Impact of surface tension on the conversion rate of large to small surfactant aggregates.

The extracellular alveolar surfactant can be separated into the highly surface active large surfactant aggregates (LA) and the less active small surfactant aggregates (SA). Conversion of LA to SA is encountered upon cyclic surface area changes and demands the presence of enzymatic activity. In the present study we investigated the influence of surface tension on the conversion of LA to SA.

Selective inhibition of large-to-small surfactant aggregate conversion by serine protease inhibitors of the bis-benzamidine type.

Conversion of the biophysically active large surfactant aggregate subtype (LA) of alveolar surfactant into the less surface active small surfactant aggregates (SA) occurs in vivo and is reproduced under conditions of cyclic surface area changes in vitro. A serine-active carboxyl esterase has been suggested as the responsible enzymatic activity, although the exact mechanisms underlying the conversion process are presently unclear. We investigated the influence of exogenous serine proteases and synthetic and natural serine protease inhibitors on the conversion kinetics of natural rabbit surfactant, obtained as bronchoalveolar lavage fluid (BALF).

Surfactant subtype conversion is related to loss of surfactant apoprotein B and surface activity in large surfactant aggregates. Experimental and clinical studies.

Conversion of the highly surface-active subtype of pulmonary surfactant known as large surfactant aggregates (LA) to small aggregates (SA) with poor surface activity has recently been shown to occur upon cyclic changes of the air-liquid interface area in vitro. By subjecting pooled rabbit bronchoalveolar lavage fluid (BALF) to this maneuver, we found that conversion of LA to SA was accompanied by a marked decline in the ability of the remaining LA fraction to reduce surface tension by adsorption and during film compression on a pulsating bubble surfactometer. SA obtained by centrifugation of noncycled rabbit BALF had a similar phospholipid (PL) but different neutral lipid (NL) composition than did the LA.