Abstract
Drug metabolism in rat and mouse skin was investigated using subcellular fractions and skin strips. The ability to homogenize skin and any resulting unwanted damage to organelles was investigated. Relatively mild homogenization conditions were eventually employed. A scheme of subcellular fractionation was carried out and microsomes harvested and some indication of the extent of contamination by other fractions obtained. The chronology of the hair cycle in rat and mouse was ascertained. Drug metabolizing activities at different phases of the hair cycle were investigated, but no major changes were observed. The induction and inhibition of cutaneous cytochrome P-450 activities were investigated. The mouse had higher constitutive levels but the rat was the more responsive to inducers. Activities in both species were inhibited by benzoflavone isomers and metyrapone. The mouse was more sensitive to inhibition by various solvents than the rat. Spectral and electrophoretic studies were also carried out. UDP-Glucuronyltransferase activity to 1-naphthol was shown to be present in rat and hairless mouse skin microsomes and was activated by detergents. The possibility of interference with the assay by other enzymes was checked. Apparent Km values were lower than those quoted for liver. Esterase activity to indoxyl acetate was found in both microsomal and high speed supernatant fractions. Apparent Km values were much higher than those quoted for liver. The distribution of enzyme activities between the epidermis and dermis was investigated. There was some evidence for a differential distribution of oxidation and conjugation reactions in mouse skin. Deethylation, sulphation and glucuronidation activities in rat and hairless mouse skin strips were investigated. Induction of deethylation was shown and this resulted in changed patterns of metabolism in respect to the percentages of free and conjugated metabolites. Patterns of activity and inducibility were similar to those observed in microsomes, except that the levels of induction were higher in the strips.