Early studies indicate that the hypertension observed in the Schlager inbred mouse strain may be attributed to a neurogenic mechanism. In this study, we examined the contribution of the sympathetic nervous system in maintaining hypertension in the BPH/2J mouse and used c-Fos immunohistochemistry to elucidate whether neuronal activation in specific brain regions was associated with waking blood pressure. Male hypertensive (BPH/2J; n=14), normotensive (BPN/3J; n=18), and C57/Bl6 (n=5) mice were implanted with telemetry devices, and after 10 days of recovery, recordings of blood pressure, heart rate, and locomotor activity were measured to determine circadian variation. Mean arterial pressure was higher in BPH/2J than in BPN/3J or C57/Bl6 mice (P<0.001), and BPH/2J animals showed exaggerated day-night differences (17+/-2 versus 6+/-1 mm Hg in BPN/3J or +8+/-2 mm Hg in C57/Bl6 mice; P<0.001). Acute sympathetic blockade with pentolinium (7.5 mg/kg IP) during the active and inactive phases reduced blood pressure to comparable levels in BPH/2J and BPN/3J mice. The number of c-Fos-labeled cells was greater in the amygdala (+180%; P<0.01), paraventricular nucleus (+110%; P<0.001), and dorsomedial hypothalamus (+48%; P<0.001) in the active (hypertensive) phase in BPH/2J compared with BPN/3J mice. The level of neuronal activation was mostly similar in these regions in the inactive phase. Of all of the regions studied, neuronal activation in the medial amygdala, as detected by c-Fos, was highly correlated to mean arterial pressure (r=0.98). These findings indicate that the hypertension is largely attributable to sympathetic nervous system activity, possibly generated through greater levels of arousal regulated by neurons located in the medial amygdala.

Tissue hypoxia has been demonstrated, in both the renal cortex and medulla, during the acute phase of reperfusion after ischemia induced by occlusion of the aorta upstream from the kidney. However, there are also recent clinical observations indicating relatively well preserved oxygenation in the nonfunctional transplanted kidney. To test whether severe acute kidney injury can occur in the absence of widespread renal tissue hypoxia, we measured cortical and inner medullary tissue Po2 as well as total renal O2 delivery (Do2) and O2 consumption (Vo2) during the first 2 h of reperfusion after 60 min of occlusion of the renal artery in anesthetized rats. To perform this experiment, we used a new method for measuring kidney Do2 and Vo2 that relies on implantation of fluorescence optodes in the femoral artery and renal vein. We were unable to detect reductions in renal cortical or inner medullary tissue Po2 during reperfusion after ischemia localized to the kidney. This is likely explained by the observation that Vo2 (-57%) was reduced by at least as much as Do2 (-45%), due to a large reduction in glomerular filtration (-94%). However, localized tissue hypoxia, as evidence by pimonidazole adduct immunohistochemistry, was detected in kidneys subjected to ischemia and reperfusion, particularly in, but not exclusive to, the outer medulla. Thus, cellular hypoxia, particularly in the outer medulla, may still be present during reperfusion even when reductions in tissue Po2 are not detected in the cortex or inner medulla.

RG. Diffusive oxygen shunting between vessels in the preglomerular renal vasculature: anatomic observations and computational modeling. Am J Physiol To understand how geometric factors affect arterial-to-venous (AV) oxygen shunting, a mathematical model of diffusive oxygen transport in the renal cortex was developed. Preglomerular vascular geometry was investigated using light microscopy (providing vein shape, AV separation, and capillary density near arteries) and published micro-computed tomography (CT) data (providing vessel size and AV separation; Nordsletten DA, Blackett S, Bentley MD, Ritman EL, Smith NP. IUPS Physiome Project. http://www. physiome.org.nz/publications/nordsletten_blackett_ritman_bentley_ smith_2005/folder_contents). A "U-shaped" relationship was observed between the arterial radius and the distance between the arterial and venous lumens. Veins were found to partially wrap around the artery more consistently for larger rather than smaller arteries. Intrarenal arteries were surrounded by an area of fibrous tissue, lacking capillaries, the thickness of which increased from ϳ5 m for the smallest arteries (Ͻ16-m diameter) to ϳ20 m for the largest arteries (Ͼ200-m diameter). Capillary density was greater near smaller arteries than larger arteries. No capillaries were observed between wrapped AV vessel pairs. The computational model comprised a single AV pair in cross section. Geometric parameters critical in renal oxygen transport were altered according to variations observed by CT and light microscopy. Lumen separation and wrapping of the vein around the artery were found to be the critical geometric factors determining the amount of oxygen shunted between AV pairs. AV oxygen shunting increases both as lumen separation decreases and as the degree of wrapping increases. The model also predicts that capillaries not only deliver oxygen, but can also remove oxygen from the cortical parenchyma close to an AV pair. Thus the presence of oxygen sinks (capillaries or tubules) near arteries would reduce the effectiveness of AV oxygen shunting. Collectively, these data suggest that AV oxygen shunting would be favored in larger vessels common to the cortical and medullary circulations (i.e., arcuate and proximal interlobular arteries) rather than the smaller vessels specific to the cortical circulation (distal interlobular arteries and afferent arterioles). hypoxia; kidney circulation; oxygen tension; renal oxygenation FIFTY YEARS AGO Levy et al. (17,18) provided evidence that oxygen is transported more rapidly than erythrocytes through the renal circulation, suggesting the existence of diffusional oxygen shunting between intrarenal arteries and veins. Shunting reduces the delivery of oxygen to renal tissue (26,27). In further support of the existence of arterial-to-venous (AV) oxygen shunting, Welch et al. (29) observed that the PO 2 of renal venous blood exceeds that of blood in the efferent arterioles of the outer cortex. In common with other countercurrent systems in biology and chemical engineering, it...

Oxygen tension (Po2) of urine in the bladder could be used to monitor risk of acute kidney injury if it varies with medullary Po2 Therefore, we examined this relationship and characterized oxygen diffusion across walls of the ureter and bladder in anesthetized rabbits. A computational model was then developed to predict medullary Po2 from bladder urine Po2 Both intravenous infusion of [Phe(2),Ile(3),Orn(8)]-vasopressin and infusion of N(G)-nitro-l-arginine reduced urinary Po2 and medullary Po2 (8-17%), yet had opposite effects on renal blood flow and urine flow. Changes in bladder urine Po2 during these stimuli correlated strongly with changes in medullary Po2 (within-rabbit r(2) = 0.87-0.90). Differences in the Po2 of saline infused into the ureter close to the kidney could be detected in the bladder, although this was diminished at lesser ureteric flow. Diffusion of oxygen across the wall of the bladder was very slow, so it was not considered in the computational model. The model predicts Po2 in the pelvic ureter (presumed to reflect medullary Po2) from known values of bladder urine Po2, urine flow, and arterial Po2 Simulations suggest that, across a physiological range of urine flow in anesthetized rabbits (0.1-0.5 ml/min for a single kidney), a change in bladder urine Po2 explains 10-50% of the change in pelvic urine/medullary Po2 Thus, it is possible to infer changes in medullary Po2 from changes in urinary Po2, so urinary Po2 may have utility as a real-time biomarker of risk of acute kidney injury.

Koeners MP, Ow CP, Russell DM, Abdelkader A, Eppel GA, Ludbrook J, Malpas SC, Evans RG. Telemetry-based oxygen sensor for continuous monitoring of kidney oxygenation in conscious rats.

We determined whether adenine-induced chronic kidney disease (CKD) in rats is associated with renal tissue hypoxia. Adenine (100 mg) or its vehicle was administered to male Sprague-Dawley rats, daily by oral gavage, over a 15-day period. Renal function was assessed before, and 7 and 14 days after, adenine treatment commenced, by collection of a 24-hour urine sample and a blood sample from the tail vein. On day 15, arterial pressure was measured in conscious rats via the tail artery. Renal tissue hypoxia was then assessed by pimonidazole adduct immunohistochemistry and fibrosis was assessed by staining tissue with picrosirius red and Masson's trichrome. CKD was evident within 7 days of commencing adenine treatment, as demonstrated by increased urinary albumin to creatinine ratio (30 ± 12-fold). By day 14 of adenine treatment plasma creatinine concentration was more than 7-fold greater, and plasma urea more than 5-fold greater, than their baseline levels. On day 15, adenine-treated rats had slightly elevated mean arterial pressure (8 mmHg), anaemia and renomegaly. Kidneys of adenine-treated rats were characterised by the presence of tubular casts, dilated tubules, expansion of the interstitial space, accumulation of collagen, and tubulointerstitial hypoxia. Pimonidazole staining (hypoxia) co-localised with fibrosis and was present in both patent and occluded tubules. We conclude that renal tissue hypoxia develops rapidly in adenine-induced CKD. This model, therefore, should prove useful for examination of the temporal and spatial relationships between tubulointerstitial hypoxia and the development of CKD, and thus the testing of the 'chronic hypoxia hypothesis'.

Ow CP, Abdelkader A, Hilliard LM, Phillips JK, Evans RG. Determinants of renal tissue hypoxia in a rat model of polycystic kidney disease. Am J Physiol Regul Integr Comp Physiol 307: R1207-R1215, 2014. First published September 10, 2014 doi:10.1152/ajpregu.00202.2014.-Renal tissue oxygen tension (PO2) and its determinants have not been quantified in polycystic kidney disease (PKD). Therefore, we measured kidney tissue PO2 in the Lewis rat model of PKD (LPK) and in Lewis control rats. We also determined the relative contributions of altered renal oxygen delivery and consumption to renal tissue hypoxia in LPK rats. PO2 of the superficial cortex of 11-to 13-wk-old LPK rats, measured by Clark electrode with the rat under anesthesia, was higher within the cysts (32.8 Ϯ 4.0 mmHg) than the superficial cortical parenchyma (18.3 Ϯ 3.5 mmHg). PO2 in the superficial cortical parenchyma of Lewis rats was 2.5-fold greater (46.0 Ϯ 3.1 mmHg) than in LPK rats. At each depth below the cortical surface, tissue PO2 in LPK rats was approximately half that in Lewis rats. Renal blood flow was 60% less in LPK than in Lewis rats, and arterial hemoglobin concentration was 57% less, so renal oxygen delivery was 78% less. Renal venous PO2 was 38% less in LPK than Lewis rats. Sodium reabsorption was 98% less in LPK than Lewis rats, but renal oxygen consumption did not significantly differ between the two groups. Thus, in this model of PKD, kidney tissue is severely hypoxic, at least partly because of deficient renal oxygen delivery. Nevertheless, the observation of similar renal oxygen consumption, despite markedly less sodium reabsorption, in the kidneys of LPK compared with Lewis rats, indicates the presence of inappropriately high oxygen consumption in the polycystic kidney. chronic kidney disease; anoxia; ischemia; oxygen; oxygen consumption; oxygen delivery; renal circulation POLYCYSTIC KIDNEY DISEASE (PKD) is characterized by enhanced proliferation of the epithelium (25) resulting in the formation of renal cysts (20), renomegaly (50), and abnormalities of the renal vasculature (3, 52). Renal tissue hypoxia also appears to be characteristic of PKD, having been demonstrated using pimonidazole adduct immunohistochemistry, an indirect method for assessing tissue oxygenation (4, 10). These observations indicate that hypoxia is present throughout the renal parenchyma, but that the epithelium lining the cysts is particularly hypoxic (2, 4, 10). However, we are not aware of any previous studies in which renal tissue oxygen tension (PO 2 ) has been measured directly in PKD. Renal hypoxia might be important in PKD in at least two respects. First, there is evidence that in chronic kidney disease renal tissue hypoxia can activate sensory nerves within the kidney to activate the sympathetic nervous system (18). Second, hypoxia may exacerbate progression of PKD by hypoxia-inducible factor-dependent cystogenesis (6, 41).In chronic kidney disease, an imbalance between renal oxygen delivery (DO 2 ) and consumption (V O 2 ), the main determinants of ...

In the present study, we tested whether polycystic kidney disease (PKD) is associated with renal tissue hypoxia and oxidative stress, which, in turn, contribute to the progression of cystic disease and hypertension. Lewis polycystic kidney (LPK) rats and Lewis control (Lewis) rats were treated with tempol (1 mmol/L in drinking water) from 3 to 13 weeks of age or remained untreated. The LPK rats developed polyuria, uraemia and proteinuria. At 13 weeks of age, LPK rats had greater mean arterial pressure (1.5-fold), kidney weight (sixfold) and plasma creatinine (3.5-fold) than Lewis rats. Kidneys from LPK rats were cystic and fibrotic. Renal hypoxia was evidenced by staining for pimonidazole adducts and hypoxia-inducible factor (HIF)-1α in cells lining renal cysts and upregulation of HIF-1α and its downstream targets vascular endothelial growth factor (VEGF), glucose transporter-1 (Glut-1) and heme oxygenase 1 (HO-1). However, total HO activity did not differ greatly between kidney tissue from LPK compared with Lewis rats. Renal oxidative and/or nitrosative stress was evidenced by ninefold greater immunofluorescence for 3-nitrotyrosine in kidney tissue from LPK compared with Lewis rats and a > 10-fold upregulation of mRNA for p47phox and gp91phox. Total renal superoxide dismutase (SOD) activity was sevenfold less and expression of SOD1 mRNA was 70% less in kidney tissue from LPK compared with Lewis rats. In LPK rats, tempol treatment reduced immunofluorescence for 3-nitrotyrosine and HIF1A mRNA while upregulating VEGF and p47phox mRNA expression, but otherwise had little impact on disease progression, renal tissue hypoxia or hypertension. Our findings do not support the hypothesis that oxidative stress drives hypoxia and disease progression in PKD.