Compression of the central airways by a dilated aorta in infants and children with congenital heart disease.

BACKGROUND: Children with congenital heart disease often experience respiratory symptoms in the preoperative and perioperative periods, which can complicate their management. An uncommon but important cause of respiratory insufficiency in such children is external airway compression. METHODS: We operated on 5 patients (median age, 6 months) with significant respiratory distress attributable to compression of the central airways by a dilated ascending aorta before or after repair of concomitant cardiovascular defects. Four of these patients had right aortic arch and 3 had pulmonary atresia with a ventricular septal defect and major aortopulmonary collaterals. In all patients, aortopexy was performed at the time of operation for the cardiovascular defects (n = 3) or after symptoms developed in the postoperative period (n = 2). The 3 patients in whom airway compression produced symptoms preoperatively also underwent reduction ascending aortoplasty. RESULTS: Symptoms resolved immediately after operation in 3 patients, whereas symptoms persisted in the other 2 patients and tracheostomy was required. At follow-up of 20 months to 5 years, all patients are alive and well, with mild or moderate respiratory symptoms in the 2 patients who required tracheostomy, both of whom were decannulated within 13 months. CONCLUSIONS: External airway compression can cause significant morbidity in patients with congenital heart defects other than vascular rings. In patients with respiratory symptoms in the context of a lesion that involves increased aortic outflow during intrauterine life and consequently, an enlarged ascending aorta, such as tetralogy of Fallot with pulmonary atresia, airway compression should be considered as a cause, especially if a right aortic arch is present or the patient also has pulmonary atresia with a ventricular septal defect and collaterals. Attempts to address this problem surgically may provide substantial relief, but increasing duration of airway compression is likely to lead to tracheal or bronchial malacia and persistent symptoms even after the compression is relieved.

Lipoprotein-stimulated surfactant secretion in alveolar type II cells: mediation by heterotrimeric G proteins.

Low- and high-density lipoproteins (LDL and HDL, respectively) stimulate alveolar type II cells to secrete surfactant. Increases in phosphoinositide hydrolysis, cytosolic Ca2+, and membrane-associated protein kinase C activity precede LDL- and HDL-stimulated secretion. We report three lines of evidence supporting the hypothesis that Gi mediates LDL- and HDL-stimulated surfactant secretion and signal transduction in type II cells. First, pertussis toxin (PTX) inhibited secretion stimulated by the apolipoprotein ligands for either the LDL receptor or the HDL binding protein. Second, PTX inhibited protein kinase C activity in cell membranes stimulated by LDL or HDL. Third, treatment of cell membranes with LDL or HDL inhibited PTX-catalyzed labeling of substrates corresponding in molecular mass to Gi alpha. These observations suggest that receptor-mediated activation of Gi is required for LDL- and HDL-stimulated secretion and that LDL and HDL activate Gi. These studies in type II cells are the first to support the hypothesis that Gi mediates the effects of LDL or HDL on important phenotype-specific functions of differentiated cells.

Maintenance of the differentiated type II cell phenotype by culture with an apical air surface.

The study of differentiated functions of alveolar type II cells has been hampered because of the lack of good in vitro systems. We report that culture of type II cells on collagen gels with an apical surface exposed to air promotes expression of differentiated type II cell characteristics. Cells cultured in this manner are cuboidal, contain lamellar bodies, and produce tubular myelin; in addition, they secrete phosphatidylcholine in response to exogenous ATP. Cultures contain mRNA for surfactant proteins A, B, and C and surfactant proteins A, B, and D. In contrast, when type II cells are cultured with an apical surface exposed to liquid rather than to air, the cells are squamous, do not express surfactant proteins or their respective mRNA, and do not contain lamellar bodies or produce tubular myelin. Type II cells cultured on plastic for 7 days, which no longer express mRNA for surfactant proteins, can be induced to express these mRNA by changing culture conditions to that of an air surface. The culture system described in this paper should be useful for studies of surfactant metabolism, regulation of alveolar epithelial phenotypic expression, and the processing of transiently expressed transgenes.

Exotoxin A stimulates fluid reabsorption from distal airspaces of lung in anesthetized rats.

To determine whether exotoxin A may affect the transport of fluid across the lung epithelium, two isogenic strains of Pseudomonas aeruginosa PA103 (10(8) colony-forming units), one (PA103 tox omega) with a structural gene mutation in exotoxin A, were instilled into the distal airspaces of anesthetized rats. PA103 parental strain, but not its mutant, stimulated the removal of fluid from the distal airspaces of the lung. Instillation of exotoxin A alone caused a dose-dependent increase in the fluid transport across the lung epithelium. Instillation of amiloride (10(-3) M) with exotoxin A demonstrated that this effect partially depended on increased uptake of sodium across the lung epithelium. The absence of stimulation after instillation of an exotoxin A mutant (PE delta Glu553) without ADP-ribosyltransferase activity demonstrated that the effect of exotoxin A depended on its ADP-ribosyltransferase activity. Finally, the instillation of exotoxin A in rats depleted of macrophages indicated that the effect of exotoxin A was not secondary to the activation of alveolar macrophages by this toxin. In conclusion, these results indicate that the in vivo release of exotoxin A by live airspace P. aeruginosa directly stimulates the fluid removal from the airspaces by the lung epithelium. This may alter the volume or composition of airway secretions, and may contribute to the lung disease in patients infected with P. aeruginosa.

Evidence for G beta gamma-mediated cross-talk in primary cultures of lung alveolar cells. Pertussis toxin-sensitive production of cAMP.

In the presence of activated Gs alpha, the beta gamma complex of heterotrimeric G proteins (beta gamma) stimulates adenylyl cyclase (AC) in membranes prepared from cells expressing recombinant AC II or AC IV. Conditional stimulation of AC by beta gamma has been hypothesized to integrate cross-talk between Gs- and non-Gs-coupled regulation of cellular cAMP (Tang, W. J., and Gilman, A. G. (1991) Science 254, 1500-1503). Although observations in cells expressing recombinant receptors, G alpha s, and AC support this hypothesis (Federman, A. D., Conklin, B. R., Schrader, K. A., Reed, R. R., and Bourne, H. R. (1992) Nature 356, 159-161), this mechanism has not been investigated in differentiated cells. Expression of AC II has been reported only in lung, olfactory, and brain tissue. We found that rat lung alveolar type II cells express AC II and IV. Therefore, we hypothesized that beta gamma conditionally stimulates AC in type II cells. Consistent with this hypothesis, we found that the alpha 2-adrenergic agonist UK14304 did not affect basal cAMP in type II cells but potentiated terbutaline-stimulated cAMP accumulation. Treatment of cells with pertussis toxin partially inhibited terbutaline-stimulated cAMP accumulation and completely inhibited the effects of UK14304. In type II cell membranes, purified beta gamma tripled the terbutaline-stimulated increase in AC activity. In contrast, beta gamma inhibited AC activity in the absence of terbutaline. The addition of purified Go alpha blocked beta gamma-induced effects. In summary, type II cells expressing endogenous AC II and IV regulate cAMP accumulation and AC activity in a manner consistent with conditional stimulation by beta gamma. These observations support the overall hypothesis that conditional stimulation of AC by beta gamma integrates cross-talk between signal transduction systems in differentiated cells.

Activation of G proteins may inhibit or stimulate surfactant secretion in rat alveolar type II cells.

To investigate how G proteins regulate surfactant secretion, we subjected rat alveolar type II cells to conditions known to activate or to inactivate G proteins. AlF-4, which activates G proteins, inhibited secretion in intact cells. Guanosine-5'-O-(3-thiotriphosphate), which activates G proteins in permeabilized cells, stimulated secretion at basal cytosolic [Ca2+], but inhibited secretion at higher [Ca2+]. In contrast, guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), which inactivates G proteins, stimulated secretion at each [Ca2+] tested. Because treatment with GDP beta S stimulated secretion at basal cytosolic [Ca2+], surfactant secretion appears to be subject to G protein-regulated tonic inhibition. Pertussis toxin (PTX) inhibited terbutaline- and ionomycin-stimulated secretion in intact cells, but did not inhibit secretion stimulated by either forskolin or 8-bromoadenosine 3',5'-cyclic monophosphate. Inhibition by PTX of terbutaline-stimulated, but not 8-bromoadenosine 3',5'-cyclic monophosphate- or forskolin-stimulated secretion, suggests that PTX-sensitive G proteins regulate beta-adrenergic-stimulated surfactant secretion proximal to second messenger generation. Inhibition of ionomycin-stimulated secretion, however, suggests that PTX-sensitive G proteins may also regulate non-receptor-mediated secretory events.

Prolonged transgene expression in rodent lung cells.

We tested the efficiency of several different cationic liposome formulations, complexed to one of two different chloramphenicol acetyltransferase (CAT) reporter plasmids, in transfecting freshly isolated, highly purified rat lung alveolar type II cells, alveolar macrophages, and three different human lung carcinoma cell lines, as well as NIH 3T3 cells, a rapidly dividing, transformed mouse fibroblast line. Our results demonstrated that several different cationic liposome formulations can mediate high-level CAT gene expression in all the cell types tested. Electron microscopic analysis confirmed that cationic liposome-DNA complexes are avidly bound and internalized by lung cells. The time course of expression of transfected genes in nontransformed cell types with low mitotic indices, such as type II cells, is poorly characterized. NIH 3T3 cells expressed maximal CAT activity by day 4 following transfection, with virtual disappearance of activity by day 11. Conversely, type II cells expressed maximal CAT activity between days 5 and 11, and CAT activity was still clearly present 35 days after transfection. Southern blot analysis of DNA isolated from transfected type II cells revealed that the CAT gene was largely present in an extrachromosomal form, rather than integrated into genomic DNA. These observations indicate that following cationic liposome-mediated transfection, rat alveolar type II cells (the majority of which do not divide in culture) can express transfected genes for prolonged periods, apparently mediated by expression of the transgene in an episomal form.

Positive correlation between cytosolic free calcium and surfactant secretion in cultured rat alveolar type II cells.

To determine whether increases in the cytosolic free Ca2+ concentration ([Ca2+]i) accompany agonist-stimulated surfactant secretion by cultured alveolar type II cells, we measured the [Ca2+]i of quin2-loaded cells isolated from adult rats before and after cells were stimulated with ionomycin, terbutaline or tetradecanoylphorbol acetate (TPA). To determine whether increases in [Ca2+]i are necessary for stimulated surfactant secretion to occur, we measured secretion in cells after [Ca2+]i had been reduced by loading cells with quin2 in medium containing low [Ca2+]. Ionomycin increased [Ca2+]i and stimulated surfactant secretion in a dose-dependent manner. Reductions in [Ca2+]i correlated with reductions in secretion stimulated by ionomycin, terbutaline or TPA. Ionomycin-stimulated secretion was most sensitive to reductions in [Ca2+]i; terbutaline-stimulated secretion was more sensitive than TPA-stimulated secretion. When [Ca2+]i was less than 65 nM, all stimulated secretion was blocked. Restoration of [Ca2+]i to greater than 100 nM restored ionomycin-stimulated secretion. We conclude that ionomycin increases [Ca2+]i and stimulates surfactant secretion in cultured alveolar type II cells, and that increased [Ca2+]i appears to be necessary for ionomycin-stimulated secretion to occur. Terbutaline-stimulated surfactant secretion seems to be more easily inhibited by a reduction in [Ca2+]i than does TPA-stimulated secretion.

An acute reduction in the fraction of inspired oxygen increases airway constriction in infants with chronic lung disease.

Infants with chronic lung disease have acute episodes of hypoxemia that are often accompanied by wheezing. To test whether a sudden reduction in FIO2 might increase airway obstruction in such infants, we measured the flow-volume relationship, O2 saturation, and skin-surface CO2 tension in 19 sedated infants, 11 with chronic lung disease, and 8 control infants, before and during 10 min of continuous hypoxemia. In the infants with chronic lung disease, a 20 to 25% reduction in FIO2 caused acute hypoxemia (O2 saturation, 77 +/- 8%) and an associated decrease in mid-expiratory flow from 103 +/- 55 to 69 +/- 37 ml/s (mean +/- SD; p less than 0.05) in the absence of a significant change in tidal volume or skin-surface CO2 tension. In the infants without lung disease, breathing 17% O2 led to a significant increase in minute ventilation (26 +/- 25%; p = 0.05), but there was no consistent change in mid-expiratory flow. To further study the effects of an acute reduction in FIO2 on pulmonary function in infants with chronic lung disease, we measured lung mechanics in 6 infants and end-expiratory lung volume in 5. Baseline lung resistance was high (49 +/- 35 cm/l/s) and increased by 55 +/- 30% (p less than 0.05) in response to hypoxemia. Baseline dynamic lung compliance was low (2.5 +/- 1.5 ml/cm) and decreased by 24 +/- 10% (p less than 0.05). Functional residual capacity increased from 26 +/- 13 to 33 +/- 14 ml/kg (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Caffeine stimulates beta-endorphin release in blood but not in cerebrospinal fluid.

Plasma beta-endorphin and prolactin profiles were obtained from groups of unstressed, adult male rats. The infusion of caffeine (20 mg/kg) via a chronic, indwelling intra-atrial cannula results in a prompt and sustained (2-2.5 h) rise In plasma beta-endorphin levels. The infusion of the opiate antagonist naloxone causes a modest (40%) decrease in plasma beta-endorphin and blunts the elevation in plasma beta-endorphin following caffeine administration. In contrast, plasma prolactin levels were unchanged following caffeine administration and were decreased by treatment with naloxone. Caffeine treatment did not effect CSF beta-endorphin levels or the release of beta-endorphin from hemipituitaries incubated in vitro.