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Am J Physiol Renal Physiol 270: F862-F868, 1996;
0363-6127/96 $5.00
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AJP - Renal Physiology, Vol 270, Issue 5 862-F868, Copyright © 1996 by American Physiological Society

ARTICLES

Demethylation of 3-O-methyldopa in the kidney: a possible source for dopamine in urine

F. R. Ibarra, J. Aguirre, S. Nowicki, M. Barontini, E. E. Arrizurieta and I. Armando
Instituto de Investigaciones Medicas A. Lanari, Consejo Nacional de Investigaciones Cientificas y Tecnicas, Buenos Aires, Argentina.

The possibility that demethylation of 3-O-methyldopa (OM-dopa) in the kidney could provide a source for dopamine in the urine was explored in male Wistar rats aged 60-90 days, using in vivo and in vitro approaches. The results showed that endogenous OM-dopa is filtered, reabsorbed and extensively metabolized in the kidney. Infusion of OM-dopa into anesthetized rats increased significantly urinary excretion of Na+, dopa, dopamine, and 3,4 dihydroxyphenylacetic acid. Whole kidney homogenates, slices from renal cortex, and microdissected proximal tubules produced significant amounts of both dopa and dopamine when incubated with OM-dopa. Renal cortex slices produced dose-dependent amounts of dopa and dopa-mine when incubated with 1-100 microM OM-dopa. Incubation of microdissected proximal tubule segments with 1 microM OM-dopa produced a fourfold (P < 0.025) increment in dopa and a twofold (P < 0.05) increment in dopamine (an effect similar to that observed with 1 microM L-dopa). One micromolar OM-dopa or 1 microM L-dopa decreased (P < 0.05) Na(+)-K(+)-adenosinetriphosphatase activity measured at maximal velocity condition in proximal tubules. In conclusion, these experiments show that in vitro the kidney is able to produce dopamine by demethylation of OM-dopa, while the results of the OM-dopa infusion suggest that this conversion may also occur in vivo.


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[Abstract] [Full Text] [PDF]


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