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.