Evidence of changes in renal charge selectivity in patients with Type 1 (insulin-dependent) diabetes mellitus

Summary Altered filtration of macromolecules due to decreased electrical charge of the glomerular basement membrane might be the initial step in the development of albuminuria in patients with Type 1 (insulin-dependent) diabetes mellitus. We therefore investigated the selectivity index, i. e. renal clearance of non-glycated plasma albumin/clearance of glycated plasma albumin in 38 patients with Type 1 diabetes mellitus. The two albumin molecules differed slightly in charge, non-enzymatic glycated albumin being more anionic at physiological pH compared with unmodified plasma albumin. Glycated albumin in plasma and urine was determined by a specific, sensitive and highly reproducible chromatographic procedure. In diabetic patients with normal urinary albumin excretion, the selectivity index was increased threefold compared with that of non-diabetic subjects (2p< 0.01). A significant correlation (r=0.53, 2p < 0.01) between haemoglobin A_1c and selectivity index was demonstrated in these patients, indicating a change in charge-dependent renal filtration could possibly be attributed to non-enzymatic glycation of components in the glomerular basement membrane and tubuli. Diabetic patients with increased albumin excretion rate had a significantly lower selectivity index compared with patients with normal albumin excretion (2p < 0.01). A significant negative correlation (r=0.85, 2p <0.001, exponential curve fit) was seen between urinary albumin excretion and selectivity index in the diabetic patients, indicating that the capability of differentiating between macromolecules of different charges is again lost with increasing urinary albumin excretion.In conclusion, the selectivity index is significantly increased in Type 1 diabetic patients with normal urinary albumin excretion, possibly due to non-enzymatic glycation of structural glomerular proteins. The selectivity index is again reduced with increasing urinary albumin excretion, possibly due to structural changes different from non-enzymatic glycation. This observation is in accordance with the hypothesis that loss of anionic charges due to reduced heparan sulphate content in glomerular basement membranes plays an important role in the early stages of diabetic renal disease.     

Urinary excretion of glycated albumin in insulin-dependent diabetic patients with normal urinary albumin excretion

Summary Glycation involves both circulating proteins, such as albumin, and structural proteins, such as the components of the glomerular basement membrane. A preferential excretion of glycated albumin (more anionic at physiological pH compared with unmodified plasma albumin) has been reported by some authors, but not by others. We therefore investigated the selectivity index (renal clearance of non-glycated albumin/clearance of glycated albumin) in 25 insulin-dependent diabetic patients with normal urinary albumin excretion and in 19 well-matched control subjects. The selectivity index was significantly higher in diabetic patients than in control subjects: 1.38±0.05 SEMvs 0.98±0.02, p<0.0001. This result is not consistent with a preferential urinary excretion of glycated albumin, at least in normoalbuminuric uncomplicated insulin-dependent diabetic patients.     

Longitudinal evaluation of the renal clearance of glycated albumin in the diabetic rat

This study has examined glycation of serum albumin and its role in evolving diabetic proteinuria. Renal clearances of endogenous glycated and nonglycated albumin were studied in groups of normal and streptozotocin-induced diabetic Wistar-Kyoto rats over a 32 week period. Concentrations of glycated and nonglycated albumin in serum and urine were measured by rat albumin radioimmunoassay following separation on m-aminophenylboronate affinity columns. Levels of glycated serum albumin in diabetic rats were significantly higher than in normal rats (5.9 +/- 0.7% vs 4.4 +/- 0.3%, P less than 0.05). Median total urinary albumin excretion increased from 120 micrograms/24 h at baseline to 879 micrograms/24 h (P less than 0.05) 28-32 weeks after induction of diabetes. The renal clearance of glycated albumin was approximately twice as great as that of nonglycated albumin in both normal (P less than 0.01) and diabetic (P less than 0.01) rats. However, the glycated albumin/nonglycated albumin clearance ratio in diabetic rats did not correlate with duration of diabetes or with the level of albuminuria. These results indicate that glycation of albumin does not contribute disproportionately to the development of proteinuria in the diabetic rat, during which median renal albumin clearance increased 7-fold. Other factors, such as glycation of the glomerular filtration surface, may have a more important role in the pathogenesis of proteinuria in experimental diabetes.     

Glomerular basement membrane selective permeability in short-term streptozotocin-induced diabetic rats

In diabetes, the glomerular basement membrane undergoes thickening and structural alterations with loss of glomerular permselectivity properties. However, the onset of the alterations at early phases of diabetes is unclear. Aiming to determine the functional and structural alterations of the glomerular wall in the early stages of diabetes, we have studied the distribution of endogenous circulating albumin and type IV collagen in the glomerular basement membrane, using the immunocytochemical approach. The streptozotocin-injected hyperglycemic rat was our animal model. Renal tissues were examined after 10 days, 2, 4 and 6 months of hyperglycemia. Upon immunogold labelings, changes in the glomerular permeability to endogenous albumin were found altered as early as upon ten days of hyperglycemia. In contrast, no structural modifications were detected at this time point. Indeed, glomerular basement membrane thickening and an altered type IV collagen labeling distribution were only observed after four months of hyperglycemia, suggesting that functional alterations take place early in diabetes prior to any structural modification. In order to evaluate the reversibility of the glomerular alterations, two-month-old diabetic animals were treated with insulin. These animals showed a significant restoring of their glomerular permselectivity. Our results suggest a link between glycemic levels and alteration of glomerular permeability in early stages of diabetes, probably through high levels of glycated serum proteins.     

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)     

Plasma disappearance of glycated and non-glycated albumin in Type 1 (insulin-dependent) diabetes mellitus: evidence for charge dependent alterations of the plasma to lymph pathway

Summary The fractional plasma escape rates of glycated and non-glycated albumin have earlier been measured in groups of Type 1 (insulin-dependent) diabetic patients and control subjects. The escape of non-glycated albumin was similar in control subjects and normoalbuminuric patients, but elevated in patients with micro or macroalbuminuria. In all groups the escape rate of glycated albumin was lower than that of non-glycated albumin. Glycation increases the anionic charge of albumin. To assay for charge-dependent alterations of transport a selectivity index (non-glycated albumin/glycated albumin transport ratio) was determined from the disappearance data. The index was high in control subjects (1.021±0.0057 (SEM)). This reflects a mean difference between the two escape rates of 2.1% per hour (for comparison the mean of the fractional escape rate of non-glycated albumin of the normal control subjects was 4.7% per hour). The index was numerically even higher in normoalbuminuric patients (1.031±0.0047 (SEM)), but reached significantly lower levels in patients with microalbuminuria (1.013±0.0030 (SEM), p<0.02). Patients with clinical nephropathy had very low levels indicating loss of selectivity (1.002±0.0068 (SEM), p<0.001). This pattern accords well with measurements of renal clearance selectivity indices, suggesting a general, progressive deterioration of anionic perivascular barrier components in diabetic microangiopathy. The structural target for these changes is likely to be the glycosaminoglycans of the glomerular basal membrane and the interstitial matrix.     

Reactivity with diazonium salts of albumin from micro and macroalbuminuric diabetic patients

A recent theory of the pathogenesis of diabetic microalbuminuria points to an involvement of glycated albumin, which has been demonstrated as being able to fluetrate the renal filter. The chemical characterization of urinary albumin, initially performed on the electrical charge and conformation of the protein has now been extended to the affinity properties for specific chemical probes. In this context, urinary albumin from Albustix-negative diabetic patients was found to be highly reactive towards diazonium salts (a dye specific for pyrrole rings) while the same protein purified from macroproteinuric diabetics showed no difference in reactivity towards diazonium salts compared to serum or normal albumin. These data indicate that, beside being highly anionic and conformationally deranged, urinary albumin in conditions of normal renal selectivity contains pyrrole structures. The reasons for considering this reactivity as an indirect sign of rearranged structure are presented here.     

Alterations of glomerular basement membrane charge and structure in diabetic nephropathy

Summary We examined glomerular basement membrane anionic site distribution identified by cationic gold in seven patients with insulin-dependent and four patients with non-insulin-dependent diabetes mellitus, presenting a spectrum of clinical and glomerular changes. Anionic sites were investigated by pretreatment of tissue with glycosaminoglycan-degrading enzymes prior to cationic gold staining. The distribution of chondroitin sulphate proteoglycans — a previously unrecognized glomerular basement membrane component — and type IV collagen was examined by immunoelectron microscopy to identify structural changes in the basement membrane. Findings were compared with those of non-diabetic patients showing minor proteinuria and morphologically normal glomerular basement membranes. Two patients, originally diagnosed as having diabetic nephropathy were also examined at 19 weeks and 5 years after renal transplantation. Characteristic redistribution of type IV collagen and chondroitin sulphate proteoglycans was noted in thickened glomerular basement membrane segments (>400 nm) of diabetic patients and those with renal transplants. Extension of anionic sites deep into the glomerular basement membrane at pH 2.5, together with loss of interna sites at pH 5.8 is unique to diabetic nephropathy. Reduced charge density was apparent in some patients due to thickening of the glomerular basement membrane, although the number of anionic sites per unit length of membrane was actually increased. Thus, charge aberration in diabetic nephropathy is due to displacement rather than loss of anionic sites. Removal of more than 90% of these sites by heparitinase, confirms their association with heparan sulphate proteoglycans. Similar derangement of anionic sites in all patients with diabetic nephropathy irrespective of the degree of proteinuria, suggests that a heparan sulphate proteoglycan-related charge barrier plays a minor role in controlling permeability of the diabetic glomerular basement membrane.Abbreviations BSA Bovine serum albumin - CG cationic gold - CSPG chondroitin sulphate proteoglycans - GAG glycosaminoglycan - GBM glomerular basement membrane - HSPG heparan sulphate proteoglycans - LRE lamina rara externa - LRI lamina rara interna - PCI protein:creatinine index     

Renal clearance, tubular reabsorption and urinary excretion of albumin in monkeys infected with Plasmodium knowlesi

The glomerular filtration rate (GFR) and the glomerular clearance rate of albumin were determined in 6 rhesus monkeys infected with P. knowlesi as well as in 6 control monkeys by using 51Cr-EDTA and 125I-HSA respectively. The excreted albumin in the urine was also determined and used for calculating the renal clearance value. The amount and rate of albumin filtered in the glomeruli and reabsorbed by the tubules were then calculated from these parameters. The present study showed that the rate and amount of albumin filtered through the glomeruli, reabsorbed by tubules and excreted in the urine of normal monkeys, which were similar to results reported earlier in normal human, dogs and rats. In the monkeys infected with P. knowlesi the glomerular filtration rate was reduced while the glomerular clearance rate of albumin increased which resulted in the significantly elevated filtered albumin in the glomeruli. The tubular reabsorptive capacity to plasma albumin was also found to be significantly increased in parallel to the elevated filtered load of albumin. However, as this capacity was limited, the excess albumin was therefore excreted into the urine in the infected monkeys. All these findings indicated that the albuminuria in P. knowlesi-infected monkeys was due to the increased glomerular capillary permeability to plasma albumin, although the tubular reabsorptive capacity increased but could not cope with a very high filtered load, therefore, excess albumin was detected in the urine.     

Relative contribution of vasopressin and angiotensin II to the altered renal microcirculatory dynamics in two-kidney Goldblatt hypertension

The renal microcirculation was assessed in non-clipped kidneys of 23 Munich-Wistar rats with two-kidney one-clip Goldblatt hypertension. Four weeks after placement of a renal arterial clip, mean systemic arterial pressure averaged 163 +/- 5 mm Hg in hypertensive rats as compared to 108 +/- 2 in sham-operated controls (n = 6 rats). Non-clipped kidneys in hypertensive rats were characterized by higher glomerular capillary hydraulic pressures, single nephron glomerular filtration rate, and afferent arteriolar resistance. The glomerular capillary ultrafiltration coefficient was significantly reduced in hypertensive rats. In 10 of these rats, intravenous infusion of the angiotensin antagonist, saralasin, or the converting enzyme inhibitor, SQ20881, led to significant reductions in systemic arterial pressure and in afferent and efferent arteriolar resistance, on average by 8 +/- 3%, 15 +/- 4%, 28 +/- 5%, respectively. These changes were associated with significant increase in glomerular plasma flow, while ultrafiltration coefficient remained unaffected. In the presence of saralasin or SQ20881, infusion of a specific antagonist of the vascular action of arginine vasopressin led to significant systemic but not renal vasodilation. Thus, whereas systemic arterial pressure fell further, on average by 23 +/- 2%, renal arteriolar resistance remained constant, resulting in marked reduction in glomerular capillary hydraulic pressures (by 18 +/- 2%) and glomerular plasma flow rate (by 28 +/- 10%). Because of these pronounced reductions in glomerular pressures and flows induced by vasopressin antagonist, single nephron glomerular filtration rate fell markedly in hypertensive rats (by 34 +/- 6%) despite normalization of ultrafiltration coefficient. When hypertensive rats (n = 7) were treated with vasopressin antagonist alone, a modest fall in systemic arterial pressure was again observed in the absence of changes in renal arteriolar resistance. Due to this selective extrarenal vasodilatory action of vasopressin antagonist, glomerular capillary hydraulic pressure, plasma flow rate, and single nephron glomerular filtration rate again fell markedly. When these vasopressin antagonist pre-treated hypertensive rats were given saralasin or SQ20881, marked reductions in renal arteriolar resistance were observed in association with a significant increase in glomerular plasma flow rate. These observations made during acute inhibition of angiotensin II and vasopressin indicate that both of these vasopressin hormones may play important roles in maintaining systemic hypertension in hypertensive rat. By virtue of its preferential constrictor effects on extrarenal rather than renal vasculature vasopressin serves to maintain high glomerular pressures and flows in the non-clipped kidney of Goldblatt hypertensive rats.     

Hepatorenal syndrome. Studies of the effect of vascular volume and intraperitoneal pressure on renal and hepatic function

Eleven patients with well-documented hepatorenal syndrome were studied by measurement of blood volume, glomerular filtration rate, renal plasma flow, plasma aldosterone concentration, renin substrate concentration, and plasma renin activity. They were then given 750 ml of stored plasma, 750 ml of fresh frozen plasma, and then an infusion of angiotensin II, in random order on successive days. Infusion of fresh frozen plasma improved function more than did stored plasma and in addition returned a very low filtration fraction toward normal. Angiotensin II infusion increased filtration fraction, but decreased glomerular filtration rate, renal plasma flow, and urine flow sharply. Patients were then given a daily infusion of 1,000 ml of fresh frozen plasma for seven to 18 days to expand the blood volume to supranormal levels as assayed by serial measurement of blood volume. Plasma aldosterone levels decreased to a normal range, glomerular filtration rate and renal plasma flow both increased, and urinary excretion of sodium and potassium both returned toward normal. The effect of intraperitoneal pressure was then studied by measuring glomerular filtration rate, renal plasma flow, pressure in the vena cava, hepatic vein free flow, and hepatic vein wedged pressure before, during, and after paracentesis to reduce the intraperitoneal pressure from 30 to 40 cm H2O to 12 to 17 cm H2O. Venous pressures moved parallel to ascitic fluid pressures, and glomerular filtration rate, renal plasma flow, and urine flow all improved sharply; then, as ascitic fluid continued to form, reducing vascular volume, urine flow, glomerular filtration rate, and renal plasma flow all decreased slowly. Six patients then underwent placement of a LeVeen shunt. Improvement in glomerular filtration rate and renal plasma flow and clinical condition was dramatic. During postoperative observation of up to two years, progressive improvement in hepatic function has occurred.     

Localization of sialic acid in kidney glomeruli: regionalization in the podocyte plasma membrane and loss in experimental nephrosis.

Sialic acid residues were localized by electron microscopy in renal glomeruli of normal and puromycin-treated rats with a cytochemical technique that utilized the Limax flavus lectin. In Lowicryl K4M thin sections from normal rats, sialic acid residues were found along the plasma membrane of the various glomerular cell types and in the glomerular basement membrane as well as the mesangial matrix. In NaDodSO4/PAGE, sialic acid residues of normal glomeruli were mainly confined to a 140-kDa protein previously identified as podocalyxin. The distribution of sialic acid residues in the podocyte plasma membrane was found to be remarkably regionalized. Based on the differential labeling intensity, three plasma membrane domains could be defined: the foot process base, the foot process region above the slit diaphragm, and the body of podocytes. Cytochemical and biochemical analysis of glomeruli from puromycin-treated rats showed a loss of sialic acid residues from glomerular sialoglycoconjugates indicating a perturbated glycosylation.     

Glomerular epithelial foot processes and filtration slits in IDDM patients

Summary Diabetic nephropathy is associated with functional changes in the glomerular filtration barrier but the structural counterpart remains unknown. Width of glomerular epithelial cell foot processes and of filtration slits were determined by morphometric methods in 11 non-diabetic kidney donors and in 28 diabetic patients with albumin excretion rates ranging from normal to proteinuria. Foot process width was estimated from the ratio of tuft surface density to length density of slits. At high magnification independently sampled, perpendicularly cut slits were classified. Foot process width on peripheral basement membrane was increased in microalbuminuric compared to normoalbuminuric diabetic patients (p<0.05) but showed no significant correlation with the level of albumin excretion when patients with increased barrier permeability were considered. Width of filtration slits in normo- and microalbuminuric diabetic patients exceeded that in non-diabetic control subjects (p<0.05). Filtration slits were narrower in patients with overt proteinuria than in patients with microalbuminuria (p<0.05) and correlated with glomerular filtration rate in all of the diabetic patients (r=0.65, p<0.005). The results show that insulin-dependent diabetic patients with nephropathy present changes of epithelial cells and filtration slits, demonstrable already in the stage of microalbuminuria. The mechanism of albumin leakage is not achieved by these measures. The dimension of filtration slits may play a contributing role in the level of glomerular filtration rate in diabetic patients.Abbreviations IDDM Insulin-dependent diabetes mellitus - GFR glomerular filtration rate - AER albumin excretion rate - HbA_1c glycated haemoglobin - ND non-diabetic control subjects - D_NA diabetic patients with normal albumin excretion rate - D_MI diabetic patients with microalbuminuria - D_P diabetic patients with proteinuria - CV coefficient of variation (SD/mean) - FPW_PBM width of foot processes on peripheral basement membrane - FPW_MES width of foot processes on glomerular mesangium - ANOVA analysis of variance - PBM peripheral basement membrane     

Distribution of endogenous albumin in the glomerular wall of streptozotocin-induced diabetic rats as revealed by high-resolution immunocytochemistry

Endogenous albumin was revealed with high resolution in the glomerular wall of renal tissue from normoglycaemic and long-term streptozotocin-induced hyperglycaemic rats applying the protein A-gold immunocytochemical approach. In tissues from normal animals, albumin antigenic sites were detected at the level of the endothelial cell basal plasma membrane and in the subendothelial side of the lamina densa of the glomerular basal laminae. The epithelial side of the laminae was weakly labelled, while the urinary space was devoid of labelling. In the podocytes, labelling for albumin was confined to few lysosomal structures. In diabetic animals, concomitant with hyperglycaemy, low insulin levels, significant glycosuria, proteinuria and albuminuria, the glomerular basal laminae displayed the characteristic increase in thickness found in diabetic microangiopathy (404 ± 45 nm versus 190 ± 10 nm). Major basal laminae deposits were also found in the mesangial regions. Albumin antigenic sites were detected throughout the entire thickness of the glomerular basal laminae without any preferential accumulation at any particular site. Labelling was also found over flocculent material present in the urinary space. Numerous densely labelled lysosomal structures were present in the podocytes. The basal laminae deposits in the mesangial regions were labelled for albumin. Morphometrical evaluations made on the distribution of the labelling confirmed the qualitative observations. Two sites for albumin retention were revealed in the glomerular wall of the normal animal: the endothelial cell basal membrane (< 10 nm) and the subendothelial side of the lamina densa (50 nm). Besides the endothelial cell basal membrane ( < 10 nm) for the diabetic animals, no other site of retention was detected; the distribution of albumin was uniform throughout the basal laminae. These results are in agreement with the physiological demonstration of restricted passage of albumin through the glomerular wall in the normal condition and its loss in diabetes.     

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.     

Normalizing glycated albumin reduces increased urinary collagen IV and prevents renal insufficiency in diabetic db/db mice

Increased excretion of type IV collagen accompanies the accumulation of mesangial matrix, which leads to compromise in the glomerular filtration surface area, during the development of diabetic nephropathy. We postulated that the response of urinary collagen IV would be useful in evaluating possible treatment strategies to arrest the nephropathic process while still at a reversible stage. To test this hypothesis, we examined the effect of a small molecule (22CPPA) that inhibits the formation of glycated albumin, which is causally linked to the pathogenesis of diabetic nephropathy, on collagen IV excretion, albuminuria, and renal function in db/db mice. Compared to nondiabetic db/m mice, db/db animals showed markedly increased urinary collagen IV and albumin, significantly elevated serum glycated albumin and creatinine concentrations, and a significantly reduced creatinine clearance. Treatment of db/db mice with test compound, which normalized glycated albumin concentrations, significantly lowered collagen IV and albumin excretion and ameliorated the fall in creatinine clearance and the rise in serum creatinine despite persistent hyperglycemia. The findings indicate that reduction of elevated collagen IV excretion in diabetes reflects a salutary influence on developing glomerulosclerosis, and that glycated albumin has an important nephropathogenic role that can be therapeutically addressed independent of glycemic status.     

Kidney function in normal man during short-term growth hormone infusion.

Kidney function was studied in 9 normal males before and during a 2 h growth hormone (GH) infusion of 50 ng/kg/min. The following variables were measured during each 20 min clearance period: glomerular filtration rate, GFR, effective renal plasma flow, RPF (steady state infusion technique with urinary collections using [125I]iothalamate and [131I]iodohippurate), and urinary albumin and beta2-microglobulin excretion rates (radioimmunoassays). The GH infusion resulted in a 10-fold increase in plasma GH concentration. All the above mentioned variables remained practically unchanged during the infusion except for a small (-5%) but significant decrease in renal plasma flow (P less than 0.01). Our negative results contrast to the findings of increased GFR and RPF during prolonged GH administration and suggest that GH requires several hours or days for its renal effects to become manifest.     

Albuminuria in hypertension is linked to altered lysosomal activity and TGF-beta1 expression

Increased intraglomerular pressure is considered a major factor for increased albumin excretion in hypertension. However, other factors should also be considered because recent studies in both humans and rats have demonstrated that proteins undergoing filtration and renal passage are extensively modified by renal cell lysosomal processing; >95% of albumin is degraded to peptides that are not detected by routine immunochemical assays. Changes in postglomerular lysosomal processing may therefore be responsible for the increased intact albumin excreted in hypertension-related kidney disease. We hypothesize that transforming growth factor-beta, which is known to decrease lysosomal activity, may be upregulated in hypertension and may play a role in increased intact albumin excretion. The aims of this study were to determine the effect that hypertension has on (1) renal cell lysosomal processing of albumin and dextran sulfate, (2) glomerular permeability, and (3) renal transforming growth factor-beta(1) expression. Spontaneously hypertensive rats and Wistar-Kyoto rats were used at 8, 16, and 24 weeks. We demonstrate that albuminuria in hypertension is linked to an inhibition of lysosomal processing as determined by (1) size exclusion chromatography analysis of urinary [(14)C]albumin structural integrity and (2) ion exchange analysis of urinary [(3)H]dextran sulfate. This inhibition gives rise to an increased proportion of radioimmunoassay detectable (intact) albumin and intact dextran sulfate independent of changes in glomerular capillary wall permeability as determined by the fractional clearance of [(3)H]Ficolls of various radii. These changes may be correlated with increased renal transforming growth factor-beta(1) expression.     

Evidence for renal vascular remodeling in angiotensin II-induced hypertension

OBJECTIVES: To determine whether 'slow pressor' hypertension from systemic angiotensin (Ang II) infusion was associated with renal vascular structural remodeling of the renal resistance vessels and glomerulus. METHODS: Ang II (4.5-10 ng/kg per min) or vehicle was infused for 10 days. Renal resistance vascular lumen changes were assessed at 10 days as changes in renal pressure flow and pressure-glomerular filtration rate (GFR) and pressure-Na+ excretion in maximally dilated, isotonically perfused kidneys. RESULTS: Low-dose, initially subpressor Ang II infusion for 10 days increased conscious arterial pressure by 27 mmHg compared to vehicle-infused rats (140 +/- 7 and 113 +/- 2 mmHg, respectively). There was no change in the pressure-flow relationship but the slope of the pressure-GFR relationship was reduced in the rats treated with Ang II. These changes are consistent with equal and opposite pre-and post-glomerular effects (i.e., increased pre-glomerular vessel resistance and reduced post-glomerular vessel resistance) and reduced glomerular ultrafiltration coefficient. There was also a significant reduction in pressure-dependent Na+ excretion. CONCLUSIONS: Slow pressor Ang II-induced hypertension was associated with apparent pro-hypertensive changes in the kidney involving pre/post-glomerular vessel remodeling as indicated by an apparent reduction in pre-glomerular lumen dimensions, a reduced glomerular filtration capacity and a reduction in the pressure natriuresis relationship.     

A change in glomerular permeability in renovascular hypertension. Participation of angiotensin and structural lesions

To characterize the decrease in glomerular permeability that occurs in contralateral kidney of renovascular hypertension, glomerular hemodynamics were studied in Goldblatt hypertensive and normotensive control rats. The effects of converting enzyme inhibition (captopril) and renal vasodilatation induced with hyperoncotic plasma were evaluated: in addition, glomerular morphometry was performed. In hypertension, glomerular capillary pressure was increased, ultrafiltration coefficient was decreased, single-nephron filtration rate was normal and afferent resistance was elevated. Captopril rose glomerular filtration rate only in normotensive rats, but ultrafiltration coefficient increased in both groups. Hyperoncotic plasma induced a 98% increment in filtration rate and ultrafiltration coefficient rose by 48% in normotensive group. In hypertensive rats, filtration rate increased only 15% and ultrafiltration coefficient diminished 6%, morphometric studies showed dilatation of capillary loops and a larger glomerular volume. Similar response to captopril in both groups of rats suggest that the reduction in ultrafiltration coefficient in hypertension is not dependent of angiotensin; lack of response to hyperoncotic plasma suggests that it could be produced by structural changes in capillary wall that diminish hydraulic permeability since the larger glomerular volume indicates a greater area for filtration.