Morphometry and histology in experimental PH models and controls. Pulmonary arteries are size-dependently differentiated into the following categories: 51-100 μm, 101-150 μm, 151-250 μm, and 251-450 μm. A: medial thickness (expressed in % of the cross-sectional external diameter of arteries). B: adventitial thickness (expressed in per cent of the cross-sectional external diameter of arteries). C: lumen area (in μm2). D: arteriolar muscularization (in % of total arteriolar number). E: virtual arteriolar occlusion (loss of visually perceptible lumen, in % of total arteriolar number). F: normal pulmonary artery (PA) (control) with adjacent bronchiole (HE staining). G: muscularized, virtually occluded arteriole in a MCT/PE-animal (HE-staining). H: excessive medial thickening in a large PA of an animal from the MCT/PE-group (HE-staining). I: intimal thickening of a pulmonary arteriole in a MCT/PE animal (HE-staining). * P < 0.05 versus control; † P < 0.05 versus MCT (Figures 2A-E).