Tissue Sensitivity of Rat Nasal Turbinate Epithelium to CdSO,: Correlation of Tissue Cadmium Levels and Energy Charge

Abstract

The toxicity of cadmium sulfate (CdSO₄) aerosol was investigated using rat nasal turbinate epithelium to provide in vivo tissue sensitivity data for comparison with data obtained previously for rat and human nasal turbinate epithelial cells exposed to CdSO₄ in vitro (Morgan et al., 1990). Fischer 344 rats were exposed to CdSO₄ aerosol (0, 5, or 10 mglm³) by nose-only inhalation for 2 h, or by intranasal instillation of a CdSO₄ solution (0.7 mglml) for 1 h. Tissue sensitivity was determined by measuring Cd levels and adenine nucleotide levels in the same tissues. The end point for CdSO₄ toxicity, tissue energy charge (EC), was calculated from adenine nucleotide levels. Nose-only inhalation exposure of male F344 rats to 5 or 10 mg CdSO₄/m³ produced only slight, nonsignificant decreases in the EC of nasal epithelium. Tissue doses of 2.56 and 3.12 ng Cd/mg wet weight were obtained by exposure to 5 or 70 mg/m³, respectively, for 2 h. The tissue dose was increased to 5.37 ng Cd/mg wet weight by intranasal instillation of a 0.1 mg/ml CdSO₄ solution for 1 h; howevec the EC of nasal tissue did not change significantly. After exposure to 70 mg CdSO₄/m³ for 2 h, approximately 75% of the Cd deposited in the nasal cavity was found in the mucous layer, 24% was extracted from the tissues, and about 7% remained bound to the tissues. Histopathological evaluation of nasal tissues from exposed rats revealed marked lesions of the olfactory epithelium that increased in severity with time after exposure. CdSO₄ had little effect on respiratory epithelium, even though Cd levels were higher and appeared to be cleared more slowly in respiratory than olfactory tissues. Although CdSO₄ was previously found to decrease the EC of rat nasal epithelial cells exposed in vitro, the EC of rat nasal epithelium was not significantly affected by in vivo CdSO₄ exposure. It is likely that the mucous layer prevented toxic levels of CdSO₄ from reaching the tissues.