Elastin and collagen in the fetal sheep lung. II. Relationship to mechanical properties of the lung

The relationship between elastin and collagen concentration and indices of lung maturation was studied in the lungs of fetal sheep. Fetal sheep of 124 days gestation were infused for 84 h with cortisol, triiodothyronine, prolactin, or epidermal growth factor alone or in combination. Pressure-volume curves with air were performed on the lungs and saturated phosphatidylcholine was measured in lung washes. Desmosine and hydroxyproline were determined in lung tissue in seven hormone-treated fetuses that displayed distensible and stable lungs similar to term lungs [volume of air at 40 cm H2O (V40) greater than 1.5 ml/g wet weight and at 5 cm H2O (V5) greater than 0.8 ml/g] and in seven fetuses whose lungs remained nondistensible and unstable (V40 less than 0.6 ml/g and V5 less than 0.4 ml/g). Alveolar saturated phosphatidylcholine was five times higher (p less than 0.001) in distensible than in nondistensible lungs, but attained less than 20% of term values. Desmonsine and hydroxyproline concentrations in parenchyma, pleura, and trachea of nondistensible, unstable lungs were similar to intact controls of 125 days gestation and those in distensible, stable lungs were similar to controls of 137 days gestation. Desmosine (p less than 0.0001) and hydroxyproline (p less than 0.001) concentrations in parenchyma of distensible, stable lungs were higher than those of nondistensible, unstable lungs. We speculate that increased distensibility of the fetal lung in response to treatment with hormones is attributable in part to changes in the composition of connective tissue.