Ozone inhibition of tissue cholinesterase in guinea pigs

This study sought to determine if ozone at levels known to induce bronchial hyperreactivity in guinea pigs would inhibit tissue cholinesterase activity. Male, Hartley guinea pigs were exposed to filtered air, 0.1 ppm ozone, or 0.8 ppm ozone for 1 hr. Two hours after exposure, brain, lung, and diaphragm tissue samples were frozen for assay of cholinesterase activity. Brain cholinesterase activity was only minimally inhibited in either ozone exposure group. Both levels of ozone significantly inhibited lung cholinesterase activity compared to control animals' activity: a 17% decrease in activity in the 0.1 ppm ozone group (P less than .05) and a 16% decrease in the 0.8 ppm ozone group (P less than .05). Ozone at 0.8 ppm also inhibited activity in the diaphragm by 14% (P less than .02). To determine the degree of involvement of cholinesterase inhibition in bronchial hyperreactivity, parathion pretreated animals were challenged with histamine and the pulmonary function changes monitored. Parathion-treated animals had a peak resistance increase of 330 +/- 104% (mean +/- SE), while the control vehicle animals' increase was 165 +/- 48%. The differences were not statistically significant, but show that cholinesterase inhibition may contribute to ozone-induced bronchial hyperreactivity.