Immunohistochemistry for Ki-67 in the lung tissues treated with ZnONP at 150 cm2
/rat. Each figure is composed of a low power view (left, 25×), high power view of bronchiolar epithelium (middle, 400×), and alveoli (right, 400×). (A) vehicle control at 24 h; (B) ZnONP at 24 h; (C) ZnONP at 1 wk; (D) ZnONP at 4 wks. Note that ZnONP increased the proliferating Ki-67 positive cells (arrow) in the bronchiolar epithelium and alveolar epithelium.