Renal handling of circulating nitrates in anesthetized dogs..
Godfrey, Murrell, and Dewan S. A. Majid.
Department of Physiology, Tulane University School of Medicine,
1430 Tulane Avenue, New Orleans, LA 70112
APStracts 5:0070F, 1998.
Nitric oxide (NO) is rapidly oxidized to nitrite (NO2-) and then to
nitrate (NO3-) in biological tissues. Although urinary excretion
rates of NO3- are often used as an index of NO production in the
body, very little is known regarding the kidneys ability to excrete
circulating NO3-. We have evaluated the renal responses to systemic
administration of sodium nitrate (NaNO3) in eight anesthetized dogs
treated with the NO synthase inhibitor, nitro-L-arginine (NLA;
50[mu]g.kg-1.min-1) intrarenally to minimize renal production of NO.
Urinary and plasma concentrations of NO3-/NO2- were determined by the
Greiss Reaction after enzymatic reduction of NO3- to NO2-. NLA
treatment alone resulted in reductions in urinary NO3-/NO2- excretion
rates (UNO3-/NO2-V; 1.13 +/- 0.2 to 0.53 +/- 0.1 nmol.min-1.g-1) and
an increase in fractional reabsorption of NO3-/NO2- ( FRNO3-/NO2- ;
93.8 +/- 0.6 to 97 +/- 0.6 %) without changes in arterial plasma
concentrations (ANO3-/NO2-; 18.7 +/- 1.4 to 21.2 +/- 3.7 [mu]M).
Administration of NaNO3 (10, 20, 30, 40 [mu]g.kg -1.min-1) resulted
in dose dependent increases in ANO3-/NO2- (34.5 +/- 8.0, 46.4 +/-
7.3, 60.7 +/- 6.3, and 78.1 +/- 6.3 [mu]M), UNO3-/NO2-V (1.8 +/- 0.7,
4.2 +/- 1.8, 7.0 +/- 2.0, and 11.4 +/- 3.3 nmol. min-1. g-1) and
decreases in FRNO3-/NO2- ( 93.8 +/- 2.3, 90.3 +/- 3.5, 88.6 +/- 3.2
and 84.6 +/- _3.5 %) . Absolute net tubular reabsorption of NO3-
showed a linear relationship with filtered loads with no evidence of
a transport maximum. These data show that in the absence of additions
from intra renal sources, urinary excretion rates of nitrate
increases progressively in response to increases in its circulating
levels without exhibiting a transport maximum but with progressive
decreases in fractional reabsorption..
Received 17 October 1997; accepted in final form 5 March 1998.
APS Manuscript Number F333-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 6 April 1998