Surfactant protein-A inhibits lavage-induced surfactant secretion in newborn rabbits.

In vitro experiments with granular pneumocytes suggest that surfactant protein-A (SP-A) inhibits secretion of pulmonary surfactant. We examined whether SP-A inhibits surfactant secretion induced by lung distention during lung lavage. Human SP-A was obtained by lung lavage in a patient with pulmonary alveolar proteinosis. After centrifugation of the lavagate, the pellet was repeatedly washed with saline and then extracted with chloroform:methanol. The methanol:saline phase was separated and lyophilized to yield the SP-A product. SDS-PAGE and immunoblot analysis indicated that our preparation of SP-A had only minor contamination with human plasma proteins. To examine secretion, we used freshly killed newborn rabbit pups of 29.5 days gestation and lavaged the lungs by 10 sequential, fresh saline washes. Littermate neighbor pairs were lavaged with SP-A or human plasma protein at concentrations of 1, 6, 10, and 50 micrograms/ml, and disaturated phosphatidylcholine (DSPC) was analyzed as a marker for surfactant. The inhibition of surfactant secretion was maximal at a concentration of 10 micrograms/ml; the average yield by the last two pairs of washes, an index of surfactant secretion, was 286 +/- 41 micrograms/g dry lung weight for SP-A, compared to 405 +/- 37 micrograms/g dry lung weight for controls, an inhibition of 30% (p < 0.005). There were no changes in the volumes of returned lavage or in the concentrations of lactate dehydrogenase or DNA. To test whether SP-A increased cellular uptake of DSPC in the lungs, we prepared radioactive exogenous surfactant, lavaged it into the lungs, and monitored recovery of radioactivity by continued lavage. Recovery was the same in treated and control lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Staining properties of bovine low molecular weight hydrophobic surfactant proteins after polyacrylamide gel electrophoresis.

Reports describing polyacrylamide gel electrophoresis patterns of bovine hydrophobic surfactant proteins are not consistent. In this study, we found unusual staining characteristics of these proteins that may explain some of these inconsistencies. Low molecular weight surfactant proteins extracted from bronchoalveolar lavage with organic solvent are partially delipidated with Sephadex LH-20 chromatography using chloroform and methanol. Fractions from the first protein peak are dried under nitrogen then subjected to SDS electrophoresis on 20% polyacrylamide gels. Under nonreducing conditions, silver staining identifies 5- and 26-kDa bands, and Coomassie blue identifies 6-, 12-, and 26-kDa bands. When gels are stained with Coomassie blue then silver, the 5- and 26-kDa bands stain with silver and 6- and 12-kDa bands remain stained with Coomassie blue. If gels are first stained with silver then Coomassie blue, similar results occur. We modified the silver staining protocol by treating gels with dithiothreitol or 2-mercaptoethanol after electrophoresis. With this modification, 5-, 6-, 12-, 26-, and also 17-kDa bands are identifiable. Using the modified protocol and restaining gels previously stained with silver, 6-, 12-, and 17-kDa bands that were not identified previously all became visible. In further experiments, protein bands of 6-, 12-, and 26-kDa that were identified by Coomassie blue were electroeluted under nonreducing conditions. After electrophoresis of the eluted 26-kDa protein, bands of 17-, and 26-kDa under nonreducing, and 8-kDa only under reducing conditions, were apparent by using the modified silver protocol.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthetic amphipathic sequences of surfactant protein-B mimic several physicochemical and in vivo properties of native pulmonary surfactant proteins.

A mixture of lipids and proteins unique to the lung lines the airspaces of all mammalian species. This mixture, termed pulmonary surfactant, is essential for normal lung function. We have synthesized selected amino acid sequences of one of the major low molecular weight surfactant proteins to find whether these peptides can duplicate effects of native protein. Peptide/lipid mixtures approximate results found with native surfactant proteins both in vitro and in vivo. Effects found with native proteins or synthetic peptides include association with, and ordering of, surfactant lipid; changes in surface tension with surface compression; rapid adsorption of lipids from subphase to surface; and improvements in oxygenation of surfactant-deficient rats.

Factors associated with surfactant treatment response in infants with severe respiratory distress syndrome.

In a prospective, randomized study of 18 infants treated with bovine surfactant (surfactant TA, Tokyo Tanabe Co, Tokyo) for severe respiratory distress syndrome, a lasting response was found in 12 infants (66%), a transient response was found in two (11%), and no response was found in four (22%) when arterial to alveolar PO2 ratios were used to define responses during the first 48 hours after treatment. In contrast, three of 23 control infants (13%) had a transient or lasting "response" to sham treatment (Pediatrics 1987;79:31-37). To determine whether maldistribution of surfactant could explain lack of response or a transient response, surfactant TA was mixed with technetium-99m sulfur colloid (approximately 300 mu Ci per infant), and eight infants with severe respiratory distress syndrome were treated six to 58 hours after birth. Scintigraphy of the lungs was performed three to 15 hours after treatment. Although a lasting response was observed in three infants, a transient one in three, and no response in two, no gross maldistribution of the radioactive label was found. Either lung received from 37% to 62% of the total radioactivity. During the past 3 years, in all infants with severe respiratory distress syndrome who were treated with surfactant (n = 29), poor or transient responses were associated with early patent ductus arteriosus and air leaks (pulmonary interstitial emphysema and pneumothoraces). Pathophysiologic conditions associated with respiratory distress syndrome are more likely to explain suboptimal responses after surfactant treatment than gross maldistribution of surfactant in the lungs.

Pharmacologic regulation of alveolar surfactant in fetal and newborn rabbits: ACTH, heroin, isoxsuprine, and glucocorticoid.

The evidence that pharmacologic doses of glucocorticoids induce lung maturation and diminish risk of respiratory distress syndrome has been reviewed briefly. Studies with heroin corroborate that pharmacologic induction of lung maturation is possible in the human fetus. Endogenous fetal glucocorticoids may serve as a physiologic mechanism that prepares the immature lungs for birth. Catecholamines may induce release of stored surfactant from type 2 cells into alveolar spaces.