Although crude, these parameters suggest a different metabolic response to the inhaled com dust extract than to the soybean dust extract. The physiologic effects of soybean dust extract were less pronounced than those of the com dust extract, and by several parameters, it was less biologically active than the endotoxin solution. As these subjects were nonsmokers, had never been exposed to soybean dust, and had no history of atopy, this supports the hypothesis that senitization must occur to exhibit the acute, severe airflow obstruction that has been seen in Barcelona and other European cities.
These observations regarding the differences between the various endotoxin containing substances in our study must be viewed with caution. Our randomization procedure resulted in all subjects receiving corn dust extract as one of the first two substances inhaled, and all but one of the subjects were exposed to the endotoxin solution as one of the last two substances. Thus, the most severe effects observed following inhalation of com dust extract may have resulted from the sequence in which these solutions were inhaled. However, the order of administration does not appear to account for the differences we observed between the mild effects of soybean dust extract and the more severe effects of the endotoxin.
In this study, subjects inhaled doses of endotoxin comparable to those to which workers might be exposed during one workshift. Airborne endotoxin levels in the desirable fraction of dusts to which farmers are exposed have been measured at 2 fig/m to over 50 |xg/m. Assuming a worker inhales 15 m per 8 h workshift, he would inhale 30 to 750 |ig endotoxin during a full day of work. In this study, subjects inhaled 30 to 60 jig endotoxin in HBSS, soybean dust extract, and corn dust extract.
The effects of inhalation of high concentrations of agricultural dusts have been well documented. They consist of flu-like symptoms with fever, leukocytosis, and airflow obstruction, and has been referred to as the organic dust toxic syndrome. It has been hypothesized that the responsible agent in these bioaerosols is endotoxin. Our results indicate that extracts of grain dust have physiologic effects similar to those of endotoxin; however, the systemic and biologic activity may be somewhat different from pure endotoxin and may be specific to the type of grain product. Further studies are needed to identify the specific components of grain dust that are responsible for these differences. In addition, the early biologic response to grain dust needs to be investigated further.