AJP - Renal Physiology, Vol 259, Issue 6 916-F923, Copyright © 1990 by American Physiological Society
Localization of arginine synthesis along rat nephron
O. Levillain, A. Hus-Citharel, F. Morel and L. Bankir
Institut National de la Sante et de la Recherche Medicale Unite 90, Hopital Necker, Paris, France.
Arginine production was measured in isolated rat nephron segments. Segments
were incubated with 0.3 mM aspartate and 0.1 mM L-[ureido-14C]-citrulline
in a sealed chamber. Arginase and urease were added to the medium to
hydrolyze arginine and to release 14CO2, which was trapped in KOH and
counted. Arginine synthesis was found only in the proximal tubule, with
decreasing intensity from proximal convoluted (PCT) to proximal straight
tubule (PST). Results were as follows (in fmol.min-1.mm tubule length-1):
PCT, 122 +/- 15; cortical PST, 71 +/- 6; outer medullary PST, 41 +/- 4; all
other segments, less than 6. Arginine synthesis changed almost
proportionally with precursor concentration of less than or equal to 0.4
mM. We had shown previously that PST but not PCT was able to hydrolyze
arginine into urea and ornithine. In this study arginine was further
hydrolyzed in cortical (40%) and medullary (64%) PST but not in PCT. These
observations suggest that the arginine formed in PCT contributes to the
maintenance of the whole body arginine pool, whereas most of the arginine
formed in PST might contribute, by its conversion to urea, to the process
of urine concentration.
