Ozone-induced hypothermia and bradycardia in rats and guinea pigs in nose-only or whole-body inhalation systems

1. Ozone (O 3 ) inhalation induces a hypothermic response in rodents characterized primarily by core body temperature ( T CO ) and heart rate (HR) decreases. 2. This preliminary study examined T CO , HR, and electrocardiographic changes in rats and guinea pigs during whole-body or nose-only exposure to 1 ppm 18 O 3 . 3. Rats exposed whole-body demonstrated an immediate hypothermic response, while that of the nose-only exposed rats was delayed ≈60 min; guinea pigs showed no hypothermic response to 18 O 3 . 4. 18 O content in lavage fluid samples suggests that dose is greater in nose-only exposures than whole-body exposures, and that guinea pigs received higher doses than rats. 5. These initial findings suggest that dosimetric differences may result from differences in species responses and exposure scenarios.