Autoradiographic localization and effects of exogenous radioactively labelled surfactant in the lung of the prematurely delivered fetal rabbit.

Adult rabbit lung surfactant was radioactively labelled with [3H]palmitate and isolated by centrifugation. This material was instilled into the trachea of fetal rabbits prematurely delivered on the 27th gestational day. A similar preparation of unlabelled surfactant was used to measure the effects on pressure-volume characteristics in lungs of 27th day fetuses. Tissue sections were prepared from the lungs of all animals and morphometric and autoradiographic determinations made. Surfactant instillation improved pressure-volume relationships in fetal rabbit lungs. Histologically, although only the middle right lobe seemed to show significant qualitative improvement in expansion after surfactant treatment, quantitative assessment indicated that the surfactant preparation had significantly increased the mean alveolar cross-sectional areas in all three lobes of right lungs. In addition, distribution of autoradiographic grains indicated that 8-25% were located over the alveolar spaces while approximately half this percentage was present over tissue at the level of the alveolus. These results indicate that intratracheal instillation of surfactant supplements the endogenous surfactant at the level of the alveolus.