Selected contribution: long-term effects of beta(2)-adrenergic receptor stimulation on alveolar fluid clearance in mice.

Stimulation of active fluid transport with beta-adrenergic receptor (betaAR) agonists can accelerate the resolution of alveolar edema. However, chronic betaAR-agonist administration may cause betaAR desensitization and downregulation that may impair physiological responsiveness to betaAR-agonist stimulation. Therefore, we measured baseline and terbutaline- (10(-3) M) stimulated alveolar fluid clearance in mice that received subcutaneously (miniosmotic pumps) either saline or albuterol (2 mg. kg(-1). day(-1)) for 1, 3, or 6 days. Continuous albuterol administration increased plasma albuterol levels (10(-5) M), an effect that was associated with 1) a significant decrease in betaAR density and 2) attenuation, but not ablation, of maximal terbutaline-induced cAMP production. Forskolin-mediated cAMP-release was unaffected. Continuous albuterol infusion stimulated alveolar fluid clearance on day 1 but did not increase alveolar fluid clearance on days 3 and 6. However, terbutaline-stimulated alveolar fluid clearance in albuterol-treated mice was not reduced compared with saline-treated mice. Despite significant reductions in betaAR density and agonist-mediated cAMP production by long-term betaAR-agonist exposure, maximal betaAR-agonist-mediated increase in alveolar fluid clearance is not diminished in mice.

Rapid alveolar epithelial fluid clearance following lung lavage in pulmonary alveolar proteinosis.

STUDY OBJECTIVE: To measure the in vivo rate of alveolar epithelial fluid clearance of the human lung in patients with pulmonary alveolar phospholipoproteinosis (PAP). DESIGN: Prospective clinical study. SETTING: The medical-surgical ICUs of a university teaching hospital. PATIENTS: Four patients with idiopathic PAP requiring therapeutic lung lavage. INTERVENTIONS: Large-volume lung lavage with isotonic saline solution using fiberoptic bronchoscopy followed by serial sampling of alveolar fluid using a wedged bronchial catheter. MEASUREMENTS AND RESULTS: The rate of alveolar epithelial fluid clearance was calculated by measuring the concentration of protein in sequential samples. Alveolar epithelial fluid clearance over the first hour after lung lavage was 53 +/- 14% (mean +/- SD). Sequential samples in two patients indicated a sustained high rate of clearance over several hours. Plasma and alveolar fluid epinephrine levels were in the normal range in two patients. CONCLUSIONS AND SIGNIFICANCE: Alveolar fluid clearance is rapid after lung lavage in patients with PAP and appears to be driven by catecholamine-independent mechanisms. The rapid rate of alveolar epithelial fluid transport explains why patients with PAP tolerate large-volume lung lavage.

Contribution of amiloride-insensitive pathways to alveolar fluid clearance in adult rats.

The contributions of amiloride-sensitive and -insensitive fractions of alveolar fluid clearance in adult ventilated rats were studied under control conditions and after beta-adrenergic stimulation. Rats were instilled with a 5% albumin solution containing terbutaline (10(-4) M) or dibutyryl-cGMP (DBcGMP; 10(-4) M) with or without the cyclic nucleotide-gated cation channel inhibitor l-cis-diltiazem (10(-3) M) and/or amiloride (10(-3) M). Alveolar fluid clearance over 1 h was 18 +/- 2% in controls. In controls, amiloride inhibited 46 +/- 15% of alveolar fluid clearance, whereas l-cis-diltiazem had no inhibitory effect. Terbutaline and DBcGMP stimulated alveolar fluid clearance by 85 +/- 3 and 36 +/- 5%, respectively. Amiloride and l-cis-diltiazem inhibited nearly equal fractions of terbutaline-stimulated alveolar fluid clearance when given alone. Amiloride and l-cis-diltiazem given together inhibited a significantly larger fraction of alveolar fluid clearance in terbutaline-stimulated rats and in DBcGMP-stimulated rats. Based on these data, terbutaline stimulation recruited both amiloride-sensitive and l-cis-diltiazem-sensitive pathways. In contrast, DBcGMP mainly recruited l-cis-diltiazem-sensitive pathways. Therefore, the amiloride-insensitive fraction of Na+-driven alveolar fluid clearance may be partly mediated through cyclic nucleotide-gated cation channels and activated by an increase in intracellular cGMP.

Alveolar fluid clearance in late-gestational guinea pigs after labor induction: mechanisms and regulation.

We tested the hypothesis that labor-induced epinephrine release would stimulate alveolar fluid clearance in preterm fetuses. Preterm fetuses were obtained by cesarean section from timed-pregnant guinea pigs at 61-69 days postconception. Fetal guinea pigs were euthanized and placed on continuous positive airway pressure oxygenation, and an isosmolar 5% albumin solution was instilled. Alveolar fluid clearance was measured over 1 h. The fetal lung began to absorb fluid at 64-66 days postconception, and at birth, alveolar fluid clearance quadrupled. Baseline alveolar fluid clearance when present was sensitive to propranolol inhibition and depended on beta-adrenergic stimulation. Measurements of plasma epinephrine in fetal animals confirmed high epinephrine levels in 66- to 69-day postconception fetuses. Prenatal alveolar fluid clearance when present was highly amiloride sensitive, suggesting that amiloride-sensitive Na+ channels were critical. Oxytocin-induced labor initiated an amiloride- and propranolol-sensitive net alveolar fluid clearance in 61-day-gestation animals. Moreover, oxytocin induced significant epinephrine release in all fetuses. These results have clinical implications for infants delivered by cesarean section before the onset of labor. Use of pharmacological agents to induce labor may reduce the occurrence and severity of perinatal respiratory distress.

Fosfructose (Questcor).

Fosfructose is a cytoprotective natural sugar phosphate under development by Questcor (formerly Cypros) for the potential treatment of cardiovascular ischemia, sickle cell anemia and asthma. It acts by stimulating anaerobic glycolysis which generates adenosine triphosphate under ischemic conditions. It is in phase III trials for sickle cell anemia [309234] and is in phase II/III trials for cardiovascular ischemia resulting from bypass surgery [337683]. The company has also commenced preclinical trials of fosfructose for asthma [337683]. In September 1999, the FDA granted fosfructose Fast Track designation for the treatment of the acute complications associated with coronary artery bypass graft surgery [340368].

Relationship of interstitial fluid volume to alveolar fluid clearance in mice: ventilated vs. in situ studies.

Our recent report (Garat C, Carter EP, and Matthay MA. J Appl Physiol 84: 1763-1767, 1998) described a new method to measure alveolar fluid clearance (AFC) in an in situ mouse preparation. However, in vivo preparations may be more suitable for studying alveolar fluid transport under some pathological conditions. Therefore, we developed a ventilated mouse model and compared AFC in the ventilated and the in situ mouse models. After 15 min, AFC was similar in both groups, but, after 30 min, AFC was 38% slower in the in situ mice (P < 0.05). Bilateral adrenalectomy and propranolol did not inhibit AFC after 15 min. Amiloride inhibited 90% of AFC in both groups. To evaluate the mechanism for the slower AFC in the in situ mouse preparation, we measured the extravascular lung water and calculated interstitial fluid volume. Extravascular lung water and interstitial fluid volume were greater in the in situ mice than in the ventilated mice at 30 min (P < 0.05). These results indicate that mouse AFC is fast, highly amiloride sensitive, and independent of endogenous catecholamines during the first 15 min. Accumulation of interstitial fluid probably plays an important role in slowing AFC in the in situ mouse lung model at later time intervals. These mouse models will be useful to quantify alveolar epithelial fluid transport under pathological conditions.

Dexamethasone and thyroid hormone pretreatment upregulate alveolar epithelial fluid clearance in adult rats.

The in vivo effect of 48-h glucocorticoid and thyroid hormone 3,3', 5-triiodine-L-thyronine (T(3)) pretreatment on alveolar epithelial fluid transport was studied in adult rats. An isosmolar 5% albumin solution was instilled, and alveolar fluid clearance was studied for 1 h. Compared with controls, dexamethasone pretreatment increased alveolar fluid clearance by 80%. T(3) pretreatment stimulated alveolar fluid clearance by 65%, and dexamethasone and T(3) had additive effects (132%). Propranolol did not inhibit alveolar fluid clearance in either group, indicating that stimulation was not secondary to endogenous beta-adrenergic stimulation. With the use of bromodeoxyuridine in vivo labeling, there was no evidence of cell proliferation. Alveolar fluid clearance was partially inhibited by amiloride in all groups. Fractional amiloride inhibition was greater in dexamethasone- and dexamethasone-plus-T(3)-pretreated rats than in control animals, but less in T(3)-pretreated rats. In summary, pretreatment with dexamethasone, T(3), or both in combination upregulate in vivo alveolar fluid clearance similarly to short-term beta-adrenergic stimulation. The effects are mediated partly by increased amiloride-sensitive Na(+) transport, because the stimulated alveolar fluid clearance was more amiloride sensitive than in control rats. These observations may have clinical relevance because glucocorticoid therapy is commonly used with acute lung injury.

The influence of mode of delivery, hormonal status and postnatal O2 environment on epithelial sodium channel (ENaC) expression in perinatal guinea-pig lung.

We have studied factors that potentially modulate the expression of mRNA coding for subunits of the amiloride-sensitive sodium channel, alphaENaC and betaENaC, in lungs of vaginally and Caesarean (CS)-delivered late gestation fetal guinea-pigs. Expression of alphaENaC and betaENaC mRNAs was developmentally regulated in the late gestation fetus, reaching peak levels at term (68 days post conception, PC) and postnatally, respectively. In animals delivered by CS at 65 days PC and term, alphaENaC mRNA expression was significantly increased by day 1 post partum, reaching levels greater than those normally achieved in vaginally delivered animals at term. In contrast, betaENaC mRNA levels remained significantly lower postnatally in animals delivered by CS at 65 days PC compared with those in vaginally and CS-delivered animals at term. Plasma cortisol and total triiodothyronine (T3) levels increased towards term, were higher 1 day after vaginal delivery but declined towards pre-term levels by day 3. Cortisol levels also increased rapidly in the CS-delivered animals, reaching levels similar to those in vaginally delivered animals at day 1. Plasma T3 levels at days 1 and 3 were significantly lower in animals delivered by CS at 65 days PC. The increase in alphaENaC mRNA paralleled the increase in plasma cortisol after delivery, but not T3, and inhibition of cortisol synthesis with 2-methyl-1,2-di-3-pyridyl-1-propanone (metyrapone) after CS delivery suppressed the increase in alphaENaC mRNA expression. Concomitant with the increase in alphaENaC mRNA expression after CS delivery at 65 days PC was an increase in the amiloride-blockable component of lung fluid clearance by day 3 postnatally. We conclude that in late gestation guinea-pigs delivered by CS there is a significant increase in lung alphaENaC expression postnatally, which is mediated, in part, by the postnatal rise in cortisol at delivery. This in turn leads to an increase in amiloride-sensitive lung fluid clearance, which is unrelated to labour.

TNF-alpha stimulates alveolar liquid clearance during intestinal ischemia-reperfusion in rats.

Intestinal ischemia-reperfusion commonly occurs in critically ill patients and may lead to the development of remote organ injury, frequently involving the lungs. In the present study, alveolar liquid clearance was studied in ventilated, anesthetized rats subjected to 45 min of intestinal ischemia followed by 3 h of reperfusion. An isosmolar 5% albumin solution was instilled into the lungs, and alveolar liquid clearance was measured from the increase in alveolar protein concentration as water was reabsorbed over 45 min. Intestinal ischemia-reperfusion resulted in a 76% increase in alveolar liquid clearance compared with the control value (P < 0.05). The stimulated alveolar liquid clearance seen after intestinal ischemia-reperfusion was not inhibited by propranolol, indicating stimulation through a noncatecholamine-dependent pathway. Intestinal ischemia-reperfusion did not result in increased intracellular cAMP levels. Amiloride inhibited similar fractions in animals subjected to ischemia-reperfusion and control animals. Administration of a neutralizing polyclonal anti-tumor necrosis factor-alpha antibody before induction of intestinal ischemia completely inhibited the increased alveolar liquid clearance observed after intestinal ischemia-reperfusion. In conclusion, our results suggest that intestinal ischemia-reperfusion in rats leads to stimulation of alveolar liquid clearance and that this stimulation is mediated, at least in part, by a tumor necrosis factor-alpha-dependent mechanism.

Alveolar epithelial fluid transport can be simultaneously upregulated by both KGF and beta-agonist therapy.

Although keratinocyte growth factor (KGF) protects against experimental acute lung injury, the mechanisms for the protective effect are incompletely understood. Therefore, the time-dependent effects of KGF on alveolar epithelial fluid transport were studied in rats 48-240 h after intratracheal administration of KGF (5 mg/kg). There was a marked proliferative response to KGF, measured both by in vivo bromodeoxyuridine staining and by staining with an antibody to a type II cell antigen. In controls, alveolar liquid clearance (ALC) was 23 +/- 3%/h. After KGF pretreatment, ALC was significantly increased to 30 +/- 2%/h at 48 h, to 39 +/- 2%/h at 72 h, and to 36 +/- 3%/h at 120 h compared with controls (P < 0.05). By 240 h, ALC had returned to near-control levels (26 +/- 2%/h). The increase in ALC was explained primarily by the proliferation of alveolar type II cells, since there was a good correlation between the number of alveolar type II cells and the increase in ALC (r = 0.92, P = 0.02). The fraction of ALC inhibited by amiloride was similar in control rats (33%) as in 72-h KGF-pretreated rats (38%), indicating that there was probably no major change in the apical pathways for Na uptake in the KGF-pretreated rats at this time point. However, more rapid ALC at 120 h, compared with 48 h after KGF treatment, may be explained by greater maturation of alpha-epithelial Na channel, since its expression was greater at 120 than at 48 h, whereas the number of type II cells was the same at these two time points. beta-Adrenergic stimulation with terbutaline 72 h after KGF pretreatment further increased ALC to 50 +/- 7%/h (P < 0.5). In summary, KGF induced a sustained increase over 120 h in the fluid transport capacity of the alveolar epithelium. This impressive upregulation in fluid transport was further enhanced with beta-adrenergic agonist therapy, thus providing evidence that two different treatments can simultaneously increase the fluid transport capacity of the alveolar epithelium.

Acid-induced lung injury. Protective effect of anti-interleukin-8 pretreatment on alveolar epithelial barrier function in rabbits.

Although prior experimental work has demonstrated that anti-interleukin-8 (anti-IL-8) therapy reduces lung endothelial injury after acid instillation, there is no information regarding the effect of anti-IL-8 on the function of the alveolar epithelial barrier after acid-induced lung injury. Therefore, the primary objective of this study was to determine the effect of acid-induced lung injury on the function of the alveolar epithelium, and secondly to determine whether pretreatment with anti-IL-8 attenuates acid-induced injury to the lung epithelial barrier. Hydrochloric acid (pH = 1.5 in 1/3 normal saline) was instilled into the lungs of anesthetized, ventilated rabbits. Anti-IL-8 monoclonal antibody (2 mg/kg) or saline was given intravenously 5 min before acid instillation. Acid instillation into the distal airspaces caused an increase in the alveolar epithelial permeability to protein and an approximately 50% reduction in net alveolar fluid clearance. Because a decrease in net alveolar fluid clearance could be due to lung endothelial injury and increased fluid flux from the blood into the airspaces, additional experiments were carried out in which pulmonary blood flow was eliminated. In the absence of pulmonary blood flow, acid instillation led to a 50% decrease in net alveolar fluid clearance. Pretreatment with anti-IL-8 antibody significantly reduced the acid-mediated increase in bi-directional transport of protein across the alveolar epithelium and restored alveolar fluid clearance to normal. The results indicate that acid instillation causes injury to the alveolar epithelial barrier that can be distinguished from the injury to the lung endothelium. Furthermore, pretreatment with anti-IL-8 therapy prevents acid-induced alveolar epithelial injury, a finding of potential clinical importance.

Indomethacin does not influence alveolar liquid clearance in anesthetized sheep or rats.

Active transport of sodium has been shown to be the predominant mechanism involved in alveolar liquid clearance. One regulatory mechanism involved in the modulation of this transport system is cAMP. Although it was initially thought that cAMP could directly modulate transepithelial Na+ transport, recent data suggest that this cAMP modulation could be secondary to the production of arachnidonic acid metabolites. The purpose of this study was thus to evaluate if prostaglandin products could have an indirect or direct role to play in lung liquid clearance. Addition of 10(-5) M salmeterol, known to increase intracellular cAMP, to the instilled fluid in rats stimulated lung liquid clearance. However, addition of indomethacin did not influence the stimulating effect of salmeterol. Furthermore, addition of prostaglandin E2 to the instilled fluid did not stimulate alveolar fluid clearance. In order to determine if this response could be species related, we evaluated if indomethacin could modulate alveolar liquid clearance in sheep. Presence of cAMP and aminophylline stimulated lung liquid clearance in sheep, but indomethacin did not inhibit this response. The present study demonstrates that cyclooxygenase products are not involved in the modulation of basal or stimulated alveolar or lung liquid clearance in sheep or rats.

Role of endogenous cortisol in basal liquid clearance from distal air spaces in adult guinea-pigs.

1. We investigated the role of endogenous cortisol in the modulation of distal air space liquid clearance in adult guinea-pigs. Cortisol synthesis was inhibited with the 11-beta-hydroxylase inhibitor metyrapone (0-7 days pretreatment). After cortisol synthesis inhibition, distal air space liquid clearance was measured by the increase in concentration of an instilled 5 % albumin solution after 1 h. 2. Two days of metyrapone pretreatment resulted in a 46+/-19 % decrease in plasma cortisol levels compared with control, which was paralleled by a 60+/-13 % decrease in distal air space liquid clearance. The Na+ channel inhibitor amiloride inhibited 40+/-22 % of distal air space liquid clearance in control animals but did not inhibit distal air space liquid clearance in the metyrapone-pretreated group. Co-injection of dexamethasone prevented the inhibition by metyrapone and the amiloride sensitivity of distal air space liquid clearance was greater than in control animals. After 7 days of metyrapone pretreatment, plasma cortisol levels and distal air space liquid clearance were not significantly different from normal, but amiloride sensitivity was greater than in control animals (91+/-37%). 3. Pretreatment with emetine, a protein synthesis inhibitor, reduced distal air space liquid clearance in control animals and in dexamethasone-co-injected animals, but failed to inhibit distal air space liquid clearance after metyrapone pretreatment. Expression of the epithelial sodium channel alpha-subunit (alphaENaC) mRNA in lung tissue was decreased after 2 days of metyrapone pretreatment and after 7 days pretreatment or after co-injection with dexamethasone, alphaENaC mRNA expression was restored towards control levels. 4. Thus, endogenous cortisol is important for maintaining normal liquid balance in the adult guinea-pig lung and a critical regulatory pathway is by modulation of ENaC expression and/or function.

Alveolar epithelial fluid clearance persists in the presence of moderate left atrial hypertension in sheep.

The effect of moderate left atrial (LA) hypertension on alveolar liquid clearance (ALC) was investigated in anesthetized, ventilated sheep, surgically prepared to measure lung lymph flow as well as hemodynamics. To simulate alveolar edema, 3-4 ml/kg of isosmolar 5% albumin in Ringer lactate were instilled into each lower lobe, and ALC was measured. After 4 h of LA hypertension (24 cmH2O), ALC was similar to that in control sheep (31 +/- 3% with LA hypertension vs. 34 +/- 10% with normal LA pressure). Because plasma epinephrine levels were moderately elevated in the presence of LA hypertension, ALC was then studied in the presence of LA hypertension following bilateral adrenalectomy. Without endogenous release of epinephrine, ALC was significantly reduced compared with normal LA pressure (20 +/- 7% compared with 34 +/- 10%, P < 0.05). Thus endogenous catecholamines caused a submaximal stimulation of ALC in the presence of LA hypertension. Exogenous administration of aerosolized beta2-agonist therapy with salmeterol increased ALC in the presence of normal LA pressure but had no stimulatory effect in the presence of moderate LA hypertension. Therefore, we tested the hypothesis that endogenous release of atrial natriuretic factor (ANF) may downregulate alveolar epithelial Na+ and fluid transport in the presence of LA hypertension. There was a modest twofold increase in plasma ANF levels after LA hypertension. Additional in vitro studies demonstrated that, in the presence of beta2-agonist stimulation, ANF decreased Na+ pump activity (Na+-K+-ATPase) in isolated rat alveolar epithelial type II cells. ANF may downregulate vectorial Na+ and fluid transport stimulated by endogenous or exogenous beta-adrenergic agonist stimulation in the presence of LA hypertension. In summary, ALC continues even in the presence of moderate LA hypertension. Aerosolized beta2-adrenergic agonist therapy significantly increased ALC, but only when LA pressure was normal.

Reduced osmotic water permeability of the peritoneal barrier in aquaporin-1 knockout mice.

Aquaporin-1 (AQP1) water channels are expressed widely in epithelia and capillary endothelia involved in fluid transport. To test whether AQP1 facilitates water movement from capillaries into the peritoneal cavity, osmotically induced water transport rates were compared in AQP1 knockout [(-/-)], heterozygous [(+/-)], and wild-type [(+/+)] mice. In (+/+) mice, RT-PCR showed detectable transcripts for AQP1, AQP3, AQP4, AQP7, and AQP8. Immunofluorescence showed AQP1 protein in capillary endothelia and mesangium near the peritoneal surface and AQP4 in adherent muscle plasmalemma. For measurement of water transport, 2 ml of saline containing 300 mM sucrose (600 mosM) were infused rapidly into the peritoneal cavity via a catheter. Serial fluid samples (50 microliter) were withdrawn over 60 min, with albumin as a volume marker. The albumin dilution data showed significantly decreased initial volume influx in AQP1 (-/-) mice: 101 +/- 8, 107 +/- 5, and 42 +/- 4 (SE) microliter/min in (+/+), (+/-), and (-/-) mice, respectively [n = 6-10, P < 0.001, (-/-) vs. others]. Volume influx for AQP4 knockout mice was 100 +/- 8 microliters/min. In the absence of an osmotic gradient, 3H2O uptake [half time = 2.3 and 2.2 min in (+/+) and (-/-) mice, respectively], [14C]urea uptake [half time = 7.9 and 7.7 min in (+/+) and (-/-) mice, respectively], and spontaneous isosmolar fluid absorption from the peritoneal cavity [0.47 +/- 0.05 and 0.46 +/- 0.04 ml/h in (+/+) and (-/-) mice, respectively] were not affected by AQP1 deletion. Therefore, AQP1 provides a major route for osmotically driven water transport across the peritoneal barrier in peritoneal dialysis.

Salt and water transport across the alveolar epithelium in the developing lung: correlations between function and recent molecular biology advances (Review).

Significant progress have been made in understanding the mechanisms of alveolar fluid clearance at the time of birth and the transition from placental oxygenation to air breathing. During fetal life, the mammalian lung is a fluid filled secretory organ that fills no respiratory function. Its potential air spaces are filled with fluid that is actively secreted in response to an osmotic force generated by Cl(-)-secretion and the fluid-filled lung is necessary for a proper development of the air-breathing lung. As term approaches, net Cl(-)-secretion decreases, which is accompanied by a decreased secretion rate of the fluid into the air spaces. Concomitantly with the decreased Cl(-)-secretion, the alveolar epithelium begins to absorb Na+ to prepare for fluid absorption and the air breathing life. The causes for the decreased Cl(-)-secretion and the beginning of the Na+ absorption are not clear. Alterations in the hormonal milieu of the lung as well as changes in plasma stress hormone levels have been suggested to play roles. The switch from a placental oxygenation to pulmonary oxygenation requires that the fluid in the air spaces be rapidly removed from the lung lumen. Recent studies have demonstrated that removal of the alveolar fluid at birth is regulated via endogenous plasma epinephrine in the newborn. Molecular, cellular, and whole animal in vivo studies have demonstrated that fluid absorption at birth is related to expression and function of the epithelial sodium channel (ENaC). Several different in vivo and in vitro preparations have been used to investigate the mechanisms of alveolar fluid transport, primarily in adult lungs and have demonstrated that alveolar fluid absorption is driven by active Na+ transport. Both catecholamine-dependent and -independent regulatory mechanisms have been identified, probably acting on ENaC and other apical sodium channels and/or the basolaterally located Na+, K(+)-ATPase. Future studies are needed to integrate new insights to the molecular mechanisms behind fluid clearance with their function in both normal and pathological lungs.

Upregulation of alveolar epithelial fluid transport after subacute lung injury in rats from bleomycin.

Alveolar epithelial fluid transport was studied 10 days after subacute lung injury had been induced with intratracheal bleomycin (0.75 U). An isosmolar Ringer lactate solution with 5% bovine serum albumin and 125I-labeled albumin as the alveolar protein tracer was instilled into the right lung; the rats were then studied for either 1 or 4 h. Alveolar fluid clearance was increased in bleomycin-injured rats by 110% over 1 h and by 75% over 4 h compared with control rats (P < 0.05). The increase in alveolar fluid clearance was partially inhibited by amiloride (10(-3) M). Alveolar fluid clearance decreased toward normal levels in rats that were studied 60 days after bleomycin instillation. Remarkably, the measured increase in net alveolar fluid clearance occurred in the presence of a significant increase in alveolar epithelial permeability to protein. Moreover, the increase in alveolar epithelial fluid clearance occurred even though the mRNA for the alpha-subunit of the epithelial sodium channel was decreased in alveolar epithelial type II cells isolated from these rats. In addition, 22Na uptake by isolated alveolar epithelial type II cells from rats treated with bleomycin demonstrated a 52% decrease in uptake compared with type II cells from control rats. Morphological results demonstrated a significant hyperplasia of alveolar type II epithelial cells 10 days after bleomycin injury. Thus, these results provide evidence that proliferation of alveolar epithelial type II cells after acute lung injury may upregulate the transport capacity of the alveolar epithelium, even though the expression of epithelial sodium channels is reduced and the uptake of 22Na per cell is also reduced. These results may have clinical relevance for the resolution of alveolar edema in the subacute phase of lung injury.

Anti-Lewis X antibody and Lewis X-anti-Lewis X immune complexes in Helicobacter pylori infection.

A molecular similarity of Lewis antigens expressed by Helicobacter pylori bacteria and those present in human gastric mucosa has been recognised as a cause of autoimmunity involved in the pathogenesis of chronic type B gastritis and gastric and duodenal ulcers. In this study, the expression of Lewis X determinants was found on 56% of H. pylori strains isolated from patients with chronic gastritis/gastroduodenitis. Anti-Lewis X IgG as well as Lewis X-anti-Lewis X IgG complexes were detected in the sera from patients and even more frequently in the sera from healthy blood donors producing antibodies against surface antigens of H. pylori. It suggested that the initial H. pylori-induced lesions were independent of anti-Lewis X antibody production. When H. pylori bacteria expressing Lewis X antigen were treated with anti-Lewis X monoclonal antibody (mAb) of IgM isotype, they were more susceptible to ingestion by polymorphonuclear leukocytes (PMN) than untreated bacteria. This fact may lead us to believe that anti-Lewis X antibody limits the growth of H. pylori on gastric mucosa.

Alveolar epithelial fluid clearance is mediated by endogenous catecholamines at birth in guinea pigs.

Transition from placental to pulmonary oxygenation at birth depends on a rapid removal of fetal lung fluid from the developing alveoli. Alveolar fluid clearance was examined in ventilated, anesthetized developing guinea pigs of the ages newborn, 2-d-old, 5-d-old, 30-d-old, and 60-d-old (adult). An isosmolar 5% albumin solution was instilled into the lungs of the guinea pigs; the guinea pigs were then studied for 1 h. Alveolar fluid clearance was measured from the increase in alveolar protein concentration as water was reabsorbed. Newborn guinea pigs had a very high alveolar fluid clearance rate that declined rapidly within the first 5 postnatal days towards adult levels. The high alveolar fluid clearance at birth was apparently mediated by the beta-adrenergic system as demonstrated by the elevated plasma epinephrine levels and the increased sensitivity to inhibition by the beta-adrenergic antagonist propranolol immediately after birth. Surprisingly, exogenous addition of epinephrine was not able to stimulate alveolar fluid clearance in the newborn lung, but exogenous epinephrine stimulation increased over time to adult levels. The elevated alveolar fluid clearance at birth was associated with a significantly greater amiloride sensitivity in the newborn guinea pig lung. Northern blot analysis of distal lung tissue as well as isolated alveolar epithelial type II cells showed and confirmed higher levels of the alpha-subunit of the epithelial sodium channel mRNA in the newborn lung that rapidly tapered off toward adult levels. In conclusion, these data demonstrate the importance of the beta-adrenergic system and amiloride-sensitive sodium transporting pathways for clearance of fetal lung fluid at birth.