Abstract 1857 Poster Session IV, Tuesday, 5/4 (poster 291)

Fetal tracheal obstruction (TO) accelerates lung growth, but dramatically reduces the number of type II cells. We have recently shown that release of occlusion (R) 7 days before delivery restores the number and the function of type II cells. Antenatal steroids are used in clinic to accelerate lung maturation. We hypothesized that antenatal steroids (S) would potentiate the effect of R on the recuperation of type II cell number and function. Four groups of fetal sheep were compared. At 117 d of gestation, TO was performed using a Swan-Ganz catheter in all experimental groups. At 136 d, occlusion was released by balloon deflation in TO+R and TO+R+S groups. At 137 d, TO+S and TO+R+S groups received 0.5 mg/kg of betamethasone. Animals were sacrificed at 138 d. The number and function of type II cells were evaluated by the surfactant protein C (SP-C) and B (SP-B) mRNA expression. In situ hybridization was used to quantify both the density of cells expressing the mRNA (positive cells per field) and the degree of expression per cell (grains per positive cells). At least 1 slide from 3 different lobes was studied. (Table)

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Three secondary hypotheses were tested by ANOVA after verification of variances. The effect of steroids alone was tested by comparing TO Vs TO+S: for SP-B the differences were not significant, however for SP-C the density of (+) per field but not grains/cell was different (α < 0.05). The additive effect of steroids was tested by comparing TO+R Vs TO+R+S: the differences were significant (α < 0.01) for the density of SP-B and SP-C positive cells per field as well as for the amount of SP-C per cell. Finally, the effect of release was tested by comparing TO±S Vs TO+R±S: differences were significant (α < 0.01) for both the density and the grains per cell of SP-B and SP-C. We conclude that steroid treatment alone produces marginal results; whereas it has an additive effect when combined with a short release of TO.

Support: Canadian MRC, Fonds de Recherche en Sante du Quebec, and the Fondation de la recherche sur les maladies infantiles.