Exogenous surfactant in ischemia/reperfusion: effects on endogenous surfactant pools.

Background: Pre-ischemic surfactant treatment attenuates ischemia/reperfusion (I/R) injury. In this study we investigate whether exogenous surfactant acts by influencing endogenous intra-alveolar and intracellular surfactant pools and subtype composition.
Methods: Rat lungs from control with (C + S) or without (C - S) surfactant treatment and I/R with (I/R + S) or without (I/R - S) surfactant treatment were analyzed. In I/R groups, lungs underwent ischemic storage for 4 hours at 4 degrees C and reperfusion for 60 minutes. The ultrastructure of intra-alveolar and intracellular surfactant forms fixed in their natural localization and microorganization was investigated by light- and electron-microscopic stereology.
Results: Only slight differences in alveolar epithelial Type II cell number or volume and lamellar body parameters were observed. Intra-alveolar surfactant volume was significantly enhanced in C + S and I/R + S. I/R increased inactivated surfactant forms (unilamellar vesicles) in untreated [mean (SD): C - S: 26.0% (8.0%) vs I/R - S: 64.8% (5.5%); p < 0.01], but not in surfactant-treated rats [I/R + S: 23.5% (11.5%); p < 0.01 vs I/R - S]. The increase in unilamellar vesicles was closely correlated with intra-alveolar edema and decreased perfusate oxygenation.
Conclusions: Attenuation of I/R injury by pre-ischemic exogenous surfactant treatment is mainly based on stabilizing and increasing the active endogenous intra-alveolar surfactant pool.