Relative mRNA expression, determined with RT-PCR, of surfactant proteins A (A), -B (B), -C (C) and -D (D) and Clara cell secretory protein CC10 (E) in oxygen-exposed (black bars) and control pups (white bars) in neonatal lungs on days 1, 3, 6, and 10. In panel F adult mRNA expression is depicted by black bars and neonatal expression in room air-exposed controls on day 3 by white bars. Data are expressed as mean ± SEM of 9 (day 1) or 6 (days 3, 6 and 10, and 6 months) rats. *: p < 0.05; **: p < 0.01, ***: p < 0.001 versus age-matched controls (panels A-E) or versus day 3 room air (panel F). Δ: p < 0.05, ΔΔ: p < 0.01, ΔΔΔ: p < 0.001 versus day 1.