Hyperthyroidism increases the risk of ozone-induced lung toxicity in rats

The risk of lung injury from ozone exposure has been well documented. It is also known that various factors may significantly influence the susceptibi lity of animals to the toxic effects of ozone. In the present study, we inv estigated the possibility that hyperthyroidism might be associated with inc reases in ozone-induced pulmonary toxicity. To create a hyperthyroid condit ion, mature male Sprague-Dawley rats were given injections of thyroxine (do se range: 0.1 to 1 mg/kg body wt daily for 7 days). Control rats received v ehicle injections. The animals were then exposed to air or ozone (dose rang e: 0.5 to 3 ppm for 3 h). At 18 h postexposure, bronchoalveolar lavage flui d and cells were harvested. In hyperthyroid animals, ozone exposure was ass ociated with three- to sixfold increases in bronchoalveolar lavage fluid la ctate dehydrogenase activities and albumin levels as well as the number of poIymorphonuclear leukocytes harvested by bronchoalveolar lavage above leve ls observed in ozone-exposed control rats. Additional results from the pres ent study suggest that these thyroid hormone-linked effects cannot be fully explained by differences in whole-body metabolic rate or changes in the in haled dose of ozone. These findings indicate that the risk of ozone-induced lung toxicity is substantially increased in a hyperthyroid state and sugge st that the susceptibility of the lung to damage from ozone exposure may be significantly influenced by individual thyroid hormone status.