Kidney ageing and renal excretion of amylase

In a cross-sectional study, the amylase to creatinine clearance ratio (ACCR) was determined in 180 patients, age range 18-93 years. An inverse correlation was found between ACCR and creatinine clearance (r = -0.40, p less than 0.001) in keeping with the known inverse relationship between the sieving fraction of macromolecules and the glomerular filtration rate. The fractional clearance of amylase was not significantly affected by amylasemia nor by age when the creatinine clearance was also considered in a multiple regression analysis. No increase in ACCR was observed in patients with low molecular weight proteinuria or with induced urine dilution. The authors assume that the tubular reabsorption of amylase is minimal and that the enhancement of ACCR in the elderly mainly reflects modifications in the glomerular filtration dynamics.     

Retention of albumin in the circulation is governed by saturable renal cell-mediated processes

OBJECTIVE: To examine the role of renal processing in the turnover of circulating albumin in the model of reversible overload proteinuria. Specifically, this study determines whether proteinuria due to hyperalbuminemia may be attributed to saturation of renal cell processing of albumin or alterations in diffusive/convective transport of albumin across the glomerular capillary wall. METHODS: Overload proteinuria was induced in male Wistar rats by daily intraperitoneal injections of 1.5 g bovine serum albumin (BSA; endotoxin free) for 3 days. Plasma concentration and urinary excretion of total protein and rat serum albumin (RSA) were determined by the biuret assay and radioimmunoassay, respectively. Glomerular size selectivity was assessed by examining the fractional clearance (FC) of neutral [3H]Ficoll using a short-term, steady-state approach. Cellular processing was examined by size exclusion chromatography analysis of urinary [14C]albumin and [14C]transferrin structural integrity. RESULTS: Total protein excretion (n = 4-15) increased 7-fold in BSA-treated rats (58 +/- 26 mg/24 h at baseline vs. 417 +/- 259 mg/24 h at day 3), while intact RSA excretion (n = 4-6) increased 200-fold (0.27 +/- 0.15 mg/24 h vs. 53 +/- 26 mg/24 h) despite a significant decrease in its plasma concentration. Total protein and albumin excretion returned to basal levels by day 7 (82 +/- 16 mg/24 h and 0.93 +/- 0.42 mg/24 h, respectively). FC of [3H]Ficoll of equivalent size to albumin did not change in BSA-treated rats as compared to vehicle controls. Tubular lysosomal processing of proteins was altered at peak proteinuria, as determined by changes in the structural integrity of urinary [14C]albumin, as well as [14C]transferrin, but returned to normal by day 7. CONCLUSIONS: This study demonstrates the lack of proportionality between changes in plasma concentration and urinary excretion of albumin, as well as the lack of change in the glomerular size selectivity to albumin. The profound but reversible changes in the amount and integrity of excreted protein suggest that cell-mediated processes are saturated by albumin concentrations, leading to the development of proteinuria in this model.     

Monitoring glomerular function in diabetic nephropathy. A prospective study

Glomerular function was monitored prospectively in 13 patients with insulin-dependent diabetes and diabetic nephropathy for up to 51 months. Glomerular filtration rate, measured by 51Cr-EDTA clearance, showed a linear decline in all patients. Rates of fall ranged between 0.63 and 2.4 ml/minute per month (mean +/- SEM 1.2 +/- 0.16). Plasma creatinine concentration proved to be an insensitive marker of glomerular function, especially in the early phase of nephropathy. A good correlation was found between the rate of change of 51Cr-EDTA glomerular filtration rate and that of inverse creatinine levels when plasma creatinine concentrations exceeded 200 mumol/liter. Inverse plasma beta 2-microglobulin concentrations, however, showed a highly significant correlation (r = 0.93; p less than 0.001) with 51Cr-EDTA glomerular filtration rate over the whole range of values, making it sensitive in screening for early impairment of renal function. A significant relationship (r = 0.85; p less than 0.01) was found between the rates of change of the 51Cr-EDTA glomerular filtration rate and of inverse beta 2-microglobulin levels for plasma beta 2-microglobulin concentrations above 3 mg/liter. A progressive increase in the fractional clearance of albumin, IgG, and beta 2-microglobulin was noted as the glomerular filtration rate fell, indicating an evolving defect in the renal handling of proteins. The rate of decline of the glomerular filtration rate was unrelated to age, sex, duration of diabetes, duration of diabetes before onset of proteinuria, glomerular filtration rate, initial albumin clearance, blood glucose control, and arterial pressure, when diastolic values were below 100 mm Hg. The effect of therapeutic intervention (e.g., blood glucose, blood pressure, or diet) on the progression of diabetic nephropathy can be reliably evaluated by precise measures of rate of decline of glomerular filtration rate and changes in fractional clearance of plasma proteins. The factor(s) determining the individual rate of decline of renal function still remain obscure.     

Mechanisms of the impaired diuretic and natriuretic responses to a sustained and moderate saline infusion in rats with experimental cirrhosis

Kidney function and tubular handling of water and sodium by superficial nephrons, packed cell volume, total plasma proteins and albumin distribution space were studied in control and cirrhotic rats before and after a moderate and sustained saline infusion (3% body weight per 30 min + reposition of urinary losses). Tubular fluid samples were obtained from late proximal, early distal and late distal convolutions of superficial nephrons using micropuncture. Protein distribution was assessed by intravenous injection of 0.5 muCi of (125I)-albumin. In basal conditions, both groups of rats showed similar glomerular filtration rate and renal plasma flow, but cirrhotic animals had lower sodium excretion (fractional excretion of sodium = 0.04 +/- 0.01% vs. 0.22 +/- 0.02%, p less than 0.05) and urinary volume (4.31 +/- 0.41 vs. 7.57 +/- 0.53 microliter per min; p less than 0.05). After saline infusion, total plasma proteins decreased more in cirrhotic than in control rats (-18.5 +/- 2.7 vs. -12.9 +/- 2.2%, p less than 0.05). The opposite was observed for albumin distribution space (34.5 +/- 6.1 vs. 22.1 +/- 3.5%, p less than 0.05). Fractional sodium excretion increased to 2.98 +/- 0.15% in control rats but only to 0.61 +/- 0.080% in cirrhotic rats. The ratio single nephron glomerular filtration rate/glomerular filtration rate increased from 19.6 +/- 0.7 to 21.2 +/- 1.0 (X10(-6), p less than 0.005) in control animals but did not change in cirrhotic rats. These animals were unable to decrease adequately fractional fluid reabsorption in the proximal tubule and the loop of Henle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rapid nongenomic effects of aldosterone on the renal vasculature in humans

There is increasing evidence for the importance of rapid nongenomic effects of aldosterone on the human vasculature. In vitro animal experiments in renal arterioles also suggest the presence of such effects on the renal vasculature. We conducted a clinical study to explore these effects in vivo in humans. Thirteen healthy male volunteers were examined. Aldosterone (500 microg) or placebo was injected intravenously with or without coinfusion of N(G) monomethyl-L-arginine (L-NMMA) in a randomized, double-blinded 4-fold crossover design. Renal plasma flow and glomerular filtration rate were measured by constant infusion clearance technique using inulin and para-aminohippuric acid. Injection of aldosterone without concomitant infusion of L-NMMA changed the renal plasma flow and glomerular filtration rate not statistically significant compared with placebo. Coinfusion of L-NMMA unmasked the effect of aldosterone: aldosterone with L-NMMA decreased the glomerular filtration rate slightly (-1.4+/-6.2 mL/min), whereas infusion of L-NMMA alone increased the glomerular filtration rate (8.3+/-9.8 mL/min; P=0.004). L-NMMA alone decreased renal plasma flow by 58.2+/-97.5 mL/min, and aldosterone with L-NMMA decreased renal plasma flow by 190.0+/-213.7 mL/min (P=0.074). Accordingly, Aldosterone with L-NMMA increased renal vascular resistance much more than L-NMMA alone (1588+/-237 versus 614+/-240 dynxsxcm(-5); P=0.014). These data indicate that aldosterone acts via rapid nongenomic effects in vivo in humans at the renal vasculature. Antagonizing the endothelial NO synthase unmasks these effects. Therefore, rapid nongenomic aldosterone effects increase renal vascular resistance and thereby mediate arterial hypertension if endothelial dysfunction is present.     

Role of angiotensin II in the altered renal function of congestive heart failure

Glomerular and tubule functions were assessed by micropuncture in rats with extensive myocardial infarction produced by ligation of the left coronary artery 4 weeks prior to study. When compared to sham-operated control rats, rats with myocardial infarction involving 40 +/- 4% of the left ventricular circumference had lower mean arterial pressure (96 +/- 5 vs. 122 +/- 4 mm Hg, P less than 0.005), and higher left ventricular end-diastolic pressure (24 +/- 3 vs. 5 +/- 0 mm Hg, P less than 0.001). Renal cortical microcirculatory dynamics of rats with myocardial infarction were characterized by reduced glomerular plasma flow rate (75 +/- 8 vs. 165 +/- 17 nl/min, P less than 0.005), but a proportionately lesser decline in single nephron glomerular filtration rate (28.0 +/- 2.8 vs. 41.7 +/- 3.1 nl/min, P less than 0.025), accounting for the observed rise in single nephron filtration fraction (0.38 +/- 0.02 vs. 0.25 +/- 0.02, P less than 0.005). These renal hemodynamic alterations in myocardial-infarcted rats were accompanied by a striking elevation in efferent arteriolar resistance (3.03 +/- 0.31 vs. 0.95 +/- 0.16 X 10(10) dyn X sec X cm-5, P less than 0.001). In addition, fractional proximal fluid reabsorption, assessed by end-proximal tubule fluid-to-plasma inulin concentration ratio, was elevated (2.21 +/- 0.12 vs. 1.64 +/- 0.09, P less than 0.025). The intravenous infusion of teprotide, an angiotensin I-converting enzyme inhibitor, led to the return of glomerular plasma flow rate, single nephron filtration fraction, single nephron glomerular filtration rate, efferent arteriolar resistance, and fractional proximal fluid reabsorption in myocardial-infarcted rats to, or toward, the levels found in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute effects of a somatostatin analogue on kidney function in type 1 diabetic patients

Suppression of growth hormone by means of somatostatin has been suggested as a possible adjunct therapy in Type 1 diabetes. To assess the acute effect of the somatostatin analogue SMS 201-995 on kidney function in uncomplicated Type 1 diabetes, 13 normoalbuminuric, normotensive diabetic patients were investigated before and during IV infusion of SMS 201-995 (8 micrograms h-1). A control experiment with infusion of carrier only was also performed. The SMS infusion induced a reduction in the glomerular filtration rate (clearance of 125I-iothalamate) and renal plasma flow (131I-hippuran) from 140 +/- 15 (mean +/- SD) and 550 +/- 69 to 131 +/- 14 (2p less than 0.005) and 492 +/- 73 ml min-1 1.73-m-2 (2p less than 0.001), while filtration fraction and total renal resistance rose (both 2p less than 0.001). Urinary albumin excretion rate, blood pressure, and blood glucose concentration were unchanged. Plasma growth hormone and glucagon were significantly suppressed. The reduction in glomerular filtration rate and renal plasma flow correlated with the fall in glucagon concentration (r = 0.57, 2p = 0.04, and r = 0.63, 2p = 0.02). The urinary flow rate was markedly reduced, urine osmolality increased, and fractional excretion of sodium, calcium, and phosphate were reduced. Arginine vasopressin, atrial natriuretic peptide, angiotensin II, and aldosterone were unchanged by the SMS infusion. Thus SMS 201-995 acutely reduces glomerular filtration rate and renal plasma flow in uncomplicated Type 1 diabetes and has an antidiuretic effect. The effects may be related to suppression of glucagon secretion.     

Dipyridamole decreases glomerular filtration in the sodium-depleted dog. Evidence for mediation by intrarenal adenosine

To determine the renal effects of inhibiting the uptake and subsequent metabolism of endogenous adenosine, dipyridamole, a nucleoside transport inhibitor, was infused intrarenally into anesthetized dogs. Dipyridamole (24 micrograms/kg per min) inhibited the cellular extraction of [14C]adenosine (72 +/- 3% vs. 9 +/- 3%) and elevated the excretion of endogenous adenosine (0.60 +/- 0.08 to 1.70 +/- 0.21 nmol/min, P less than 0.05). The action of exogenous adenosine to decrease glomerular filtration rate is known to be enhanced by sodium depletion, and is minimal or absent in sodium-loaded animals. To ascertain whether dietary sodium intake alters the renal effects of elevated endogenous adenosine, dipyridamole was infused into sodium-depleted and sodium-loaded dogs. In the sodium-depleted dogs (n = 9), dipyridamole infusion decreased the glomerular filtration rate by 59 +/- 7% (20 +/- 1 to 8 +/- 2 ml/min, P less than 0.05) which returned to control levels within 30 minutes after stopping infusion of dipyridamole. Renal vascular resistance was unchanged during dipyridamole infusion. In the sodium-loaded dogs (n = 5), dipyridamole had no effect on glomerular filtration rate (22 +/- 4 vs. 25 +/- 3 ml/min) or renal vascular resistance. In a separate series of sodium-depleted dogs (n = 8), the dipyridamole-induced decrease in glomerular filtration rate was completely reversed or inhibited by theophylline, an adenosine receptor antagonist. These experiments demonstrate that inhibition of cellular uptake of adenosine elevates adenosine levels, that dipyridamole decreases glomerular filtration rate in sodium-depleted but not sodium-loaded dogs, and that the decrease in glomerular filtration rate is inhibited by theophylline. We conclude that the decrease in glomerular filtration rate during dipyridamole administration is mediated by increased endogenous adenosine.     

Evidence for a prostaglandin-independent defect in chloride reabsorption in the loop of Henle as a proximal cause of Bartter's syncrome.

Maximal free-water clearance was measured in five patients with Bartter's syndrome and in five patients with the hypokalemic alkalosis of persistent psychogenic vomiting. Hypokalemic alkalosis, hyperreninemia, hyperaldosteronism and excessive renal production of prostaglandin E2 were present in the patients with both disorders. Maximal free water clearance was abnormally low, in association with a high clearance of chloride, in all the patients with Bartter's syndrome; it was normal in all the patients with psychogenic vomiting. In the patients with Bartter's syndrome, apparent distal delivery of proximal tubular fluid was inversely related to glomerular filtration rate and was excessive only in those patients with a low glomerular filtration rate. Patients with psychogenic vomiting showed mean distal fractional chloride reabsorption of 0.92 +/- 0.04 (standard error [SE]). In the patients with Bartter's syndrome, distal fractional reabsorption of chloride was 0.49 +/- 0.08 and was the same (0.46 +/- 0.06) during inhibition of prostaglandin synthesis with indomethacin therapy. Thus, a prostaglandin-independent defect in chloride reabsorption in the loop of Henle is the most proximal cause for the abnormalities in Bartter's syndrome thus far identified.     

Nitric oxide and renal functions in liver cirrhosis.

BACKGROUND/AIMS: Nitric oxide, a potent vasodilating agent, has been proposed to play a role in pathogenesis of ascites and hepatorenal syndrome. The aim of this study was to evaluate the interaction between the plasma nitric oxide, nitric oxide synthetase levels and renal functions in patients with different degrees of chronic liver disease. METHODS: The study population included 38 subjects: 14 patients with chronic hepatitis, 11 with preascitic cirrhosis and 13 with ascitic cirrhosis. Nitric oxide and nitric oxide synthetase were determined by colorometric assay. We calculated glomerular filtration rate and fractional sodium excretion. RESULTS: Nitric oxide levels in groups were as follows: 79.28+/-24.86, 99.03+/-21.31, 197.05+/-49.61 microm, respectively. Nitric oxide synthetase levels were 2.64+/-0.56, 3.64+/-0.89, 7.75+/-2.46 micromol/L/sec, respectively. Nitric oxide and nitric oxide synthetase levels in the ascitic cirrhotic group were significantly higher than in the others (p<0.05). When glomerular filtration rates were compared, the only significant difference was determined between the groups with chronic hepatitis and ascitic cirrhosis (92.31+/-25.21, 48.46+/-16.45, p<0.05). Fractional sodium excretion was significantly increased in the ascitic cirrhotic group (4.42+/-2.76, p<0.05). CONCLUSIONS: Nitric oxide and nitric oxide synthetase increased with progression of liver disease, especially in ascitic cirrhosis. We also showed that this increase negatively affects the renal tubular and glomerular functions.     

Renal handling of high-density lipoproteins by isolated perfused kidneys

Recent studies show that the normal and diseased kidney is an important organ in the catabolism of high-density lipoproteins (HDL). However, little is known about the renal handling of HDL. To investigate this aspect, kidneys were isolated from normal rats and rats made nephrotic with puromycin aminonucleoside. They were perfused in a chamber at 37 degrees C with a modified Krebs-Hensleit Bicarbonate Buffer containing 1%, 3%, 6%, and 10% Bovine Serum Albumin (BSA). Presence of 10% BSA in the perfusate prevented glomerular filtration and urine formation. Thus, the filtering and the nonfiltering kidney perfusion models distinguish the renal parenchymal function independently of luminal events that follow filtration. 125I-labeled rat HDL was injected into the perfusate and radioactivity in perfusate, urine, and kidney was examined. At the end of perfusion (30 minutes or four hours), each kidney was flushed with 125I-HDL-free perfusate and kidney radioactivity was measured. At four hours, 1.9% +/- 0.5% of injected radioactivity was present in urine from kidneys perfused with 6% BSA. Kidneys with intact glomerular filtration sequestered significantly more radioactivity (1.1% +/- 0.2% of injected radioactivity) than nonfiltering kidneys (0.7% +/- 0.2%); P less than 0.05. Radioactivity in filtering kidneys was significantly higher than in nonfiltering kidneys (33.9 +/- 7.8 v 15.6 +/- 2.6 cpm/mg kidney tissue protein, respectively; P less than 0.001). Nephrotic kidneys (filtering and nonfiltering) sequestered two to four times more 125I-HDL than normal kidneys. These data support the hypothesis that prior to urinary excretion, partial reabsorption of filtered HDL (or subfractions) occurs in the normal kidney.(ABSTRACT TRUNCATED AT 250 WORDS)     

Abnormal renal responses to calcium entry blockade in normotensive offspring of hypertensive parents

In nine young normotensive subjects with no family history of hypertension and nine age-matched normotensive subjects with one parent with essential hypertension, effective renal plasma flow (p-aminohippuric acid clearance), glomerular filtration rate (inulin clearance), and excretion of sodium and exogenously administered lithium were measured for 90 minutes before and after administration of a single 20-mg oral dose of the calcium entry blocker nifedipine. Segmental tubular handling of fluid and sodium was estimated using lithium clearance as a marker of proximal tubular reabsorption. Nifedipine did not cause any change in subjects with no family history of hypertension, but in those with one hypertensive parent there was a marked increase in effective renal plasma flow (from 644 +/- 39 to 847 +/- 42 [SEM] ml/min x 1.73 m2; p less than 0.001) and a decrease in filtration fraction (from 17.6 +/- 1.0 to 12.6 +/- 0.4%; p less than 0.001), while the glomerular filtration rate was unchanged, thus suggesting a prevailing efferent vasodilation. Sodium excretion rate (p less than 0.02) and fractional sodium excretion (p less than 0.025) increased slightly but significantly in subjects with one hypertensive parent, but not in normotensive subjects with no family history of hypertension. Lithium clearance also rose (from 29.0 +/- 2.0 to 32.8 +/- 1.9 ml/min, p less than 0.001), and the derived value of fractional proximal reabsorption diminished (from 75.8 +/- 1.0 to 71.3 +/- 1.2%, p less than 0.001). Estimated distal delivery of sodium and absolute distal sodium reabsorption both increased significantly (p less than 0.005), while fractional distal sodium reabsorption was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blunted natriuretic response and low blood pressure after atrial natriuretic factor in early cirrhosis

We compared the natriuretic response to a standard dose of atrial natriuretic factor in nine patients with early cirrhosis (no ascites or edema) with the response in normal subjects displaying a range of baseline sodium excretions due to different sodium intakes (20 mmoles per day, n = 9; 100 mmoles per day, n = 9, and 200 mmoles per day, n = 9). In these normal subjects, sodium output rose, in the same order, from 49 +/- 12 to 177 +/- 26, from 116 +/- 21 to 365 +/- 106 and from 228 +/- 29 to 901 +/- 85 mumoles per min in the first 20 min after 100 micrograms atrial natriuretic factor (human atrial natriuretic factor 99-126). Thus, irrespective of basal excretion, natriuresis rose by at least 2-fold. In the cirrhotic patients, natriuresis rose from 173 +/- 42 to 305 +/- 77 mumoles per min, that is by hardly 1-fold, significantly less than in the normal subjects (p less than 0.01). Renal function studies indicated that atrial natriuretic factor caused less rise in glomerular filtration rate and in fractional sodium excretion. Atrial natriuretic factor induced a fall in blood pressure only in the cirrhotic group, from 130 +/- 4/81 +/- 2 to 108 +/- 4/68 +/- 3 mmHg (p less than 0.001). Plasma atrial natriuretic factor was not low in the cirrhotic patients. Although these data are compatible with a primary disturbance of sodium excretion in early cirrhosis without ascites, such an explanation is complicated by the concomitant drop in blood pressure after atrial natriuretic factor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glomerular selective permeability to macromolecular neutral dextrans in experimental diabetes

Summary Rats with streptozotocin-induced chronic diabetes mellitus develop a glomerulopathy functionally manifested by proteinuria. The ability of the glomerular capillary wall to retard filtration of macromolecules was examined in 5 chronically diabetic Munich-Wistar rats exhibiting excessive proteinuria (39±7mg/24h, mean±SEM) and 5 age-matched normal Munich-Wistar rats without increased proteinuria (4.7±0.2 mg/24 h). Urinary albumin excretion was not increased in the diabetic rats (2.0±0.6 mg/24h vs 1.6±0.3 mg/24h) suggesting that the normal net electronegative charge of the glomerular capillary wall was not altered. Fractional clearances of macromolecular neutral dextrans were similar in diabetic and normal rats throughout a wide range of molecular size (18–42 Å). Glomerular filtration rate was the same in the two groups of rats (2.77±0.16ml/min in diabetics and 2.72±0.11ml/ min in normals) suggesting that renal haemodynamic factors did not influence fractional clearances of neutral dextrans in diabetic rats. We conclude that the proteinuria exhibited by these chronically diabetic rats is not attributable to alterations of size-selective properties of the glomerular capillary wall, such as increases in the size or the number of pores.     

Renal effects of prolonged synthesis inhibition of endothelium-derived nitric oxide.

The aim of the present study was to investigate in conscious dogs the long-term effects of nitric oxide synthesis inhibition on glomerular filtration rate, sodium and water excretion, and plasma levels of renin and aldosterone. After a control period of 3 days, an inhibitor of endothelium-derived nitric oxide synthesis, NG-nitro-L-arginine-methyl ester, was infused for 3 consecutive days at a dose (50 ng/kg/min) that did not induce significant changes in arterial pressure (n = 6). The inhibition of nitric oxide synthesis led to a large and sustained decrease (p less than 0.05) in glomerular filtration rate of approximately 35%. This change was accompanied by a decrease (p less than 0.05) in urinary sodium excretion from 78.9 +/- 4.6 meq/day to 49.8 +/- 6.8, 60.1 +/- 4.2, and 53.5 +/- 9.0 meq/day by days 1, 2, and 3 of nitric oxide synthesis inhibition, respectively. Changes in fractional sodium excretion failed to achieve statistical significance. Nitric oxide synthesis inhibition also induced a significant and sustained decrease in urine flow rate. The decrease in glomerular filtration rate, natriuresis, and diuresis was accompanied by a 45% increase in plasma renin activity (p less than 0.05) and no change in plasma aldosterone concentration. By day 3 of the recovery period, glomerular filtration rate, natriuresis, diuresis, and plasma renin activity returned to values similar to those found during the control period. The administration of L-arginine during 3 consecutive days (5 micrograms/kg.min i.v.) did not modify any of the parameters measured but effectively prevented all the renal changes induced by the 3 days of nitric oxide synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hypoxemia on sodium and water excretion in chronic obstructive lung disease

To determine the role of hypoxemia in the pathogenesis of impaired sodium and water excretion in advanced chronic obstructive lung disease, 11 clinically stable, hypercapneic patients requiring long-term supplemental oxygen were studied. The renal, hormonal, and cardiovascular responses to sodium and water loading were determined during five-and-a-half-hour studies on a control day (arterial oxygen tension = 80 +/- 6 mm Hg) and on an experimental day under hypoxic conditions (arterial oxygen tension = 39 +/- 2 mm Hg). Hypoxemia produced a significant decrease in urinary sodium excretion but did not affect urinary water excretion. Hypoxemia also resulted in concomitant declines in mean blood pressure, glomerular filtration rate, and filtered sodium load. Renal plasma flow and filtration fraction were unchanged whereas cardiac index rose. On the control day, plasma renin activity and norepinephrine levels were elevated whereas aldosterone and arginine vasopressin levels were normal; none of these four hormones was affected by hypoxemia. Renal tubular function did not appear to be altered by hypoxemia as there was no significant change in fractional reabsorption of sodium. The concurrent decreases in glomerular filtration rate, filtered sodium load, and mean blood pressure at constant renal plasma flow suggest that the reduction in urinary sodium excretion was due to an effect of hypoxemia on glomerular function, possibly related to impaired renovascular autoregulation.     

Juxtaglomerular apparatus T-cell infiltration affects glomerular structure in Type 1 diabetic patients

Aims/hypothesis Type 1 diabetes is an autoimmune disorder associated with T-cell mediated injury to multiple endocrine tissues. T-cell infiltration of the juxtaglomerular apparatus could be associated with changes in local renin angiotensin system activity and, thus, with changes in the renal microenvironment. We examined the frequency of juxtaglomerular apparatus T-cell infiltration early in Type 1 diabetes and tested whether this is associated with renal structure and function.Methods We classified 89 Type 1 diabetic patients by immunohistochemical analysis as either juxtaglomerular apparatus T-cell positive (n=37) or T-cell negative (n=38). Borderline cases (n=14) were not considered further.Results T-cell positive patients had a shorter duration of diabetes (6.7±2.5 years) than T-cell negative patients (9.2±5.0 years, p=0.011) and lower albumin excretion rate, but they had a similar glomerular filtration rate and blood pressure. Renal biopsy morphometric analysis showed similar glomerular basement membrane width and mesangial fractional volume in these two groups. However, glomerular capillary surface density (p=0.0012) and filtration surface per glomerulus (p=0.0155) were greater in the T-cell positive patients.Conclusion/Interpretation Increased filtration surface per glomerulus could be associated with glomerular filtration rate preservation in diabetes. Thus, juxtaglomerular apparatus immunologic injury in Type 1 diabetes patients could delay the clinical consequences of diabetic nephropathy.Abbreviations ECM Extracellular matrix - RAS renin-angiotensin-system - JGA juxtaglomerular apparatus - NHDN natural history of diabetic nephropathy - IP immunoperoxidase - GV mean glomerular volume - TGF-B transforming growth factor-B - Vv(Mes/glom) mesangial fractional volume per glomerulus - GBM glomerular basement membrane - Sv(PGBM/glom) surface density of the peripheral glomerular capillary perglomerulus - TFS total filtration surface per glomerulus - Vv(Int/cortex) fractional volume of renal cortical interstitium See the Acknowledgements for the list of investigators of the International Diabetic Nephropathy Study Group (IDNSG)     

Fluorescent dyes modify properties of proteins used in microvascular research

OBJECTIVE: Fluorescent dyes, used frequently to label proteins for microvascular experiments, are assumed to not alter the protein's physicochemical characteristics. We tested the validity of that assumption for two probes, bovine serum albumin (BSA) and alpha-lactalbumin. METHODS: Standard electrophoretic techniques were used to examine the influence of five fluorescent dyes on the following three properties of BSA: molecular size (sodium dodecyl sulfate-polyacrylamide gel electrophoresis [PAGE]); relative molecular charge (native PAGE); and isoelectric point (pI) (i.e., isoelectric focusing). Also examined were the influence of the dyes on the relative charge of alpha-lactalbumin (native PAGE). Paired measures of single-vessel flux were made using two commercial preparations of dye-BSA on porcine coronary arterioles and venules. RESULTS: The addition of fluorescein isothiocyanate (FITC) to BSA altered significantly its size (p < 0.01; n = 6), relative charge (p < 0.02; n = 7), and pI. The other dyes caused minimal, yet significant, changes on the relative charge of BSA without influencing size or pI. Only FITC altered the relative charge of alpha-lactalbumin. While arteriolar fluxes of FITC-BSA and tetramethyl rhodamine isothiocyanate (TRITC)-BSA did not differ (p = 0.43; n = 5), in venules the FITC-BSA flux was greater than the TRITC-BSA flux (p < 0.001; n = 6). CONCLUSIONS: The addition of fluorescent dyes, particularly FITC, alters the physicochemical characteristics of two widely used protein probes. These findings may affect the interpretation of microvascular permeability experiments performed using fluorescent dyes, and they suggest care in the selection of dyes for such experiments.     

Glomerular hyperfiltration in hypertensive African Americans

The incidence of end-stage renal disease attributable to hypertension is 5-fold greater in African Americans than in whites. To determine whether glomerular hyperfiltration is an antecedent to renal failure, we compared responses of renal blood flow and glomerular filtration rate to graded infusions of norepinephrine (0. 01, 0.025, and 0.05 microg. kg(-1). min(-1) for 30 minutes each) in 29 African Americans and 33 age-matched French Canadian whites with essential hypertension. Renal blood flow and glomerular filtration rate were measured by using a constant-infusion technique of PAH and inulin, respectively. Studies were conducted on an inpatient clinical research center, and antihypertensive medications had been discontinued for at least 1 week. Based on 24-hour blood pressure monitoring, nighttime blood pressures decreased (P<0.01) in the French Canadians but not in the African Americans. Baseline renal blood flow was higher (P<0.05) in the African Americans (1310+/-127 mL. min(-1) per 1.73 m(2)) than in the French Canadians (1024+/-42 mL. min(-1) per 1.73 m(2)); baseline glomerular filtration rate was also higher (P<0.01) in the African Americans (140+/-4 versus 121+/-4 mL. min(-1) per 1.73 m(2)). In response to norepinephrine-induced blood pressure increases, renal blood flow was autoregulated and did not change in either patient group. In the African Americans, glomerular filtration rate increased (P<0.01) to 167 mL. min(-1) per 1.73 m(2) during the first norepinephrine infusion, without subsequent change. In contrast, glomerular filtration rate did not change with norepinephrine-induced increases of blood pressure in the French Canadians. In the African Americans, the elevation of baseline glomerular filtration rate, with a further increase in response to norepinephrine, may be indicative of glomerular hyperfiltration. Glomerular hyperfiltration and lack of nocturnal blood pressure decline may contribute to the higher incidence of end-stage renal disease in hypertensive African Americans.     

Effect of hemoglobin levels on cardiovascular outcomes in patients with isolated systolic hypertension and left ventricular hypertrophy (from the LIFE study)

The optimal hemoglobin level in patients with hypertension or heart failure is not yet defined. The aim of the present investigation was to examine the relation of hemoglobin with cardiovascular outcomes in high-risk patients with isolated systolic hypertension (ISH) and left ventricular hypertrophy (LVH). In 1,326 patients with ISH in the Losartan Intervention For Endpoint Reduction in Hypertension (LIFE) study, hemoglobin and cardiovascular outcomes were examined using Cox proportional hazard models. Baseline hemoglobin was negatively related to rate of cardiovascular death (hazard ratio 0.81 per 1 g/dl, 95% confidence interval [CI] 0.67 to 0.98, p = 0.032) after adjusting for baseline Framingham risk score, LVH, treatment, and estimated glomerular filtration rate. Hemoglobin decreased slightly during the study and the decrease was more pronounced in the losartan group (13.9 +/- 1.3 to 13.6 +/- 1.4 g/dl) than in the atenolol group (13.9 +/- 1.2 to 13.8 +/- 1.4 g/dl). Hemoglobin as a time-varying covariate was negatively associated with rate of cardiovascular death (hazard ratio 0.75, 95% CI 0.63 to 0.90, p <0.001) and stroke (hazard ratio 0.84, 95% CI 0.72 to 0.99, p = 0.040) after adjusting for baseline Framingham risk score, LVH, treatment, and estimated glomerular filtration rate. In conclusion, in this high-risk population with ISH and LVH, lower hemoglobin at baseline was associated with higher probability of cardiovascular death, and decrease in hemoglobin over time was associated with higher probability of cardiovascular death or stroke; this effect was attenuated by treatment with losartan.