Carboxylesterases in the respiratory tracts of rabbits, rats and Syrian hamsters.

Esters are a widespread class of organic compounds found both in industry and the environment. Because esters are often volatile and, therefore, readily inhaled, the capacity of respiratory tract tissues as well as liver S-9 homogenates from rats, rabbits, and Syrian hamsters to hydrolyze a variety of esters was investigated. A new technique to determine hydrolysis rates by measuring carboxylic acid residues using ion chromatography was proven effective. The results indicated that esters, including potentially carcinogenic beta-lactones, are readily hydrolyzed by respiratory tract enzymes. Species and tissue differences were apparent. The nasal ethmoturbinates had especially high levels of esterase activity with tissue weight-normalized activities from rabbits and hamsters for most substrates exceeding all other tissues tested, including liver. Phenyl acetate was the most rapidly hydrolyzed by ethmoturbinate tissue of the esters tested. Among straight chain aliphatic alcohol acetates, hydrolysis rates increased with carbon number up to pentyl alcohol and then decreased. Branched 4-carbon alcohol acetates were less rapidly hydrolyzed than n-butyl acetate. Correlation of hydrophobicity constants with hydrolysis rates indicated that, for the straight chain aliphatic acetates, a bilinear model best fit the data.