Effect of ozone on respiratory response of guinea pigs to histamine

Abstract

The effect of preexposure to ozone on the respiratory response to histamine was studied. The Amdur‐Mead technique was used to measure respiratory mechanics in Charles River Hartley guinea pigs. Groups of animals were exposed for 1 h to filtered control air or ozone. Control measurements were made 1½> h after exposure, followed by sc injection of 0.125 mg/kg histamine dihydrochloride. Respiratory measurements were continued at 2‐min intervals for 16 min, at which time resistance and compliance had returned to control values. The 2‐h interval between exposure and injection and the 0.125 mg/kg histamine were the optimum time interval and dose, respectively, as determined by appropriate time‐response and dose‐response studies. Although control values did not differ between air‐exposed and ozone‐exposed animals, animals preexposed to 0.1, 0.2, 0.4, and 0.8 ppm ozone had increases in resistance of 111, 110, 93, and 97% after histamine administration, compared to the air‐exposed animals, which had increases of 86, 86, 67, and 46%, respectively. Whereas the only significant difference in resistance between air and ozone animals was at the 0.8‐ppm level (p < 0.05), significant differences in compliance changes were found at all levels of ozone exposure. Ozone animals had compliance decreases of 40, 45, 46, and 46% after histamine injection, while their respective air controls decreased 24, 24, 27, and 31%. Exposures to ozone of 0.2 ppm for 4 h and 0.4 ppm for 2 h provided doses equal to that of 0.8 ppm for 1 h, yet no significant dose‐time relationship was found. Lingering sensitivity to pharmacologically active agents is a subtle but important manifestation of ozone toxicity.