O,O,S-Trimethyl phosphorothioate (
OOS-TMP), an impurity present in widely used organophosphorus
insecticides, has been shown to induce pneumotoxicity after
oral administration. To date very little is known about the pathogenesis of the injury.
Protease-anti-
protease imbalance has been proposed as a mechanism of various
lung injuries; thus, the effect of
OOS-TMP on
alpha 1-protease inhibitor capacity, pulmonary alveolar macrophage (PAM)
esterases, cytotoxic activity and on specific
esterase inhibitors in the bronchopulmonary lavage fluid and serum were measured.
OOS-TMP (20 mg/kg) administered orally to rats produced a 27% increase in PAM
esterase activity 6 h
after treatment. The activity then declined to 63% of control value on day 3 and had not recovered to any significant extent on day 7. The cytotoxic activity of PAM was significantly increased at 6 h and 24 h following treatment.
Chymotrypsin inhibitory capacity (CIC) of the lavage fluid was decreased by 45% at 6 h but recovered rapidly and reached control levels by 24 h.
Trypsin inhibitory capacity (
TIC) of serum was affected to a lesser extent such that no change was detected after 6, 12 or 24 h. These data, early elevation of PAM
esterase levels with a concomitant increase in cytotoxic activity and decreased
TIC and CIC in bronchopulmonary lavage fluid, support the view that pathogenesis of
OOS-TMP produced
lung injury could be due to increased
protease levels.