Fig. 2

Structural and functional immaturity of rabbit pups born on day 28 of gestation. a Lm and (b) Lmw are measurements of alveolar size and septal thickness respectively and are both increased in preterm pups at birth. c Representative pictures of lung slides stained with HE,Miller and CD31 indicate more rounded and less complex airspaces, more muscularized arteries and a comparable density of small to medium size vessels in preterm pups at birth. Arrows indicate 20-50 μm vessels with CD31-positive lining. d Left lung volume, as measured by water displacement, is not significantly different, however e total alveolar surface is significantly decreased in preterm pups, however proportionate to the decreased body size. f Arterial medial thickness is higher in preterm pups at birth. g The number of small to medium size vessels per high power field is comparable in term and preterm pups at birth. *p < 0.05