NITRIC-OXIDE IN RENAL-CORTEX AND MEDULLA - AN IN-VIVO MICRODIALYSIS STUDY

Authors
Citation
Ap. Zou et Aw. Cowley, NITRIC-OXIDE IN RENAL-CORTEX AND MEDULLA - AN IN-VIVO MICRODIALYSIS STUDY, Hypertension, 29(1), 1997, pp. 194-198
Citations number
29
Categorie Soggetti
Peripheal Vascular Diseas
Journal title
ISSN journal
0194911X
Volume
29
Issue
1
Year of publication
1997
Part
2
Pages
194 - 198
Database
ISI
SICI code
0194-911X(1997)29:1<194:NIRAM->2.0.ZU;2-E
Abstract
This study examined the production of nitric oxide (NO) in the renal c ortex and medulla through the use of an in vivo microdialysis techniqu e. Oxyhemoglobin (OxyHb) at a concentration of 3 mu mol/L was perfused through the dialysis system to trap tissue NO. Methemoglobin (MetHb), which was formed by NO oxidation of OxyHb in the dialysate, was spect rophotometrically assayed at 401 nm. Because the oxidation of OxyHb to produce MetHb is stoichiometric with NO, the production of NO can be determined by the rate of MetHb formation. We found that NO concentrat ion was significantly higher (P < .05) in the medulla (57.1 +/- 5.57 n mol/L, n = 10) than in the cortex (31.2 +/- 5.7 nmol/L, n = 9). The mi nimal detectable NO level of this assay is approximate to 10 nmol/L. I ntravenous infusion of L-arginine (3 mg/kg per minute) for 30 minutes produced a twofold to threefold increase in cortical and medullary NO; N-G-nitro-L-arginine methyl ester (L-NAME) (10 mu g/kg per minute) de creased NO by 33% in the renal cortex and by 46.5% in the renal medull a. We have also compared under the same conditions the degradation pro ducts of NO, nitrite, and nitrate in the renal cortex and medulla usin g in vivo microdialysis combined with microtiter plate colorimetry. Ni trite/nitrate concentration was significantly higher (P < .05) in the medulla (2.7 +/- 0.6 mu mol/L, n = 4) than in the cortex (2.1 +/- 0.2 mu mol/L, n = 4). Infusion of L-arginine increased cortical and medull ary nitrite/nitrate by 65% and 39%, respectively. L-NAME reduced corti cal and medullary nitrite/nitrate by 18% and 23%, respectively. The re sults indicate that the OxyHb-NO microdialysis trapping technique is a highly sensitive in situ method for detecting regional tissue NO conc entration and changes in the NO synthase activity in the kidney. These studies have shown that NO concentration is higher in medullary tissu e than in the cortex.