Lung RE concentration after a single treatment with VA alone, or VARA or VAAm prepared with different percentages of acidic retinoid. In A, neonatal rats were treated on PD4-5 with a single dose and tissue was collected 6 h later (A). In B, neonatal rats were treated with multiple doses on PD4, 7, 11, and 14 and lung tissue was collected 6 h after the last dose. Data are presented as means ± SEM. Statistical analysis was conducted on log10-transformed data using one-factor ANOVA and Fisher’s Least Significant Difference posthoc test. Groups with different letters differed significantly, P < 0.05.