The pharmacology of chymotrypsin administered by inhalation.

The ability of chymotrypsin to reach the limits of the bronchial tree has been studied in cats receiving the enzyme by inhalation as a very fine powder. For this purpose derivatives of chymotrypsin were used which had been labelled with a fluorescent molecule or with [(131)I]. Quantitative measurements of the absorption and distribution of inhaled chymotrypsin- [(131)I] revealed a rapid removal of radioactivity from the lungs over the first 24 hr. and corresponding excretion of labelled inorganic iodide in the urine. High levels of activity were not attained in the blood or thyroid. Subcutaneous administration of labelled enzyme led to more rapid accumulation of radioactivity in the blood and thyroid. Consideration of these and other results leads to the conclusion that, while some enzyme ascends the respiratory tract by ciliary movement of mucus, a substantial part is absorbed into the lungs and the [(131)I] subsequently detached from it.The changes in tidal air accompanying inhalation of labelled trypsin and chymotrypsin were followed in anaesthetized cats. Trypsin brings about a decrease in tidal air in distinctly lower doses than does chymotrypsin. Prior administration of mepyramine had an antagonistic effect, and it is suggested that the change in tidal air is essentially the result of bronchial spasm.