Benitez-King, G., F. Anton-Tay, and E. Hong: Characterization of indorenate effects on brain monoamine metabolism. Drug Dev. Res. 23: 325-331, 1991. The effect of indorenate, a central antihypertensive agent, on the catecholamine and indolamine metabolism was studied in the rat brain. Acute administration of 10 mg/kg of indorenate causes an increase in 5-HT concentrations and a decrease on its metabolite 5-hydroxyindolacetic acid (5-HIAA) in the brain stem, cerebral cortex, hypothalamus, and striatum. Maximal effects were observed between 1.5 and 3 hr after indorenate administration. Additionally, a significant decrease in homovanilic acid (HVA) and 3,4-dihydroxyphenylacetic (DOPAC) concentrations was noted after 1.5 hr of a 10 mg/kg indorenate injection. Modification of both catecholamine and indolamine metabolites was dose related. Control values were recovered 24 hr after indorenate administration. Activity of monoamine oxidase present in crude homogenates obtained from the cerebral cortex, brain stem, hypothalamus, and striatum was not affected by indorenate. The present results suggest that indorenate acts as an agonist at serotonin receptors in the central nervous system (CNS).