Enzyme histochemical observations of diffuse pulmonary fibrosis of rats experimentally induced by ionizing...

The right lungs of Sprague-Dauley rats were irradiated with single doses of 1000 r, 2000 r or 3000 r to induce radiation pneumonitis and diffuse fibrosis, and the alkaline and acid phosphatase (A1-Pase, Ac-Pase) activities of the lungs were observed histochemically. Only the lungs irradiated with 3000 r steadily exhibited sequential changes leading to radiation pneumonitis and subsequent diffuse fibrosis, whereas the lungs irradiated with 2000 r developed only some degree of radiation pneumonitis. Alveolar capillary endothelia in the lesion of pulmonary fibrosis exhibited an intense activity of A1-Pase, while the endothelia in all the other experimental conditions did not show this activity. Alveolar macrophages increased their sizes and the activity of Ac-Pase after the irradiation. In the later stages, large foamy macrophages with thin diffuse deposits of the reaction products became predominant. These macrophages never exhibited A1-Pase activity. Type II alveolar epithelial cells showed an intense A1-Pase activity on their microvilli, and their Ac-Pase activity was negligible in non-irradiated lungs. Bizarre cells, appearing at the stage of radiation pneumonitis, showed an intense A1-Pase activity on their cell membranes and a weak and diffuse Ac-Pase activity in their cytoplasms. Septal cells achieved the A1-Pase activity 3 or 4 weeks after the irradiation when mast cells were not yet seen in the alveolar septa.