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(Hypertension. 1999;34:666-672.)
© 1999 American Heart Association, Inc.
Scientific Contributions |
Aging, High Salt Intake, and Renal Dopaminergic Activity in Fischer 344 Rats
From the Institute for Cardiovascular Studies (T.H., V.K., M.F.L.), College of Pharmacy, University of Houston, Houston, Tex; and the Institute of Pharmacology and Therapeutics (M.A.V., M.P.S.,J.T.G., M.P., P.S.), Faculty of Medicine, University of Porto, Portugal.
Correspondence to M.F. Lokhandwala, Institute for Cardiovascular Studies, College of Pharmacy, University of Houston, TX 77204-5511. E-mail MLokhandwala{at}uh.edu
Abstract—The present study
examined renal dopaminergic activity and its response to high salt (HS)
intake in adult (6-month-old) and old (24-month-old) Fischer 344 rats.
Daily urinary excretion of L-3,4-dihydroxyphenylalanine
(L-DOPA), dopamine, and its metabolites
3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid was
similar in adult and old rats; by contrast, daily urinary excretion of
norepinephrine in old rats was almost twice that in adult
animals. HS intake (1% NaCl) over a period of 24 hours resulted in a
2-fold increase in the urinary excretion of dopamine, DOPAC, and
norepinephrine in adult animals but not in old animals.
Norepinephrine and L-DOPA plasma levels did not change
during HS intake and were similar in both groups of rats. The
natriuretic response to an HS intake in old rats (from
4.7±0.4 to 10.7±2.0 nmol · kg-1 ·
d-1; 
=6.0±0.9 nmol · kg-1 ·
d-1) was less than in adult rats (from 5.2±0.4 to
13.5±2.5 nmol · kg-1 · d-1;
=8.3±0.8 nmol · kg-1 ·
d-1). A diuretic response to HS intake was
observed in adult rats (from 20.9±2.3 to 37.6±2.8 mL ·
kg-1 · d-1) but not in old rats (from
37.7±5.7 to 42.3±6.0 mL · kg-1 ·
d-1). Dopamine levels and dopamine/L-DOPA ratios in the
renal cortex of old rats were greater than in adult rats. HS intake
increased both dopamine levels and dopamine/L-DOPA ratios in the renal
cortex of adult rats but not in old rats. Aromatic L-amino
acid decarboxylase activity was higher in old rats than in adult rats;
HS intake increased L-amino acid decarboxylase activity
(nmol · mg protein-1 · l5
min-1) in adult rats (from 67±1 to 93±1) but not in old
rats (from 86±2 to 87±2). Dopamine inhibited
Na+,K+-ATPase activity in proximal tubules
obtained from adult rats, but it failed to exert such an
inhibitory effect in old rats. It is concluded that renal
dopaminergic tonus in old rats is higher than in adult rats but fails
to respond to HS intake as observed in adult rats. This may be due in
part to the inability of dopamine to inhibit
Na+,K+-ATPase activity in old rats.
Key Words: aging • kidney • dopamine • sodium • Na+,K+-ATPase
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