Monoamine oxidase in developing rat renal cortex: effect of dexamethasone treatment

The expression of the biogenic amine degrading enzyme monoamine oxidases-A and -B depends on several factors including regional distribution, developm ent and hormonal environment. In the present study. we investigated the exp ression of monoamine oxidases in developing kidney and their regulation by dexamethasone treatment. Immunoblots and enzyme assays, performed using [C- 14]S-hydroxytriptamine and C-14]beta -phenylethylamine as substrates for mo noamine oxidases-A and -B, respectively, showed that monoamine oxidase-A is the isoenzyme largely predominant in 9-day-old rats renal cortex. Experime nts performed in 5-week-old rats showed an increase in monoamine oxidase-B activity and a decrease in monoamine oxidase-A activity and substrate affin ity. The changes of monoamine oxidase-A activity and affinity were mimicked by dexamethasone treatment (0.60 mg/kg body weight injected subcutaneously three times at intervals of 24 h) of 9-day-old rats. In contrast, dexameth asone administration induced a modification of monoamine oxidase-B activity opposite to that found between 9-day- and 5-week-old rats. Dexamethasone t reatment did not modify immunoreactivity and mRNA corresponding to monoamin e oxidases-A and -B indicating that changes of enzyme activities were unrel ated to regulation of protein synthesis and mRNA turnover. These results sh ow that monoamine oxidases-A and -B are differently expressed in developing renal cortex and are regulated by dexamethasone treatment. (C) 2001 Publis hed by Elsevier Science B.V.