Angiotensin II-induced hypertension in rats is only transiently accompanied by lower renal oxygenation

 This is the final version. Available from Springer Nature via the DOI in this record. Activation of the renin-angiotensin system may initiate chronic kidney disease. We hypothesised that renal hypoxia is a consequence of hemodynamic changes induced by angiotensin II and occurs prior to development of severe renal damage. Male Sprague-Dawley rats were infused continuously with angiotensin II (350 ng/kg/min) for 8 days. Mean arterial pressure (n = 5), cortical (n = 6) and medullary (n = 7) oxygenation (pO2) were continuously recorded by telemetry and renal tissue injury was scored. Angiotensin II increased arterial pressure gradually to 150 ± 18 mmHg. This was associated with transient reduction of oxygen levels in renal cortex (by 18 ± 2%) and medulla (by 17 ± 6%) at 10 ± 2 and 6 ± 1 hours, respectively after starting infusion. Thereafter oxygen levels normalised to pre-infusion levels and were maintained during the remainder of the infusion period. In rats receiving angiotensin II, adding losartan to drinking water (300 mg/L) only induced transient increase in renal oxygenation, despite normalisation of arterial pressure. In rats, renal hypoxia is only a transient phenomenon during initiation of angiotensin II-induced hypertension.British Heart FoundationBritish Heart FoundationDutch Kidney FoundationEuropean Union, Seventh Framework Programm

Monitoring renal hemodynamics and oxygenation by invasive probes: experimental protocol

Renal tissue hypoperfusion and hypoxia are early key elements in the pathophysiology of acute kidney injury of various origins, and may also promote progression from acute injury to chronic kidney disease. Here we describe methods to study control of renal hemodynamics and tissue oxygenation by means of invasive probes in anesthetized rats. Step-by-step protocols are provided for two setups, one for experiments in laboratories for integrative physiology and the other for experiments within small-animal magnetic resonance scanners.This publication is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This experimental protocol chapter is complemented by a separate chapter describing the basic concepts of quantitatively assessing renal perfusion and oxygenation with invasive probes

Quantitative assessment of renal perfusion and oxygenation by invasive probes: basic concepts

Renal tissue hypoperfusion and hypoxia are early key elements in the pathophysiology of acute kidney injury of various origins, and may also promote progression from acute injury to chronic kidney disease. Here we describe basic principles of methodology to quantify renal hemodynamics and tissue oxygenation by means of invasive probes in experimental animals. Advantages and disadvantages of the various methods are discussed in the context of the heterogeneity of renal tissue perfusion and oxygenation.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by a separate chapter describing the experimental procedure and data analysis

Determinants of renal oxygen metabolism during low Na+ diet : effect of angiotensin II AT1 and aldosterone receptor blockade

Reducing Na(+)intake reduces the partial pressure of oxygen in the renal cortex and activates the renin-angiotensin-aldosterone system. In the absence of high blood pressure, these consequences of dietary Na(+)reduction may be detrimental for the kidney. In a normotensive animal experimental model, reducing Na(+)intake for 2 weeks increased renal oxygen consumption, which was normalized by mineralocorticoid receptor blockade. Furthermore, blockade of the angiotensin II AT(1)receptor restored cortical partial pressure of oxygen by improving oxygen delivery. This shows that increased activity of the renin-angiotensin-aldosterone system contributes to increased oxygen metabolism in the kidney after 2 weeks of a low Na(+)diet. The results provide insights into dietary Na(+)restriction in the absence of high blood pressure, and its consequences for the kidney. Reduced Na(+)intake reduces thePO2(partial pressure of oxygen) in the renal cortex. Upon reduced Na(+)intake, reabsorption along the nephron is adjusted with activation of the renin-angiotensin-aldosterone system (RAAS). Thus, we studied the effect of reduced Na(+)intake on renal oxygen homeostasis and function in rats, and the impact of intrarenal angiotensin II AT(1)receptor blockade using candesartan and mineralocorticoid receptor blockade using canrenoic acid potassium salt (CAP). Male Sprague-Dawley rats were fed standard rat chow containing normal (0.25%) and low (0.025%) Na(+)for 2 weeks. The animals were anaesthetized (thiobutabarbital 120 mg kg(-1)) and surgically prepared for kidney oxygen metabolism and function studies before and after acute intrarenal arterial infusion of candesartan (4.2 mu g kg(-1)) or intravenous infusion of CAP (20 mg kg(-1)). Baseline mean arterial pressure and renal blood flow were similar in both dietary groups. Fractional Na(+)excretion and cortical oxygen tension were lower and renal oxygen consumption was higher in low Na(+)groups. Neither candesartan nor CAP affected arterial pressure. Renal blood flow and cortical oxygen tension increased in both groups after candesartan in the low Na(+)group. Fractional Na(+)excretion was increased and oxygen consumption reduced in the low Na(+)group after CAP. These results suggest that blockade of angiotensin II AT(1)receptors has a major impact upon oxygen delivery during normal and low Na(+)conditions, while aldosterone receptors mainly affect oxygen metabolism following 2 weeks of a low Na(+)diet.List of authors in thesis manuscript: Daniela Patinha, Carla Carvalho, Patrick Persson, Liselotte Pihl, Julie O'Niell, Fredrik Palm</p