ROLE OF MONOAMINE-OXIDASE AND CATHECOL-O-METHYLTRANSFERASE IN THE METABOLISM OF RENAL DOPAMINE

Incubation of slices of rat renal cortex with 50 mu M L-DOPA during 15 min resulted in the formation of dopamine and of its deaminated (3,4- dihydroxyphenylacetic acid; DOPAC), methylated (3-methoxytyramine; 3-M T) and deaminated plus methylated (homovanillic acid; HVA) metabolites . The presence of pargyline (100 mu M) resulted in a 90% reduction in the formation of DOPAC and HVA; levels of dopamine and 3-MT were found to be significantly increased. A concentration dependent decrease in the formation of methylated metabolites was obtained in the presence o f (10, 50 and 100 mu M) tropolone (10-50% reduction) and (0.1, 0.5, 1. 0 and 5.0 mu M). Ro 40-7592 (50-95% reduction). Ro 40-7592 was also fo und to significantly increase DOPAC (20-40%) and dopamine (10-30%) lev els, whereas tropolone slightly increased DOPAC (10%) levels. These re sults show that deamination represents the major pathway in the metabo lism of newly formed dopamine under in vitro experimental conditions i n the rat kidney. In addition, only when MAO is inhibited does methyla tion appear to represent an alternative metabolic pathway.