Clearance of sulfuric acid-introduced 35S from the respiratory tracts of rats, guinea pigs and dogs following inhalation or instillation.

The clearance of sulfuric acid-introduced 35S from the upper and lower respiratory tracts of rats, guinea pigs and dogs was measured. Sulfuric acid was administered by instillation and by inhalation for each species. Clearance into the blood and gastrointestinal tract was measured along with determination of 35S remaining at the site of administration at sacrifice. Different rates of clearance from different sites within the dog lung were indicated with rates of clearance increasing with decreasing airway diameter. Half-times of clearance from all sites in the lung and for all species were from 2-9 min. There appeared to be some species differences, with clearance for dogs being slower than for guinea pigs, which was slower than for rats. Upper respiratory tract clearance was much slower than for lung and may not have been primarily by way of the blood. The data indicate that the clearance of sulfuric acid-introduced 35S in vivo is faster than previous studies in isolated perfused lungs had indicated. The results may be general for water soluble, ionized chemical species.