FIGURE 2.

Lung alveolar structure identified by hematoxylin‐eosin (H & E) staining of paraffin embedded lung sections obtained at postnatal day 21 (P21), cut to 5 μm thickness and imaged at 20×. Scale bars are 200 μm. Summary data shown in bar graphs for radial alveolar count (RAC) and mean linear intercept (MLI) were from eight pups in each group and are shown as mean ± SD. * Indicates p < .05 by ANOVA and Tukey's post‐hoc test from normoxia + saline and # from hyperoxia + saline groups. Pups exposed to hyperoxia from P1 to P10 continue to show decreased RAC and alveolar simplification at P21 despite 10 days of recovery in normoxia. Metformin treatment from P1 to P10 increased RAC and improved alveolar simplification at P21, indicated by decreased MLI compared to saline‐treated hyperoxia pups. HOX, hyperoxia; NOX, normoxia