Mechanical and morphologic effects of long-term corticosteroid administration on the rat lung.

Pressure-volume measurements were performed on excised lungs of rats subjected to prolonged treatment with methylprednisolone. Pressure-volume curves performed with saline were identical in treated and control animals. Measurements performed with air inflation revealed a significant increase of elastic recoil in the lungs of treated animals. On light and electron microscopic exam­ ination, lung tissue of treated animals was similar to that of control animals except for the Type II alveolar cells. These cells were increased in size and number and contained significantly more osmiophilic material, often within giant lamellar bodies. A steroid-mediated impairment of surfactant secretion is postulated.