Enhanced natriuretic response to neutral endopeptidase inhibition in patients with moderate chronic renal failure.

Atrial natriuretic factor (ANF) has natriuretic, renin-suppressing and chronic hypotensive actions that may be utilized by inhibition of ANF degradation by neutral endopeptidase, E.C.24.11 (NEP). Three groups of 8 male patients [GFR 103 +/- 8 (Normal), 64 +/- 6 (Moderate CRF), and 16 +/- 2 ml/min (Severe CRF)] received 100 mg i.v. bolus of the NEP inhibitor candoxatrilat or placebo in random order in a double-blind crossover study. GFR (51CR-EDTA), ERPF (125I-hippuran). ANF (IRMA), urinary cGMP (RIA) and albumin (RIA) and sodium excretion and flow rate were measured hourly for two hours before and for seven hours after candoxatrilat administration. After candoxatrilat plasma ANF rose two- to threefold from baseline, and remained elevated for 5(N) and 7(M,S) hours (P < 0.01(N,S), P < 0.03(M)) associated with an immediate rise in urine cGMP excretion from 23.5(N), 25.4(M) and 10.4(S) nmol/hr (base) to 51.7(N), 73.8(M) and 27.5(S)(peak) lasting 7(N,M,S) hours (P < 0.01(N,M,S)). There was a marked natriuresis in all three groups, the cumulative sodium excretion at seven hours post-candoxatrilat being 104(N), 140(M), 102(S) mmol (P < 0.05(N,M,S)). This was greatest in those with moderate CRF (moderate CRF vs. normal, P = 0.036, moderate vs. severe CRF, P = 0.01, normal vs. severe CRF, P = 0.74). Following candoxatrilat there was a near doubling of the urine flow rate (P < 0.01(N,S), P < 0.02(M)). Urine albumin excretion increased in patients with renal failure (P < 0.01), but there was no change in GFR, ERPF or systemic blood pressure. We conclude that the marked natriuretic effects of acute NEP inhibition seen in normal subjects are enhanced in the presence of moderate CRF and sustained even in severe renal impairment.

In vitro formation of advanced glycation end products in peritoneal dialysis fluid.

Glycation of proteins in the peritoneum might occur due to the extremely high glucose concentrations (75 to 214 mmol/liter) in the dialysate of patients on continuous ambulatory peritoneal dialysis (CAPD) and may be involved in the etiology of ultrafiltration failure. Formation of both early (glycated albumin) and late (advanced glycation end products; AGE, measured as protein-derived fluorescence intensity, FI) Maillard reaction products was studied in vitro in dialysis fluids obtained from seven patients on CAPD and in phosphate buffered saline (PBS) controls paired for glucose and albumin concentrations. Percentage glycated albumin (median, range) increased (P < 0.02) from baseline after 10 and 21 days in both dialysate and PBS but did not differ (P > 0.05) between the two media at any time point (day 0, 3.6, 3.1-4.5 vs. 4.1, 3.0-4.6; day 10, 19.4, 7.9-54.8 vs. 19.1, 8.7-50.1; day 21, 29.0, 12.0-75.6 vs. 30.0, 11.7-69.8). Glycated albumin formation was linearly related to the glucose concentration (r > 0.98, P < 0.001) in both dialysate and PBS at 10 and 21 days. FI (U/g/liter albumin, median, range) increased (P < 0.02) from baseline after 10 and 21 days in dialysate but only after 21 days in PBS; this increase was significantly greater (P < 0.02) in dialysate than in PBS after 10 and 21 days (day 0, 41, 36-46 vs. 42, 37-46; day 10, 99, 88-161 vs. 51, 34-68; day 21, 113, 102-239 vs. 68, 54-91). After 21 days, FI was significantly related to glucose concentration (r = 0.90, P < 0.01) and to % glycated albumin (r = 0.92, P < 0.01) in PBS but not in dialysate (P > 0.05). AGE formation, but not glycation, decreased as a function of the dialysate dwell time and was inhibited by aminoguanidine. Our results demonstrate that formation of AGE products occurs in dialysis fluid and that factors in dialysate can modulate this process.

Effect of diabetes and peritonitis on the peritoneal equilibration test.

Peritoneal equilibration tests (PET) were performed on 47 patients (15 diabetics) who had been on CAPD for 1 to 112 months. Among new patients on CAPD (1 to 3 months) with no history of peritonitis, diabetics had higher D/PCr than non-diabetics (P < 0.02). However, after > or = 7 months of CAPD, in patients with < or = 2 episodes of peritonitis, glucose and creatinine transport rates were lower (P < 0.05) in diabetic than non-diabetic patients. Among patients on CAPD for > or = 7 months, creatinine (P < 0.05) and glucose transport (P < 0.01) were higher in patients with a history of > or = 3 episodes of peritonitis than in those with < or = 2 episodes. Drain volumes did not differ between any of the subgroups (all P > 0.05). The observations in patients newly established on CAPD were substantiated in a larger study of 55 non-diabetic and 35 non-insulin dependent diabetic patients. D/D0 glucose correlated with plasma glucose (r = 0.40, P < 0.02) in the diabetic group. Net ultrafiltration was reduced in hyperglycemic (P = 0.022) but not normoglycemic diabetics (non-diabetics 231 +/- 167 ml, hyperglycemic diabetics 127 +/- 177 ml, normoglycemic diabetics 238 +/- 159 ml). Creatinine clearance was higher in normoglycemic (P = 0.02) but not hyperglycemic diabetics (non-diabetics 6.8 +/- 0.9 ml/min, hyperglycemic diabetics 6.9 +/- 0.8 ml/min, normoglycemic diabetics 7.4 +/- 0.7 ml/min). These data show that diabetes and peritonitis incidence should be borne in mind when interpreting results of the PET.(ABSTRACT TRUNCATED AT 250 WORDS)

What is the value of measuring renal parenchymal thickness before renal biopsy?

Reduced renal length is widely used to diagnose chronicity in patients with renal impairment. A length of 9 cm or less measured ultrasonographically is considered to indicate irreversible disease. However, some patients with normal renal length have thin parenchyma. The aim of this study was to determine the relationship between ultrasonographically measured parenchymal thickness and renal length and to correlate parenchymal thickness with the histology obtained at renal biopsy. Sixty-four patients, aged 16-74 years, who had had a renal biopsy were evaluated retrospectively. Histology was considered in five categories: I, interstitial nephritis (n = 13); II, glomerulonephritis (28); III, diabetes mellitus/metabolic/other (8); IV, chronic renal disease (CRD) (11); V, hypertension/vascular disease (4). There was a good linear correlation between renal length and renal parenchymal thickness (r = 0.64, P < 0.001). Both were reduced most in patients with CRD. Sixty-four per cent of patients with CRD had renal parenchymal thickness 1.5 cm or less, compared to 38% in group I, 25% in groups II and V, and 7% in group II. Although 11/37 (30%) of patients whose serum creatinine had increased 3 months post-biopsy had parenchymal thickness 1.5 cm or less, so did 6/27 (23%) whose creatinine decreased. Like renal length, parenchymal thickness gives an indication of the chronicity of renal failure. However, some patients with parenchymal thickness 1.5 cm or less still have potential for improvement. This measurement alone should not be used to obviate renal biopsy.

Glycated albumin in serum and dialysate of patients on continuous ambulatory peritoneal dialysis.

1. Chronic use of hyperosmolar glucose solutions in continuous ambulatory peritoneal dialysis may cause glycation of peritoneal structural proteins which could contribute to membrane dysfunction and ultrafiltration failure. To determine whether glycation can occur in the environment of the dialysate, we have carried out studies using albumin as a model protein. 2. Glycated albumin was measured in the serum and dialysate of 46 patients on continuous ambulatory peritoneal dialysis (31 non-diabetic patients, 15 diabetic patients). Dialysate and serum glycated albumin (ranges 1.0-12.7% and 0.9-10.2%, respectively) were related to each other (r = 0.988, P < 0.001), but dialysate glycated albumin was significantly higher than serum glycated albumin (P < 0.0001), with the dialysate to serum glycated albumin ratio being greater than unity in 76% of patients (mean ratio 1.14). This implies either preferential transfer of glycated albumin across the peritoneal membrane or intraperitoneal glycation during the dwell period. 3. In vitro, significant glycation occurred in dialysate during a 6 h incubation period (P < 0.01) at a rate related to the glucose concentration in the dialysate (rs = 0.63, P < 0.05). The glycation rate was not significantly affected (P = 0.05) by factors other than the glucose concentration. 4. Our results demonstrate that protein glycation occurs within the peritoneum during continuous ambulatory peritoneal dialysis. Further studies are required to establish the relationship of glycation of structural proteins in the peritoneal membrane to membrane function.

Serum glycated albumin and fructosamine in renal dialysis patients.

The effect of uraemia on protein glycation was studied by measuring glycated albumin and fructosamine in 50 non-diabetic dialysis patients (31 continuous ambulatory peritoneal dialysis, CAPD, 19 haemodialysis). After correction for serum albumin concentration, glycated albumin (g/100 g) was increased in the haemodialysis group (1.94 +/- 0.40) compared with both CAPD patients (1.46 +/- 0.37; p < 0.001) and controls (1.52 +/- 0.29; p < 0.001), but did not differ between CAPD patients and controls (p > 0.05). Serum fructosamine, corrected for either serum albumin or total protein concentration (mumol/100 g), was raised in CAPD (828 +/- 90, 386 +/- 41, respectively) and haemodialysis patients (802 +/- 123, 391 +/- 42, respectively) compared with controls (609 +/- 69, 332 +/- 27, respectively; p < 0.0001 in all cases), but did not differ between the two dialysis groups (p > 0.05). A single haemodialysis cycle had no effect on the measurement of glycated albumin or fructosamine (p > 0.05). The results confirm that glycated protein levels are generally raised in dialysis patients. In CAPD patients, altered albumin metabolism resulting from large peritoneal losses is likely to have caused a decrease in the amount of albumin glycated, an effect less apparent on the concentration of fructosamine because of the additional contribution of glycated globulins.

Microalbuminuria in systemic sclerosis.

A prospective study was performed to determine urinary albumin excretion in a group of 28 patients with systemic sclerosis. At the initial screen one patient had proteinuria and three had microalbuminuria. One year later these abnormalities persisted and in two of of the patients serum creatinine had significantly increased. In addition, a further three patients had developed microalbuminuria. In a control group of 10 patients with primary Raynaud's disease none had microalbuminuria. In a second control group of 16 patients with unrelated skin diseases one patient had microalbuminuria and one proteinuria, but both these patients had a history of hypertension. It is concluded that microalbuminuria is more common in patients with systemic sclerosis than in patients of equivalent age with other dermatological conditions but no vascular disease.

Renal haemodynamic, hormonal and excretory effects of low-dose atrial natriuretic factor infusion in renal transplant recipients.

1. In experimental studies, activation of renal sympathetic nerves attenuates the natriuretic response to atrial natriuretic factor. We therefore investigated the response to low-dose infusion of atrial natriuretic factor in renal transplant recipients. 2. Eight male cyclosporin-treated renal transplant recipients received human-alpha atrial natriuretic factor (1-28) at a dose of 1.2 pmol min-1 kg-1 or placebo for 2 h in a placebo-controlled, randomized, cross-over study. The plasma atrial natriuretic factor concentration rose from 18.5 to 49.2 pmol/l in association with an immediate natriuresis (a rise of 49.1 mumol/min in the first 30 min, P less than 0.05; peaking at a 61% increase from baseline, P less than 0.01), diuresis (from 3.37 to 7.46 ml/min) and a threefold rise in urinary cyclic GMP excretion. 3. In response to infusion of atrial natriuretic factor, the packed cell volume rose by 4.2% (P less than 0.001) and the filtration fraction by 5% (from 22 to 27%, P less than 0.05), but there was no significant change in renal plasma flow, glomerular filtration rate or mean arterial blood pressure. Likewise, the plasma catecholamine concentrations, plasma renin activity and serum erythropoietin concentration remained unchanged. 4. The sensitivity of the renal allograft to plasma atrial natriuretic factor concentrations in the high physiological range suggests a role for endogenous atrial natriuretic factor in the modulation of graft function. Furthermore, the immediate natriuretic response to atrial natriuretic factor in the effectively denervated transplant kidney, in contrast to the delayed response seen in normal subjects, may imply that sympathetic nerves have an inhibitory effect on the renal response to atrial natriuretic factor in normal man.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation and validation of the affinity chromatography method for measuring glycated albumin in serum and urine.

Affinity chromatography on m-aminophenyl boronate columns together with albumin measurement by radioimmunoassay has been validated as a method for determining glycated albumin in serum and urine. Optimisation of sample volume and of elution buffer composition and volume ensured reproducibility of results. Fructosamine assay confirmed the absence of glycated albumin species from the non-glycated fraction. It was possible to elute the glycated fraction from the affinity columns with Tris or glycine which do not contain 1,2 diols but have similar functional groups. Column affinity was, therefore, not specific for glycated protein moieties. Inhibition of binding by glucose, and other small molecules in urine, necessitated ultrafiltration or dialysis of samples before analysis. Reference ranges for glycated albumin in non-diabetic subjects were 0.6-1.8% in serum and 0.9-2.6% in urine. In patients with diabetes mellitus, glycated albumin ranged from 1.4-10.9% in serum and from 1.5-12.5% in urine.

Pitfalls after total parathyroidectomy and parathyroid autotransplantation in chronic renal failure.

We have described 4 patients with chronic renal failure receiving regular haemodialysis treatment who underwent total parathyroidectomy with autotransplantation of parathyroid fragments into the forearm musculature for hypercalcaemic hyperparathyroidism. In all, there was an immediate and profound fall in plasma calcium levels. Hypercalcaemia recurred 1-5 years post-operatively and was resistant to resection of the autograft. In 3 cases, thallium-technetium subtraction scanning and multiple venous sampling for estimation of parathyroid hormone levels suggested multiple sites of hypersecretion of parathyroid hormone in the neck. In 1 case, these investigations revealed a mediastinal adenoma which was successfully removed. These cases reinforce previous suggestions that total parathyroidectomy is frequently incomplete and undermine the procedure of total parathyroidectomy with autotransplantation in patients with persisting uraemia.

Immunoradiometric assay of atrial natriuretic peptide in unextracted plasma.

We have developed and validated a two-site liquid-phase immunoradiometric assay (IRMA) of atrial natriuretic peptide (ANP) in unextracted human plasma. Both radiolabeled rabbit anti-ANP IgG and polyclonal mouse anti-ANP must bind to ANP for detection, and the assay is specific for peptides with both an intact C-terminus and a disulfide bridge. The assay sensitivity (detection limit) is 0.96 pmol/L, and the working range is 2.3-300 pmol/L, with the hook effect occurring above 500 pmol/L. Results for diluted plasma from normal subjects and from patients with renal failure paralleled the standard curve; analytical recovery of ANP added to such samples averaged 94%. The between- and within-assay CVs at 8 pmol/L were 10% and 5%, respectively. The assay is sufficiently sensitive and precise to detect the postural change in ANP concentrations in normal subjects.

Renal biopsy in patients with unexplained renal impairment and normal kidney size.

We report renal biopsy findings in 109 patients with unexplained renal impairment (serum creatinine greater than 0.15 mmol/l) and normal-sized non-obstructed kidneys. The most common histological lesions were interstitial nephritis, rapidly progressive glomerulonephritis and a variety of other types of glomerulonephritis. The groups could not be distinguished by the presence or absence of hypertension, haematuria, proteinuria, or features of systemic disease. However interstitial nephritis was found more frequently in patients presenting with one or none of these features and rapidly progressive glomerulonephritis in patients presenting with three or more. All four patients with none of these features had interstitial lesions. Fifty-two per cent of patients with interstitial nephritis improved and 60 per cent of the patients with rapidly progressive glomerulonephritis who received immunosuppressive treatment improved or remained stable with treatment. The benefits of a biopsy diagnosis were almost wholly confined to these two groups. Complications were recorded in nine patients - prolonged macroscopic haematuria in six and symptomatic perirenal haematomata in three. Six required blood transfusion. One required nephrectomy to control haemorrhage and subsequently died. Percutaneous renal biopsy is not without risk in patients with renal impairment but the benefits of diagnosing interstitial nephritis and rapidly progressive glomerulonephritis outweigh the disadvantages.