Proteinuria precedes cerebral edema in stroke-prone rats: a magnetic resonance imaging study

BACKGROUND AND PURPOSE

Stroke-prone spontaneously hypertensive rats (SHRSP) subjected to high sodium intake develop severe hypertension, cerebral edema, and proteinuria, culminating in organ damage and early death. MRI, which can be applied serially, provides the unique opportunity to study temporal and quantitative relations between these changes and whether diminution of sodium intake can attenuate established cerebral edema.

METHODS

SHRSP were subjected to 1% NaCl in drinking water. Cerebral MRI, proteinuria and systolic blood pressure (SBP) were measured serially. After detection of cerebral edema (T2-weighted MRI), 6 rats were killed for histology, to confirm the diagnosis of cerebral edema. The others were followed up for 7 more days while salt loading was continued (n = 10, group 1) or after sodium intake was normalized (n = 7, group 2).

RESULTS

SHRSP invariably developed cerebral edema in 30 days (range, 8 to 54 days). At this point neurological signs were absent in 16 of 23 rats. SBP rose until 1 week before detection of cerebral edema, and then stabilized at approximately 265 mm Hg. Proteinuria invariably preceded cerebral edema, with a concentration exceeding 40 mg/d predicting development of cerebral edema in 9 days (range, 3 to 15 days). There was linear correlation (R=.62, P<.0001) between proteinuria and cerebral edema (pixels with an intensity above a defined threshold). Rats in group 1 showed an increase in cerebral edema (from 5.8+/-1.1% to 12.5+/-2.8%; P<.05), and proteinuria remained high (from 305+/-44 to 338+/-29 mg/d); and 2 died spontaneously. Rats in group 2 showed no significant change in edema (from 4.9+/-0.5% to 6.9+/-1.3%) but a marked fall in proteinuria (from 294+/-24 to 119+/-10 mg/d; P<.05), both significantly different from group 1 (P<.05); all survived. SBP remained unaltered in both groups.

CONCLUSIONS

Our data establish MRI as a sensitive method for detection of cerebral edema, often prior to neurological signs, in SHRSP. Proteinuria predicts cerebral edema, and these two variables, both obtained noninvasively, are quantitatively related. Moreover, in SHRSP normalizing sodium intake after salt loading attenuates development of cerebral edema and reduces proteinuria.

Progressive vascular damage in hypertension is associated with increased levels of circulating P-selectin

OBJECTIVE

To assess whether increased shedding of adhesion molecules in plasma provides an index for endothelial damage in hypertension.

DESIGN AND METHODS

Three groups of hypertensive patients with increasing severity of vascular damage were studied: 20 essential hypertensives, 21 atherosclerotic, renovascular hypertensives and four malignant hypertensives. Twenty healthy subjects were included as a control group. Levels of P-selectin, E-selectin, intracellular adhesion molecule 1, vascular cell adhesion molecule and von Willebrand factor in venous blood were measured, using sandwich-type enzyme-linked immunosorbent assay.

RESULTS

For essential hypertensives a trend for increased P-selectin and E-selectin values compared with those in controls was observed (159+/-44 versus 132+/-40 ng/ml, P = 0.062 and 40+/-13 versus 34+/-17 ng/ml, P = 0.055, respectively). P-selectin (210+/-84 ng/ml, P = 0.0021) and E-selectin (42+/-12 ng/ml, P = 0.012) levels in renovascular hypertensives were significantly higher than those in healthy controls. There were no significant increases in circulating levels of intracellular adhesion molecule 1, vascular cell adhesion molecule and von Willebrand factor either in essential hypertensives or in renovascular hypertensives. Marked increases in circulating levels of adhesion molecules and von Willebrand factor relative to those in controls were observed in malignant hypertensives (P-selectin 634+/-332 versus 132+/-40 ng/ml, P = 0.0004; vascular cell adhesion molecule 968+/-187 versus 493+/-139 ng/ml, P = 0.0004; and von Willebrand factor 259+/-75 versus 130+/-72 U/dl, P = 0.016).

CONCLUSIONS

Progression of vascular damage in essential, renovascular and malignant hypertension is associated with a rise in circulating levels of P-selectins and, to a lesser extent, E-selectins, whereas levels of intracellular adhesion molecule 1, vascular cell adhesion molecule and von Willebrand factor are elevated only in diseases associated with acute severe vascular damage, including malignant hypertension. Our data suggest that selectins may be useful as indicators of vascular damage in hypertension.

Hyperlipidemia is secondary to proteinuria and is completely normalized by angiotensin-converting enzyme inhibition in hypertensive fawn-hooded rats

Two substrains of the fawn-hooded (FH) rat have been developed, one of which develops progressive hypertension and proteinuria, the FHH, and one which shows little increase in blood pressure and no renal damage, the FHL. Other hypertensive rodent models show primary metabolic disturbances before the development of renal damage, notably hypertriglyceridemia, which may also contribute to progression of renal disease. In this study we evaluated whether hyperlipidemia is a primary disturbance in FHH, or only occurs secondary to proteinuria. Lipid levels were determined before and after development of proteinuria, and compared to those found in age-matched FHL. We also determined whether reducing proteinuria with lisinopril would normalize lipid levels in aging FHH. At 4 weeks of age, proteinuria was very low (2-3 mg/day) in both FHH and FHL. While proteinuria increased steadily in aging FHH, reaching 350 +/- 62 mg/day at 40 weeks, much less increase was observed in FHL over the same period (32 +/- 5 mg/day at 40 weeks). Blood pressure was markedly higher in adult FHH than in FHL (158 +/- 2 vs. 129 +/- 2 mm Hg, p < 0.01). In 4-week-old FHL and FHH, plasma cholesterol levels were similar. Subsequently, cholesterol increased in FHH, reaching 3.4 +/- 0.9 mmol/l at 40 weeks, whereas cholesterol was barely affected by aging in FHL (2.1 +/- 0.2 mmol/l at 40 weeks). At 4 weeks, triglyceride levels were lowest in FHH. Subsequently, triglycerides increased in FHH, reaching 3.5 +/- 1.5 mmol/l at 40 weeks, as compared to 1.3 +/- 0.2 mmol/l in FHL. Besides a transient increase in triglyerides in lisinopril-treated FHH at 11 weeks, increments in blood pressure, proteinuria, cholesterol, triglycerides and apolipoproteins A-I, B and E aging FHH were effectively prevented by lisinopril. These data strongly suggest that there is no primary difference in lipid metabolism between FHH and FHL and that changes in plasma lipids in FHH as compared to FHL are all secondary to proteinuria.

Estrogen replacement during hypoalbuminemia may enhance atherosclerotic risk

Estrogen replacement therapy is considered antiatherosclerotic because it reduces LDL cholesterol and fibrinogen and increases HDL cholesterol concentrations. However, exogenous estrogen is also known to increase hepatic triglyceride production. Hyperlipidemia in the nephrotic syndrome is probably due to increased lipoprotein secretion into plasma and decreased clearance of lipoprotein cholesterol and triglycerides. Previously, lipid-lowering effects of ovariectomy in analbuminemic rats were observed, suggesting that in the presence of hypoalbuminemia, estrogen replacement may have adverse effects on the lipid profile. To test this hypothesis, ovariectomized control rats and rats with Adriamycin-induced nephrotic syndrome were treated with estradiol. In ovariectomized controls, estradiol reduced plasma LDL cholesterol, apolipoprotein B, and fibrinogen and increased apolipoprotein A-I and triglycerides. Nephrotic rats were characterized by a marked decrease in plasma colloid osmotic pressure, hyperfibrinogenemia, hyperlipidemia, and stimulated hepatic fatty acid synthesis. The beneficial effects of estradiol on LDL cholesterol, apolipoprotein B, and fibrinogen found in ovariectomized controls were not present in estradiol-treated nephrotic rats. This suggests that in hypoalbuminemia, downregulation of the LDL receptor overrides putative estradiol-induced increases in LDL receptor activity. Moreover, estrogen replacement in the nephrotic syndrome doubled fatty acid synthesis and triglyceride secretion, and markedly exacerbated hypertriglyceridemia, suggesting saturation of triglyceride clearance. Thus, severe hypoalbuminemia in rats induces an atherosclerotic metabolic response that is aggravated by estrogen replacement. These findings suggest that estrogen replacement in hypoalbuminemic subjects could be contra-indicated.

Pressure or flow recordings for the surveillance of hemodialysis grafts

Venous pressures (VP) measured by the dialysis machine are widely used for access surveillance and have significantly improved outcomes. VP reflect the resistance in the venous outflow tract, which will rise in the presence of stenosis. Low graft flow caused by high graft resistance predicts thrombosis. In this study we investigated whether high VP coincides with low graft flow (measured by ultrasound dilution technique). Of 70 forearm bridge grafts in 42 chronic hemodialysis patients, 31 had an angiographically proven outflow stenosis. VP at 200 ml/min blood flow (VP200), total graft resistance and venous outflow resistance were higher whereas graft flow was lower in patients with venous outflow tract stenosis as compared to patients without stenosis. Diagnostic power of the tests for identifying patients with venous stenosis showed no important differences. However, arterial inflow resistance, which is not reflected in VP measurements, represented a substantial and, more importantly, a highly variable percentage of total graft resistance. As a result graft flow showed no correlation with VP measurements. In conclusion, although patients with venous outflow stenosis may be identified accurately using venous pressure assessments, graft flow measurements seem to be more suitable for selecting patients at risk for thrombosis.

Hypoalbuminemia causes high blood viscosity by increasing red cell lysophosphatidylcholine

Albumin deficiency is accompanied by a reduction in red cell deformability and blood hyperviscosity. Albumin deficiency increases plasma fibrinogen and triglyceride levels and may alter red cell membrane lipid composition. These options, which could all contribute to reduced red cell deformability (RCD) and hyperviscosity, were studied in the Nagase analbuminemic rat (NAR), a mutant Sprague Dawley rat (CON), characterized by normal total protein levels, with an absolute deficiency of albumin, but elevated levels of non-albumin proteins and hyperlipidemia. Plasma protein-binding of the polar phopholipid lysophosphatidylcholine (LPC) was markedly decreased. LPC comprised only 26 +/- 1% of total plasma phospholipids as compared to 42 +/- 2% in CON. NAR red cells in CON plasma had a viscosity that was similar to CON red cells in CON plasma. Conversely, CON red cells in NAR plasma show an increased viscosity as compared to CON red cells in CON plasma. The maximum deformation index of both NAR and CON red cells was markedly decreased in NAR plasma as compared to either NAR or CON cells in CON plasma (0.04 +/- 0.03 and 0.02 +/- 0.02 vs. 0.22 +/- 0.06 and 0.15 +/- 0.04, respectively; P < 0.05). Thus, plasma composition causes hyperviscosity and reduced RCD in NAR. Fibrinogen is not responsible since red cells in serum and red cells in plasma had a similar viscosity and differences in viscosity and RCD between NAR and CON were maintained. Plasma triglycerides are also not responsible since the viscosity of red cells in serum with a 50% reduction in triglycerides was not reduced. LPC levels in red cells were increased in NAR (8.7 +/- 0.2 vs. 5.5 +/- 0.3% of total phospholipids; P < 0.01). Adding albumin to NAR blood dose-dependently decreased whole blood viscosity, despite marked increases in plasma viscosity, and increased RCD of NAR cells (from 0.04 +/- 0.03 to 0.21 +/- 0.01; P < 0.05). There was also some effect on CON RCD of similar albumin addition to CON blood (from 0.15 +/- 0.04 to 0.29 +/- 0.03; P < 0.05). Adding albumin to NAR blood reduced red cell LPC content and increased plasma LPC content in a dose-dependent fashion, whereas there were only slight effects of adding albumin to CON blood. There was a reciprocal relation between red cell LPC and the other polar phospholipids in the red cell membrane, probably indicating exchange. The maximum deformability index of either NAR or CON cells was not affected much by adding LPC to CON plasma (NAR, from 0.22 +/- 0.06 to 0.18 +/- 0.10; CON, from 0.15 +/- 0.04 to 0.12 +/- 0.05; NS), whereas adding LPC to NAR plasma caused the red cells to become rigid. Adding LPC to CON red cells in NAR plasma caused a much stronger increase in relative LPC content (from 6.6 +/- 0.7 to 10.9 +/- 0.9%; P < 0.05) than adding LPC to CON red cells in CON plasma (from 5.6 +/- 0.4 to 6.4 +/- 0.8%; NS). Thus, in the absence of albumin, LPC in red blood cells is increased. As a consequence of the latter, RCD is decreased and whole blood viscosity increased. Alterations in red cell phospholipids are far more important than increases in plasma fibrinogen or triglycerides in determining hyperviscosity of blood and reduced RCD in NAR.

Pulmonary embolism after thrombolysis of hemodialysis grafts

The aim of this study was to determine the incidence of pulmonary embolization occurring after mechanical or pharmacomechanical percutaneous intravascular thrombolysis in 23 patients with occluded hemodialysis grafts. In all patients, pulmonary perfusion scintigraphy was performed before and immediately after thrombolysis. In eight (35%) of the patients, there was evidence of pulmonary embolism resulting from the interventional procedure; however, in only one was there clinical symptoms. It is concluded that there is substantial risk of pulmonary embolism in patients undergoing percutaneous intravascular thrombolysis for an occluded hemodialysis graft.

Endothelin-1-induced vasopressor responses in essential hypertension

The potential role of endothelin-1 (ET-1) in essential hypertension in humans is still subject to debate. We recently reported strong sodium retention and renal vasoconstriction during pathophysiological increments in plasma ET-1. Apart from this vasoconstrictor action, ET-1 also has mitogenic properties that play a role in the pathophysiology of hypertension. On the other hand, some data refute an important role of ET-1 in hypertension. We therefore investigated in nine subjects with essential hypertension the constrictor actions of ET-1 by challenging these subjects with a systemic infusion of ET-1 (0.5 ng/kg per minute for 60 minutes, then 1.0 ng/kg per minute for 60 minutes, and finally 2.0 ng/kg per minute for 60 minutes). Furthermore, we studied whether these effects of ET-1 could be modulated by oral use of the angiotensin-converting enzyme inhibitor enalapril (20 mg BID) or the calcium channel blocker nifedipine (60 mg OD). ET-1 infusion increased plasma ET-1 levels from 2.5+/-0.4 to 11.6+/-1.0 pmol/L (P<.05). Blood pressure rose by approximately 10 mm Hg (P<.05). Cardiac index decreased by 21+/-22%, whereas calculated systemic vascular resistance increased by 27+/-6% (P<.05). Renal blood flow decreased from 1051+/-94 to 707+/-60 mL/min at the end of the ET-1 infusion (P<.05), and calculated renal vascular resistance increased from 118+/-19 to 189+/-19 mm Hg x min/L (P<.05). Sodium excretion decreased from 227+/-39 to 111+/-15 micromol/min (P<.05). Both enalapril and nifedipine treatment prevented the systemic effects of ET-1 infusion in these subjects. However, during enalapril treatment, despite renal predilatation, ET-1 reduced renal blood flow (from 1119+/-132 to 701+/-75 mL/min, P<.05) and increased renal vascular resistance (from 111+/-16 to 187+/-28 mm Hg x min/L, P<.05) to the same levels as during ET-1 infusion alone. Nifedipine pretreatment attenuated the ET-1-induced fall in renal blood flow (from 1088+/-93 to 907+/-68 mL/min) and increase in renal vascular resistance (from 105+/-9 to 133+/-10 mm Hg x min/L). Although neither drug modulated the antinatriuretic effect of ET-1, nifedipine increased basal sodium excretion (P<.05), which compensated for the decrease during ET-1 infusion. In conclusion, essential hypertensive subjects are sensitive to the vasoconstrictor effects of ET-1. Both enalapril and nifedipine can prevent the systemic effects of ET-1, but nifedipine seems more effective in attenuating the renal constrictor effects of ET-1.

Causes of edema in the intensive care unit

Patients in emergencies necessitating treatment in the intensive care unit (ICU) often develop generalized gross edema. The usual scenario is that in the emergency situation characterized by hypotension and (impending) organ failure, large amounts of fluids are administered that subsequently cannot be excreted adequately, even if the emergency situation subsides to a more stable condition. Three main factors underlie the inadequate restoration of volume balance: (1) impaired edema mobilization, due to the negative influence on lymphatic flow of reduced muscle activity and increased central venous pressure by mechanical ventilation; (2) secondary renal sodium retention by circulatory impairment and hypotension caused by mechanical ventilation and by the cardiodepressant and vasodilatory effects of (endo-)toxemia; and (3) primary renal sodium retention by renal vasoconstriction and filtration impediment, due to a complex of systemic and intrarenal vasomodulator activation and intrarenal endothelitis, or acute renal failure. Edema itself, as far as impeding organ function and necessitating mechanical ventilation, may further perpetuate this difficult to handle and vicious circle.

Cold stress provokes sympathoinhibitory presyncope in healthy subjects and hemodialysis patients with low cardiac output

BACKGROUND

Sudden hypotension in progressive hypovolemia or during hemodialysis is attributed to sudden inhibition of sympathetic activity. Critical ventricular underfilling seems responsible for this paradox, but it is unknown why the transition from sympathoactivation accompanying hypovolemia to sympathoinhibition is so abrupt. We studied whether brief fluctuation of sympathetic activity induced by cold pressor test (CPT) evokes sympathoinhibition if applied during low cardiac output.

METHODS AND RESULTS

Fourteen healthy subjects underwent CPT, lower-body negative pressure (LBNP; -45 mm Hg for 60 minutes), or the combination thereof. CPT alone caused vasoconstriction and increased muscle sympathetic nerve activity, followed by uneventful relaxation. When applied during reduced cardiac output, tachycardia, and vasoconstriction induced by prior LBNP for 6 minutes, CPT again caused vasoconstriction, now followed by acute hypotension in 10 subjects, and was associated with vasorelaxation, relative bradycardia, and fall in muscle sympathetic nerve activity. Eight subjects also experienced acute LBNP-induced hypotension in the absence of CPT, but not until 17 +/- 6 minutes of LBNP. We also performed CPT before and in the final phase of hemodialysis in 8 patients. Before dialysis, the patients tolerated CPT uneventfully, but during hemodialysis, CPT provoked acute hypotension in 5 cases, showing similar withdrawal of vasoconstriction.

CONCLUSIONS

This is the first study showing that brief cold stress, tolerated well in normal circulatory conditions, can provoke sudden sympathoinhibition and hypotension when applied during decreased cardiac output induced by LBNP or hemodialysis. We suggest that during conditions of a decreased cardiac output, subtle sympathetic relaxation such as follows cold stress triggers self-enhancing relaxation that cannot be controlled.

Nifedipine attenuates systemic and renal vasoconstriction during nitric oxide inhibition in humans

Clinical states associated with nitric oxide deficiency are often accompanied by vasoconstriction. We studied the effects of prolonged infusion of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) on systemic and renal hemodynamics in humans and the reversibility of the established vasoconstriction by calcium channel blockade with nifedipine. Seven healthy men underwent three 7-hour clearance studies. During one study, L-NMMA (3 mg/kg priming dose plus 3 mg.kg-1.h-1) was infused during hours 2 through 5, and during another study, nifedipine (0.015 mg/kg priming dose plus 0.015 mg.kg-1.h-1) was coinfused during hours 4 and 5. A third study served as time control. L-NMMA elicited reproducible systemic and renal vasoconstriction that was stable during the 4 hours of infusion. Systemic vascular resistance index, calculated from bioimpedance-derived cardiac index, increased from 22 +/- 1 to 29 +/- 2 mm Hg.min.m2.L-1 (P < .05). Mean arterial pressure rose by 4 +/- 1 mm Hg (P < .05), and heart rate, stroke index, and cardiac index decreased. Renal blood flow, calculated from renal plasma flow, decreased from 1182 +/- 101 to 785 +/- 53 mL/min, and renal vascular resistance increased from 73 +/- 5 to 115 +/- 6 mm Hg.min.L-1 (P < .05). Glomerular filtration rate decreased from 114 +/- 6 to 104 +/- 6 mL/min (P < .05), and filtration fraction increased. Sodium excretion fell from 89 +/- 9 to 32 +/- 7 mumol/min (P < .05). Nifedipine completely reversed systemic vasoconstriction. Nifedipine caused partial restoration of renal vascular resistance and complete normalization of glomerular filtration rate and sodium excretion but left the elevated filtration fraction unaltered. We conclude that sustained nitric oxide deficiency in humans is accompanied by strong systemic and renal vasoconstriction, decreased glomerular filtration rate, and sodium retention. Nifedipine can reverse most of these effects, suggesting a role for calcium channel blockade in pathological states of impaired nitric oxide activity.

Cyclosporin A increases nitric oxide activity in vivo

The use of cyclosporine is complicated by its vaso-constrictive actions. In vitro cyclosporine has been associated with both decreased endothelium-dependent vasodilatation and increased nitric oxide activity. We studied the interaction between cyclosporine and endothelium-derived nitric oxide in seven healthy volunteers. Using venous-occlusion plethysmography, we measured forearm blood flow during intra-arterial infusion of serotonin, which in the concentrations used is a selective agonist of endothelial nitric oxide release, or NG-monomethyl-L-arginine, a specific inhibitor of nitric oxide synthase, during coinfusion of saline or cyclosporine (75 micrograms/min), respectively. During coinfusion of cyclosporine, forearm blood flow increased on maximal serotonin infusion from 2.9 (SE, 0.2) to 8.1 (0.9) mL/100 mL per minute in forearm tissue, which was significantly higher than the increase during saline coinfusion (3.0[0.3] to 6.0 [0.5]; P < .05). Cyclosporine infusion during a "free" nitric oxide system had no effect on basal forearm blood flow, but in significantly decreased forearm blood flow (21.7[2.8]%; P < .05) during fixed nitric oxide activity. These data suggest that acute administration of cyclosporine enhances both basal and receptor-stimulated nitric oxide activity. The mechanism is not clear but may include cyclosporine-induced shear stress as well as direct effects of cyclosporine. The latter was supported by our observation that gene expression of the enzyme nitric oxide synthase III was enhanced by approximately 50% after coincubation with cyclosporine. In conclusion, the present observation demonstrates that nitric oxide constitutes an important regulating mechanism that protects against cyclosporine-associated vasoconstriction in vivo.

Angiotensin-converting enzyme inhibition in the prevention and treatment of chronic renal damage in the hypertensive fawn-hooded rat

The spontaneously hypertensive fawn-hooded rat (FHH) develops accelerated albuminuria and focal glomerular sclerosis (FGS), leading to ESRD and shortening of lifespan. The FHH is characterized by moderate systemic hypertension, a relatively low afferent to efferent arteriolar resistance ratio, and glomerular hypertension. The FHH study presented here was designed to examine the efficacy of early-onset, late-onset, or early-temporary angiotensin I-converting enzyme inhibition (ACE-i) in ameliorating long-term hypertension and FGS, and improving survival, as well as to relate its protective efficacy to preexistent FGS and to reduction of glomerular pressure (PGC) Untreated rats developed hypertension and high PGC, and all (N = 22) except one died of ESRD within the 72-wk follow-up period. Early-onset (at 7 wk of age) ACE-i prevented development of systemic and glomerular hypertension, and it largely prevented proteinuria and FGS; all rats survived throughout the follow-up period. Rats treated with late-onset (22 wk) ACE-i were hypertensive and proteinuric at the start of ACE-i, and they showed beginning FGS. ACE-i corrected the hypertension, albuminuria, and PGC but could not fully prevent some hypertension, albuminuria, and FGS at the later stage. Early-temporary (7 to 22 wk) ACE-i adequately controlled blood pressure and development of FGS during therapy, but after withdrawal of ACE-i, systemic and glomerular hypertension developed as in untreated animals. This regimen postponed but did not control FGS development and early mortality. The results of this study indicate that: (1) early-onset ACE-i very effectively protects against development of renal damage in the FHH; (2) this protection is associated with normalization of the elevated glomerular capillary pressure; (3) ACE-i cannot completely prevent further development of previously established FGS, despite lowering glomerular capillary pressure; (4) early-temporary ACE-i has no long-term controlling effect on arterial and glomerular pressure, and it cannot control development of FGS.

Endothelial function and the kidney. An emerging target for cardiovascular therapy

Endothelial dysfunction is emerging as an important factor in the early development of acute and chronic renal disease. Drugs aimed specifically at rectifying this aberration are being developed, although other established agents such as calcium antagonists, angiotensin converting enzyme (ACE) inhibitors and HMG CoA reductase inhibitors also have beneficial effects in this setting. Calcium antagonists are particularly effective at ameliorating acute renal ischaemia associated with endothelial dysfunction. Combination therapy with a calcium antagonist and an ACE inhibitor might optimise the beneficial effects of calcium channel blockade on the sequelae of endothelial dysfunction in chronic renal failure.

Effects of reduced renal perfusion pressure and acute volume expansion on proximal tubule and whole kidney angiotensin II content in the rat

In previous studies high luminal concentrations of angiotensin II (Ang II) were found in rat proximal tubules. The physiological role of intraluminal Ang II remains to be established. In the present study, we investigated whether the luminal angiotensin II concentration in the proximal tubules ([Ang II]prox) can be modulated. Micropuncture studies were performed in control rats (C, N = 8) and rats subjected to acute volume expansion (VE, N = 8) or reduced renal perfusion pressure (RRP, N = 7). Changes in [Ang II]prox were compared to changes in whole kidney Ang II content ([ANG II]kidney) and the plasma concentration ([Ang II] plasma). In C rats, [Ang II]prox was 460 +/- 48 pmol/liter (10 to 20 times lower than hitherto reported), while [Ang II]kidney and [Ang II]plasma were 369 +/- 81 pmol/kg and 90 +/- 29 pmol/liter, respectively. In agreement with previous data, VE failed to suppress [Ang II]prox (674 +/- 132 pmol/liter), while at the same time [Ang II]kidney (42 +/- 10 pmol/kg) and [Ang II]plasma (12 +/- 3 pmol/liter) were markedly suppressed. This points to dissociated regulation of [Ang II] in the renal luminal compartment on the one hand and the extraluminal renal and systemic plasma compartments on the other hand. During RRP, [Ang II]prox increased significantly to 1675 +/- 465 pmol/liter. No dissociation between the three compartments was observed in this situation, as [Ang II]kidney (969 +/- 85 pmol/kg) and [Ang II]plasma (245 +/- 72 pmol/liter) increased in parallel. In summary, we confirm that Ang II is present in proximal tubules of rat kidneys at concentrations which exceed those in plasma. Its concentration could be modulated (approximately 3.5 increase) by reduction of renal perfusion pressure but not by acute volume expansion. In the latter condition, we observed a clear dissociation from Ang II generation in the extraluminal renal compartment, as whole kidney Ang II content was markedly suppressed.

Role of endothelin receptor subtypes in the systemic and renal responses to endothelin-1 in humans

The authors recently reported that infusion of endothelin-1 in humans to obtain pathophysiological plasma levels causes profound renal vasoconstriction and sodium retention. The relative roles of the ETA- and ETB-receptor subtypes in these effects in humans is unknown. Such information is essential in view of the recent introduction of endothelin-receptor blockers in clinical medicine. The study presented here was designed to define the role of the ETA- and ETB-receptor subtypes in the renal actions of endothelin-1 in humans. Systemic infusion of endothelin-1, a nonselective receptor agonist, was compared with infusion of equimolar dosages of the ETB-selective agonist endothelin-3 in healthy volunteers. Endothelin-1 infusion was associated with an approximate 2.5-fold increase in plasma levels of endothelin-1. This was accompanied by an increase in blood pressure by approximately 6 mm Hg (P < 0.05). During endothelin-1 infusion, RPF decreased from 642 +/- 42 to 480 +/- 36 mL/min (P < 0.05) and GFR from 121 +/- 4 to 109 +/- 7 mL/min (P < 0.05). Sodium excretion rate decreased during endothelin-1 infusion, from a baseline value of 182 +/- 33 to 84 +/- 28 mumol/min at the end of the endothelin-1 infusion. Endothelin-3 infusion also resulted in a approximate 2.5-fold increase of plasma levels of endothelin-3. However, in contrast to the endothelin-1 infusion, endothelin-3 had no effect on blood pressure, renal hemodynamics, and electrolyte excretion. These results suggest that the systemic and renal vasoconstrictor effects of endothelin-1 in humans are predominantly mediated by the ETA receptors.

Renal sodium handling in children with nephrotic relapse: relation to hypovolaemic symptoms

We studied renal sodium handling during water diuresis in children in the early phase of relapse of minimal lesion nephrotic syndrome (MLNS). Findings were related to presence or absence of symptoms suggestive of hypovolaemia, and to neurohumoral factors, and were compared to results of similar studies in the same children in remission. Nine children (aged 7.8 +/- 3.1 years) presented with hypovolaemic symptoms, and 10 (7.4 +/- 4.3 years) without such symptoms. Both groups displayed severe proteinuria, hypoproteinaemia and oedema. Symptomatic patients showed tendency for a low glomerular filtration rate, and significantly impaired urine dilution, decreased fractional sodium and lithium excretions, and elevated diluting segment reabsorption [CH2O/(CH2O + CNa)] and sodium/potassium exchange [UK/(UK + UNa)]. In the non-symptomatic patients these parameters were normal. Plasma renin and aldosterone were significantly elevated in the symptomatic children, and strongly correlated with all parameters of tubule sodium reabsorption. Weaker associations were found for plasma noradrenaline and atrial natriuretic peptide. Vasopressin was also relatively high in the symptomatic group, but showed no association with impaired urine dilution. The diffusely stimulated tubular sodium reabsorption in the symptomatic children, in association with stimulated neurohumoral factors, indicates that secondary sodium retention contributes to oedema formation in at least a subset of children developing a nephrotic relapse. This may be limited to the early stage, and be more pronounced in some patients than in others. The tubular defect responsible for maintenance of oedema in stabilized MLNS remains unclear.

Ovariectomy decreases plasma triglyceride levels and both prevents and alleviates glomerular disease in uninephrectomized female analbuminemic rats

Female Nagase analbuminemic rats (NAR) are profoundly hypertriglyceridemic and develop proteinuria and glomerulosclerosis when aging and after uninephrectomy (UNX). Ovariectomy (OVX) markedly decreases plasma triglyceride levels in this species. This study evaluated whether decreasing triglyceride levels by OVX could prevent renal disease or alleviate its progression in UNX female NAR. Female NAR underwent OVX at 0, 12, 24, or 36 wk after UNX. In the absence of OVX, the animals developed progressive proteinuria from 18 wk after UNX and showed extensive glomerular sclerosis, lipid deposition, and hypertrophy at euthanasia (49 wk after UNX). These changes were prevented by OVX carried out at 0 or 12 wk, and attenuated by OVX at 24 wk after UNX. If performed at 36 wk after UNX, OVX had no effect on glomerulosclerosis, although it reduced proteinuria. In 95% (20 of 21) of the rats with proteinuria over 10 mg/day, proteinuria decreased in the first 6 wk after OVX. The percentage decrease in proteinuria correlated inversely with the glomerulosclerosis score at euthanasia (r = -0.58, P < 0.01). OVX had no effect on hyperfiltration and hyperperfusion in the UNX rats. OVX consistently reduced plasma triglyceride levels in rats both with and without proteinuria, and it also reduced plasma cholesterol, but only in conjunction with reduction in proteinuria. It was concluded that OVX in UNX female NAR prevents glomerulosclerosis if performed before proteinuria and attenuates further development of established renal disease if performed in a timely manner. This study's data suggest that in UNX female NAR, the lowering of plasma triglyceride levels plays a central role in the renoprotective action of OVX.

Access flow measurements in hemodialysis patients: in vivo validation of an ultrasound dilution technique

In this study, access flow in hemodialysis patients with bridge grafts was measured by a newly developed device. The technique is based on the measurement of changes in the ultrasound characteristics of blood. These changes were initiated by an injection of isotonic saline and measured in the tubes of the extra-corporeal circuit. The access flow rate (mean +/- standard variation) was 880 +/- 440 mL/min (range, 166 to 1740) (N = 46). The mean coefficient of variation was 13.4 +/- 6.8% (median, 13.0%; range 3.5 to 29.4%). Measurements correlated well (r = 0.91, N = 22, P < 0.001) with flow rates determined by magnetic resonance angiography and by a technique based on intra-access flow-pressure curves (r = 0.84, N = 14, P < 0.001). In conclusion, access flow can be measured easily, noninvasively, and reliably by the ultrasound dilution device.