Diet restriction modulates lung response and survivability of rats exposed to ozone

Ozone (O(3)) is a powerful oxidant component of photochemical smog polluting the air of urban cities. Exposure to low-level O(3) causes lung injury and increased morbidity of the sensitive segment of population, and exposure to high levels can be lethal to experimental animals. Injury from O(3) exposure is generally associated with free radical formation and oxidative stress. Because diet restriction is proposed to enhance antioxidant status, we examined whether it would influence the response to inhaled O(3). Twenty-four Sprague-Dawley rats, 1 month old, weighing 150 g, were divided into two dietary regimens (12 rats/regimen); one was freely-fed (FF), and the second was diet-restricted (DR) to 20% the average daily intake of the FF. After 60 days of dietary conditioning, the body weight of DR rats was reduced to 50% that of FF rats. Then, in one experiment, two groups (six rats/group), one FF and the other DR, were exposed to 0.8+/-0.1 p.p.m. (1570+/-196 microg/m(3)) O(3), continuously for 3 days. Another two similar groups of rats were exposed to filtered room air and served as matched controls. After exposure, all rats were euthanized and the lungs analyzed for biochemical markers of oxidative stress. In a second experiment, 24 rats were divided into two groups (12 rats/group), one FF and the other DR, then exposed to high-level O(3) for 8 h (4 p.p.m., 7848+/-981 microg/m(3)) and the mortality noted during exposure and for 16 h post-exposure. Following low-level O(3), inhalation, greater alterations were observed in FF rats compared with DR rats. With high-level O(3) exposure, DR rats exhibited a much greater survivability compared with FF rats (90% versus 8%, respectively). These observations suggest that diet restriction leading to significant reduction of body weight is beneficial, and may play a role in the resistance to the adverse effects of O(3).