Size selectivity of lung protein accumulation in preterm ventilated lambs

The 1-hour net accumulation of four labeled proteins of different sizes (6.5, 29, 69 and 150 kD) from the vascular space into the lungs and airspaces was measured in preterm ventilated lambs at 132 days gestational age. Lambs treated with Survanta, a surfactant prepared from bovine lung, were studied at 1, 3, 5 and 8 h after birth, while lambs not treated with this surfactant were studied up to 5 h of age because of severe respiratory failure. The labeled proteins were lost from the vascular space more rapidly over the first 1 h of life than at later times (p less than 0.01). Labeled protein recoveries were similar at 1 and 3 h in surfactant and control lambs and decreased by 8 h in surfactant-treated lambs (p less than 0.05). In both the surfactant-treated and control animals, there was a sequential decrease in labeled protein recoveries based on protein size (p less than 0.01). There was no change with time in size selectivity for accumulation of the labeled proteins into the lungs for either the control or surfactant-treated lambs, although surfactant treatments decreased accumulation of the 6.5 and 29 kD proteins at 5 h when compared to the control group (p less than 0.05). Labeled protein recoveries in alveolar washes demonstrated less size selectivity. These studies documented that size selectivity of the vascular endothelium did not change over the first 8 h of life in preterm ventilated lambs, a pattern that was not indicative of progressive lung injury.