Abstract 1863 Neonatal Disease Oriented Research: Ductus and Surfactant Platform, Sunday, 5/2

Surfactant protein-D (SP-D) is a collagen-like lectin (collectin) secreted by pulmonary epithelial type II cells and non-ciliated bronchiolar epithelial cells. Gene-targeted mice deficient in SP-D accumulate surfactant and enlarged foamy alveolar macrophages in the alveolar space but the underlying alteration in surfactant metabolism is unknown.

Aim. To determine if turnover of saturated phosphatidylcholine (PC) is altered in SP-D null mice.

Methods. Littermate wild type and SP-D null mice were given 50 µCi of 3H-choline intraperitonealy. At time points from 0.5 to 144 hours after labeling the lungs were lavaged and then homogenized. The alveolar wash was centrifuged to remove cells prior to analysis. Saturated PC was isolated from the organic solvent extract of tissue homogenate and alveolar wash on silica gel chromatography plates after treatment with osmium tetroxide. Duplicate samples of saturated PC were assayed for phosphorus content and incorporated radioactivity. Tissue and alveolar wash saturated PC pools, 3H-choline incorporation and saturated PC specific activity were calculated.

Results. Tissue and alveolar wash saturated PC pool sizes were increased in the null compared to wild type mice by 6 and 8.4 fold respectively (n=30 in each group). Total 3H-choline incorporation was significantly greater in tissue and alveolar wash in null compared to wild type at all time points (0.5, 2, 6, 24, 48, 72, and 144 hours after labeling). Peak tissue and alveolar wash 3H-choline incorporation into saturated PC was increased in the null compared to wild type mice 4.7 and 4.2 fold respectively. In contrast, the calculated peak specific activities in the tissue and alveolar washes from wild type and null animals were similar. Peak 3H-choline incorporation into saturated PC and peak specific activities in both tissue and alveolar wash saturated PC pools were reached significantly later in null compared to wild type mice. In wild type mice the calculated peak specific activity was reached at 6 and 24 hours in the tissue and alveolar wash respectively. In null mice the calculated peak specific activity was reached at 48 hours in both the tissue and alveolar wash.

Conclusion. These results suggest that, despite marked differences in tissue and alveolar saturated PC pool sizes, there is a similar throughput of saturated PC in wild type and null mice. Additional time points will be needed to precisely define the surfactant turnover times in both groups.

Funded by HL24075 and HL58047 from NHLBI