RESPIRATORY EPITHELIUM EXPOSED TO SULFUR-DIOXIDE - FUNCTIONAL AND ULTRASTRUCTURAL ALTERATIONS

The value of morphological investigations of airway mucosa should be c ompared to a functional method when estimating the toxicity of airborn e pollutants, In 34 guinea pig tracheas, mucociliary activity was meas ured using a modified light beam reflex method before and following ex posure to sulfur dioxide for 30 minutes in concentrations ranging betw een 7.5 and 37.5 mg/m(3). Exposure to air served as a control, Simulta neously, specimens were taken for light and electron microscopy. Mucoc iliary activity decreased from 8.4 +/- 2.9 Hz (control exposure) to 4. 0 +/- 2.9 Hz following exposure to 7.5 mg/m(3), to 3.4 +/- 2.7 Hz at 1 5 mg/m(3) sulfur dioxide, to 1.8 +/- 2.2 Hz at 22.5 mg/m(3) sulfur dio xide, to 1.5 +/- 1.8 Hz at 30 mg/m(3) sulfur dioxide, and to 2.0 +/- 1 .2 Hz at 37.5 mg/m(3) sulfur dioxide, respectively (P<.01). Despite a 56% decrease in mucociliary activity, only minor morphological alterat ions were observed following exposure to 7.5 mg/m(3) sulfur dioxide. H owever, following exposure to 15 mg/m(3) sulfur dioxide or higher, str uctural alterations of respiratory mucosa such as epithelial sloughing , intracellular edema and mitochondrial swelling, widened intercellula r space, and ciliary cytoplasmic extrusions were found. Thus measureme nt of mucociliary activity proved to be a more sensitive indicator of airway toxicity than structural investigations alone.