Hydrolysis of cyclomethasone by the human lung

The hydrolysis rate of 9-chloro-11 beta, 17a-dihydroxy-16 beta-methyl-21-(1'4'N-acetyltransaminomethyl- cyclohexancarbonyloxy) pregna-1,4-diene-3,20-dione (cyclomethasone) and of beclomethasone 17,21-dipropionate was studied on human lung slices. Cyclomethasone is hydrolysed more slowly than beclomethasone 17,21-dipropionate. This difference may be ascribed to a different affinity and/or activity of the tissue esterases towards the two substrates or to a different transport rate in the sites of the esterase activity. Since the steroid moiety is the same for both molecules studied it appears that the hydrolysis and/or the transport rate of the esterified steroids depends on the chemical properties of the substituent at C-21.