Magnesium lithospermate B ameliorates renal cortical microperfusion in rats.

AIM: To investigate the effects of magnesium lithospermate B (MLB) isolated from Salviae miltiorrhizae on renal microcirculation, and renal and systemic hemodynamics in Sprague-Dawley rats. METHODS: MLB (10, 30, and 60 mg/kg) was injected intravenously and renal blood flow (RBF), renal cortical microperfusion (RCM), and systemic hemodynamic function parameters including heart rate (HR), mean arterial pressure (MAP), left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), and maximal velocity of pressure increase (dp/dt(max)) were measured for 45 min after administration. RESULTS: Intravenous MLB at doses of 10, 30, and 60 mg/kg increased RCM significantly, but had no obvious effects on RBF or systemic hemodynamics. The effect of MLB on RCM reached its peak 15 min after injection and returned to baseline after 45 min. Up to 60 mg/kg MLB increased RCM by 62.4%+/-20.2% (changes from baseline, P<0.01), whereas RBF (3.7%+/-9.7% vs baseline) and renal vascular resistance (-1.4%+/-9.1% vs baseline) did not obviously change. CONCLUSION: These results indicate that MLB ameliorates renal microcirculation in a dose-dependent manner, which may be related to the renoprotective effects of MLB.

Cortical microvascular remodeling in the stenotic kidney: role of increased oxidative stress.

OBJECTIVE: Mechanisms of renal injury distal to renal artery stenosis (RAS) remain unclear. We tested the hypothesis that it involves microvascular remodeling consequent to increased oxidative stress. METHODS AND RESULTS: Three groups of pigs (n=6 each) were studied after 12 weeks of RAS, RAS+antioxidant supplementation (100 IU/kg vitamin E and 1 g vitamin C daily), or controls. The spatial density and tortuousity of renal microvessels (<500 microm) were tomographically determined by 3D microcomputed tomography. The in situ production of superoxide anion and the expression of vascular endothelial growth factor (VEGF), its receptor VEGFR-2, hypoxia-inducible-factor (HIF)-1alpha, von Hippel-Lindau (VHL) protein, and NAD(P)H oxidase (p47phox and p67phox subunits) were determined in cortical tissue. RAS and RAS+antioxidant groups had similar degrees of stenosis and hypertension. The RAS group showed a decrease in spatial density of cortical microvessels, which was normalized in the RAS+antioxidant group, as was arteriolar tortuousity. RAS kidneys also showed tissue fibrosis (by trichrome and Sirius red staining), increased superoxide anion abundance, NAD(P)H oxidase, VHL protein, and HIF-1alpha mRNA expression. In contrast, expression of HIF-1alpha, VEGF, and VEGFR-2 protein was downregulated. These were all significantly improved by antioxidant intervention. CONCLUSIONS: Increased oxidative stress in the stenotic kidney alters growth factor activity and plays an important role in renal microvascular remodeling, which can be prevented by chronic antioxidant intervention.

Acute renal hemodynamic effects of dimanganese decacarbonyl and cobalt protoporphyrin.

BACKGROUND: Heme oxygenase (HO) products have a protective role in acute renal failure (ARF) that may be hemodynamically mediated because the HO-derived carbon monoxide (CO) is an important control system of arteriolar tone. The vascular effects of HO may be caused directly through changes in CO synthesis, and indirectly by alterations in nitric oxide (NO) release. The present study evaluated in vivo the renal effects of a heme oxygenase inhibitor, Co(III)Protoporphyrin (CoPP) alone or in combination with the CO donor dimanganese decacarbonyl (Mn2(CO)10). METHODS: All drugs were administered into the renal artery of anesthetized rats. Changes in renal cortical nitric oxide concentration were measured in vivo electrochemically. RESULTS: The intrarenal administration of the CO donor Mn2(CO)10 increased blood carboxyhemoglobin levels (+74%), renal blood flow (+54%), glomerular filtration (+38%), and urinary cGMP excretion (+128%). On the other hand, the inhibition of renal HO with CoPP progressively induced an ARF characterized by a drop in renal blood flow (-77%), glomerular filtration (-93%), and urinary cGMP excretion (-93%). These deleterious effects of HO inhibition on renal function were nearly abolished by supplementing CO with the coadministration of Mn2(CO)10+ CoPP, indicating that they may be caused by inhibition of CO synthesis and the resulting hemodynamic changes. In addition, CoPP lowered the renal cortical NO concentration (-21%) and also decreased the urinary excretion of nitrates/nitrites, while Mn2(CO)10 increased renal NO levels (+20%) and raised the excretion of nitrates/nitrites, suggesting that changes in NO release may contribute to the renal effects of the HO-CO system. CONCLUSION: These results indicate that heme oxygenase-derived CO plays a cardinal role in the control of renal hemodynamics and glomerular filtration.

Tissue temperature oscillations in an isolated pig kidney during surface heating.

In the present study, an isolated pig kidney was used to study tissue temperature oscillations due to vascular thermoregulation, frequently observed during hyperthermia treatments. The kidney was perfused with the distilled water pumped through the renal artery to simulate blood flow. When the local perfusion rate was increased with a time delay, temperature oscillations were observed in the kidney as its surface temperature raised linearly with time in a water bath. The magnitude of tissue temperature decreased as the flow rate increased during the surface heating. A 3D transient model was developed to predict the temperature oscillations, which was validated by the measurements. Using the model, relationships of the changes in perfusion rate and heating rate with temperature oscillations were investigated. It was found that the heating rate, and the magnitude and time delay of the flow response to the temperature elevation, each significantly affected tissue temperature oscillations. The magnitude of oscillation was primarily determined by the spatial gradient of temperature, while the oscillation type depended on the change of flow rate and the time delay. In conclusion, to accurately predict and control the tissue temperature distribution during hyperthermia treatment, understanding of the local perfusion change with respect to tissue temperature is essential.

Hypoperfusion in the renal outer medulla after injection of contrast media in rats.

PURPOSE: The effect on regional renal blood was studied after injection of nonionic iso-osmolar iotrolan or ionic high-osmolar iothalamate. MATERIAL AND METHODS: Laser-Doppler flowmetry was used to measure outer medullary (OMBF) and superficial cortical blood flow (CBF) simultaneously in anesthetized rats. Iotrolan (320 mOsm/kg H2O) was injected i.v. at a dose of 600 mg I/kg b.w. (normal dose) over 2 min or 1,600 (high dose) mg I/kg b.w. over 2 or 8 min. Iothalamate (2,580 mOsm/kg H2O) was injected i.v. at a dose of 1,600 (high dose) or 2,900 (extremely high dose) mg I/kg b.w. over 2 min. RESULTS: At the normal dose and 2-min injection of iotrolan, OMBF was reduced by 25+/-9% over 20 min. The high dose of iotrolan injected over 8 min resulted in a reduction in OMBF slightly smaller (17+/-9%) than that induced by the normal dose but lasting longer (30 min). Compared to the normal dose, the high dose and fast (2 min) injection of iotrolan resulted in a greater and more prolonged decrease in OMBF (32+/-6% lasting 50 min). After the high dose of iothalamate (1,600 mg I/kg) there was a decrease in OMBF by 21+/-6%, lasting 30 min. An extremely high dose (2,900 mg I/kg b.w.) gave a heterogeneous response with a mean increase in OMBF of 48+/-24% occurring 60 min after the injection. CONCLUSION: Iso-osmolar and high-osmolar contrast media (CM), at normal and high doses, decrease OMBF, while an extremely high dose of iothalamate may result in an increase. The depression of outer medullary perfusion may have implications for CM-induced acute renal failure in view of the vulnerability of this region to a decrease in oxygen tension.

Effect of iloprost infusion on the resistance index of renal vessels of patients with systemic sclerosis.

OBJECTIVE: To investigate the effect of iloprost, a stable prostacycline analog, on kidney blood flow in patients with systemic sclerosis (SSc), using color flow Doppler sonography. METHODS: The acute effect of the drug was studied in 10 patients with SSc with elevated resistance index (RI) levels (all RI values reported are multiplied by 100). Iloprost was administered intravenously (2 ng/kg/min for a period of 8 h). To study the effects of chronic drug administration, 16 patients with SSc were randomly assigned to 2 groups of 8 cases each. The first group was treated with 9 infusions of iloprost in 6 mo. The second group was treated with slow release nifedipine (40 mg/day) for 6 mo. RESULTS: Interlobar artery RI (median 67 vs 61; p = 0.02) and cortical vessel RI (median 65 vs 54; p = 0.001) were reduced after acute treatment. In chronic drug administration, RI values were not modified by nifedipine, while iloprost reduced the RI of the interlobar (median 69 vs 61; p < 0.03) and cortical arteries (median 66 vs 58: p < 0.01). CONCLUSION: Our findings suggest iloprost might be useful for treatment of scleroderma renal vasospasm.

The efficacy of antioxidants administered during low temperature storage of warm ischemic kidney tissue slices.

Accumulation of products of lipid peroxidation (malondialdehyde, conjugated dienes, lipid peroxides, and Schiff bases) was evaluated in rabbit kidney cortex slices made ischemic for 60 min followed by 18 h storage at 5 degrees C in UW Na gluconate solution and 210 min normothermic reoxygenated incubation. In addition, the effect of adding Trolox (1 mM), deferoxamine (1 mM), and ascorbate (1 mM) as supplemental antioxidants to the UW gluconate solution was evaluated. Lipid peroxidation was slightly increased after hypothermic storage compared to slices subjected to ischemia alone but was not significantly different than ischemic slices during subsequent incubation at normothermia. The addition of either deferoxamine or Trolox to the storage solution substantially reduced lipid peroxidation both during hypothermic storage and subsequent to normothermic incubation. Ascorbate had a mild prooxidant effect as a sole additive to the UW gluconate solution but was clearly prooxidant when combined with either deferoxamine or Trolox. These results suggest that supplemental antioxidants added to the UW gluconate solution under conditions analogous to machine perfusion preservation have a potential role in reducing oxidative stress in kidney tissues harvested after warm ischemia and that hypothermia may be a valuable adjunct to resuscitative therapeutic regimens developed for salvage of ischemic kidneys for transplantation.

Influence of the renal endothelin system on the autoregulation of renal blood flow in spontaneously hypertensive rats.

The renal endothelin (ET) system has been claimed to play an important role in the regulation of renal blood flow (RBF) and sodium excretion in primary hypertension. The aim of the present study was to investigate the contribution of the endogenous ET system in the autoregulation of total RBF, cortical blood flow (CBF), pressure-dependent plasma renin activity (PRA) and pressure natriuresis in spontaneously hypertensive rats (SHR) by means of the combined (A/B) ET-receptor antagonist, bosentan. In anesthetized rats, RBF was measured by transit-time flow probes and CBF by laser flow probes. During the experiments, the rats received an intrarenal infusion of either bosentan (1 mg/kg/h) or vehicle. Renal perfusion pressure (RPP) was lowered in pressure steps of 5 mm Hg with a servo-controlled electropneumatic device via an inflatable suprarenal cuff. Bosentan had no effect on resting RPP, CBF, PRA and renal sodium excretion, whereas RBF was lowered by 30% (p < 0.05). Furthermore after bosentan the rats revealed a complete loss of RBF autoregulation. In contrast no changes in autoregulation of CBF, pressure-dependent PRA and pressure natriuresis were observed. Our findings demonstrate a significant impairment in total RBF autoregulatory ability during renal ET-receptor blockade which is not confined to the cortical vessels. These data suggest that the renal ET system plays an important role in the dynamic regulation of renal blood flow in SHR.

Evaluation of gadobutrol in a rabbit model as a new lanthanide contrast agent for computed tomography.

RATIONALE AND OBJECTIVES: The efficacy of the neutral lanthanide contrast agent gadobutrol was compared to that of the iodinated contrast agent iopromide in rabbits. METHODS: The computed tomography (CT) attenuation of increasing concentrations of gadolinium (Gd) (gadobutrol) and iodine (I) (iopromide) was measured in Hounsfield units (HU) in aqueous solution at 80, 120, and 137 kV. The peak enhancement (net increase in CT attenuation compared with baseline) and the time-enhancement product in the aorta and in the renal parenchyma of the outer and inner cortex were measured in rabbits over a 5-minute period after the animals were given single intravenous injections of 0.7, 1.0, and 1.5 mmol Gd/kg of gadobutrol and 1.0 and 2.4 mmol I/kg of iopromide. RESULTS: In vitro, the CT attenuation of gadolinium was 40% higher than that of iodine at equivalent mass concentrations (120 kV). The mean peak enhancements in the aorta after the injections of 0.7, 1.0, and 1.5 mmol Gd/kg and 1.0 and 2.4 mmol I/kg were 216, 313, 591, 224, and 498 HU, respectively. In addition, a 30-second injection of the high dose of gadobutrol resulted in an attenuation profile that was suitable for a three-dimensional reconstruction of the aorta and the renal vasculature. CONCLUSIONS: Because of the higher CT attenuation of gadolinium compared with that of iodine, the neutral macrocyclic chelate gadobutrol is a more effective contrast agent than iopromide for CT at lower doses of the imaging atom.

Stimulation of renal microvascular development under organotypic culture conditions.

The development of the renal vascular system requires the coordinated action of soluble morphogenic factors and specific extracellular matrix components. Despite intensive research it remains unknown whether the humoral or the environmental component is more important in the development of renal microvessels. The prolonged serum-free culture of embryonic kidney cortex explants was achieved by means of a newly developed perfusion culture system. This system made the investigation of renal vascular development under defined organotypic conditions possible. Thus, growth factors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and hormones (aldosterone, vitamin D3) could be applied without the interference with serum components. Medium supplementation with VEGF or aldosterone in combination with vitamin D3 resulted in the coordinated proliferation of endothelial cells in the explant. A well-developed collecting duct epithelium and numerous tubular structures were always observed. In contrast, only a uniform cell layer was found between fibrous organ capsule and the collecting duct epithelium after bFGF application, but neither tubular structures nor endothelial cells. Thus, the experiments indicate that bFGF alone has no stimulating effect on the growth of the renal microvasculature under perfusion culture conditions.

Dietary myo-inositol supplementation does not prevent retinal and glomerular vascular structural changes in chronically diabetic rats.

To assess effects of dietary myo-inositol supplementation on diabetes-induced vascular structural lesions, diabetes was induced in Sprague-Dawley rats with streptozotocin; one-third of these rats was fed a 2% myo-inositol diet for 9 months, one-third was left untreated for 5 months then treated with myo-inositol for the last 4 months, and one-third was untreated for the entire 9 months. Controls included untreated and myo-inositol-treated groups. Weight gain was impaired and plasma glucose, glycosylated hemoglobin, food consumption, urine volume, and albuminuria were increased significantly in diabetic versus age-matched control rats. Plasma myo-inositol levels were increased approximately fivefold in controls and approximately six- to eightfold in diabetic rats treated with myo-inositol. In general, myo-inositol did not affect any of the above parameters in control or diabetic rats. Retinal capillary basement membrane width (CBMW) was increased significantly (approximately 50% versus controls) after 9 months of diabetes. In the control group myo-inositol increased CBMW to the level of untreated diabetic rats; myo-inositol had no effect on CBMW in each diabetic group. The number of retinal capillaries containing pericyte nuclei and pericyte capillary coverage were increased in untreated as well as myo-inositol-treated diabetic rats and in the myo-inositol-treated control group. Glomerular CBMW was increased after 5 and 9 months of diabetes versus age-matched controls, and was increased even more by myo-inositol. Mesangial fractional volume of the glomerulus was increased 36% by diabetes and was decreased slightly but significantly by myo-inositol. These results indicate that diets supplemented with 2% myo-inositol (1) cause capillary basement membrane (CBM) thickening and pericyte changes in retinal capillaries of normal rats, (2) are ineffective in preventing or reversing diabetes-induced retinal CBM thickening, and (3) cause further thickening of glomerular CBM in diabetic rats.

Renal vascular response to left atrial injection. An experimental study in the pig.

It has previously been shown that a rapid, transient and pronounced reduction in superficial renal cortical blood flow can be elicited by injection of 1 ml of plasma into the left atrium of the anaesthetized pig. This renal vascular response might constitute an important error in measurements of renal blood flow by means of the microsphere technique. In the present study we have investigated total renal (ultrasonic Doppler) and superficial renal cortical (laser Doppler flowmetry) blood flow after left atrial injections of saline and autologous blood. The average reductions in total renal blood flow were 4.7 +/- 2.4% (mean +/- s.d.) and 18.4 +/- 12.5% (mean +/- s.d.) for the blood and saline injections, respectively. The flow reduction was more pronounced in the superficial renal cortex with average reductions of 17.4 +/- 26.0% (mean +/- s.d.) and 59.4 +/- 38.5% (mean +/- s.d.) for blood and saline, respectively (laser Doppler flowmetry). Furthermore, two consecutive injections of microspheres were performed. The results from the second injection were compared with those from the first injection. In the superficial renal cortex the second injection indicated a significant reduction in blood flow and an significantly increased heterogeneity in the blood flow in two different tissue volumes. No corresponding differences were found in the juxtamedullary cortex. These results indicate that the renal vascular response to a left atrial injection is detectable as a reduction in total renal blood flow and is most pronounced in the superficial renal cortex. All these results taken together constitute an important error in measurements of superficial renal cortical blood flow by the microsphere technique.

Compensatory hypertrophy and adaptation in the cortical collecting duct.

The cortical collecting duct (CCD) undergoes hypertrophy and functional adaptation following reduction of renal mass. The nature and mechanisms of these changes have been investigated using microperfusion of isolated CCD from rabbit remnant kidneys. By 1 week after reduction of renal mass, tubule hypertrophy and increased sodium transport are fully developed. The transport adaptations are specific or selective, since bicarbonate transport in these CCD is unchanged. Mineralocorticoids may play an important role in the hypertrophy and increased sodium transport, since plasma aldosterone increases early after reduction of renal mass. Also, adrenalectomy abolishes the changes in size and sodium transport, even with supplementation of aldosterone to unstressed physiologic levels. Epidermal growth factor also has immediate effects on CCD sodium transport; however, the direction of the effect is opposite--an inhibition of transport.

Stimulation of p-aminohippurate transport in renal cortical slices prepared from rats treated with ginsenosides.

The effect of treatment of rats with ginsenosides (extracted from Panax ginseng) on transport of p-aminohippurate (PAH) in renal cortical slices was studied for an in vitro reflection of PAH secretion in the proximal tubules in the kidney. The treatment of rats with ginsenosides stimulated PAH accumulation in the slices and tended to prevent the decrease in PAH accumulation in incubated slices from the rats with acute renal failure caused by cisplatin or ischemia followed by reperfusion. Ginsenoside treatment affected other biochemical responses in renal cortical slices, with a decrease in adenosine triphosphate level and an increase in potassium level. The latter may lead to the stimulation of PAH transport in the slices, but additional information on the cellular action of ginsenosides is needed for this conclusion. It may be that the stimulatory effect of ginsenosides on PAH accumulation in the slices counterbalances the decrease in PAH accumulation in the slices from rats with acute renal failure.

Effects of nifedipine on renal cortical and medullary blood flow in two-kidney, one-clip renovascular hypertension in rabbits.

The effects of nifedipine, a calcium antagonist, on blood pressure and renal regional blood flow were investigated in two-kidney, one-clip renovascular hypertensive rabbits. At 1 week after left renal artery constriction, in the constricted group, systemic blood pressure (BP) significantly rose with the elevation of plasma renin activity (PRA). In both kidneys, renal vascular resistance (RVR on the constricted group was significantly increased as compared to that in the control group. In the clipped kidney, total renal blood flow (RBF) and renal cortical blood flow (RCBF) of the constricted group were significantly decreased, while renal medullary blood flow (RMBF) remained at the control value. In the nonclipped kidney, RBF and RCBF of the constricted group did not significantly change, and RMBF was significantly increased as compared to that of the control group. After administration of nifedipine for 1 week (1.0 mg/kg/day), BP in the constricted group was decreased to the control level and PRA in both groups was increased. The percent change of BP in the constricted group was significantly decreased and the percent change of PRA in the constricted group was significantly increased as compared to those in the control group. Nifedipine increased RBF, RCBF and RMBF and decreased RVR of both kidneys in each group. In the nonclipped kidney, the percent change of RBF, RCBF and RMBF of the constricted group was significantly increased and the percent change of RVR was significantly decreased as compared to those of the control group. In the clipped kidney, only the percent change of RBF of the constricted group was significantly lower than that in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

[Change in the cortical and medullary renal circulation in centrogenic forms of arterial hypertension]. / Izmenenie korkovogo i medulliarnogo krovoobrashcheniia pochek pri tsentrogennykh formakh arterial'noi gipertenzii.

It was shown on 36 nonanesthetized rats by polarography from H2 elimination and PO2 recording that cortical and medullary circulation in the kidneys undergoes continuous fluctuations. A definite relation of these fluctuations with circulatory changes in the cerebral limbicoreticular structures was noted. In electric stimulation of the reticular formation and the hypothalamus on the background of arterial hypertension the cortical circulation decreased by 88.5% while the medullary circulation increased by 82.8%. In hypertension of over 180--235 mm Hg, the blood flow both in the cortical and in the medullary substance ceased practically. Chronic disturbance in the blood supply to the brain led to arterial hypertension and short-lived (10--20 days) increase of the blood plasma renin activity to 417.8% and its subsequent normalization by the 65th day. At the same time, renal blood flow dropped progressively and the reaction of the renal vessels to hypercapnic load became less manifest, which testified to changes in their reactive-structural characteristics. Summarizing the results obtained and the data of other investigators, the author concludes that neurogenous disorders of renal blood flow hold one of the key positions in the formation of arterial hypertension of different etiology.

Tissue blood flow in brain, liver, renal cortex, and renal medulla in experimental hemorrhagic shock.

Cerebral, hepatic, renal cortical, and medullary tissue blood flows of the dog during hemorrhagic shock were measured continuously using the thermoelectrical method. The effects of blood replacement, adrenergic alpha-stimulator and -blockade and hydrocortisone on the tissue blood flows were studied. After hemorrhage, cerebral blood flow was well maintained while renal cortical blood flow was poorly maintained. Following retransfusion, the blood flow returned rapidly to the brain and slowly to the renal cortex. Norepinephrine, phentolamine, and hydrocortisone were not effective in maintaining the organ blood flows in shock. However, when norepinephrine was given systemically and phentolamine administered to the renal artery simultaneously during shock, both cerebral and renal flows were well maintained. After the blood replacement and administration of alpha-blockade or hydrocortisone, all the measured blood flows returned to normal levels.

Radiology of the urinary tract: some physiological considerations. Annual oration in memory of John S. Bouslog, M.D., 1890-1973.

This paper reviews some of the fundamental technical and diagnostic problems in clinical uroradiology, such as (a) the reason for the obstructive nephrogram; (b) why high-dose urography gives better studies than low-dose; (c) why the Trueta phenomenon has not been demonstrated in man; (d) the case for an intrarenal arterial collateral pathway via the pericalyceal network (these vessels can be demonstrated in man and must not be misinterpreted as tumor vessels or vascular malformations). One of the most baffling problems sometimes occurs with the sudden partial block of a single segmental vessel: the kidney ceases to excrete urine and eventually becomes atrophic even though some excretory function returns. To date, there is no satisfactory explanation for this course of events.

Intrarenal distribution of blood flow and renin in chronic congestive heart failure.

Intrarenal distribution of blood flow was measured by the 133xenon washout curve in 33 patients with heart disease. Plasma renin activity and sodium concentration were also measured on the day when the xenon study was performed. The patients were divided into three groups according to cardiac index: Group I whose cardiac index showed higher than 3.50 1/min/M2, BSA, group II whose index ranged from 2.50 to 3.50, and group III who had lower than 2.50. Total renal blood flow was significantly decreased in group II (p less than 0.001), as compared with normal controls. The percents of the total renal blood flow supplied to component I decreased significantly in group I, II (p less than 0.05) and group III (p less than 0.01). The flow rate in component I decreased significantly only in group II (p less than 0.05) and group III (p less than 0.01). There was a significant increase in the percent distribution of component II in group II (p less than 0.05) and in group III (p less than 0.01). The flow rate of component II showed a slight increase in group I and III. The study of autoradiographs done in dogs with heart failure demonstrated that component I corresponded to a cortical area having a relatively faster flow rate, whereas component II corresponded to the cortical area which was perfused more slowly. Accordingly, component III indicated outer medulla. There was no apparent relation between intrarenal distribution of blood flow and plasma renin activity although the latter tended to be elevated in patients treated with diuretics. In view of the data available it was concluded that outer cortical as well as outer medullary blood flow are decreased in chronic congestive heart failure and that there is no apparent correlation between outer cortical flow and plasma renin activity.