Hyperplasia of Type 2 Pneumocytes and Nitrogen Dioxide (10 ppm) Exposure

An ultrastructural quantitative study of the lungs of 12 guinea pigs exposed continuously to 10 ppm nitrogen dioxide for six weeks, and eight control lungs, revealed greatly increased ratios of type 2 pneumocytes to other cells for the exposed group. The findings, derived from 304 electron photomicrographs at a magnification of 1,700× and a total of 9,307 cells counted, implicate an adverse effect by 10 ppm NO2 on cellular ecology and function, in particular a thickening of the blood-gas barrier through replacement of ultrathin type 1 cells by cuboidal or columnar type 2 pneumocytes. Of 676 type 2 pneumocytes of the exposed group studied for the frequency of “fine and closely packed lamellae,” 66 (9.8%) contained 170 such bodies (2.6/cell) versus 10 of 247 (4%) control type 2 cells containing 17 bodies (1.7/cell). The lungs of the exposed animals also exhibited more frequent intra-cellular and extracellular lipid bodies.