Effect of Aminophyllin and Dexamethasone on Secretion of Pulmonary Surfactant in Fetal Rabbits

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Abstract
Summary: Aminophyllin, dexamethasone, or saline was injected into 27.5-day fetal rabbits 2.5 hr before sacrifice, after which static pressure-volume curves with air were performed. In further similar experiments the lungs were lavaged with physiologic saline which was analyzed for total phospholipid content. There were no changes in total lung capacity (TLC) induced with either aminophyllin or dexamethasone. The lungs of fetal rabbits injected with saline retained 44% TLC (±3 SE) after deflation to 10 cm H2O trans-pulmonary pressure compared with 48% TLC (±3 SE) in those injected with dexamethasone, a difference which was not statistically significant. In contrast, the lungs of fetal rabbits injected with aminophyllin retained 53% TLC (±2 SE) after deflation to 10 cm H2O pressure, a significant increase when compared with saline controls (P < 0.01). There were no changes in lung weight or lung water. These results were interpreted to mean that aminophyllin decreased surface tension and augmented secretion of pulmonary surfactant. This was supported by finding significantly increased total phospholipid recovered in the lung lavage fluid of fetal rabbits injected with aminophyllin, 62 μg/g dry lung weight (±6 SE) compared with 32 μg/g dry lung weight (±3 SE) in saline controls (P < 0.05). Phospholipid recovered from dexamethasone-injected fetal rabbits was not significantly increased, 38 μg/g dry lung weight (±4 SE). Speculation: Although other explanations cannot be excluded, the effect of aminophyllin in promoting secretion of surfactant is consistent with proposals that the secretory process is under control of cAMP.