Dexamethasone selectively increases monoamine oxidase type a in human skin fibroblasts

The effects of several hormones known to affect monoamine oxidase activity $\text{in}\text{vivo}$ have been studied in living human skin fibroblasts grown in culture. Of the hormones tested, the synthetic glucocorticoid dexamethasone caused the greatest increases in activity at physiologic concentrations. Increases of 10–12 fold were observed after 8–9 days of exposure to 5 × 10^?8 M dexamethasone. This increase in activity was accompanied by a change in the relative proportion of the A and B types of activity in fibroblasts, from about 35% A:65% B in control cultures to 90% A:10% B in cultures exposed to dexamethasone. The increase in activity and the shift in the proportion of A and B activities could be accounted for almost exclusively by a specific increase in the number of Type A molecules.