Demethylation of 3-0-methyldopa in the kidney: a possible source
for dopamine in the urine.
Ibarra, Fernando R., Jorge Aguirre, Susana Nowicki, Marta Barontini,
Elvira E. Arrizurieta, Ines Armando.
Centro de Investigaciones Endocrinologicas, Instituto de
Investigaciones Medicas A. Lanari, Consejo Nacional de
Investigaciones Cientificas y Tecnicas.
APStracts 3:0002F, 1996.
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 dihyroxyphenylacetic 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 dopamine when incubated with 1-100
[mu]M OM-dopa. Incubation of microdissected proximal tubule segments
with 1 [mu]M OM-dopa produced a 4 fold (p<0.025) increment in
dopa and a two fold (p<0.05) increment in dopamine (an effect
similar to that observed with 1 [mu]M L-dopa). 1 [mu]M OM-dopa or 1
[mu]M L-dopa decreased (p<0.05) Na+,K+-ATPase activity measured
at Vmax 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.
Received 24 July 1995; accepted in final form 12 December 1995.
APS Manuscript Number F245-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96