Development of the pulmonary surfactant system in two oviparous vertebrates

In birds and oviparous reptiles, hatching is often a lengthy and exhausting process, which commences with pipping followed by lung clearance and pulmo nary ventilation. We examined the composition of pulmonary surfactant in th e developing lungs of the chicken, Gallus gallus, and of the bearded dragon , Pogona vitticeps. Lung tissue was collected from chicken embryos at days 14, 16, 18 (prepipped), and 20 (postpipped) of incubation and from 1 day an d 3 wk posthatch and adult animals. In chickens, surfactant protein A mRNA was detected using Northern blot analysis in lung tissue at all stages samp led, appearing relatively earlier in development compared with placental ma mmals. Chickens were lavaged at days 16, 18, and 20 of incubation and 1 day posthatch, whereas bearded dragons were lavaged at day 55, days 57-60 (pos tpipped), and days 58-61 (posthatched). In both species, total phospholipid (PL) from the lavage increased throughout incubation. Disaturated PL (DSP) was not measurable before 16 days of incubation in the chick embryo nor be fore 55 days in bearded dragons. However, the percentage of DSP/PL increase d markedly throughout late development in both species. Because cholesterol (Chol) remained unchanged, the Chol/PL and Chol/DSP ratios decreased in bo th species. Thus the Chol and PL components are differentially regulated. T he lizard surfactant system develops and matures over a relatively shorter time than that of birds and mammals. This probably reflects the highly prec ocial nature of hatchling reptiles.