Regional distribution of xenobiotic metabolizing enzymes in respiratory airways of dogs.
There is a varied distribution of airway epithelia throughout the respiratory tract that may explain the apparent differential susceptibility of respiratory tract tissues to carcinogens. The objective of this research was to characterize the distribution of xenobiotic metabolizing enzymes in the respiratory tract of the dog and to determine if regional variances in metabolic capability are associated with morphologic differences of surface epithelium among airways. Specific regions from one-half of the nasal, tracheal, bronchial, and pulmonary airways were excised and analyzed for the presence of xenobiotic metabolizing enzymes. Complementary halves of airways were fixed and processed for light microscopy. Substrates for different isozymes of cytochrome P-450, including benzo(a)pyrene, nitropyrene, ethoxycoumarin, and ethoxyresorufin and select Phase II enzymes were measured. The data for benzo(a)pyrene and nitropyrene were qualitatively similar in that there was high metabolic activity in certain regions of the nasal tissue (e.g. ethmoid turbinates) and in the intrapulmonary airway generations 3-18 compared with the major conducting airways (e.g. larynx, trachea, and bronchi). Most ethoxycoumarin O-deethylase activity was in the nasal region with much less activity observed in the major airways or the pulmonary airways. The specific activity of ethoxycoumarin O-deethylase in the ethmoid turbinates was, in general, 5-10 times that observed for the other portions of the nasal cavity sampled. Only the ethmoid turbinates showed evidence of ethoxyresorufin metabolism. Both epoxide hydrolase and glutathione transferase activity was higher in the various tissues of the nasal cavity and in the pulmonary airways compared with the major conducting airways. UDP-glucuronyltransferase was relatively evenly distributed throughout the respiratory tract.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004285:Dogs; D008297:Male; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D012137:Respiratory System / Q000187:drug effects / Q000201:enzymology*
D001564:Benzo(a)pyrene; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases