Stimulation of pulmonary neoangiogenesis by estrogen (E2). (A) Single confocal images of lung sections of male rats immunostained for von Willebrand Factor (green, upper panels), overlay of von Willebrand factor and nuclei (stained red with TO PRO, middle panels), and at higher magnification of the respective fields (lower panels). (B) Quantification of vessels per high power field (HPF) in control (CTRL; black bar), pulmonary hypertension (PH; red bar), and E2 (blue bar). **P < 0.001 versus CTRL; ††P < 0.001 versus PH (n = 4 animals per group).