Tubular Na Reabsorption Research Articles

Early Interleukin-6 Mediated Activation of SGK1 is Primarily via Variant 6

Hypertension is associated with inflammation, including elevated interleukin-6 (IL-6) levels. IL-6 is an inflammatory cytokine, which we have previously shown to activate the mineralocorticoid receptor (MR) and the downstream sodium (Na) transporters- Na-chloride cotransporter (NCC) and the epithelial Na channel (ENaC). However, how IL-6 activates the MR is still unknown. IL-6 is also linked to Serum and Glucocorticoid-regulated Kinase 1 (SGK1), which is a downstream effector of the MR. SGK1 regulates both NCC and ENaC, increasing activity and tubular reabsorption of Na. This increased Na reabsorption favors water retention, thus increasing blood pressure. Previously, IL-6 has also been linked with SGK1 activation. We hypothesize that IL-6 increases SGK1 mRNA and protein expression in renal epithelial cells. To test this, we used in vitro renal epithelial cell models of both the late distal convoluted tubule (DCT2) and inner medullary collecting duct (IMCD), mDCT15 and IMCD3, respectively. Cells were treated with an IL-6 time-course (100ng/ml for 1, 3 and 6 hours). There are 6 known transcriptional variants for SGK1. We designed variant-specific PCR primers and, a pilot study based on regular PCR concluded that expression levels of only variants 5 and 6 (V5, V6) are significant. Using Real Time quantitative RT-PCR, we were then able to quantify transcript levels of both SGK1 V5 and V6 variants. With IL-6 treatment, we observed a 160%-211% increase at early time points (30mins-1hr) in SKG1 V6 and a lesser response (26%-88% increase) with V5 as compared to vehicle treated mDCT15 cells. Since SGK1 has been observed in the membrane fraction and in the cytoplasm, protein extracts from cells were fractionated (mPER kit) to assess membrane and cytosolic SGK1 protein levels using immunoblots. Densitometric analysis of immunoblots demonstrated a 5.5- and 3.1-fold increase in SGK1 protein expression at 1hr in mDCT15 and IMCD3 cells, respectively. These data suggest that IL-6 induces increases in SGK1 transcription and translation. Interestingly, we also found that majority of SGK1 was in the membrane fraction and the level was consistent. Together, these data suggest that SGK1 V6 may be responsible for the increased sodium reabsorption in response to IL-6 stimulation in renal epithelial cells. NIH funding This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hypoxia-inducible factor-1α activation improves renal oxygenation and mitochondrial function in early chronic kidney disease.

The pathophysiology of chronic kidney disease (CKD) is driven by alterations in surviving nephrons to sustain renal function with ongoing nephron loss. Oxygen supply-demand mismatch, due to hemodynamic adaptations, with resultant hypoxia, plays an important role in the pathophysiology in early CKD. We sought to investigate the underlying mechanisms of this mismatch. We utilized the subtotal nephrectomy (STN) model of CKD to investigate the alterations in renal oxygenation linked to sodium (Na) transport and mitochondrial function in the surviving nephrons. Oxygen delivery was significantly reduced in STN kidneys because of lower renal blood flow. Fractional oxygen extraction was significantly higher in STN. Tubular Na reabsorption was significantly lower per mole of oxygen consumed in STN. We hypothesized that decreased mitochondrial bioenergetic capacity may account for this and uncovered significant mitochondrial dysfunction in the early STN kidney: higher oxidative metabolism without an attendant increase in ATP levels, elevated superoxide levels, and alterations in mitochondrial morphology. We further investigated the effect of activation of hypoxia-inducible factor-1α (HIF-1α), a master regulator of cellular hypoxia response. We observed significant improvement in renal blood flow, glomerular filtration rate, and tubular Na reabsorption per mole of oxygen consumed with HIF-1α activation. Importantly, HIF-1α activation significantly lowered mitochondrial oxygen consumption and superoxide production and increased mitochondrial volume density. In conclusion, we report significant impairment of renal oxygenation and mitochondrial function at the early stages of CKD and demonstrate the beneficial role of HIF-1α activation on renal function and metabolism.

Addition of hydrochlorothiazide to angiotensin receptor blocker therapy can achieve a lower sodium balance with no acceleration of intrarenal renin angiotensin system in patients with chronic kidney disease.

Objective:Angiotensin receptor blockers (ARBs) produce a lower sodium (Na) balance, and the natriuretic effect is enhanced under Na deprivation, despite falls in blood pressure (BP) and glomerular filtration rate (GFR).Methods:The effect of additional hydrochlorothiazide (HCTZ; 12.5 mg/day) to ARB treatment (valsartan; 80 mg/day) on glomerulotubular Na balance was evaluated in 23 patients with chronic kidney disease.Results:Add-on HCTZ decreased GFR, tubular Na load, and tubular Na reabsorption (tNa), although 24-hour urinary Na excretion (UNaV) remained constant. Daily urinary angiotensinogen excretion (UAGTV, 152±10→82±17 μg/g Cre) reduced (p=0.02). Changes in tubular Na load (r2=0.26) and tNa (r2=0.25) correlated with baseline 24-hour UAGTV. Changes in filtered Na load correlated with changes in nighttime systolic BP (r2=0.17), but not with changes in daytime systolic BP. The change in the tNa to filtered Na load ratio was influenced by the change in daytime UNaV (β=−0.67, F=16.8), rather than the change in nighttime UNaV.Conclusions:Lower Na balance was produced by add-on HCTZ to ARB treatment without an increase of intra-renal renin-angiotensin system activity, leading to restoration of nocturnal hypertension. A further study is needed to demonstrate that the reduction of UAGTV by additional diuretics to ARBs prevents the progression of nephropathy or cardiovascular events.

Increased renal oxygen consumption leads to hypoxia in sepsis‐associated acute kidney injury (890.9)

We have shown in subtotal nephrectomy (STN), a model of chronic kidney disease, there is increased oxygen consumption (QO2) factored for tubular Na reabsorption (TNa) leading to hypoxia. To demonstrate the universality of hypoxia in the pathogenesis of kidney disease, we have now examined renal oxygenation (oxygen delivery and consumption), mitochondrial function and tubular transport in acute kidney injury (AKI) due to sepsis in a rat model of cecal ligation and puncture (CLP). Data presented as mean±sem.At 6 and 24 hours, GFR was significantly lower in CLP (2.5±0.4 vs. 3.6±0.2 ml/min and 1.2±0.3 vs. 3.3±0.2 ml/min, p<0.001). While RBF and O2 delivery was largely unchanged, renal O2 extraction and QO2 factored for GFR was higher compared to shams, (0.023±0.002 vs. 0.01±0.001 vol%ml/min and 0.11±0.01 vs. 0.05±0.01 ml/min,p<0.04). HIF‐1a expression was upregulated in the CLP kidneys at both 6 and 24 hours. In CLP, we found elevated rates of mitochondrial QO2 (199.9 ± 31.6 pMol/min vs. 163.2 ± 28.81 pMol/min, p<0.05), but significantly lower ATP generation with reduced expression of complex Va and complex III (p<0.05 for both). Proteins regulating mitochondrial morphology were also altered with increased expression of fission protein DRP1 (P<.0004) and decreased expression of PGC‐1alpha, a factor in mitochondrial biogenesis (2.2‐fold lower) in CLP. HIF‐1α activation by DMOG improved GFR at both time points.We demonstrate increased renal QO2 despite lower GFR leading to hypoxia and dissociation between excess QO2 and ATP generation in CLP mitochondria. We are investigating alterations in mitochondrial dynamics which could explain mitochondrial dysfunction and tubular injury, and the role of HIF‐1α pathway in this. In conclusion, our data in both acute and chronic kidney injury model demonstrates early hypoxia due to increased oxygen consumption leading to oxygen demand‐supply mismatch and strongly supports the role of hypoxia as a unifying mechanism for kidney disease.Grant Funding Source: NIH

Pathophysiology of Renal Calcium Handling in Acromegaly: What Lies behind Hypercalciuria?

Hypercalciuria is frequent in patients with acromegaly, but it is unclear how GH/IGF-I regulate renal calcium handling. Elevated fasting plasma calcium levels despite increased glomerular filtration suggest enhanced renal calcium reabsorption. The aim of this study was to investigate the impact of acromegaly on phosphocalcium metabolism. We conducted a prospective sequential study at a tertiary referral medical center and clinical investigation center (www.ClinicalTrials.gov Identifier: NCT00531908). Sixteen consecutive patients (five females/11 males) with acromegaly received a single iv infusion of 25 mg of furosemide to induce an acute increase in calcium and magnesium delivery to distal tubular segments during a high-sodium diet with stable dietary calcium, magnesium, and phosphate intake. Baseline plasma and urine electrolytes, plasma calciotropic hormones, and furosemide-induced changes in the fractional excretion and tubular reabsorption of Na, Ca, and Mg were measured before and 6 months (range, 1-12) after effective treatment of acromegaly. Serum IGF-I concentrations normalized in all the patients after acromegaly treatment. Compared with controlled acromegaly, active acromegaly was associated with higher fasting plasma (P = 0.0002) and urinary calcium (P = 0.0003) levels, lower PTH levels (P = 0.0075), higher calcitriol levels (P = 0.0137), higher phosphatemia (P<0.0001) and tubular phosphate reabsorption (P = 0.0002), and a lower calciuric (P = 0.0327) but not magnesiuric response to furosemide related to higher baseline and postfurosemide tubular calcium (P = 0.0034 and P = 0.0081, respectively), but not magnesium reabsorption. The IGF-I-mediated and PTH-independent increase in calcitriol synthesis in acromegaly is responsible for both absorptive hypercalciuria and increased fasting plasma calcium linked to enhanced distal tubular calcium reabsorption, as shown by the selectively diminished calciuric response to furosemide.

PST 2238: a new antihypertensive compound that modulates renal Na-K pump function without diuretic activity in Milan hypertensive rats.

PST 2238 is a new antihypertensive compound that is able to correct the molecular and functional alterations of the renal Na-K pump and the pressor effect associated with either alpha-adducin mutations or high circulating levels of endogenous ouabain (EO) in genetic and experimental rat models. Due to the close relationship between renal Na-K pump function and tubular Na reabsorption, PST 2238 was investigated to determine whether it is endowed with diuretic activity and consequently might trigger alterations of the renin-aldosterone system and the carbohydrate and lipid metabolism often associated with chronic diuretic therapy. In Milan hypertensive (MHS) rats, in which hypertension is genetically associated with alpha-adducin mutation, increased tubular Na reabsorption, and hyperactivation of the renal Na-K pump. PST 2238 reduced blood pressure and normalized the renal Na-K pump activity at oral doses of micro g/kg, but did not induce, either acutely or chronically, any diuretic activity or hormonal or metabolic alterations. In contrast, HCTZ, given to MHS rats orally at 40 mg/kg, although it displayed diuretic activity and reduced the renal Na-K pump activity, did not lower blood pressure and caused hyperactivation of the renin-aldosterone system, hypokaliemia, and hyperglycemia. The findings lead to the conclusion that PST 2238 is a new antihypertensive compound that normalizes the altered function of the renal Na-K pump associated with hypertension in rat models, but that it is devoid of diuretic activity and does not induce the diuretic-associated side effects.

Kidney retrieval conditions influence damage to renal medulla: evaluation by proton nuclear magnetic resonance (NMR) pectroscopy.

In the present investigation, the influence of retrieval condition on medullary damage in kidneys was assessed. The isolated perfused pig kidney was used to assess initial renal function from multiorgan donors or single organ donors after cold flush and 24 h cold storage preservation with two preservation solutions: Euro-Collins and University of Wisconsin solutions. Kidneys flushed with cold heparinized saline and immediately perfused were used as a control group. Kidneys were perfused for 90 min at 37.5 degrees C and renal perfusion flow rate, glomerular filtration rate, tubular reabsorption of Na+ and lactate dehydrogenase and N-acetyl-beta-D-glucosaminidase excretion were determined. Ischaemia reperfusion impairment was also determined by 1H NMR (proton nuclear magnetic resonance) spectroscopy. Renal function was significantly decreased in experimental groups when compared to the control group, but there was no significant difference between experimental groups after 24 h cold storage. The release of lactate dehydrogenase in the effluent and the urinary excretion of N-acetyl-beta-D-glucosaminidase were not significantly different after 24 h cold storage. The most relevant resonances determined by 1H NMR spectroscopy were citrate, trimethylamine-N-oxide, lactate, acetate and amino acids. Excretion of these markers was significantly different when compared to biochemical markers. A resonance P (Peak) detected particularly in Euro-Collins solution multiorgan donors after 24 h cold storage was identified and well correlated to renal dysfunction. N-acetyl-beta-D-glucosaminidase spectroscopy, which is a non-invasive and non-destructive technique, is more efficient to assess renal damage than conventional histology and biochemical analysis.

Influence of retrieval conditions on renal medulla injury: evaluation by proton NMR spectroscopy in an isolated perfused pig kidney model.

Delayed graft function (DGF) has remained an important complication after renal transplantation. The exact causes of DGF remain to be clarified, particularly the impact of retrieval conditions and preservation factors. In the present investigation, (1)HNMR spectroscopy of urine was assessed in order to detect the influence of retrieval condition on renal medulla damage. The isolated perfused pig kidney (IPK) was used to assess initial renal function from multiorgan donors (MOD) or single organ donors (SOD) after in situ cold flush and 24-h cold storage (CS) preservation with two standard preservation solutions: Euro-Collins (EC) and University of Wisconsin (UW) solutions. Kidneys flushed with cold heparinized saline and immediately perfused were used as the control group. Kidneys were perfused for 90 min at 37.5 degrees C for functional evaluation. During reperfusion, renal perfusion flow rate (PF) was measured. Glomerular filtration rate (GFR), tubular reabsorption of Na(+), and lactate dehydrogenase (LDH) and N-acetyl-beta-d-glucosaminidase (NAG) excretions were determined. Ischemia-reperfusion impairment was also determined by histological techniques and (1)HNMR spectroscopy. PF, GFR, and tubular reabsorption of Na(+) were significantly decreased in experimental groups when compared to the control group but there was no significant difference between experimental SOD groups. GFR was significantly greater in UW-MOD than in EC-MOD and tubular reabsorption of Na(+) was significantly greater in UW-MOD than in EC-MOD after 45 min of reperfusion. The release of LDH in the effluent and the urinary excretion of NAG were not significantly different after 24-h CS in the various experimental groups. The most relevant resonances determined by (1)HNMR spectroscopy were citrate, trimethylamine-N-oxide, lactate, acetate, and amino acids. Excretion of these markers was significantly different when compared to biochemical markers. A resonance (P) detected particularly in EC-MOD after 24-h CS was identified and well correlated to renal dysfunction. Histological study showed that ultrastructural damage and mitochondrial injury were more pronounced in the EC-MOD group. These results show that retrieval condition influences renal medullary damage. NMR spectroscopy, which is a noninvasive and nondestructive technique, is more efficient in assessing renal damage than conventional histology and biochemical analysis.

Attenuation of urinary sodium excretion during cold-air exposure in trained athletes.

To clarify whether an increase in urinary sodium (Na) excretion during cold-air exposure is attenuated in trained athletes, we analyzed the urinary and hormonal responses to cold-air exposure at 15 degrees C in trained (TR, n = 9) and untrained men (UT, n = 9). During 15 degrees C exposure in the UT group, the urinary Na excretion (UNaV), fractional excretion of Na and urinary Na to K ratio (UNa/K) increased significantly (p<0.01-0.05), but there were no variations in creatinine clearance or the filtered Na load. In the TR group, however, no significant changes were demonstrated in these parameters. The amount of increase in plasma noradrenaline and of decrease in plasma volume were greater, and the ADH and adrenaline responses were smaller in the TR group than those found in the UT group during 15 degrees C air exposure. A significant positive correlation was demonstrated between the increase of UNaV and both the relative changes of UNa/K and mean blood pressure. These results indicated that natriuresis during cold-air exposure was induced by the decrease in tubular reabsorption of Na, and that natriuresis was attenuated in trained athletes.

Effects of a Meat Meal on Renal Sodium Handling and Sodium Balance

Protein ingestion increases renal blood flow and glomerular filtration rate (GFR). This study investigated in healthy adults if the renal response to protein ingestion includes changes in urinary sodium (Na) excretion rate and Na balance. Renal clearance of Na and inulin (used as index of GFR) were measured in 25 healthy adults before (90 min) and after (180 min) a standard meal and, as control, before and after administration of water and Na-chloride (saline). The meal consisted of red lean meat (2 g protein/kg body weight); in control experiments, water and Na were given to match water and Na content of the meal. ANOVA for repeated measures, Student’s t-test, and linear regression were used for statistical analysis. GFR and urinary Na excretion increased over baseline after the meal (p < 0.001), not after saline. The post-meal natriuretic response was accounted for an early (0–90 min) increase in glomerular filtered load of Na (p < 0.001) and a late (90–180 min) reduction in tubular Na reabsorption (p < 0.02). Urine flow rate and plasma Na did not significantly change after the meal and in control experiments. Analysis of Na balance showed that post-meal Na excretion was significantly higher than baseline also after Na balance returned to pre-meal values. In healthy individuals, a meat meal stimulates natriuresis and causes a net decrease in Na balance. The renal natriuretic response to the meal appears secondary to the meal-induced changes in renal hemodynamics. The data are in keeping with the hypothesis that dietary protein intake affects also renal Na handling.

Nifedipine improves recovery function of kidneys preserved in a high-sodium, low-potassium cold-storage solution: study with the isolated perfused rat kidney technique.

Extracellular types (high-Na) of cold-storage solution (CSS) have been shown to be more effective in preserving kidneys than intracellular CSS (high-K). On the other hand, calcium entry blockers (CEB) have been demonstrated to improve graft function when administered after and/or prior to transplantation. The ischaemia reperfusion syndrome involves, in part, an alteration in intracellular calcium metabolism that induces an increase in renal vascular resistances (RVR) and other cellular dysfunction, and high-K CSS per se are vasoconstrictive. Since CEB act via a modification in intracellular calcium metabolism on vascular smooth muscle, glomerular, and tubular cells, we evaluated the actual benefit on CEB on kidneys preserved in Belzer's CSS (K-UW) and a high-Na version of Belzer's CSS (Na-UW). The isolated perfused rat kidney (IPK) was used, first as a vascular bed to test the effects of CSS on RVR, and the influence of nifedipine. Second, the recovery function of the IPK was assessed by GFR and tubular Na reabsorption, after 24 h preservation in K-UW and Na-UW, with or without nifedipine. Results were compared with a control group in which renal function was measured without prior cold-storage. K-UW but not Na-UW induced an increase in RVR when flushed into the kidney. This vasoconstriction is prevented by nifedipine. K-UW CSS was more deleterious to renal function than Na-UW. Addition of nifedipine to the flush, the CSS for 24 h, and to the normothermic reperfusate further improved recovery function of the IPK cold stored in Na-UW but not in K-UW, without any modification of RVR. Nifedipine may be of potential effect in attenuating ischaemic injury by a mechanism which does not involve its vasodilatory properties.

Endogenous angiotensin II inhibits natriuresis after acute volume expansion in the neonatal rat.

Compared with the adult, the neonatal renal natriuretic response to acute volume expansion (VE) is attenuated. To test the hypothesis that antinatriuresis is mediated by endogenous angiotensin I (ANG II), Sprague-Dawley rats were given losartan, an ANG II type 1 (AT1)-receptor inhibitor (40 mg.kg-1.day-1) from birth to 14-17 days. Control littermates received saline vehicle. Anesthetized rats underwent acute saline VE for measurement of mean arterial blood pressure (MAP), plasma aldosterone concentration (Paldo), plasma atrial natriuretic peptide (PANP), glomerular filtration rate (GFR), sodium excretion (UNaV), potassium excretion (UKV), and urine guanosine 3',5'-cyclic monophosphate excretion (UcGMPV). Losartan increased basal urine flow fivefold, UNaV 10-fold, and UKV twofold. Acute VE induced marked diuresis, natriuresis, and kaliuresis in the losartan but not in the saline group. This occurred without change in Paldo and PANP and despite lower MAP, GFR, and UcGMPV. In addition, losartan did not affect release of cGMP from isolated glomeruli stimulated by ANP or sodium nitroprusside. We conclude that the limited renal response to acute VE in the neonate results from stimulation of tubular Na reabsorption by ANG II acting on the AT1 receptor.

Digoxin-specific Fab fragments impair renal function in the rabbit.

A 2 mg kg-1 intravenous bolus dose of digoxin-specific Fab fragments produced a 28% reduction in creatinine clearance in rabbits after 24 h. Urine output was reduced, while plasma and urinary creatinine concentrations were unaffected and increased, respectively. By 5 days the creatinine clearance had returned to normal. The fractional excretion of Na+ was nearly halved, indicating that the tubular reabsorption of Na+ increased to compensate for the reduced glomerular filtration rate, suggesting that tubular (as opposed to glomerular) function was not impaired.

Renal effects of alpha-adrenoceptor blockade during furosemide diuresis in conscious rats.

Clearance experiments were performed in conscious rats in order to investigate whether intravenous infusion of the non-selective alpha-adrenoceptor antagonist phentolamine could block compensatory sodium reabsorption during furosemide-induced volume contraction. By measuring inulin clearance, urinary excretion rates of sodium and water, and lithium clearance, the effects on proximal and distal nephron segments were dissociated. The renal effect of intravenous infusion of 0.3 mg/kg/hr phentolamine (n = 6) was compared with time control animals (n = 9). Furosemide was administered as constant intravenous infusion (7.5 mg/kg/hr) with simultaneous phentolamine infusion at four dose levels: 0 (n = 9), 0.3 (n = 6), 1.0 (n = 7) and 3.0 mg/kg/hr (n = 6). Phentolamine infusion reduced norepinephrine-induced increase in blood pressure at all three dose levels (n = 5). Phentolamine infusion induced transient antidiuresis and a prolonged antinatriuretic response. Compared with rats given furosemide only, phentolamine attenuated dose-dependently the diuretic and natriuretic peak response to furosemide. This effect was associated with dose-dependent reductions in mean arterial pressure. The reduced natriuretic response was due to a reduced fractional sodium excretion in the distal nephron segment (at all doses of phentolamine) and a reduction of the glomerular filtration rate (1.0 and 3.0 mg/kg/hr phentolamine). The fractional lithium excretion (FELi) increased to 65 +/- 3% at 0.3 mg/kg/hr phentolamine during the natriuretic peak response of furosemide, while it only increased to 52 +/- 3% during furosemide alone. At steady-state conditions (120-180 min. after start of furosemide infusion) after infusion with furosemide plus 0.3 mg/kg/hr phentolamine the animals were still volume-depleted, but the compensatory tubular Na reabsorption in the proximal tubules was inhibited (FELi = 48 +/- 2% versus 39 +/- 1% in rats given furosemide alone). During furosemide infusion plasma epinephrine increased 700% and plasma norepinephrine increased 50%. These results are compatible with increased systemic sympathetic nervous activity and a contributory role of proximal tubular alpha-adrenoceptors in mediating compensatory sodium reabsorption during acute furosemide-induced volume contraction.

Role of neutrophil derived oxidants and elastase in lipopolysaccharide-mediated renal injury

Gram-negative bacterial sepsis is frequently associated with acute renal failure but the specific effects of lipopolysaccharide (LPS) and other bacterial products on kidney function are not known. Since either LPS or formyl-methionyl-leucyl-phenylalanine (FMLP)--a chemotactic peptide from bacterial cell walls--activate neutrophils (PMN) to release a number of potentially toxic factors in vitro, we determined the effect of adding PMN with LPS and/or FMLP to isolated perfused rat kidneys. Isolated rat kidneys perfused with LPS alone or LPS and normal PMN had normal glomerular filtration rates (GFR) and tubular Na reabsorption (TNa). Kidneys perfused with FMLP alone or FMLP and normal PMN also had normal GFR and TNa. In contrast, addition of PMN with both FMLP and LPS caused progressive renal dysfunction. For example, after 60 minutes of perfusion, GFR was reduced from 610 +/- 31 to 147 +/- 17 microliters/min/g and TNa from 97 +/- 1 to 72 +/- 2%, both P less than 0.01. Perfusion with the O2 metabolite scavengers catalase or dimethylthiourea afforded no protection while perfusion with the neutrophil elastase inhibitor Eglin C conferred substantial, but not complete, protection: GFR 492 +/- 34 microliters/min/g; TNa 91 +/- 3%. However, perfusion with both Eglin C and catalase completely prevented the toxic effects of LPS and FMLP-treated PMN on renal function. We conclude that in isolated kidneys, 1) the toxic effects of LPS requires FMLP-treated PMN and that 2) LPS and FMLP treated PMN cause progressive renal injury which is mediated by both O2 metabolites and neutrophil elastase.

Renal and endocrine effects of physiological variations of atrial natriuretic factor in normal humans

The renal and endocrine effects of incremental infusions of 3 and 6 ng.kg-1.min-1 of exogenous atrial natriuretic factor (ANF)-(99-126) or placebo were investigated in 10 normal subjects. A 90-min basal period was followed by two 2-h infusion periods with urine collection in the last 90 min of each period. Plasma ANF concentration increased by 50 and 150%, respectively, from a basal value of 6.2 +/- 3.1 pmol/l. Plasma guanosine 3',5'-cyclic monophosphate concentration increased in parallel with ANF. Blood pressure and heart rate were unchanged, whereas hematocrit was stepwise increased. 51Cr-EDTA clearance (GFR) did not change, but ANF caused an increase in Li clearance (a measure of end-proximal fluid delivery), Na clearance, and urine flow compared with time-matched control values. These excretory effects of ANF were mainly due to prevention of the 20- to 50% decreases occurring in the placebo series. Calculated values of fractional proximal and distal tubular Na reabsorption decreased significantly. ANF caused a decrease in plasma concentrations of active renin and aldosterone, whereas renin substrate, angiotensin I, and angiotensin II concentrations were unaltered. A subtle increase in plasma concentrations of norepinephrine and epinephrine was observed during the ANF infusions. These data suggest that the natriuretic effect of ANF is caused by an increased fluid delivery from the proximal tubule in addition to a fall in fractional distal Na reabsorption.

Regulatory effect of cytokines on polumorphonuclear leukocetes (PMNs)-derived superoxide production

Role of neutrophil derived oxidants and elastase in lipopolysaccharide-mediated renal injury. Gram-negative bacterial sepsis is frequently associated with acute renal failure but the specific effects of lipopoly-saccharide (LPS) and other bacterial products on kidney function are not known. Since either LPS or formyl-methionyl-leucyl-phenylalanine (FMLP)—a chemotactic peptide from bacterial cell walls—activate neutrophils (PMN) to release a number of potentially toxic factors in vitro, we determined the effect of adding PMN with LPS and/or FMLP to isolated perfused rat kidneys. Isolated rat kidneys perfused with LPS alone or LPS and normal PMN had normal glomerular filtration rates (GFR) and tubular Na reabsorption (TNa). Kidneys perfused with FMLP alone or FMLP and normal PMN also had normal GFR and TNa. In contrast, addition of PMN with both FMLP and LPS caused progressive renal dysfunction. For example, after 60 minutes of perfusion, GFR was reduced from 610 ± 31 to 147 ± 17 µl/min/g and TNa from 97 ± 1 to 72 ± 2%, both P < 0.01. Perfusion with the O2 metabolite scavengers catalase or dimethylthiourea afforded no protection while perfusion with the neutrophil elastase inhibitor Eglin C conferred substantial, but not complete, protection: GFR 492 ± 34 µl/min/g; TNa 91 ± 3%. However, perfusion with both Eglin C and catalase completely prevented the toxic effects of LPS and FMLP-treated PMN on renal function. We conclude that in isolated kidneys, 1) the toxic effects of LPS requires FMLP-treated PMN and that 2) LPS and FMLP treated PMN cause progressive renal injury which is mediated by both O2 metabolites and neutrophil elastase.

Pathophysiology of increased urinary N-acetyl-beta-D-glucosaminidase activity in human hypertension: effect of cilazapril therapy.

To investigate the pathophysiology of elevated urinary N-acetyl-beta-D-glucosaminidase (NAG) activity in human hypertension, total and fractional urinary NAG activities were correlated with Li clearance, a measure of proximal renal tubular Na reabsorption, in 15 white hypertensive subjects, aged 56 years, and in 13 normotensive control subjects. In 11 hypertensive subjects, the measurements were repeated after 2 months of antihypertensive therapy with the converting enzyme inhibitor cilazapril (2.5 or 5.0 mg daily). Urinary NAG activity was increased in hypertensives and correlated directly with Li clearance in both hypertensive and normotensive subjects. Li clearance and urinary NAG activity were reduced by antihypertensive therapy. The findings indicate an inverse correlation between urinary NAG activity and proximal renal tubular Na reabsorption, suggesting that NAG is reabsorbed in the proximal renal tubules with Na and other proteins. High Li clearance and urinary NAG activity in hypertension are in part functional and, therefore, reversible disturbances of renal function.

O2 metabolites cause reperfusion injury after short but not prolonged renal ischemia.

Toxic O2 metabolites have been postulated to contribute to renal ischemia-reperfusion injury, but their biochemical assessment and contribution as a function of the duration of ischemia is unclear. To address this issue we measured renal function and renal cortical glutathione levels following 20, 30, or 45 min of ischemia in situ and then 60 min of reperfusion by the isolated kidney technique. Increasing durations of ischemia were associated with progressive decreases in perfusion flow rate, glomerular filtration rate, tubular Na reabsorption, and renal cortical glutathione following reperfusion. However, reperfusion following simultaneous addition of the permeable O2 metabolite scavenger dimethylthiourea (DMTU; but not urea) prevented glutathione consumption and attenuated reperfusion-induced injury after 20 and 30 min of ischemia. In contrast, reperfusion with DMTU prevented glutathione consumption but did not improve renal function after 45 min of ischemia. Similarly, reperfusion with dimethyl sulfoxide also attenuated renal injury after 20 and 30 min, but not after 45 min of ischemia. Thus reperfusion of kidneys made ischemic for 20 or 30 min is associated with decreases in tissue glutathione and renal function that were both inhibitable by addition of O2 metabolite scavengers during reperfusion. In contrast, addition of O2 metabolite scavengers during reperfusion of kidneys previously made ischemic for 45 min prevented decreases in glutathione but did not improve renal function. We conclude that O2 metabolites formed during reperfusion contribute to functional impairment in kidneys made ischemic for short durations up to 30 min) but that after prolonged ischemia (greater than 30 min) injury is primarily mediated by non-O2 metabolite-dependent cellular events.

The effects of prolonged epinephrine infusion on the physiology of the rainbow trout, Salmo gairdneri. III. Renal ionic fluxes.

Rainbow trout were infused continuously for 24 h with epinephrine in order to evaluate the effects of elevated circulating levels of epinephrine on selected renal variables. Pronounced effects of epinephrine included elevation of urine flow rate and concomitant increases in the excretion of all measured electrolytes (Na+, Cl-, K+, Ca2+, inorganic phosphate) with the exception of ammonium and bicarbonate ions. Significant reductions in the tubular reabsorption of Na+ and Cl- also contributed to enhanced excretion of these ions. Similarly, epinephrine affected the tubular handling of NH4+ and HCO3- with NH4+ secretion decreasing and HCO3- reabsorption increasing. We speculate that the stimulation of HCO3- reabsorption was a consequence of elevated tubular H+ secretion. Such a mechanism may be important to permit plasma HCO3- retention during periods of internal acidosis. The results are discussed with reference to the role of the fish kidney in regulating acid-base disturbances and the possible interactive effects of elevated epinephrine.