Diminished vascular response to noradrenaline in experimental chronic uremia

Baroreflex dysfunction in chronic kidney disease

Chronic kidney disease (CKD) patients have high cardiovascular mortality and morbidity. The presence of traditional and CKD related risk factors results in exaggerated vascular calcification in these patients. Vascular calcification is associated with reduced large arterial compliance and thus impaired baroreflex sensitivity (BRS) resulting in augmented blood pressure (BP) variability and hampered BP regulation. Baroreflex plays a vital role in short term regulation of BP. This review discusses the normal baroreflex physiology, methods to assess baroreflex function, its determinants along with the prognostic significance of assessing BRS in CKD patients, available literature on BRS in CKD patients and the probable patho-physiology of baroreflex dysfunction in CKD.

Defective Store-Operated Calcium Entry Causes Partial Nephrogenic Diabetes Insipidus

Store-operated calcium entry (SOCE) is the mechanism by which extracellular signals elicit prolonged intracellular calcium elevation to drive changes in fundamental cellular processes. Here, we investigated the role of SOCE in the regulation of renal water reabsorption, using the inbred rat strain SHR-A3 as an animal model with disrupted SOCE. We found that SHR-A3, but not SHR-B2, have a novel truncating mutation in the gene encoding stromal interaction molecule 1 (STIM1), the endoplasmic reticulum calcium (Ca(2+)) sensor that triggers SOCE. Balance studies revealed increased urine volume, hypertonic plasma, polydipsia, and impaired urinary concentrating ability accompanied by elevated circulating arginine vasopressin (AVP) levels in SHR-A3 compared with SHR-B2. Isolated, split-open collecting ducts (CD) from SHR-A3 displayed decreased basal intracellular Ca(2+) levels and a major defect in SOCE. Consequently, AVP failed to induce the sustained intracellular Ca(2+) mobilization that requires SOCE in CD cells from SHR-A3. This effect decreased the abundance of aquaporin 2 and enhanced its intracellular retention, suggesting impaired sensitivity of the CD to AVP in SHR-A3. Stim1 knockdown in cultured mpkCCDc14 cells reduced SOCE and basal intracellular Ca(2+) levels and prevented AVP-induced translocation of aquaporin 2, further suggesting the effects in SHR-A3 result from the expression of truncated STIM1. Overall, these results identify a novel mechanism of nephrogenic diabetes insipidus and uncover a role of SOCE in renal water handling.

Abnormalities associated with progressive aortic vascular dysfunction in chronic kidney disease

Increased stiffness of large arteries in chronic kidney disease (CKD) has significant clinical implications. This study investigates the temporal development of thoracic aortic dysfunction in a rodent model of CKD, the Lewis polycystic kidney (LPK) rat. Animals aged 12 and 18 weeks were studied alongside age-matched Lewis controls (total n = 94). LPK rodents had elevated systolic blood pressure, left ventricular hypertrophy and progressively higher plasma creatinine and urea. Relative to Lewis controls, LPK exhibited reduced maximum aortic vasoconstriction (R_max) to noradrenaline at 12 and 18 weeks, and to K⁺ (12 weeks). Sensitivity to noradrenaline was greater in 18-week-old LPK vs. age matched Lewis (effective concentration 50%: 24 × 10⁻⁹ ± 78 × 10⁻¹⁰ vs. 19 × 10⁻⁸ ± 49 × 10⁻⁹, P < 0.05). Endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) relaxation was diminished in LPK, declining with age (12 vs. 18 weeks R_max: 80 ± 8% vs. 57 ± 9% and 92 ± 6% vs. 70 ± 9%, P < 0.05, respectively) in parallel with the decline in renal function. L-Arginine restored endothelial function in LPK, and L-NAME blunted acetylcholine relaxation in all groups. Impaired nitric oxide synthase (NOS) activity was recovered with L-Arginine plus L-NAME in 12, but not 18-week-old LPK. Aortic calcification was increased in LPK rats, as was collagen I/III, fibronectin and NADPH-oxidase subunit p47 (phox) mRNAs. Overall, our observations indicate that the vascular abnormalities associated with CKD are progressive in nature, being characterized by impaired vascular contraction and relaxation responses, concurrent with the development of endothelial dysfunction, which is likely driven by evolving deficits in NO signaling.

Endovascular renal denervation: a novel sympatholytic with relevance to chronic kidney disease

Endovascular renal denervation (sympathectomy) is a novel procedure developed for the treatment of resistant hypertension. Evidence suggests that it reduces both afferent and efferent sympathetic nerve activity, which may offer clinical benefit over and above any blood pressure-lowering effect. Studies have shown objective improvements in left ventricular mass, ventricular function, central arterial stiffness, central haemodynamics, baroreflex sensitivity and arrhythmia frequency. Benefits have also been seen in insulin resistance, microalbuminuria and glomerular filtration rate. In chronic kidney disease, elevated sympathetic activity has been causally linked to disease progression and cardiovascular sequelae. Effecting a marked reduction in sympathetic hyperactivity may herald a significant step in the management of this and other conditions. In this in-depth review, the pathophysiology and clinical significance of the sympatholytic effects of endovascular renal denervation are discussed.

Effect of medial calcification on vascular function in uremia

The contribution of medial calcification to vascular dysfunction in renal failure is unknown. Vascular function was measured ex vivo in control, noncalcified uremic, and calcified uremic aortas from rats with adenine-induced renal failure. Plasma urea was 16 ± 4, 93 ± 14, and 110 ± 25 mg/dl, and aortic calcium content was 27 ± 4, 29 ± 2, and 4,946 ± 1,616 nmol/mg dry wt, respectively, in the three groups. Maximal contraction by phenylephrine (PE) or KCl was reduced 53 and 63% in uremic aortas, and sensitivity to KCl but not PE was increased. Maximal relaxation to acetylcholine was impaired in uremic aortas (30 vs. 65%), and sensitivity to nitroprusside was also reduced, indicating some impairment of endothelium-independent relaxation as well. None of these parameters differed between calcified and noncalcified uremic aortas. However, aortic compliance was reduced in calcified aortas, ranging from 17 to 61% depending on the severity of calcification. We conclude that uremic vascular calcification, even when not severe, significantly reduces arterial compliance. Vascular smooth muscle and endothelial function are altered in renal failure but are not affected by medial calcification, even when severe.

A review of drug-induced hypernatraemia

Drug-induced electrolyte abnormalities have been increasingly reported and may be associated with considerable morbidity and/or mortality. In clinical practice, hypernatraemia (serum sodium higher than 145 mmol/L) is usually of multifactorial aetiology and drug therapy not infrequently is disregarded as a contributing factor for increased serum sodium concentration. Strategies to prevent this adverse drug effect involve careful consideration of risk factors and clinical and laboratory evaluation in the course of treatment. Herein, we review evidence-based information via PubMed and EMBASE and the relevant literature implicating pharmacologic treatment as an established cause of hypernatraemia and discuss its incidence and the underlying pathophysiologic mechanisms.

Cardiac hypertrophy in neonatal nephrectomized rats: the role of the sympathetic nervous system

Cardiac hypertrophy is frequently encountered in patients with renal failure and represents an independent risk factor for cardiovascular morbidity and mortality. The pathogenesis of cardiac hypertrophy is related to multiple factors, including excess adrenergic activity. This study investigated how renal injury in the early stages of life affects the adrenergic system and thereby potentially influences cardiac growth. Biomarkers of cardiac hypertrophy were used to assess adrenergic function. Newborn male Sprague-Dawley rats were allocated to three groups of five rats each: 5/6 nephrectomy (Nx), pair-fed controls (PF), and sham-operated (SH). Nx animals had significantly higher plasma urea nitrogen, serum creatinine, and mean arterial blood pressure. The heart-weight/body-weight ratio of the Nx cohort was higher than SH and PF (p < 0.001) groups. Plasma norepinephrine (NE) of Nx animals was almost twofold higher than SH and PF (p < 0.01) animals. Compared with SH and PF, Nx animals had higher alpha1A-receptor protein expression, lower cardiac beta1- and beta2-receptor protein expression (p < 0.05), but higher G-protein-coupled receptor kinase-2 (GRK2) expression (p < 0.05). Norepinephrine transporter protein (NET) and renalase protein expression in cardiac tissue from Nx pups were significantly lower than SH and PF. Our data suggest that early age Nx animals have increased circulating catecholamines due to decreased NE metabolism. Enhancement of cardiac GRK2 and NE can contribute to cardiac hypertrophy seen in Nx animals. Furthermore, AKT (activated via alpha1A receptors), as well as increased alpha1A receptors and their agonist NE, might contribute to the observed hypertrophy.

Sympathetic overactivity--the Cinderella of cardiovascular risk factors in dialysis patients

Cardiovascular morbidity and mortality is exceedingly high in patients with chronic renal failure. Sympathetic overactivity is an important pathomechanism contributing to progression of renal disease as well as cardiovascular complications. For more than 30 years it has been known that plasma levels of norepinephrine are elevated in chronic renal failure pointing to increased sympathetic nerve activity. The kidneys are richly innervated by efferent sympathetic and afferent sensory nerves. They participate in many reflex adjustments of renal function. Initially, this finding had not been attributed to increased efferent sympathetic drive, but rather to reduced renal clearance and defective neuronal reuptake of norepinephrine. At this time, however, the evidence for increased sympathetic drive is solid. Interventions to reduce sympathetic overactivity will provide new therapeutic approaches. The available experimental and clinical evidence to suggest such a pathophysiological role of sympathetic overactivity is summarized in this current review.

Effects of novel vasopressin receptor antagonists on renal function and cardiac hypertrophy in rats with experimental congestive heart failure

Arginine vasopressin (AVP) plays an important role in renal hemodynamic alterations, water retention, and cardiac remodeling in congestive heart failure (CHF). The present study evaluated the acute and chronic effects of vasopressin V(1a) receptor subtype (V(1a)) and vasopressin V(2) receptor subtype (V(2)) antagonists on renal function and cardiac hypertrophy in rats with CHF. The effects of acute administration of SR 49059 [(2S)1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide)] (0.1 mg/kg) and SR 121463B (1-[4-(N-tert-butylcarbamoyl)-2-methoxybenzenesulfonyl]-5-ethoxy-3-spiro-[4-(2-morpholinoethoxy)cyclohexane]indol-2-one, fumarate; equatorial isomer) (0.3 mg/kg), V(1a) and V(2) antagonists, respectively, on renal function, and of chronic treatment (3.0 mg/kg/day for 7 or 28 days, via osmotic minipumps or p.o.), on water excretion and cardiac hypertrophy were studied in rats with aortocaval fistula and control rats. CHF induction increased plasma AVP (12.8 +/- 2.5 versus 32.2 +/- 8.3 pg/ml, p < 0.05). Intravenous bolus injection of SR 121463B to controls produced dramatic diuretic response (from 5.5 +/- 0.8 to 86.3 +/- 21.9 microl/min; p < 0.01). In contrast, administration of SR 49059 did not affect urine flow. Likewise, administration of SR 121463B, but not SR 49059, to rats with CHF significantly increased urinary flow rate from 20.8 +/- 6.4 to 91.6 +/- 26.5 microl/min (p < 0.01). The diuretic effects of SR 121463B were associated with a significant decline in urinary osmolality and insignificant change of Na+ excretion. In line with its acute effects, chronic administration of SR 121463B to CHF rats increased daily urinary volume 2 to 5-fold throughout the treatment period. Both SR 121463B and SR 49059 significantly reduced heart weight in CHF rats when administered for 4 weeks, but not 1 week. These results suggest that V(2) and V(1a) antagonists improve water balance and cardiac hypertrophy in CHF and might be beneficial for the treatment of water retention and cardiac remodeling in CHF.

Beta blockers in the management of chronic kidney disease

The sympathetic nervous system modulates renal function through its receptors namely beta1 (cardiac output and renin release), alpha1 (systemic and renovascular constriction), and beta2 renovascular dilation. Sympathetic overactivity is commonly seen in chronic kidney disease (CKD) and is an important contributor to increasing the risk of cardiovascular events as well as increasing renal disease progression. Recent evaluations of drug use in people with CKD shows a remarkably low percentage of patients receiving beta-blockers, especially in more advanced stage CKD when cardiovascular risk is higher. This is in large part due to tolerability of these agents. Moreover, water-soluble beta-blockers such as atenolol and metoprolol are dialyzable and require supplementation to avoid exacerbation of arrhythmias following dialysis. Newer vasodilating beta-blockers have better tolerability and different effects on renal hemodynamics as well as metabolic variables. These effects are related to the relative alpha1-blocking effect of agents such as carvedilol and labetolol, with carvedilol having relatively greater alpha-blocking effects. Few studies evaluate beta-blockers on cardiovascular risk in CKD patients. Studies with carvedilol demonstrate attenuated increases in albuminuria as well as reduction in cardiovascular events in CKD patients with hypertension. This paper reviews the animal and clinical trial data that evaluate beta-blockers in CKD highlighting the vasodilating beta-blockers. It is apparent that greater use of this drug class for blood pressure control would further enhance reduction of risk of heart failure, the most common cause of death in the first year of starting dialysis.

Nonhypotensive dose of β-adrenergic blocker ameliorates capillary deficits in the hearts of rats with moderate renal failure

Renal failure causes sympathetic overactivity and inadequate capillary growth in response to cardiomyocyte hypertrophy in experimental renal failure, as well as in uremic patients. In nonuremic animals, sympathetic overactivity was shown to suppress capillary growth. The purpose of this study was to examine whether blockade with alpha- and beta-adrenoblockers ameliorates the capillary deficit that was documented in the hearts of rats with moderate renal failure. Male Sprague-Dawley rats, 3 days after surgical ablation [subtotal nephrectomy (SNX)] or sham operation (sham), were treated with phenoxybenzamine, metoprolol, or a combination of both: After 12 weeks, the hearts were investigated using morphometric and stereologic techniques. The length density of myocardial capillaries was lower (p<0.05) in untreated SNX than in sham (2,786+/-372 vs 3,397+/-602 mm/mm3); the decrease was abrogated by metoprolol (3,305+/-624 mm/mm3), but not by phenoxybenzamin (2,628+/-480 mm/mm3). The intercapillary distance increased (p<0.05) in SNX (20.5+/-1.5 microm) and tended to be lower after metoprolol treatment (19.0+/-1.9 microm). The media area of intramyocardial arterioles was significantly higher in untreated SNX (1,158+/-1,343 vs 686+/-771 microm2 in sham). Metoprolol in nonhypotensive doses prevents the capillary deficit in the hearts of rats with moderate renal failure and presents an argument for an important role of sympathetic overactivity in the genesis of the capillary deficit in moderate chronic renal insufficiency.

Childhood thin GBM disease: review of 22 children with family studies and long-term follow-up

Thin glomerular basement membrane (GBM) disease is generally known to have a good renal prognosis, although renal insufficiency has sometimes been reported and the overlap with Alport syndrome implies that a good prognosis cannot be guaranteed. In order to shed light on long-term prognosis of thin GBM disease we have retrospectively evaluated 22 children with persistent haematuria and biopsy-proven thin GBM. Mean follow up was 7 years (range 2-17 years), mean age at onset was 7 years (range 1.5-15). Biopsies were performed a mean of 3.8 years after detection of hematuria. The light microscopy (LM) and immunofluorescence (IF) findings were essentially unremarkable in all of the children, while electron microscopy (EM) showed thinning of the GBM in all cases and no changes characteristic of Alport syndrome. The family history was positive for renal disease in 17 (77.3%) patients with hematuria in 8 (36.3%) families, and hematuria with renal failure (RF) or deafness in 9 (40.9%). It was completely negative for renal disease in 4 (18.2%) and unavailable in 1 (4.5%). Four patients (18%) showed a decline in renal function after 6, 8, 9 and 12 years of follow-up, and 1 of these also developed hearing impairment. None developed hypertension. Our study suggests that thin GBM disease is not always benign and a child with thin GBM should never be assigned such a prognosis, especially if there is a family history of renal impairment or deafness, where careful follow-up is needed due to the risk of late onset renal failure.

Hypertension in Chronic Kidney Disease and Dialysis: Pathophysiology and Management

Hypertension affects 24% of the adult US population. In the United States, 3% of the adult population has an elevated serum creatinine level, and 70% of these patients have hypertension. The prevalence of hypertension in chronic kidney disease (CKD) depends on the patient's age and the severity of renal failure, proteinuria, and underlying renal disease. As patients with CKD progress to end-stage renal disease (ESRD), 86% are diagnosed with hypertension. It has long been recognized that kidney function affects and is affected by hypertension. This article discusses the pathophysiology and management of hypertension in patients with CKD.

Etiology and management of hypertension in chronic kidney disease

The kidneys are vital in the pathogenesis of hypertension and are also pathologically affected by the presence of hypertension. The prevalence of hypertension in chronic kidney disease (CKD) depends on age, the severity of renal failure, and proteinuria. The intricate and inextricable relationship between CKD and hypertension seems to cause cardiovascular disease that has assumed epidemic proportions. This article discusses the etiology and treatment of hypertension in CKD so that it can be better controlled.

Midodrine improves chronic hypotension in hemodialysis patients

BACKGROUND

The effects of midodrine on chronic hypotension in hemodialysis (HD) patients have not been well investigated.

METHODS

We evaluated midodrine's effect on autonomic function and hemodynamics in 12 HD patients who had chronic systolic blood pressure less than 100 mm Hg. Midodrine (5.0 mg) twice a day was given for 4 weeks. Another 12 age- and sex-matched HD patients with normotension were selected as a control group. Autonomic function tests included the heart-rate responses to the Valsalva maneuver and 30:15 ratio as well as supine and standing blood pressure (BP) and sustained hand-grip test. Hemodynamic changes included 24-hour blood pressure, cardiac output, total peripheral resistance (TPR), and plasma renin and aldosterone concentrations.

RESULTS

Compared with the control subjects, HD patients with chronic hypotension had more severe autonomic dysfunction and significantly lower TPR. After 4 weeks of midodrine therapy, sympathetic function (orthostatic and hand-grip tests) improved in conjunction with significant increases in mean arterial pressure (MAP) (79.5 +/- 4.9 to 85.0 +/- 5.1 mm Hg, P < 0.05) and TPR (768 +/- 37 versus 1097 +/- 72 dyne/sec/cm-5, P < 0.01) despite no significant change in Valsalva ratio, 30:15 ratio, and cardiac output. MAP changes were positively correlated with TPR changes (r = 0.82, P < 0.001). Supine plasma renin activity was significantly increased. In addition, MAP during HD was also significantly increased during midodrine therapy.

CONCLUSIONS

Midodrine improves chronic hypotension in HD patients by modulating autonomic function and its direct effects on peripheral vessels.

Cyclosporine a slows the progressive renal disease of alport syndrome (X-linked hereditary nephritis): results from a canine model

Alport syndrome refers to a hereditary disorder characterized by progressive renal disease and a multilaminar appearance to the glomerular basement membrane (GBM). In a small group of patients with Alport syndrome, cyclosporine A was reported to decrease proteinuria and maintain stable renal function over 7 to 10 yr of follow-up. The present study examined the effect of cyclosporine A on GBM structure and the progression to renal failure in a canine model of X-linked Alport syndrome. Affected male dogs and normal male dogs treated with cyclosporine A underwent serial renal biopsies. Body weight, serum concentrations of creatinine and albumin, and GFR were sequentially determined. Controls consisted of untreated dogs that developed end-stage renal failure by 8 mo of age. Renal biopsies were assessed for glomerulosclerosis and the percent of multilaminar GBM as measured by image analysis. Significant differences were found between treated and untreated affected dogs for weight, serum creatinine, and GFR. There was a significant delay in the progression of multilaminar change to the GBM, although treated affected dogs at termination had attained approximately 100% split GBM as did untreated affected dogs. A significant difference in the number of sclerotic glomeruli was also noted; treated dogs rarely developed obsolete glomeruli during the period studied. Interstitial fibrosis was not significantly affected by cyclosporine A treatment. These findings indicate that cyclosporine A is beneficial in slowing, but not stopping, the clinical and pathologic progression of Alport syndrome. At least part of this beneficial effect comes from a delayed deterioration of GBM structure, which in turn may be related to glomerular hemodynamics altered by cyclosporine A.

Abnormal glomerular basement membrane laminins in murine, canine, and human Alport syndrome: aberrant laminin alpha2 deposition is species independent

Kidneys from mice, dogs, and humans with X-linked and autosomal-recessive forms of Alport syndrome were examined by immunofluorescence for expression of laminin alpha, beta, and gamma chains using monospecific antibodies. Laminin alpha2 chain was absent from glomerular basement membranes (GBM) in normal human, murine, and canine kidneys but was abnormally deposited in Alport GBM, regardless of species or inheritance pattern. In murine and canine Alport kidneys, laminin alpha2 seems to be deposited as part of both laminin-2 (alpha2beta1gamma1) and laminin-4 (alpha2beta2gamma1) but as part of only laminin-4 in human Alport kidneys. GBM laminin alpha2 chain deposition was not observed in a variety of non-Alport human glomerulopathies. This finding adds to the list of proteins that are aberrantly deposited in Alport GBM as a consequence of the absence of the alpha3, alpha4, and alpha5 chains of type IV collagen: (1) type IV collagen alpha1 and alpha2 chains, (2) type V collagen, (3) type VI collagen, and most recently (4) the laminin alpha2 chain and (5) the laminin alpha1 and beta1 chains in mice and dogs. These findings emphasize further the critical role played by the alpha3, alpha4, and alpha5 chains of type IV collagen in establishing and maintaining the composition, structure, and function of mature GBM.

Cardiac disease in chronic uremia: pathophysiology

In chronic uremia, apart from frequent coronary lesions, further abnormalities of the heart recently reported include (1) left ventricular hypertrophy, not completely explained by hypertension, (2) interstitial myocardial fibrosis, for which parathyroid hormone is a permissive factor, (3) reduced myocardial perfusion reserve, secondary to functional and structural changes of intramyocardial arteries and to reduced capillary density, (4) abnormalities of myocardial metabolism, which act in concert with restriction of blood flow by microvascular abnormalities to reduce ischemic tolerance. Such metabolic abnormalities include diminished responsiveness to beta-adrenergic stimulation, abnormal control of intracellular calcium concentration, impaired maintenance of energy-rich nucleotide concentrations under conditions of ischemia, impaired insulin-mediated glucose uptake, and abnormalities of myocardial oxidative metabolism.

Coordinate gene expression of the alpha3, alpha4, and alpha5 chains of collagen type IV. Evidence from a canine model of X-linked nephritis with a COL4A5 gene mutation

Canine X-linked hereditary nephritis is an animal model for human X-linked hereditary nephritis with a premature stop codon in the alpha5(IV) gene of collagen type IV. We used this model to examine the other alpha(IV) chains at the mRNA and protein level in the kidney, since in human X-linked hereditary nephritis, the alpha3(IV) and alpha4(IV) chains are often absent from the glomerular basement membrane, although both are encoded by autosomal genes. cDNA probes for the alpha1(IV)-alpha6(IV) chains were generated from normal dog kidney using the polymerase chain reaction. Sequences were >/=88% identical at the DNA level and >/=92% identical at the protein level to the respective human alpha(IV) chains. By Northern analysis, transcripts for the alpha1(IV), alpha2(IV), and alpha6(IV) chains were detected at comparable levels in both normal and affected male dog kidney RNA. As previously shown, the transcript for the alpha5(IV) chain was reduced to approximately 10% of normal. Unexpectedly, the alpha3(IV) and alpha4(IV) transcripts were both decreased >/=77% in affected male dog kidney, suggesting a mechanism coordinating the expression of these three basement membrane components. The NC1 domain of collagen type IV isolated from normal dog glomeruli was positive for the alpha3(IV), alpha4(IV), and alpha5(IV) chains by Western blotting. In contrast, in the NC1 domain isolated from affected dog glomeruli, these three chains were not detectable, except for a trace of alpha3(IV) dimer. In X-linked hereditary nephritis, the absence of the alpha3(IV) and alpha4(IV) chains from glomerular basement membrane may reflect factors acting at the transcriptional and/or translational level in addition to the protein assembly level.

Abnormal glomerular basement membrane in idiopathic multicentric osteolysis

The primary cause of nephropathy in idiopathic multicentric osteolysis is as yet unknown. We report a young girl with idiopathic multicentric osteolysis and nephropathy. An abnormal glomerular basement membrane was the only abnormality found in a renal biopsy taken 2 years before the development of end-stage renal failure. We believe that this biopsy finding represents or is related to the unknown primary lesion causing nephropathy in idiopathic multicentric osteolysis.

Hypertension and the kidney--an overview

The kidney plays a major role in the genesis of any type of hypertension, as demonstrated by experiments which show that hypertension can be "transplanted" when the kidney itself is transplanted. Hypertension is common in patients with renal disease, and may occur even at normal glomerular filtration rates. The mechanisms that promote hypertension and are involved in renal disease comprise both activation of pressor mechanisms and failure of depressor mechanisms, the latter having been considerably less well studied. The major pressor mechanisms are an abnormal pressure-natriuresis relationship and inappropriate activity of the renin-angiotensin system.

Laminin, fibronectin, and Goodpasture antigen detection in patients with Alport's syndrome

Indirect immunofluorescence study with laminin and fibronectin monoclonal antibodies on paraffin sections, as well as with serum from a patient with Goodpasture's syndrome with high titer of autoantibodies that recognize the antigenic determinants in human glomerular and tubular basement membrane, was performed on 14 patients with Alport's syndrome and 5 specimens of normal renal tissue obtained from donors in cases of renal transplantation (control group). We found no binding of Goodpasture antigen to glomerular and distal tubular basement membranes in renal biopsy tissue from all 14 patients with Alport's syndrome. In contrast, there was bright linear fluorescence of Goodpasture antigen on glomerular and tubular basement membranes of normal renal material. There was no difference in laminin and fibronectin binding in patients with Alport's syndrome and controls. In all the cases binding was strongly positive. These results suggest an abnormality or absence of immunoreactive autoantigen in the glomerular and distal tubular basement membrane in patients with Alport's syndrome. Therefore, Goodpasture antigen detection could be an important diagnostic method in early stages of Alport's syndrome when characteristic morphological changes are not yet developed.

Compliance and reactivity of the peripheral venous system in chronic intermittent hemodialysis

A reduced venous compliance and/or inadequate venoconstriction could impair hemodynamics during hemodialysis. Therefore, compliance and reactivity of the peripheral venous system were assessed in hemodialysis patients and controls using strain gauge plethysmography. Reactivity of the venous system towards an efferent sympathetic stimulus was assessed using a cold pressor test. Results showed that venous compliance was reduced in hypertensive hemodialysis patients compared to normotensive dialysis patients (P = 0.013) and normotensive controls (P = 0.004). After one dosage with a directly acting venodilator (nitroglycerin 5 mg s.l.) and 3 days of treatment with an alpha 1-sympathicolytic agent (Doxazosin 2 mg), venous compliance remained unaltered in hypertensive dialysis patients. During the cold pressor test, the blood pressure response, rise in noradrenaline levels and decline in venous compliance were normal in hemodialysis patients. However, their response to the Valsalva manoeuver was significantly impaired (P = 0.011) compared to healthy controls. We conclude that hypertension, not renal failure, causes the reduction of peripheral venous compliance in hemodialysis patients, for which structural factors might be responsible. Despite the existence of autonomous neuropathy, the reaction of the peripheral venous system towards an efferent sympathetic stimulus is intact in hemodialysis patients.

Regulation of myocardial isomyosin V1 in uraemic rats

Cardiac hypertrophy of various aetiologies is consistently associated with increased expression of V3 isomyosin. Uraemia is associated with cardiac hypertrophy. In the present study, we examined regulation of isomyosin in uraemic rats, using gel electrophoresis. Cardiac hypertrophy in uraemic animals was associated with a relative increase in V1 isomyosin. An increased proportion of V1 isomyosin was demonstrable 3 days after subtotal nephrectomy (NX 63.0 +/- 8.8%; control 43.6 +/- 7.2%; P less than 0.01) and persisted during uraemia of 80 days duration. Elevation of V1 isomyosin, relative to pair-fed controls, was observed in uraemic animals of various age. The proportion of V1 isomyosin changed in the same direction as controls when several manouevers were used which changed the isomyosin pattern, but the difference between uraemic animals and controls persisted. We studied the effect of carbohydrate loading or deprivation, starvation or administration of energetically inadequate diets, castration or administration of androgens and sodium depletion. With each of the above interventions, a difference between subtotally nephrectomized animals and sham-operated pair-fed control animals was statistically significant (P less than 0.05). Elevation of V1 isomyosin persisted during combined alpha and beta blockade and was still found when blood pressure was normalized by ACE inhibition using Ramipril. It is concluded that cardiac hypertrophy of uraemia differs from all other forms of cardiac hypertrophy by the occurrence of increased proportion of V1 isomyosin. The proportion of V1 isomyosin responds adequately to regulatory signals but is set at an abnormally high level.

Effect of circulating factors on vascular smooth muscle contraction and its calcium uptake in uremia

Uremia is often associated with alterations in calcium metabolism and vascular smooth muscle function in hypertension and atherosclerosis. The ways in which these conditions inter-relate are not clearly understood. In order to study the possibility that circulating factors might influence smooth muscle function, experiments were performed on rat aortic strips. The serum from both uremic patients and rats enhanced the norepinephrine-induced contraction (NEIC) and net 45-calcium uptake in rat aortic strips. In a similar manner, the serum of parathyroidectomized uremic rats also increased the NEIC, whereas verapamil reduced the aortic response to levels below those of the control, in the presence of uremic serum. These findings suggest that in both chronic (patients) and early (rats) stages of uremia, there is a circulating factor, different from parathyroid hormone, that affects calcium uptake and vascular smooth muscle contraction.

Alport syndrome, basement membranes and collagen

Alport syndrome, an inherited disorder of the kidney, eye and ear, has fascinated nephrologists, pathologists, and geneticists for nearly a century. With the recent application of molecular biochemical and genetic techniques, this mysterious disease has begun to yield some of its secrets. Alport syndrome can now be viewed as a generalized disorder of basement membranes that appears to result from mutations in an X-chromosome-encoded basement membrane collagen chain. This chain, along with two other novel collagen chains, is absent from Alport basement membranes, in contrast to the classical chains of collagen IV. Phenotypic heterogeneity in Alport syndrome probably arises from allelic mutations at a single genetic locus. The phenomenon of post-transplant anti-glomerular basement membrane nephritis may be a manifestation of specific mutations at the Alport locus that prevent synthesis of the gene's protein product and the establishment of immunological tolerance.

Renal biopsy and family studies in 65 children with isolated hematuria

We have investigated 65 children with isolated hematuria persisting for at least a year. Renal biopsy specimens were studied by light microscopy, electron microscopy and immunofluorescence with antisera specific against basement membrane components. The majority of the biopsies (62/65) showed variable histologic abnormalities. Four categories could be distinguished on combined histological and clinical criteria: Alport syndrome (n = 8), benign hematuria (n = 33, familial in 23), IgA nephropathy (n = 16) and increase in mesangial cells and matrix (n = 5). On the basis of our results, we suggest that a renal biopsy can establish diagnosis and prognosis in those children with isolated hematuria where the family history is negative. If the family has adult male individuals with isolated hematuria, a biopsy can usually be avoided, since this family history effectively excludes Alport syndrome. The use of antisera against basement membrane components did not allow a differentiation between Alport syndrome and benign hematuria. Goodpasture serum immunofluorescence was variable in the former and normally present in the latter.

Vascular smooth muscle function in rats with acute renal failure

Vascular smooth muscle function in rats with glycerol-induced acute renal failure (ARF) was investigated by recording both the contractile responses of portal vein segments and the relaxant responses depressed contractile responses to the alpha 1-agonist methoxamine, the alpha 2-agonist B-HT 920 and to the calcium agonist BAY K 8644 when compared with controls. Both isoprenaline and nitroprusside produced 100% reversal of KCl induced tone in control aortic rings but in rings from rats with ARF complete reversal of of tone could not be obtained with either dilator drug. It is suggested that a defect in mitochondrial function and hence energy supply may account for the diminished ability of vascular preparations from rats with ARF to constrict and relax.

Thin-basement-membrane nephropathy in adults with persistent hematuria

Thin-basement-membrane nephropathy, also called benign recurrent hematuria, is characterized by diffuse thinning of the glomerular basement membrane and by hematuria. To determine the incidence of thin-basement-membrane nephropathy among patients with idiopathic hematuria, we conducted a prospective study in the nephrology units of three large hospitals in the Netherlands. Eighty normotensive adults without azotemia underwent renal biopsy because of recurrent macroscopic hematuria (n = 26) or persistent microscopic hematuria (n = 54). Idiopathic IgA nephropathy was found in 27 of the 80 patients. Light microscopical examination showed that 42 patients had normal renal tissue. The remaining 11 patients had mesangioproliferative glomerulonephritis (n = 5), interstitial nephritis (n = 3), or focal global glomerulosclerosis (n = 3). Tissue from the 42 patients whose renal biopsy specimens were normal when examined with light microscopy was analyzed morphometrically with electron microscopy to determine the thickness of the glomerular basement membrane. Two subsets of patients were identified by this analysis. In 18, thin-basement-membrane nephropathy was found (mean basement-membrane thickness [+/- SE], 191 +/- 28 nm; normal, 350 +/- 43 nm); all but one of these 18 patients had microscopic hematuria, which persisted during follow-up (median duration, 50 months). (Of the 54 patients who presented with microscopic hematuria, 17 [31 percent] had thin-basement-membrane nephropathy.) The thickness of the glomerular basement membrane was normal in the other 24 patients (361 +/- 69 nm); during follow-up, hematuria disappeared in all 13 of these patients who had macroscopic hematuria, and hematuria resolved in 5 of the 11 patients who had microscopic hematuria. We conclude that in patients with persistent microscopic hematuria, the incidence of thin-basement-membrane nephropathy is similar to that of idiopathic IgA nephropathy. Morphometric analysis of the thickness of the glomerular basement membrane should be included in the workup of adults with persistent microscopic hematuria that is not of urologic origin.

Influence of parathyroidectomy on blood pressure and vascular reactivity in spontaneously hypertensive rats

We investigated the influence of parathyroidectomy (PTX) on blood pressure (BP) and hindlimb vascular reactivity to noradrenaline (NA) and vasopressin (AVP) in male spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKR). Three groups of SHR and WKR, respectively, were investigated: Sham-operated (SO) rats on a normal calcium intake (0.95%), SO rats on moderately elevated calcium intake (1.6% calcium diet) and PTX rats on the 1.6% calcium diet. At the end of the experiment (3 months), directly or indirectly measured BP was significantly lower in the PTX-SHR group on the 1.6% calcium diet than in SO-SHR on the same diet. In WKR groups, no changes of BP were recorded. Hindlimb perfusion with oxygenated Tyrode's solution for cumulative dose response curves with NA (0.1-1000 x 10(-6) M) and AVP (0.5-500 x 10(-9) M) showed no differences between PTX and SO groups. Maximal pressures and ED50 for agents used were significantly higher in SHR than WKR groups (p less than 0.05). The results support the hypothesis that the parathyroid glands contribute to high blood pressure in SHR. However, the antihypertensive action of PTX was not mediated by a change in hindlimb vascular reactivity.

Linkage studies in X-linked Alport's syndrome

Four kindreds segregating for Alport's syndrome (ASLN) compatible with a X-linked inheritance were studied for linkage with polymorphic markers of the human X chromosome. No recombinant was observed between the ASLN locus and the DXS101 and DXS94 loci, the maximum lod scores were z = 3.93 and 3.50 respectively. Linkage data between the ASLN locus and the other genetic markers used in the present study are in keeping with the assignment of the mutation to the proximal Xq arm.

Alpha 1 adrenergic receptors in mesenteric arteries of rats with chronic renal failure

In previous studies we have shown that patients or rats with chronic renal failure display reduced blood pressure response to norepinephrine (NE). This abnormality is related to the high levels of parathyroid hormone (PTH) which stimulates vasodilator prostaglandin production. To determine whether chronic renal failure (CRF) also affects pressor response to NE through changes in the properties of alpha 1 adrenoceptors, we have measured plasma NE and the number of binding sited (Bmax) and the KD of these receptors in isolated mesenteric arteries of normal CRF rats and of CRF rats previously parathyroidectomized (PTX). Plasma NE was greater (P less than 0.01) in CRF than in control (67 +/- 14 vs. 32 +/- 3.1 ng/dl), but it was not different from CRF-PTX rats. The Bmax of alpha 1 adrenoceptors was lower (P less than 0.05) in CRF than control (80 +/- 10 vs. 173 +/- 29 fmol/mg protein), but it was similar in CRF and CRF-PTX rats. The KD was not significantly different among the three groups of rats studied. The data show that the number of alpha 1 adrenoceptors is reduced in CRF and this is not related to excess PTH. This abnormality may contribute to the reduced pressor response to NE in CRF. The effect of PTH, on the vascular response to NE is not related to changes in plasma levels of NE or in binding sites for NE.

Arterial hypotension in chronic hemodialyzed patients

We studied in 32 patients on maintenance hemodialysis (duration of treatment 6 to 133 months) whether duration of dialysis treatment affects blood pressure, plasma noradrenaline levels and alpha 2-adrenoceptor density (assessed in platelet membranes by 3H-yohimbine binding). Plasma noradrenaline levels were a significant inverse correlation to platelet alpha 2-adrenoceptor density. In addition, mean arterial blood-pressure, plasma noradrenaline levels and platelet alpha 2-adrenoceptor density were significantly related to the duration of treatment: with increasing duration of treatment plasma noradrenaline levels increased, whereas mean arterial blood-pressure and platelet alpha 2-adrenoceptor density decreased. Furthermore, changes in mean arterial blood-pressure were inversely related to plasma noradrenaline levels and positively to platelet alpha 2-adrenoceptor density. Platelet alpha 2-adrenoceptor changes were accompanied by similar alterations in (vascular) alpha 1-adrenoceptor responsiveness (assessed by blood pressure responses to i.v. injections of phenylephrine); in hypotensive hemodialysis patients, who had high, plasma noradrenaline levels and low, platelet alpha 2-adrenoceptor density, the dose of phenylephrine necessary to increase systolic blood pressure by 20 mm Hg was nearly twice as high as in normotensive dialysis patients and healthy controls. In autonomic tests, Valsalva-ratio was lower in hypotensive than in normotensive dialysis patients and healthy controls, whereas no differences were found in blood pressure and heart rate responses during sustained hand-grip exercise as well as in beat-to-beat variation during deep breathing.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular responses in rats with chronic renal failure

Cardiovascular responses were determined in rats with chronic renal failure (CRF) produced by five sixths nephrectomy and in sham-operated rats. The conscious systolic blood pressure of rats with CRF was significantly higher than the pressure in controls although, after anaesthesia, there were no significant differences in the mean arterial pressure between the two groups of rats. The pressor responses to noradrenaline in rats with CRF were not significantly different from those recorded in sham-operated controls. The bradycardia elicited by electrical stimulation of the vagus nerve was significantly diminished in rats with CRF. However, indomethacin treatment (1 mg kg-1 s.c. twice daily for 2 days) abolished the differences in response to vagal stimulation. Changes in heart rate in response to electrical stimulation of the cervical sympathetic nerve and to bolus i.v. injections of isoprenaline and carbachol were similar in rats with CRF and controls. The most notable disturbance of cardiovascular function in rats with CRF is the diminished cardiac chronotropic response to vagal stimulation which appears to be mediated by a presynaptic action of prostaglandins.

Familial glomerulonephritis

Between 1970 and 1984, the diagnosis of glomerulonephritis was made in 860 patients on the basis of a nephritic sediment and/or renal biopsy; of these patients, 86 (10%) had at least one first-degree relative with glomerulonephritis. These patients originated from 45 families and 1674 family members were screened; 172 had glomerulonephritis, of whom 101 could be classified. The diagnostic breakdown of the 101 patients showed that 50.5% had classical Alport's syndrome; 21.8% had atypical forms; 17.8% had familial IgA glomerulonephritis; 1.9% had focal segmental glomerulosclerosis with Wolff-Parkinson-White syndrome; and 7.9% had benign familial haematuria. The proportion of patients with glomerulonephritis who had familial disease was higher than expected. The family history is an important point to consider in the examination of patients with glomerulonephritis.

Variants of Alport's syndrome

Variants of Alport's syndrome include mainly those associated with hereditary macrothrombocytopenia (and occasionally leukocyte inclusions) or with esophageal, tracheobronchial and genital leiomyomatosis. Within Alport's syndrome there appears to be no justification for differentiating those with nephritis and deafness from those with nephritis alone. However, in indirect immunofluorescence studies using the mouse monoclonal antibody, MCA-P1, which recognizes the glomerular basement membrane (GBM), reduced or absent binding was found in 20 of 42 cases of hereditary nephritis. Most of these showed typical ultrastructural GMB changes. These results suggest that there is probably a subset of patients characterized by typical GBM lesions and an absence, inaccessibility or abnormality of the GBM antigen recognized by MCA-P1.

Immunohistochemical localization of glomerular basement membrane antigens in various renal diseases

The immunofluorescent localization of glomerular basement membrane (GBM) antigens was examined in 52 specimens from normal kidneys and in various renal diseases using antisera to human GBM (HGBM), IV type collagen (IV Col) and P3 antigen, a rat nephritogen. Anti-HGBM serum normally stained the GBM and the mesangium in a restrictive pattern, anti-IV Col serum stained the GBM and the mesangium in a wider pattern and anti-P3 serum stained only the GBM. In mesangial proliferative glomerulonephritis, including IgA nephropathy and Henoch-Schönlein nephritis, the widened mesangial areas were stained with anti-HGBM and anti-IV Col sera. In membranous nephropathy, the punched-out lesions of thickened GBM were demonstrated with the three antisera in moderate cases and a double linear distribution with fine granulation with anti-HGBM and anti-IV Col sera were revealed in one severe case. In membranoproliferative glomerulonephritis, the expanded mesangium and thickened capillary walls were stained with anti-HGBM and anti-IV Col sera, while the outer line of glomerular capillary walls was only positive with anti-P3 serum. In crescentic glomerulonephritis, the collapsed glomerular tufts were stained normally with anti-HGBM and anti-P3 sera and weakly with anti-IV Col serum. In diabetic nephropathy, anti-HGBM serum stained the GBM in a double linear distribution without reacting with the expanded mesangium; anti-IV Col serum stained the mesangium and the GBM in a less clear double linear fashion while anti-P3 serum stained the GBM as single line. Thin membrane disease and Alport's syndrome had normal reactivity with all antisera. However, in one case of Alport's syndrome anti-HGBM and anti-P3 sera stained the GBM in a focal and segmental pattern, while normal staining with anti-IV Col serum was found. In lesions with adhesions and crescents the staining was positive for HGBM and IV Col and negative for P3; obsolescent glomeruli were stained with anti-HGBM and anti-P3 sera, and had diminished staining with anti-IV Col serum. The identification of the various structural glomerular antigens is useful in the classification of certain types of glomerular diseases. Further insight into the mechanisms underlying these conditions may be obtained in this way.

Plasma and brain catecholamines in experimental uremia: acute and chronic studies

To evaluate the role of catecholamines (CA) in uremia, we used "high performance" liquid chromatographic technique with electrodetection to determine plasma and brain concentration of dopamine (DA), norepinephrine (NE) and epinephrine (E) in rats with acute and chronic uremia. The results revealed a steady elevation in plasma CA (p less than 0.05) in both acutely and chronically uremic rats when compared to the level of these neurotransmitters in controls. The highest changes were observed in DA and the least in NE (16.8 +/- 3.2 vs. 0.5 +/- 0.2 ng/ml and 93.2 +/- 11.1 vs. 68.1 +/- 16.3 ng/ml). There was a positive correlation between plasma CA and the duration of uremia (r = 0.97; p less than 0.05). The elevations were more pronounced in acutely uremic rats than in chronically uremic rats. This was followed by a concomitant depletion in the concentration of DA, NE and E in the brain. The defects in catecholaminergic neurotransmission as evidence of dysfunction in the autonomic nervous system may contribute to the development of neuropathy.

Norepinephrine-related mechanism in hypertension accompanying renal failure

Various blood pressure (BP)-regulating factors were assessed before and after 4 weeks of selective norepinephrine (NE) inhibition with the sympathetic neurone blocker, debrisoquine, in nine hypertensive, nine normotensive hemodialysis patients (HDP), and 11 normal subjects. On placebo, hypertensive HDP had an increased total blood volume (P less than 0.05) and exchangeable sodium (P less than 0.001), while both HDP groups had increased (P less than 0.05) plasma clearances of NE and angiotensin II (AII), and tended to have higher basal plasma NE, renin, and AII levels, and lower BP responses to NE or AII than normal subjects. Plasma epinephrine and the chronotropic dose of isoproterenol (CDI) did not differ significantly among groups. Debrisoquine lowered supine BP markedly in hypertensive HDP (on average from 181/107 to 148/88 mm Hg) and slightly in normotensive HDP (143/78 to 131/76 mm Hg), but not in normal subjects (116/74 to 120/79 mm Hg). In all groups, plasma NE, CDI, and NE pressor dose were reduced in parallel (by 35 to 75%; P less than 0.05 to less than 0.001), and the relation between stepwise increasing plasma NE and BP changes during NE infusion was commensurably displaced to the left (P less than 0.01). The remaining parameters were not changed consistently.

CONCLUSION

HDP, as normal subjects, respond to decreased sympathetic outflow with increased alpha- and beta-receptor sensitivity. Hypertension in HDP depends strongly on a NE-related mechanism. The latter seems to complement renin-angiotensin, sodium and fluid volume in the pathogenesis of high BP.

Myocardial hypertrophy in rats with renal insufficiency

Increased defatted dry wt of the heart and increased heart calcium content were observed in subtotally nephrectomized male Sprague-Dawley rats compared with sham-operated pairfed controls. Increased heart wt contrasted with no change of the weight of viscera (liver, spleen) and markedly decreased weight of striated muscle. Heart wt was unchanged after 5 days of renal insufficiency, but significantly increased after 14 or 21 days. Increased heart wt persisted despite effective beta adrenoreceptor blockade (2 X 10 mg metroprolol/kg/day i.p.) or effective alpha-1-adrenoreceptor blockade (2 X 2 mg prazosin/kg/day i.p.). Increased heart wt was also demonstrable despite normalization of basal blood pressure (intraarterial blood pressure measurement in conscious animals): blood pressure was lowered in one series with hydralazine/nadolol in drinking water (calculated to deliver 20 and 2 mg/kg/day, respectively) and in another series with furosemide in drinking water (15 mg/kg/day) combined with metoprolol (2 X 10 mg/kg/day i.p.). Increased heart wt was also noted despite correction of anemia by blood transfusion (Hct greater than 40%) and after parathyroidectomy in animals kept eucalcemic with high dietary calcium. Micromorphometry of left ventricular myocardium in perfusion-fixed tissue showed no significant change of the relative proportion of connective tissue and myocardial fibers. Myocardial isomyosin pattern was changed with an increase of fast-migrating V1 isomyosin in animals with renal insufficiency compared to sham-operated pairfed controls.

Vascular reactivity in experimental acute renal failure

Vascular reactivity in-vivo and in-vitro was examined in rats with acute renal failure produced by bilateral nephrectomy or intramuscular glycerol injection. Bilaterally nephrectomized rats displayed enhanced pressor responses to noradrenaline and angiotensin. However, the contractile responses to noradrenaline, angiotensin and potassium chloride of aortic rings and portal vein segments from nephrectomized rats were not significantly different from the responses obtained in vessels from sham-operated controls. Rats with glycerol-induced ARF which were pretreated with indomethacin had significantly lower pressor responses to noradrenaline and angiotensin than similarly treated control animals. Aortic rings from glycerol-injected rats produced significantly smaller contractions to noradrenaline than preparations from controls. This difference was not abolished by incubation of vessels with indomethacin. The findings suggest that the absence of kidneys or the presence of damaged renal tissue and not uraemia itself have pronounced but opposite effects on vascular reactivity. The depression of vascular reactivity in glycerol-induced ARF does not appear to be a result of increased production of prostaglandins.

Hereditary chronic nephritis in India

Forty-six patients from 23 Indian families with hereditary chronic nephritis (HCN) with or without Alport's syndrome are presented. The occurrence of this disease in diverse Indian races, communities and castes is now documented. Clinical and laboratory findings in these patients are similar to those reported from temperate regions.

Cardiovascular responses in spontaneously hypertensive rats with acute renal failure

Cardiovascular status and reactivity have been investigated in spontaneously hypertensive rats (SHR) with glycerol-induced acute renal failure. SHR with acute renal failure had significantly lower mean arterial blood pressures and heart rates. The pressor responses to noradrenaline and the chronotropic responses to right cervical sympathetic and vagal nerve stimulation were diminished in uraemic SHR compared to control SHR. The cardiovascular depression observed in SHR with acute renal failure was similar to that previously noted in normotensive rats with acute renal impairment.

Vascular reactivity in rats with glycerol-induced acute renal failure

The vascular reactivity of rats with glycerol-induced acute renal failure was assessed in vitro and in vivo. The contractile responses to noradrenaline, angiotensin and potassium chloride of aortic strips and portal vein segments from uraemic rats were significantly smaller than the responses obtained in vessels from control animals. The pressor responses to angiotensin were reduced significantly in rats with acute renal failure when compared to those in control rats. The reduced vascular responses to a range of spasmogens suggests that in this model of renal failure there is a defect in some mechanism of vascular contraction common to all three constrictor agents.

Cardiovascular responses in rats with glycerol-induced acute renal failure

Autonomic and cardiovascular function were assessed in rats with glycerol-induced acute renal failure (ARF). Rats with ARF had significantly lower mean arterial blood pressure and heart rates and significantly elevated plasma noradrenaline concentrations. The chronotropic responses to right cervical sympathetic and vagal stimulation were diminished in rats with ARF. The pressor and depressor responses to noradrenaline and nitroprusside respectively when expressed as a change in mmHg pressure were significantly reduced in rats with ARF when compared to controls. However, when the depressor responses to nitroprusside were expressed as a percentage fall in basal mean arterial pressure, with the exception of the response to a dose of 10 micrograms kg-1, there were no significant differences between control and uraemic rats. The present findings show that in the rat, changes in cardiovascular responsiveness occur after a brief period of uraemia which are similar to those observed in patients and rats with chronic renal failure.