Early Response of the Canine Respiratory Tract Following Long-Term Exposure to a Sulfur(IV) Aerosol at Low Concentration. V. Morphology and Morphometry

Abstract

The respiratory system of eight male beagle dogs was examined morphologically and morphometrically after continuous exposure for 290 days to a respirable sulfur(IV) aerosol at a concentration equivalent to a sulfur dioxide (SO₂)concentration of 0.6 mg m⁻³. Three dogs served as unexposed controls.

Seven of eight exposed dogs showed hyperplastic changes in the respiratory mucosa of the posterior nasal cavity. The changes were characterized by a thickened epithelial layer resulting from epithelial proliferation, by a loss of secretory material, and by moderate mononuclear cell infiltration. Four of eight exposed dogs had an increased number of nonciliated cells and slight mononuclear cell infiltration in the larynx. Tracheal changes were limited to an increased number of nonciliated cells in the membranous portion. Transmission electron microscopy TEM) showed the changes in the trachea to be caused by disorder in the development of ciliated cells.

Morphometric examination of the pulmonary alveolar region revealed a slight decrease in the volume density of the septum in the exposure group (p<. 73). This decrease resulted in a reduction in the septal surface area, indicating enlargement of the alveolar air space. One of eight exposed dogs showed clear morphologic evidence of focal dilation of the alveoli and alveolar sacs. There was a significant decrease in the calculated diffusing capacity in the exposure group.

These findings indicate that long-term exposure to airborne S(IV) has adverse effects on the respiratory system of beagle dogs.