Sensory nerve excitability and neuropathy in end stage kidney disease.

BACKGROUND: Peripheral neuropathy is present in 65% of patients with end stage kidney disease (ESKD) starting dialysis. Studies of membrane potential and axonal ion channel function may help explain the pathophysiology. OBJECTIVES: To follow changes in median sensory axon excitability in patients with ESKD treated with haemodialysis, and correlate them with clinical rating scales and serum levels of potential neurotoxins. METHODS: Sensory nerve action potentials were recorded from the second digit following stimulation of the median nerve in 12 ESKD patients. Stimulus-response behaviour using two stimulus durations, threshold electrotonus to 100 ms polarising currents, a current-threshold relation, and recovery of excitability following supramaximal stimulation were recorded before, during, and after haemodialysis. Serum concentrations of potential neurotoxins were measured. RESULTS: Before dialysis, there were changes in nerve excitability consistent with axonal depolarisation: refractoriness was increased; superexcitability and depolarising threshold electrotonus were reduced. Following dialysis there were improvements in all indices, with correlations between excitability abnormalities and serum potassium measurements. Neuropathic symptoms correlated with excitability changes. CONCLUSIONS: Nerves are depolarised before haemodialysis in ESKD patients. The correlation of excitability abnormalities with potassium indicates that the achievement of normokalaemia should be a priority in treating such patients.

Response of the alternative complement pathway to an oral fat load in first-degree relatives of subjects with type II diabetes.

OBJECTIVE: To investigate levels of components of the alternative pathway of complement, and of two activation products, ASP and Bb, in persons ranging in insulin resistance both fasting and following the consumption of a high-fat, low-carbohydrate meal. SUBJECTS: Healthy controls (n = 17) and normoglycaemic first-degree relatives of patients with type II diabetes (n = 15). MEASUREMENTS: All subjects had normal glucose tolerance. Blood was collected for the measurement of plasma glucose, insulin, triglycerides and free fatty acids. Body composition was assessed with dual energy X-ray absorptiometry (DEXA) and whole-body insulin sensitivity with a euglycaemic, hyperinsulinaemic clamp. Basal and postprandial values over 6 h were determined for plasma C3, B, D, Bb and ASP. Basal levels of C1q, C4 and CRP were also determined. RESULTS: Controls did not differ significantly from the relatives of patients with type II diabetes for any metabolic parameter except in their degree of insulin resistance and central fat (kg). Across all subjects, basal levels of C3, but no other complement protein, were correlated with insulin resistance. Native complement proteins, but not ASP or Bb, were correlated with body mass index and the amount (kg) of central fat. Basal levels of C3 and factor B were significantly higher in the relatives group, whereas factor D and the classical pathway proteins C1q and C4 did not differ between the two groups. Postprandially, levels of factor D were significantly reduced in both groups. ASP levels also fell postprandially, the decline achieving significance in the relatives group. CONCLUSIONS: Elevated levels of C3 and factor B in the diabetic relatives group may have resulted from increased synthesis by adipose tissue. There was no evidence of alternative pathway activation in response to a fat meal in terms of ASP or Bb production, or significant consumption of C3 and factor B. These data do not support an essential requirement of the hypothesis that ASP is produced in response to the intake of fat.

The postprandial response of adiponectin to a high-fat meal in normal and insulin-resistant subjects.

OBJECTIVE: Adiponectin is an adipose-specific protein with short-term effects in vivo on glucose and fatty acid levels. We studied the plasma concentration and the proteolytic activation status of adiponectin following the consumption of a high-fat, low-carbohydrate meal. DESIGN: Analysis of adiponectin concentration and polypeptide structure after consumption of a fat meal. SUBJECTS: Normal subjects (n=24) and first-degree relatives of patients with type II diabetes (n=20). MEASUREMENTS: All subjects had a normal fasting plasma glucose and glucose tolerance. Blood was collected for the determination of plasma insulin, adiponectin, triglyceride, and free fatty acids. Body composition was assessed with dual-energy X-ray absorptiometry and whole-body insulin sensitivity with a euglycaemic, hyperinsulinaemic clamp. Postprandial response over 6 h was determined for plasma adiponectin, glucose, insulin, triglyceride, and free fatty acids. Adiponectin was measured by commercial RIA and its polypeptide structure examined by Western blotting. RESULTS: The relatives were more insulin resistant and had increased adiposity compared with control subjects. There was no significant difference in postprandial response in fatty acids, triglyceride, or insulin between the groups. Postprandial levels of adiponectin measured by radioimmunoassay were not significantly different from fasting levels, and no breakdown products of adiponectin were detectable in postprandial samples by Western blotting. CONCLUSIONS: Levels of circulating adiponectin do not alter in response to a fat meal, despite evidence in mice that acute changes in adiponectin significantly affect postprandial fatty acid flux. Moreover, a fat meal challenge did not lead to significant activation of adiponectin by proteolytic conversion.

C3a is made by proximal tubular HK-2 cells and activates them via the C3a receptor.

BACKGROUND: Some individual components of complement are synthesized by the kidney. However, it is not known whether these form functional pathways that are able to mediate more fundamental cellular events. We examined the ability of HK-2 tubular cells to produce an intact alternative pathway of complement and to respond to the C3a fragment thus produced through the C3a receptor. METHODS: The production of mRNA for alternative pathway components was detected by reverse transcription-polymerase chain reaction, whereas protein synthesis was investigated by probing Western blots of concentrated culture supernatants with polyclonal antisera. Levels of C3a and inositol phosphate produced by HK-2 cells were determined by radioimmunoassay, whereas those of transforming growth factor-beta1 (TGF-beta1) were measured by ELISA. Intracellular tyrosine phosphorylation in response to C3a was evaluated by Western blotting and chemiluminescence. RESULTS: HK-2 cells produce the complement polypeptides C3a, C3, and factors B and H. They also contain mRNA for all components of the alternative pathway and the C3a receptor. mRNA levels were up-regulated by interleukin-1alpha, interleukin-1beta, and tumor necrosis factor-alpha. Incubation of HK-2 cells with C3a led to an increase in intracellular inositol phosphate and to tyrosine phosphorylation of at least two proteins in a pertussis-toxin-sensitive fashion. C3a and C3a desarg also up-regulated the secretion of TGF-beta1 by these cells. CONCLUSION: HK-2 cells produce an intact alternative pathway of complement. In addition, both locally produced and urinary C3a have the potential to activate these cells, resulting in inflammatory events such as TGF-beta1 production.

The influence of oral lipid loads on acylation stimulating protein (ASP) in healthy volunteers.

OBJECTIVES: To examine the hypothesis that a sustained rise in plasma acylation stimulating protein (ASP, C3a desarg) accompanies the elevation in triacylglycerol that follows the ingestion of an oral fat load. DESIGN: Following an overnight fast, blood samples were obtained from healthy volunteers while fasting and 15 min, 1, 2, 4, 6 and 8 h following ingestion of: (i) a liquid meal, rich in dairy fat (eight subjects) and (ii) a semi-liquid meal, with higher total fat content and rich in polyunsaturated fat (six subjects). SUBJECTS AND METHODS: Four male and four female volunteers (age range: 22-51 y; body mass index (BMI): 17.9-26.9 kg/m2) received the first meal. Six subjects (age range: 32-60 y; BMI: 18.0-28.4 kg/m2), including three from the first study, received the second meal using the same protocol. ASP and C5a were measured by radioimmunoassay (RIA) and the complement proteins C3, factor B and C5 by radial immunodiffusion or nephelometry. Tumour necrosis factor (TNF)-alpha was measured by enhanced ELISA, and plasma cholesterol and triacylglycerol by an automated enzymatic method. The presence of chylomicrons was assessed in post-prandial plasma samples taken after the second meal. RESULTS: There was no significant change in mean ASP concentration in either group at any time point, following ingestion of either meal. However, there was a significant positive linear trend in ASP following the second fat challenge (ANOVA; P < 0.05). There was also no change in complement proteins, plasma cholesterol or TNF-alpha. Plasma triacylglycerol rose significantly after the first and second meals (P < 0.05 and P < 0.001 at 2 h post-prandially); the mean maximum rise above the fasting level was 58 +/- 41% and 89 +/- 38% respectively (mean +/- s.d.). Chylomicrons were detected in samples taken from each subject after the second meal. Analysis of individual ASP data showed a sustained rise in one subject after the first meal and two subjects after the second meal. Substantial variation in ASP concentration was observed in samples taken in the first 2 h post-prandially. CONCLUSION: There was no significant change in ASP nor other complement proteins for either group of subjects following ingestion of the lipid loads. Individual data showed substantial variation in post-prandial ASP, but multiple plasma sampling did not define the basis for this variation.

Renoprotective differences between perindopril and enalapril in the diabetic hypertensive rat do not reflect glomerular angiotensin-converting enzyme activity.

1. The various angiotensin-converting enzyme inhibitors have structural differences which affect their affinities for the catalytic sites on converting enzyme. We postulated that such differences might result in differences in renoprotective efficacy. We investigated this in the diabetic spontaneous hypertensive rat. We also investigated whether these differences might reflect variations in glomerular or plasma angiotensin-converting enzyme activity. 2. One week after induction of diabetes, rats were started on antihypertensive therapy: enalapril, 10 mg.day-1.kg-1, or perindopril, 4 mg.day-1.kg-1, in the drinking water. After 3 months, the rats were killed, blood samples were taken and tissues were harvested. Angiotensin-converting enzyme activity in isolated glomeruli and plasma was measured by fluorimetric assay. Glomerular protein content was also determined. 3. Urinary protein excretion was significantly lower in perindopril-treated rats than in either controls (P < 0.0005) or enalapril-treated rats (P < 0.05). Glomerular protein content was also lower in perindopril-treated rats (P < 0.05 versus enalapril; P < 0.005 versus control). There was no difference in glomerular angiotensin-converting enzyme activity between the two inhibitors although both were lower than control values (enalapril P < 0.025; perindopril P < 0.025). Plasma angiotensin-converting enzyme activity was significantly lower in the perindopril group than in either control (P < 0.005) or the enalapril group (P < 0.01). 4. We conclude that in the spontaneous hypertensive rat with streptozotocin-induced diabetes, perindopril is more effective than enalapril in reducing proteinuria and glomerular protein accumulation. This difference does not result from differences in glomerular-converting enzyme activity.

Detection and quantification of the control proteins of the alternative pathway of complement in 3T3-L1 adipocytes.

The complement peptide C3a desarg is identical to acylation-stimulating protein (ASP), a human plasma protein that potently stimulates adipocyte triacylglycerol synthesis and glucose transport. Both human and murine adipocytes express mRNA and/or protein for the complement components C3 and factors B and D (adipsin) required to generate ASP. However, the regulatory mechanisms controlling this process are unknown. We have established a semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique to demonstrate the presence in mouse 3T3-L1 adipocytes of mRNA for all components of the alternative pathway, including the control proteins factors I and H, CR1 and properdin. On differentiation, mRNA for C3 (fivefold) and factor D (> 50-fold) increased, whereas stimulation with tumour necrosis factor (TNF)-alpha and interleukin (IL) 1 beta led to eightfold increases in factor B mRNA. Metabolic labelling followed by immunoprecipitation showed that factor B protein is normally present in small quantities, and is greatly increased by cytokine stimulation. The larger quantities of C3 and H proteins present were little affected, whereas levels of C3a increased on cytokine stimulation. These results suggest that the rate-limiting step in the cytokine-induced production of ASP in adipocytes is factor B synthesis.

Acute but not chronic angiotensin-converting enzyme inhibition induces enzyme synthesis in the glomerulus of the spontaneously hypertensive rat.

1. Treatment with angiotensin-converting enzyme (ACE) inhibitors slows the rate of progression of nephropathy in the spontaneously hypertensive rat (SHR) with streptozotocin-induced diabetes. Paradoxically, however, chronic ACE inhibitor therapy has been reported to be associated with induction of ACE in the plasma. We sought to determine whether induction also occurred in the glomerulus. 2. Seven days after induction of diabetes rats were randomized to receive perindopril (4 mg/kg per day) in the drinking water or water alone. Blood glucoses were maintained 6-10 mmol/L by daily ultralente insulin. Rats were killed after 1 and 12 weeks of ACE inhibitor therapy and the kidneys were harvested. Angiotensin-converting enzyme activity was determined in isolated glomeruli before and after removal of perindopril and reconstitution with zinc sulphate. 3. After 1 week of ACE inhibitor therapy, glomerular ACE was significantly greater after removal of perindopril than either before its removal (P < 0.025) or in the untreated controls (P < 0.025). After 12 weeks of therapy, ACE activity was significantly lower in the perindopril-treated group than in the untreated controls (P < 0.025). There was no increase in ACE activity following removal of perindopril. 4. These studies suggest that short-term ACE inhibition is associated with induction of ACE in the glomerulus. However, there was no increase in ACE activity after removal of perindopril, suggesting that induction of synthesis of this enzyme in the glomerulus does not occur during chronic ACE inhibition.

The behaviour of human vitronectin in vivo: effects of complement activation, conformation and phosphorylation.

We examined the behaviour in vivo of native, specifically phosphorylated, and multimeric vitronectin to determine the effects of these modifications on its turnover, distribution and molecular behaviour. In normal rabbits, the plasma half-life (T1/2) of antigenically detected vitronectin was 8.00 +/- 1.26 h (mean +/- s.d.), with a fractional catabolic rate (FCR) of 18.77 +/- 1.57%/h and extravascular/intravascular ratio (EV/IV) of 1.00 (0.48-1.60, median and range). For vitronectin selectively phosphorylated by protein kinase A, T1/2 was 8.87 +/- 0.48 h, with a significantly smaller FCR of 10.85 +/- 0.71%/h (P < 0.005) and an EV/IV of 0.28 (0.15-0.36) (P < 0.05 compared with antigenically detected vitronectin). In vitro, phosphorylation had no effect on the affinity of vitronectin for heparin-Sepharose, while complement activation with cobra venom factor (CVF) led to a two-fold enrichment of 32P-vitronectin within the SC5b-9 complex. In vivo CVF caused a rapid decrease in the circulating levels of 32P-vitronectin and was accompanied by the prompt appearance of a high mol. wt species consistent with SC5b-9. Despite specific incorporation of 32P-vitronectin into SC5b-9, both forms of the molecule had similar inhibitory effects on C9-mediated haemolysis of EAC1-7 cells. Urea-activated vitronectin was rapidly cleared from circulation with less than 15% remaining after 1 h while protein-bound label accumulated in the spleen, lung and liver. These results demonstrate that vitronectin is a rapidly metabolized protein whose in vivo behaviour is markedly altered when phosphorylated or activated to form multimers and SC5b-9.

Differential efficacy of perindopril and enalapril in experimental diabetic nephropathy.

1. Treatment with angiotensin converting enzyme (ACE) inhibitors ameliorates human and experimental diabetic nephropathy, possibly as a result of changes in angiotensin II (AngII) and/or bradykinin concentrations. However, ACE is an indiscriminate enzyme, which hydrolyses numerous vasoactive peptides at two catalytic sites that are thought to be substrate specific. AngI is cleaved at the C-terminal site, bradykinin at both the C- and N-terminal sites, while other substrates may be preferentially cleaved at the N-terminal site. Of the various ACE inhibitors, some (e.g. perindopril) bind preferentially to the C-terminal site while others (e.g. enalapril) bind to both. We compared the efficacy of perindopril and enalapril in the diabetic SHR to determine whether all the benefits of ACE inhibition derive from changes in the concentrations of C-terminal related substrates. 2. Diabetes was induced by tail vein injection of streptozotocin (60 mg/kg) in 14 week old SHR. Blood glucose was maintained at 4-8 mmol/L by daily ultralente insulin injection and rats were randomized to control, enalapril (10 mg/kg per day) or perindopril (4 mg/kg per day) groups. Blood pressure, creatinine clearance and urinary protein excretion were monitored for 3 months. 3. Blood pressure in both treatment groups was lower than in control (perindopril P < 0.0001; enalapril P < 0.0001). Levels were marginally higher in the perindopril group than the enalapril group, although this difference was significant only in the second month (P < 0.025). Creatinine clearance was significantly lower in the perindopril group (0.44 +/- 0.05 mL/min) than in either the control rats (0.85 +/- 0.11 mL/min; P < 0.001) or the enalapril-treated group (0.66 +/- 0.05 mL/min; P < 0.005). Proteinuria was also lower in this group (4.3 +/- 0.9 mg/24h) than in the enalapril-treated (11.3 +/- 5.8 mg/24h; P < 0.05) or control groups (32.1 +/- 4.5 mg/24h; P < 0.0005). 4. The difference in efficacy between perindopril and enalapril that we have observed suggests that the benefits of ACE inhibition derive from changes in the concentrations of peptides catalysed by the C-terminal rather than the N-terminal site.

The metabolism of C9 in normal subjects and in patients with autoimmune disease.

The metabolism of the ninth component of complement (C9) was studied in eight healthy subjects and nine patients with autoimmune disease, including seven with systemic lupus erythematosus (SLE) and one each with mesangial IgA nephropathy and mixed essential cryoglobulinaemia. In normal subjects the metabolic parameters(mean +/- s.d.) were : fractional catabolic rate (FCR): 2.92 +/- 0.36%/h, plasma half-life (T1/2): 42.5 +/- 6.7 h, and extravascular/intravascular distribution ratio (EV/IV): 0.56 +/- 0.12. In patients the FCR was 3.38 +/- 0.70%/h, the T1/2 was 37.6 +/- 10.2 h, and the EV/IV was 0.55 +/- 0.19. Patients with reduced total serum haemolytic activity (i.e. CH50 <68% of normal human serum (NHS), N=7) had significantly higher FCR (3.57 +/- 0.67%/h) and shorter T1/2(33.5 +/- 6.8 h) than the control group (both P<0.05). The plasma concentration of the terminal complement complex (i.e. soluble TCC or SC5b-9) was higher in patients (median (range): 515 (300-1879 micrograms/l) than in normal subjects (313 (229-402 micrograms/liters): P<0.01) and showed a positive correlation with the FCR of C9 (r=0.61, P<0.01). Plasma C9 production rate was also greater in patients (0-11 +/- 0-05 mg/kg per h) compared with control subjects (0-07 +/- 0.03 mg/kg per h, P<0.05), and was associated with a higher C9 concentration in patients' sera (76 +/- 13 mg/l versus 61 +/- 14 mg/l, P<0.05). These results demonstrate that C9 is rapidly metabolized in normal humans and that hypercatabolism occurs in patients with autoimmune disease and complement activation. This was despite the presence of normal or elevated serum C9 levels and normal compartmental distribution.

Complement inhibition by human vitronectin involves non-heparin binding domains.

Vitronectin (complement S-protein), a multifunctional glycoprotein, inhibits complement-mediated cytolysis at two identified stages of terminal complement complex (TCC) formation: blocking of C5b-7 membrane binding, and prevention of C9 polymerization. However, the functional domain(s) of vitronectin involved in these reactions remains incompletely defined. In order to identify the complement inhibition site, a 12-kD heparin binding fragment and two other internal fragments (53 kD and 43 kD) of vitronectin were isolated after cyanogen bromide (CNBr) treatment of the native molecule. Potent inhibition of guinea pig erythrocyte (GPE) reactive lysis was demonstrated with native vitronectin, total CNBr digest and the 53-kD and 43-kD fragments, but only very poorly by the heparin binding 12-kD peptide. Similarly, the 43-kD fragment blocked the binding of C5b-7 to immobilized vitronectin, whereas the 12-kD fragment had no effect. These data localize the C5b-7 binding site to a 43-kD internal region. Further characterization of the fragments was carried out in an assay which detected C9 polymerization in the presence of C5b-8. Polymerized material was separated by PAGE, detected by autoradiography and quantified after excision from the gels. Results showed that polymerization did not occur in the presence of the 53-kD and 43-kD fragments. However, the 12-kD heparin binding fragment had no effect. It is proposed that prevention of C5b-8-induced C9 polymerization resides at a site in an internal region of the vitronectin molecule.

The kinetics and distribution of C9 and SC5b-9 in vivo: effects of complement activation.

Many diseases associated with complement activation are characterized by tissue deposition of components of the terminal complement complex (TCC). The ninth component of complement (C9) plays an important role in the cytolytic effects, and may contribute to the non-lethal cell-regulating functions of the TCC. In this study we examined the behaviour of radiolabelled human C9 and its soluble complexed form SC5b-9 in vivo in order to determine the effects of complement activation on its turnover, distribution and molecular size. In normal rabbits the metabolic parameters of 125I-C9 (median and range) were: plasma half-life (t1/2) 25.9 (20.6-29.5) h, fractional catabolic rate (FCR) 5.7 (5.3-7.0)%/h, and extravascular/intravascular ratio (EV/IV) 0.7 (0.6-1.1). The distribution of radiolabelled C9 amongst body tissues was similar to that observed for rabbit serum albumin (RSA). Activation of the complement cascade with i.v. injection of cobra venom factor (CVF) resulted in rapid disappearance of C9 from the plasma and accumulation of protein-bound radiolabeled in the spleen (exceeding the plasma concentration) and the liver. RSA metabolism and distribution were unaffected by CVF. Fine performance liquid chromatography (FPLC) gel filtration of plasma samples suggested that monomeric C9 was the only major radiolabelled protein present during normal turnovers, whereas CVF administration was accompanied by the prompt appearance of a high mol. wt species consistent in size with SC5b-9. When injected directly, 125I-SC5b-9 disappeared rapidly from the plasma, falling by 50% in 0.7 (0.6-0.8) h, and less than 15% remaining after 4 h with accumulation of protein-bound label in the spleen and liver. These results demonstrate the complexity of C9 metabolism during complement activation.

Relative topography of biologically active domains of human vitronectin. Evidence from monoclonal antibody epitope and denaturation studies.

A panel of monoclonal antibodies to human vitronectin was used to define some epitopes for the multifunctions of this protein. Separate antibodies were identified which strongly inhibited cell spreading activity and which prevented binding to collagen. A third group interfered with the ability of vitronectin to inhibit complement-mediated guinea pig erythrocyte reactive lysis. None of the antibodies from these three groups prevented heparin binding, providing evidence that this reaction occurs at a fourth location; a different monoclonal antibody partially inhibited the binding of heparin. The relative accessibility of each biologically active epitope was assessed by the differential binding of the monoclonals to native and denatured vitronectin. Reactivity of the antibody which inhibited heparin binding greatly increased upon denaturation of vitronectin, implying that this region is normally inaccessible in the native form of the molecule. By contrast, epitopes for cell spreading, collagen binding, and inhibition of terminal complement complex lysis were destroyed by denaturation. On the basis of denaturation data and epitope mapping by competitive exclusion of monoclonal antibodies, a Venn diagram was constructed to represent overlap of monoclonal antibody epitopes in the tertiary structure. Linear epitopes for the antibodies were identified using cyanogen bromide and plasmin-derived peptides from vitronectin. The antibody which strongly inhibited cell binding reacted with a region containing the RGD site, whereas linear epitopes for collagen binding and complement inhibition appeared to reside in a 43-kDa peptide representing the internal region of the amino acid sequence, excluding the heparin-binding site. The latter two epitopes were differentiated from each other by reactivity of the antibody which inhibited collagen binding toward a smaller 20-kDa plasmin-derived peptide.

The platelet angiotensin II receptor in type I diabetes: studies in patients with and without nephropathy.

Experimental studies demonstrate impaired regulation of the mesangial angiotensin II (AII) receptor in diabetes. This could contribute to the disturbance of glomerular blood flow and the development of diabetic nephropathy. The aim of this study was to determine whether a similar receptor abnormality occurs in patients with type I insulin-dependent diabetes mellitus (IDDM) and if so whether this is more prevalent in patients with micro- or macro-albuminuria. The platelet AII receptor was chosen because of its availability from the circulation and its comparable regulatory properties to tissue-based receptors. The interaction between plasma AII and its platelet receptor was examined in 45 patients with IDDM and 36 age- and sex-matched control subjects. Seven patients had clinical nephropathy and two had persistent micro-albuminuria. The duration of diabetes varied from 1 month to 42 years. There was a significant inverse correlation between plasma AII and the logarithm of receptor number in the control group (r = -0.555, P < 0.001). This relationship was not observed in the diabetic patients irrespective of the duration of disease or the presence of nephropathy. Receptor expression in patients without nephropathy showed no correlation with either duration of disease or the degree of glycaemic control. However, a significant relationship between AII receptor number and duration of diabetes was noted in the group with nephropathy (r = 0.723, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormality of the glomerular angiotensin II receptor in experimental diabetic nephropathy.

1. The combined effect of diabetes and hypertension on the plasma angiotensin II (AII)/glomerular AII receptor (AII-R) relationship in streptozotocin-induced diabetes was investigated as well as the effect of glycaemic control on this relationship. 2. Diabetes was induced in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats with streptozotocin 60 mg/kg and blood sugars maintained between 18-21 mmol/L (uncontrolled diabetes) and 4-8 mmol/L (controlled diabetes). Rats were killed on days 1 and 7. Angiotensin II receptor was estimated by saturation analysis and plasma AII by radio-immunoassay. 3. Angiotensin II receptors were significantly higher in non-diabetic SHR than WKY rats (708 +/- 62 and 388 +/- 36 fmol/mg protein, respectively, P = 0.0008). Plasma AII were comparable in both groups (47 +/- 2.7, 38 +/- 3.5 pg/mL, respectively) and a significant inverse relationship between AII/AII-R was observed (WKY P = 0.02 and SHR P = 0.004). 4. On day 7, plasma AII and AII-R levels in diabetic groups were comparable with those of their non-diabetic controls. Diabetic WKY rats maintained an inverse correlation between AII and AII-R (controlled P = 0.04 and uncontrolled P = 0.015), but this did not occur in the SHR. 5. Absence of receptor response to varying ligand concentrations in the diabetic SHR may contribute to the development of nephropathy. Glycaemic control does not appear to reverse this abnormality in the SHR, so that co-existent hypertension may have a more direct influence on renal function.

Vitronectin-mediated inhibition of complement: evidence for different binding sites for C5b-7 and C9.

In the activated complement system, vitronectin (complement S-protein) occupies the metastable membrane binding site of the nascent precursor complex C5b-7, so that the newly formed SC5b-7 is unable to insert into cell membranes. Some evidence also indicates that vitronectin limits on-going membrane-associated pore formation by inhibiting C9 polymerization. It has been assumed that these two stages of terminal complement complex (TCC) inhibition take place through charge interactions between the heparin-binding region of vitronectin and homologous cysteine-rich sequences of the late complement proteins C6, C7, C8 and C9. We examined SC5b-7 formation and inhibition of C9 binding in the TCC using separate haemolytic assays. The mode of action of vitronectin in these assays was compared with two 15mer peptides which span residues 348-379 of the heparin-binding region, and a heparin-affinity polypeptide, protamine sulphate. The results showed that vitronectin acts predominantly through SC5b-7 production with a lesser effect on the inhibition of C9 lytic pore formation. In contrast, protamine sulphate did not prevent C5b-7 membrane attachment, but was a potent inhibitor of C9-mediated lysis. The peptides did not inhibit C5b-7 membrane insertion and only one affected C9 binding. These data suggest that the two stages of TCC inhibition involve separate binding sites on the vitronectin molecule. The site for association with nascent C5b-7 is unknown, whereas inhibition of C9 binding and pore formation takes place through the heparin-binding region.

The value of complement measurements in the assessment of lupus activity.

The complement system was studied prospectively in 29 patients, predominantly renal (25), with systemic lupus erythematosus (SLE) to examine the value of complement assays in the distinction between active and inactive disease. Disease activity was evaluated primarily by clinical, biochemical and histological parameters which were obtained at the time of assessment. Fourteen patients had active disease, as assessed by clinical and laboratory criteria. C1q, C4, C4a, C2, C3, C3a, C5, total haemolytic activity (CH50) and complement inhibitors were measured in each patient. The ratios of C4a:C4 and C3a:C3 were also calculated. Values for all components except C5 were different between control subjects and active patients while only CH50 was different between inactive patients and controls. All parameters except C4a:C4 and C5 were different between active and inactive patients. There was a highly significant difference in the number of active patients with reduced levels of C2, C3 and C3a:C3 compared to inactive patients (i.e. p less than 0.001) whereas lesser or no difference was observed for other parameters. The concentration of complement inhibitors was elevated in both groups. We conclude that, among readily available complement parameters, C2 and C3 provide the best assessment of disease activity in patients with SLE.