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Departments of Medicine and Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905
The diuretic effects of nitric oxide (NO)
synthase inhibitors administered at subpressor dose in rats are
controversial, and the tubular segments involved are not known. In the
present study, we examined the effect of
N
-nitro-L-arginine methyl ester
(L-NAME) at a subpressor dose on renal interstitial NO and
cGMP activity and on renal tubular segmental reabsorption of fluid in
the rat. Intravenous infusion of L-NAME at 1 µg · kg
1 · min
1 in
Sprague-Dawley rats (N = 8), which did not alter mean
arterial pressure or glomerular filtration rate, significantly
increased urine flow rate (Uv; from 78.2 ± 12.7 to
117.1 ± 14.9 µl/min, P < 0.05). Paradoxically,
this effect of L-NAME was concomitant with significant
increases in nitrite/nitrate (from 10.79 ± 1.20 to 16.50 ± 2.60 µM, P < 0.05) and cGMP (from 0.65 ± 0.09 to 0.98 ± 0.18 nM, P < 0.05) concentrations in
renal cortical microdialysate as well as the nitrite/nitrate
concentration in the medullary microdialysate. Micropuncture studies in
the superficial nephron revealed that L-NAME significantly
increased the flow rate (from 8.3 ± 0.9 to 12.2 ± 1.2 nl/min, P < 0.05) and fractional delivery of fluid to
the distal tubule, but not those in the late proximal tubule. In
conclusion, L-NAME, at the subpressor dose used in this
study, increased renal nitrate/nitrite and cGMP and inhibited fluid
reabsorption in tubular segments between the late proximal tubule and
the distal tubule of superficial nephrons.
rat; nitric oxide; microdialysis; distal tubule; N
-nitro-L-arginine methyl ester
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