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Neuronal nitric oxide synthase-deficient mice have impaired renin release but normal blood pressure
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology, Integrativ Fysiologi.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology, Integrativ Fysiologi.
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2008 (English)In: American Journal of Hypertension, ISSN 0895-7061, Vol. 21, no 1, 111-116 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Nitric oxide deficiency is involved in the development of hypertension, but the mechanisms are currently unclear. This study was conducted to further elucidate the role of neuronal nitric oxide synthase (nNOS) in blood pressure regulation and renin release in relation to different sodium loads. METHODS: Blood pressure and heart rate were measured telemetrically and assessed during periods of physical activity and inactivity. Urinary solute excretion was measured by metabolism cages and plasma renin concentration (PRC) was determined by radioimmunoassay; all in nNOS knockout (nNOS(-/-)) and wild-type (nNOS(+/+)) mice after 10 days of low (0.01% NaCl) and high (4% NaCl) sodium diets. RESULTS: The resting heart rate was reduced in nNOS(-/-) mice, but the two genotypes had similar blood pressure during the low (nNOS(+/+) 104 +/- 2 mm Hg; nNOS(-/-) 103 +/- 2 mm Hg) and high (nNOS(+/+) 107 +/- 3 mm Hg; nNOS(-/-) 108 +/- 2 mm Hg) sodium diets. During the high sodium diet, PRC did not differ between the genotypes (nNOS(+/+) 743 +/- 115 10(-5) Goldblatt units; nNOS(-/-) 822 +/- 63 10(-5) Goldblatt units), but during the low sodium diet, nNOS(-/-) mice failed to increase PRC (nNOS(+/+) 2164 +/- 220 10(-5) Goldblatt units; nNOS(-/-) 907 +/- 101 10(-5) Goldblatt units) and renal renin mRNA. On the low sodium diet, nNOS(-/-) mice also showed increased urine flow rate and osmolar excretion, observations not made during a high sodium diet. CONCLUSIONS: Our results show that nNOS is necessary for stimulation of renin in response to sodium restriction. Furthermore, nNOS(-/-) mice are normotensive, and their blood pressure responds normally to an increased dietary sodium intake, indicating that nNOS deficiency does not cause salt-sensitive hypertension.

Place, publisher, year, edition, pages
2008. Vol. 21, no 1, 111-116 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-104335DOI: 10.1038/ajh.2007.16ISI: 000251938200027PubMedID: 18091753OAI: oai:DiVA.org:uu-104335DiVA: diva2:219656
Available from: 2009-05-28 Created: 2009-05-28 Last updated: 2010-01-26Bibliographically approved
In thesis
1. Functional Aspects of the Juxtaglomerular Apparatus: Control of Glomerular Filtration and Renin Release
Open this publication in new window or tab >>Functional Aspects of the Juxtaglomerular Apparatus: Control of Glomerular Filtration and Renin Release
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The juxtaglomerular apparatus (JGA) is a control unit of the kidney, that regulates glomerular filtration rate (GFR) and renin release, and hence extracellular volume and blood pressure. The tubuloglomerular feedback (TGF) mechanism is a negative feedback loop that regulates GFR. Neuronal nitric oxide synthase (nNOS) is highly expressed in the macula densa cells of the JGA, and regulates the sensitivity of the TGF mechanism. Hypertension has been proposed to be caused by an increased sensitivity of the TGF due to nNOS deficiency. In diabetes, reduced TGF activity due to increased sodium-glucose reabsorption is suggested to cause hyperfiltration. Glomerular hyperfiltration has clinical significance, since it correlates with the risk of developing nephropathy.

In this thesis, the role of nNOS in the control of blood pressure and renin release was investigated in nNOS knockout mice (nNOS-/-) treated with low- and high sodium diets. The nNOS-/- were normotensive, but displayed an impaired renin regulation, and failed to increase renin in response to a low sodium diet. A significantly larger renin increase during phosphodiesterase 3 (PDE3) inhibition was found in nNOS-/- compared to the wild types, resulting in similar renin levels.

Furthermore, the role of TGF and proximal glucose reabsorption in diabetes-induced hyperfiltration was investigated in adenosine A1-receptor knockout mice (A1AR-/-) that are known to lack a functional TGF mechanism. Diabetes was induced in A1AR-/- and wild types by injection of alloxan. The diabetic A1AR-/- displayed a similar degree of hyperfiltration as their wild-type controls. Inhibition of renal sodium-glucose transporters reduced GFR in both genotypes, but the reduction was even more pronounced in the A1AR-/-.

In conclusion, the results indicate that renin secretion during low sodium conditions is mediated by nNOS-derived nitric oxide via cGMP-mediated inhibition of PDE3, whereas deletion of the nNOS gene does not cause hypertension. Diabetes-induced hyperfiltration is not mediated by TGF, but appears to be dependent on increased renal glucose reabsorption.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 518
National Category
Medical and Health Sciences
Research subject
Medical Cell Biology
Identifiers
urn:nbn:se:uu:diva-113178 (URN)978-91-554-7715-8 (ISBN)
Public defence
2010-03-10, B22, BMC, Husargatan 3, Uppsala, 13:15 (English)
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Available from: 2010-02-17 Created: 2010-01-26 Last updated: 2010-02-17Bibliographically approved

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