Studies of response to low doses of edematogenic gases have been hampered by the insensitivity and the nonquantitative nature of the major indicators of response. A new and more sensitive indicator, the recovery of 131I-albumin from the alveolar spaces six hours after its intravenous injection in rats, has been applied. Significantly increased albumin recovery was found for all concentrations of ozone at and above 0.5 ppm. No wet weight changes were noted below 2.5 ppm ozone, and there was no consistent histologic finding except for slight sloughing of bronchial epithelium at 2.5 ppm. Application of these methods to studies of steroid effects revealed increased sensitivity to ozone following administration of methylprednisolone sodium succinate. In addition, animals treated with steroids prior to exposure to 0.25 ppm ozone became tolerant to subsequent ozone challenge, whereas animals given preexposure but no steroids did not.Short-term studies of edematogenic oxidizing air pollutants have previously involved concentra¬ tions greater than those found in the environment. At present, ways to as¬ sess edema produced by air pollu¬ tants, including histologie study, in¬ crease in percent wet weight, and mortality, are largely ineffective at ambient levels of pollutants, espe¬ cially with short exposure periods.Histology has traditionally been the most sensitive indicator of pollutant toxicity; however, rats exposed to ambient concentrations for short pe¬ riods show no consistent pathologic changes. Moreover, histology does not easily lend itself to quantitation and statistical analysis short of the very cumbersome methods of pulmo¬ nary morphometry. Increase in per¬ cent wet weight, while easily quantitated, is considerably less sensitive than histology, and pollutant concen¬ trations necessary to cause death over a short period of exposure are orders of magnitude higher than those in the environment.1 With no sound methods to measure ambient pollutant damage, subtle changes caused by modifications in the ex¬ posure conditions or in the experi¬ mental animal are not detectable.
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