Abstract 1811 Poster Session IV, Tuesday, 5/4 (poster 288)

Occlusion of the fetal trachea has been shown to accelerate lung growth. Although the mechanisms responsible for lung growth following tracheal occlusion (TO) are poorly understood, lung fluid accumulation is necessary for growth to occur. Terbutaline (terb) is a betamimetic tocolytic used after fetal surgery to prevent premature labor that may decrease fetal lung fluid production. We tested the effect of terb administration on TO induced lung growth in normal rat fetuses and fetuses with hypoplastic lungs from nitrofen induced congenital diaphragmatic hernia (CDH).

Methods: In the first series, time-dated pregnant Sprague-Dawley rats underwent laparotomy on gestation day 18.5 (day 22 term) for TO in 4-5 fetuses and implantation of a mini-osmotic pump to infuse terb (5 mg/kg/day) to the dam. Animals were sacrificed on day 21.5 and fetal dry lung weight per gram body weight (dLW/BW, mg/g) was compared among the control (no TO, no terb), TO (TO, no terb), and TO/terb (TO with terb) groups (n=10-13 per group). In the second series of experiments, left-sided CDH was induced by administration of 100 mg of nitrofen to the dam on fetal day 9.5. Laparotomy was performed on day 19 with TO and osmotic pump placement as above. On day 21.5 fetuses with left CDH were examined for lung growth.

Results: Results are expressed as mean±SD and were compared by one-way ANOVA with Scheffe's test (figure). Lungs from the TO group were significantly heavier than control in both normal and CDH fetuses (3.44±0.16 vs 2.84±0.23, p<0.01 and 3.01±0.33 vs 2.04±0.20, p<0.01, respectively). Lungs from the TO/terb group were significantly lighter than the TO group in both normal and CDH fetuses (3.19±0.20 vs 3.44±0.16, p<0.05 and 2.47±0.33 vs 3.01±0.33, p<0.01, respectively)

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Conclusion: Maternal administration of terbutaline has an adverse effect on lung growth following TO in the rat model. Further studies of lung fluid dynamics are necessary to understand the mechanisms of TO induced growth.