance stimulation, suggesting that, to reach maximal alveolar fluid clearance stimulation, PI(4,5)P(2) must reside in cell membranes. In summary, PI(4,5)P(2) instillation upregulated in vivo alveolar fluid clearance similar to short-term ß-adrenoceptor upregulation of alveolar fluid clearance. PI(4,5)P(2) stimulation was mediated partly by increased amiloride-sensitive Na transport. There exist important gender-related effects suggesting a female advantage that may have clinical implications for resolution of acute lung injury.

Fetal lung epithelial ion channels relocate in the cell membrane during late gestation.

Near the end of gestation, the direction of ion and fluid flow across the alveolar epithelium rapidly changes from secretion to absorption. Thus, the relative cell membrane location of epithelial Na channels (ENaCs) and cystic fibrosis transmembrane regulator (CFTR) Cl channels during late fetal lung development and after maternal interleukin-1ß (IL-1ß) pretreatment was the focus of our study. Western blot analysis after sucrose gradient separation of caveolin-1-(Cav-1)-rich membrane regions (CRR) and Cav-1-poor membrane (non-CRR) revealed primary CRR ENaC localization at gestation day (GD) 61 in guinea pigs. Correlating with the natural induction of distal lung fluid absorption, ENaC appeared in the non-CRR cell membrane regions at GD68. Conversely, CFTR was present in the non-CRR cell membrane regions at GD61 and in the CRRs at GD68. IL-1ß-induced conversion to distal lung fluid absorption at GD61 was associated with ENaC non-CRR presence and CFTR CRR presence, suggesting that relative ENaC and CFTR locations induced distal lung fluid absorption and decreased fluid secretion. Instilling fetal lungs with the CRR-disrupting agent methyl-ß-cyclodextrin resulted in the conversion from lung fluid secretion to absorption and ENaC non-CRR presence at GD61. Coimmunoprecipitation of Cav-1 with α- and ß-ENaC demonstrated reduced coimmunoprecipitation with increased GD and after IL-1ß pretreatment. On the other hand, coimmunoprecipitation of Cav-1 with CFTR demonstrated increased coimmunoprecipitation with increasing GD and after IL-1ß pretreatment. This concept may provide novel molecular mechanisms for the rapid transition from fetal distal lung fluid secretion to absorption in near-term lungs.

Anthocyanin-rich black currant (Ribes nigrum L.) extract affords chemoprevention against diethylnitrosamine-induced hepatocellular carcinogenesis in rats.

Anthocyanins are known to possess potent anticarcinogenic properties against several cancers thus demonstrating potential for cancer prevention. Black currant (Ribes nigrum L., Grossulariaceae) fruits have a high anthocyanin content. This "superfruit" is known to possess various pharmacological effects including alleviation of chronic oxidative stress and inflammation. In contrast to a large volume of literature on the health benefits of black currant, limited evidence on antitumor effects of black currant exists with virtually no data on the prevention of experimental carcinogenesis. In the current study, we have investigated the chemopreventive effects of an anthocyanin-rich black currant skin extract (BCSE) utilizing our well-characterized model of rat liver carcinogenesis. Initiation of hepatocarcinogenesis was done by intraperitoneal injection of diethylnitrosamine (DENA) followed by promotion with phenobarbital. The rats were exposed to dietary BCSE for 4 weeks prior to initiation, and the treatment was continued for 22 consecutive weeks. BCSE dose-dependently decreased the incidence, total number, multiplicity, size and volume of preneoplastic hepatic nodules. The antihepatocarcinogenic effect of BCSE was confirmed by histopathological examination of liver sections. Immunohistochemical analysis of proliferating cell nuclear antigen and DNA fragmentation revealed BCSE-mediated inhibition of abnormal cell proliferation and induction of apoptosis in DENA-induced rat liver tumorigenesis respectively. Mechanistic studies revealed that BCSE-mediated proapototic signal during experimental hepatocarcinogenesis may be propagated via the up-regulation of Bax and down-regulation of Bcl-2 expression at the translational level. These results along with a safety profile of BCSE encourage the development of black currant bioactive constituents as chemopreventive agents for human liver cancer.

Lung fluid absorption is induced in preterm guinea pigs ventilated with low tidal volumes.

The objective of this study was to determine if low tidal volume (V(t)) ventilation was beneficial when ventilating preterm fetuses. The authors ventilated preterm guinea pig fetuses at gestation day (GD) 67, 3 days before birth, newborn, and 10-day-old (PD10) guinea pigs with low V(t) (6 mL/kg body weight [bw]) and compared them to age-matched fetuses/animals ventilated with higher potentially injurious V(t) (12 mL/kg bw). Lung fluid absorption was measured after intratracheal instillation of 5% albumin in 0.9% NaCl. Low V(t) ventilation stimulated lung fluid absorption when compared to higher V(t) in all groups. The increased lung fluid absorption in low V(t)-ventilated fetuses was associated with increased α epithelial Na channel (αEnaC) mRNA. However, αENaC and ßENaC protein was unchanged over the 1-hour study. Because stretch induces mitogen-activated protein (MAP) kinase expression and MAP kinases may affect lung fluid absorption, the authors investigated if MAP kinase (MAPK) expression was affected by V(t). Extracellular signal-regulated kinase (ERK) and MAPK/ERK kinase (MEK) were phosphorylated in the higher V(t)-ventilated guinea pig fetuses. This suggested that a reduced activation of MAP kinases might explain the increased lung fluid absorption in the low V(t)-ventilated fetuses. Thus these data suggest that low V(t) ventilation increases fetal lung fluid absorption and thus may be preferential to use clinically.

Beta-adrenoceptor stimulation of alveolar fluid clearance is increased in rats with heart failure.

The alveolar epithelium plays a critical role in resolving pulmonary edema. We thus hypothesized that its function might be upregulated in rats with heart failure, a condition that severely challenges the lung's ability to maintain fluid balance. Heart failure was induced by left coronary artery ligation. Echocardiographic and cardiovascular hemodynamics confirmed its development at 16 wk postligation. At that time, alveolar fluid clearance was measured by an increase in protein concentration over 1 h of a 5% albumin solution instilled into the lungs. Baseline alveolar fluid clearance was similar in heart failure and age-matched control rats. Terbutaline was added to the instillate to determine whether heart failure rats responded to beta-adrenoceptor stimulation. Alveolar fluid clearance in heart failure rats was increased by 194% after terbutaline stimulation compared with a 153% increase by terbutaline in control rats. To determine the mechanisms responsible for this accelerated alveolar fluid clearance, we measured ion transporter expression (ENaC, Na-K- ATPase, CFTR). No significant upregulation was observed for these ion transporters in the heart failure rats. Lung morphology showed significant alveolar epithelial type II cell hyperplasia in heart failure rats. Thus, alveolar epithelial type II cell hyperplasia is the likely explanation for the increased terbutaline-stimulated alveolar fluid clearance in heart failure rats. These data provide evidence for previously unrecognized mechanisms that can protect against or hasten resolution of alveolar edema in heart failure.

IL-1beta-induced cortisol stimulates lung fluid absorption in fetal guinea pigs via SGK-mediated Nedd4-2 inhibition.

We tested the hypothesis that interleukin (IL)-1beta-induced cortisol synthesis stimulates distal lung fluid absorption in fetal guinea pigs via induction of serum- and glucocorticoid-regulated kinase (SGK) and inhibition of neural precursor cell expressed, developmentally downregulated protein 4-2 (Nedd4-2). IL-1beta was subcutaneously administered daily to timed-pregnant guinea pigs over 3 days. Fetuses were obtained by abdominal hysterotomy at gestation day (GD)61 and GD68 and instilled with an isosmolar 5% albumin solution into the lungs. Distal lung fluid movement was measured over 1 h from the change in distal air space protein concentration. Fetal lungs were secreting lung fluid at GD61 while absorbing lung fluid at GD68. Distal lung fluid absorption was induced at GD61 by IL-1beta but unaffected at GD68. Plasma cortisol concentrations were increased by IL-1beta at GD61 and endogenously at GD68. Distal lung fluid absorption was measured and correlated to SGK and Nedd4-2 expression and to alpha-epithelial Na channel (ENaC) expression. SGK was increased by IL-1beta and late during gestation (GD68), while Nedd4-2 was decreased by IL-1beta and late during gestation. alpha-ENaC was induced by IL-1beta at GD61 and increased late during gestation. Thus our study suggests that cortisol-stimulated fetal lung fluid absorption is mediated by increased ENaC expression and may be governed by the SGK/Nedd4-2 pathway. These observations may explain why babies delivered preterm after intrauterine inflammation have a reduced risk of developing severe respiratory distress.

Delineation of VEGF-regulated genes and functions in the cervix of pregnant rodents by DNA microarray analysis.

BACKGROUND: VEGF-regulated genes in the cervices of pregnant and non-pregnant rodents (rats and mice) were delineated by DNA microarray and Real Time PCR, after locally altering levels of or action of VEGF using VEGF agents, namely siRNA, VEGF receptor antagonist and mouse VEGF recombinant protein. METHODS: Tissues were analyzed by genome-wide DNA microarray analysis, Real-time and gel-based PCR, and SEM, to decipher VEGF function during cervical remodeling. Data were analyzed by EASE score (microarray) and ANOVA (Real Time PCR) followed by Scheffe's F-test for multiple comparisons. RESULTS: Of the 30,000 genes analyzed, about 4,200 genes were altered in expression by VEGF, i.e., expression of about 2,400 and 1,700 genes were down- and up-regulated, respectively. Based on EASE score, i.e., grouping of genes according to their biological process, cell component and molecular functions, a number of vascular- and non-vascular-related processes were found to be regulated by VEGF in the cervix, including immune response (including inflammatory), cell proliferation, protein kinase activity, and cell adhesion molecule activity. Of interest, mRNA levels of a select group of genes, known to or with potential to influence cervical remodeling were altered. For example, real time PCR analysis showed that levels of VCAM-1, a key molecule in leukocyte recruitment, endothelial adhesion, and subsequent trans-endothelial migration, were elevated about 10 folds by VEGF. Further, VEGF agents also altered mRNA levels of decorin, which is involved in cervical collagen fibrillogenesis, and expression of eNO, PLC and PKC mRNA, critical downstream mediators of VEGF. Of note, we show that VEGF may regulate cervical epithelial proliferation, as revealed by SEM. CONCLUSION: These data are important in that they shed new insights in VEGF's possible roles and mechanisms in cervical events near-term, including cervical remodeling.

RNA interference for CFTR attenuates lung fluid absorption at birth in rats.

BACKGROUND: Small interfering RNA (siRNA) against alphaENaC (alpha-subunit of the epithelial Na channel) and CFTR (cystic fibrosis transmembrane conductance regulator) was used to explore ENaC and CTFR function in newborn rat lungs. METHODS: Twenty-four hours after trans-thoracic intrapulmonary (ttip) injection of siRNA-generating plasmid DNA (pSi-0, pSi-4, or pSi-C2), we measured CFTR and ENaC expression, extravascular lung water, and mortality. RESULTS: alphaENaC and CFTR mRNA and protein decreased by approximately 80% and approximately 85%, respectively, following alphaENaC and CFTR silencing. Extravascular lung water and mortality increased after alphaENaC and CFTR-silencing. In pSi-C2-transfected isolated DLE cells there were attenuated CFTR mRNA and protein. In pSi-4-transfected DLE cells alphaENaC mRNA and protein were both reduced. Interestingly, CFTR-silencing also reduced alphaENaC mRNA and protein. alphaENaC silencing, on the other hand, only slightly reduced CFTR mRNA and protein. CONCLUSION: Thus, ENaC and CFTR are both involved in the fluid secretion to absorption conversion around at birth.

Involvement of {alpha}ENaC and Nedd4-2 in the conversion from lung fluid secretion to fluid absorption at birth in the rat as assayed by RNA interference analysis.

To explore interactions between the epithelial Na channel (ENaC) and neural precursor expressed, developmentally downregulated protein 4-2 (Nedd4-2) at the conversion of the rat lung from fluid secretion to absorption at birth, we used small-interfering RNA (siRNA) against alphaENaC and Nedd4-2. siRNA-generating plasmid DNA (pDNA) was administered via trans-thoracic intrapulmonary (ttip) injection 24 h before ENaC and Nedd4-2 expression, extravascular lung water, and mortality were measured. alphaENaC mRNA and protein were specifically reduced by approximately 65% after pSi-4 injection. Nedd4-2 mRNA and protein were reduced by approximately 60% after pSi-N1 injection. Interestingly, alphaENaC and betaENaC mRNA and protein expression were increased after Nedd4-2 silencing. Extravascular lung water was significantly increased after alphaENaC silencing and reduced after Nedd4-2 silencing. alphaENaC silencing resulted in a fourfold increase in newborn mortality, whereas silencing Nedd4-2 did not affect mortality. We also isolated distal lung epithelial (DLE) cells after in vivo alphaENaC or Nedd4-2 silencing and measured alphaENaC or Nedd4-2 expression in freshly isolated DLE cells. In these DLE cells, there were attenuated alphaENaC or Nedd4-2 mRNA and protein, thus demonstrating that alphaENaC and Nedd4-2 silencing occurred in alveolar epithelial cells after ttip injection. We also looked for pDNA by PCR to determine pDNA presence in the lungs and found strong evidence for pDNA presence in both lungs. Thus we provide evidence that ENaC and Nedd4-2 are involved in the transition from lung fluid secretion to fluid absorption near term and at birth.

Stimulation of MAP kinase pathways after maternal IL-1beta exposure induces fetal lung fluid absorption in guinea pigs.

BACKGROUND: We tested the hypothesis that maternal interleukin-1beta (IL-1beta) pretreatment and induction of fetal cortisol synthesis activates MAP kinases and thereby affects lung fluid absorption in preterm guinea pigs. METHODS: IL-1beta was administered subcutaneously daily to timed-pregnant guinea pigs for three days. Fetuses were obtained by abdominal hysterotomy and instilled with isosmolar 5% albumin into the lungs and lung fluid movement was measured over 1 h by mass balance. MAP kinase expression was measured by western blot. RESULTS: Lung fluid absorption was induced at 61 days (D) gestation and stimulated at 68D gestation by IL-1beta. Maternal IL-1beta pretreatment upregulated ERK and upstream MEK expression at both 61 and 68D gestation, albeit being much more pronounced at 61D gestation. U0126 instillation completely blocked IL-1beta-induced lung fluid absorption as well as IL-1beta-induced/stimulated ERK expression. Cortisol synthesis inhibition by metyrapone attenuated ERK expression and lung fluid absorption in IL-1beta-pretreated fetal lungs. JNK expression after maternal IL-1beta pretreatment remained unaffected at either gestation age. CONCLUSION: These data implicate the ERK MAP kinase pathway as being important for IL-1beta induction/stimulation of lung fluid absorption in fetal guinea pigs.

A noninflammatory interleukin-1beta fragment stimulates fetal lung fluid absorption in guinea pigs.

We have previously demonstrated that full-length interleukin (IL)-1beta can induce and stimulate lung fluid absorption in near-term guinea pig fetuses via stimulation of fetal cortisol synthesis and release. To develop a potentially clinically useful drug, we tested the hypothesis that maternal administration of a noninflammatory IL-1beta-fragment (IL-1beta(Fr)) induced cortisol synthesis and stimulated lung fluid absorption in preterm fetuses. IL-1beta(Fr) was administered s.c. daily to timed-pregnant guinea pigs for 3 days with and without simultaneous cortisol synthesis inhibition by metyrapone. Fetuses were obtained by abdominal hysterotomy at 61 and 68 days gestation and instilled with isosmolar 5% albumin into the lungs, and lung fluid absorption was measured over 1 h by mass balance. Lung fluid absorption was induced at 61 days and stimulated at 68 days gestation by IL-1beta(Fr), which both were attenuated by cortisol synthesis inhibition. Moreover, induction of labor by oxytocin stimulated lung fluid absorption at 61 days but had no stimulatory effect at 68 days gestation when given with the IL-1beta(Fr). Plasma adrenocorticotropin and cortisol concentrations were increased by IL-1beta(Fr) at 61 days gestation and remained high but unstimulated by IL-1beta(Fr) at 68 days gestation, and metyrapone always reduced cortisol concentrations. Prenatal lung fluid absorption, when present as well as IL-1beta(Fr)-induced, was always propranolol- and amiloride-sensitive, suggesting that beta-adrenoceptor stimulation and the epithelial Na(+) channel (ENaC) were critical for the induced/stimulated lung fluid absorption. ENaC expression was increased by IL-1beta(Fr) and attenuated by cortisol synthesis inhibition. Thus, our results suggest a potential clinical use of IL-1beta(Fr) therapeutically to induce lung fluid absorption in fetuses at risk of preterm delivery.

Integrating acute lung injury and regulation of alveolar fluid clearance.

The acute respiratory distress syndrome (ARDS) is characterized by non-cardiogenic pulmonary edema and flooding of the alveolar air spaces with proteinaceous fluid. ARDS develops in response to inflammatory stresses including sepsis, trauma, and severe pneumonia, and despite aggressive critical care management, it still has a mortality of 30-50%. At the time of its original description in 1967, relatively little was known about the specific mechanisms by which the alveolar epithelium regulated lung fluid balance. Over the last 20 years, substantial advances in our understanding of the alveolar epithelium have provided major new insights into how molecular and cellular mechanisms regulate the active transport of solutes and fluid across the alveolar epithelium under both normal and pathological conditions. Beginning with the elucidation of active sodium transport as a major driving force for the transport of water from the air space to the interstitium, elegant work by multiple investigators has revealed a complex and integrated network of membrane channels and pumps that coordinately regulates sodium, chloride, and water flux in both a cell- and condition-specific manner. At the Experimental Biology Meeting in San Francisco on April 4, 2006, a symposium was held to discuss some of the most recent advances. Although there is still much to learn about the mechanisms that impair normal alveolar fluid clearance under pathological conditions, the compelling experimental findings presented in this symposium raise the prospect that we are now poised to test and develop therapeutic strategies to improve outcome in patients with acute lung injury.

Impaired alveolar liquid clearance after 48-h isoproterenol infusion spontaneously recovers by 96 h of continuous infusion.

We previously demonstrated that 48-h isoproterenol (Iso) infusion in rats impaired the ability of beta-adrenoceptor (beta-AR) agonists to increase alveolar liquid clearance (ALC). In this study, we determined whether this impairment persisted over longer time periods by infusing 400 mug.kg(-1).h(-1) Iso by osmotic minipump for 24-144 h (n = 6-7/group). ALC in control rats was 19.0 +/- 2.4 (SD)% of instilled volume absorbed per hour. In Iso-infused rats, ALC was elevated at 24 h (34.9 +/- 2.4%) and decreased at 48 h (15.2 +/- 4.4%) and had recovered to 24 h values at 96 h (37.3 +/- 3.8%) and 144 h (35.2 +/- 3.3%). Plasma Iso concentrations remained elevated at all Iso infusion times. Peripheral lung beta(2)-AR expression exhibited a parallel time course, with a reduction in expression observed at 48 h, followed by an increase to 24 h values at 96 and 144 h. Propranolol prevented the increase in ALC observed at 96 and 144 h, indicating that the recovery in ALC was mediated by a recovery of beta-AR function and beta-AR signaling. ALC at 96 and 144 h could not be further increased by terbutaline, indicating that ALC was maximally stimulated. These data indicate that recovery of beta-AR-stimulated ALC can occur in the continued presence of Iso and is mediated by a recovery of the ability of the distal lung epithelium to respond to beta-AR stimulation.

Type VI collagen induces cardiac myofibroblast differentiation: implications for postinfarction remodeling.

Cardiac fibroblast (CF) proliferation and differentiation into hypersecretory myofibroblasts can lead to excessive extracellular matrix (ECM) production and cardiac fibrosis. In turn, the ECM produced can potentially activate CFs via distinct feedback mechanisms. To assess how specific ECM components influence CF activation, isolated CFs were plated on specific collagen substrates (type I, III, and VI collagens) before functional assays were carried out. The type VI collagen substrate potently induced myofibroblast differentiation but had little effect on CF proliferation. Conversely, the type I and III collagen substrates did not affect differentiation but caused significant induction of proliferation (type I, 240.7 +/- 10.3%, and type III, 271.7 +/- 21.8% of basal). Type I collagen activated ERK1/2, whereas type III collagen did not. Treatment of CFs with angiotensin II, a potent mitogen of CFs, enhanced the growth observed on types I and III collagen but not on the type VI collagen substrate. Using an in vivo model of myocardial infarction (MI), we measured changes in type VI collagen expression and myofibroblast differentiation after post-MI remodeling. Concurrent elevations in type VI collagen and myofibroblast content were evident in the infarcted myocardium 20-wk post-MI. Overall, types I and III collagen stimulate CF proliferation, whereas type VI collagen plays a potentially novel role in cardiac remodeling through facilitation of myofibroblast differentiation.

Congenital diaphragmatic hernia prevents absorption of distal air space fluid in late-gestation rat fetuses.

We hypothesized that congenital diaphragmatic hernia (CDH) may decrease distal air space fluid absorption due to immaturity of alveolar epithelial cells from a loss of the normal epithelial Na+ transport, as assessed by amiloride and epithelial Na+ channel (ENaC) and Na-K-ATPase expression, as well as failure to respond to endogenous epinephrine as assessed by propranolol. Timed-pregnant dams were gavage fed 100 mg of nitrofen at 9.5-day gestation to induce CDH in the fetuses, and distal air space fluid absorption experiments were carried out on 22-day gestation (term) fetuses. Controls were nitrofen-exposed fetuses without CDH. Absorption of distal air space fluid was measured from the increase in 131I-albumin concentration in an isosmolar, physiological solution instilled into the developing lungs. In controls, distal air space fluid absorption was rapid and mediated by beta-adrenoceptors as demonstrated by reversal to fluid secretion after propranolol. Normal lung fluid absorption was also partially inhibited by amiloride. In contrast, CDH fetuses continued to show lung fluid secretion, and this secretion was not affected by either propranolol or amiloride. CDH lungs showed a 67% reduction in alpha-ENaC and beta-ENaC expression, but no change in alpha1-Na-K-ATPase expression. These studies demonstrate: 1) CDH delays lung maturation with impaired distal air space fluid absorption secondary to inadequate Na+ uptake by the distal lung epithelium that results in fluid-filled lungs at birth with reduced capacity to establish postnatal breathing, and 2) the main stimulus to lung fluid absorption in near-term control fetuses, elevated endogenous epinephrine levels, is not functional in CDH fetuses.

RNA interference for alpha-ENaC inhibits rat lung fluid absorption in vivo.

We used siRNA against the alpha-ENaC (epithelial Na channel) subunit to investigate ENaC involvement in lung fluid absorption in rats by the impermeable tracer technique during baseline and after beta-adrenoceptor stimulation by terbutaline. Terbutaline stimulation of lung fluid absorption increased fluid absorption by 165% in pSi-0-pretreated rat lungs (irrelevant siRNA-generating plasmid). Terbutaline failed to increase lung fluid absorption in rats given the specific alpha-ENaC siRNA-generating plasmid (pSi-4). pSi-4 pretreatment reduced baseline lung fluid absorption by approximately 30%. alpha-ENaC was undetectable in pSi-4-pretreated lungs, regardless of condition but was normal in pSi-0-pretreated lungs. We carried out a dose-response analysis where rats were given 0-200 microg/kg body wt pSi-4, and alpha-ENaC mRNA and protein expressions were analyzed. To reach IC(50) for alpha-ENaC mRNA expression, 32 microg/kg body wt pSi-4 was needed, and to reach IC(50) for alpha-ENaC protein expression, 59 microg/kg body wt pSi-4 was needed. We tested for lung tissue specificity and found no changes in beta-ENaC expression, at either mRNA or protein level, as well as no changes in alpha(1)-Na-K-ATPase protein expression. We isolated alveolar epithelial type II cells 24 h after in vivo pSi-4 pretreatment. In these cells, alpha-ENaC mRNA was undetectable, demonstrating that alveolar epithelial ENaC expression was attenuated after intratracheal alpha-ENaC siRNA-generating plasmid DNA instillation. We tested for organ specificity and found no changes in kidney alpha- and beta-ENaC mRNA and protein expression. Thus we provide conclusive evidence that beta-adrenoceptor stimulation of lung fluid absorption is critically ENaC dependent, whereas baseline lung fluid absorption seemed less ENaC dependent.

Protective effect of endogenous beta-adrenergic tone on lung fluid balance in acute bacterial pneumonia in mice.

Some investigators have reported that endogenous beta-adrenoceptor tone can provide protection against acute lung injury. Therefore, we tested the effects of beta-adrenoceptor inhibition in mice with acute Escherichia coli pneumonia. Mice were pretreated with propranolol or saline and then intratracheally instilled with live E. coli (10(7) colony-forming units). Hemodynamics, arterial blood gases, plasma catecholamines, extravascular lung water, lung permeability to protein, bacterial counts, and alveolar fluid clearance were measured. Acute E. coli pneumonia was established after 4 h with histological evidence of acute pulmonary inflammation, arterial hypoxemia, a threefold increase in lung vascular permeability, and a 30% increase in extravascular lung water as an increase in plasma catecholamine levels. beta-Adrenoceptor inhibition resulted in a marked increase in extravascular lung water that was explained by both an increase in lung vascular permeability and a reduction in net alveolar fluid clearance. The increase in extravascular lung water with propranolol pretreatment was not explained by an increase in systemic or vascular pressures. The increase in lung vascular permeability was explained in part by anti-inflammatory effects of beta-adrenoceptor stimulation because plasma macrophage inflammatory protein-2 levels were higher in the propranolol pretreatment group compared with controls. The decrease in alveolar fluid clearance with propranolol was explained by a decrease in catecholamine-stimulated fluid clearance. Together, these results indicate that endogenous beta-adrenoceptor tone has a protective effect in limiting accumulation of extravascular lung water in acute severe E. coli pneumonia in mice by two mechanisms: 1) reducing lung vascular injury and 2) upregulating the resolution of alveolar edema.