Renal amyloidosis in intravenous drug users

BACKGROUND

Intravenous drug abuse is associated with a wide variety of acute and chronic medical complications. The increased longevity of drug users has seen the emergence of new diseases as a result of chronic bacterial and viral infection. We recently observed an increase in the number of cases of renal amyloidosis among intravenous drug users in central London.

AIM

To describe here the demographic and clinical characteristics of such patients.

METHODS

Patients were identified retrospectively from computerized patient renal biopsy records at University College London and Royal Free Hospitals from 1990-2005. Clinical information was collected from patient hospital records.

RESULTS

We identified 20 cases of AA amyloidosis; 65% occurred between January 2000 and September 2005. All were proteinuric (mean 7.3 g/l, range 0.5-14.8 g/l) and 13 required dialysis within 1 month of diagnosis. Of the remaining seven, four developed end-stage renal failure after mean follow-up of 16 months (range 6-30). Nine died, with median survival of 19 months (range 1-62); all deaths were due to sepsis.

DISCUSSION

Secondary AA amyloidosis is a serious complication of chronic soft tissue infection in intravenous drug users in central London. Affected individuals invariably presented with nephrotic range proteinuria and advanced renal failure. Treatment options are limited and the outcome for such patients on renal replacement was poor. Cross-disciplinary strategies are needed to prevent this serious complication of long-term intravenous drug abuse.

Acute administration of L-arginine does not improve arterial endothelial function in chronic renal failure

BACKGROUND

Reduced activity of the nitric oxide (NO) pathway has been implicated in the endothelial dysfunction that occurs in patients with renal failure. NO is generated from L-arginine by NO synthase, and certain uremic toxins including asymmetrical dimethyl-L-arginine (ADMA), inhibit NO synthase and might contribute to endothelial dysfunction. We hypothesized that exogenous L-arginine might improve endothelial function in patients with renal failure by overcoming the effects of uremic toxins.

METHODS

Endothelial function of the forearm resistance vasculature was assessed using plethysmography to measure the dilator response to intra-arterial acetylcholine (25 to 100 nmol/min). Endothelial function of radial and brachial arteries was assessed using vascular ultrasound to measure the dilator response to flow during reactive hyperemia (flow-mediated dilation; FMD). Studies were performed before and after administration of L-arginine by intra-arterial infusion (50 micromol/min) in 8 pre-dialysis patients or by intravenous infusion (10 g) in 18 hemodialysis patients.

RESULTS

Local L-arginine did not improve the dilator response of forearm resistance vessels (AUC 23.1 +/- 6.4 pre, 23.1 +/- 5.1 post; P = 0.9) or FMD of the radial artery (6.5 +/- 1.2% pre, 6.3 +/- 0.8% post; P = 0.8). Systemic L-arginine did not improve FMD of the brachial artery (4.1 +/- 1.1% pre, 3.0 +/- 1.1% post; P = 0.07). These data demonstrate that acute local or systemic administration of L-arginine did not improve endothelial function in resistance or conduit arteries of patients with chronic renal failure.

CONCLUSION

The results suggest that competitive inhibition of nitric oxide synthase (NOS) by circulating inhibitors is not the principal explanation for impaired endothelial dilator function in chronic renal failure.

Dialysis improves endothelial function in humans

BACKGROUND

Circulating inhibitors of endothelial function have been implicated in the pathogenesis of vascular disease in chronic renal failure. The aim of this study was to determine if lowering the plasma concentration of these and other dialysable toxins improves endothelial function. To do this we compared the acute effects on endothelial function of single episodes of haemodialysis with automated peritoneal dialysis. We hypothesized that endothelial function would improve after dialysis, with a greater effect seen after haemodialysis due to more substantial clearance of endothelial toxins per-treatment.

METHODS

Subjects with end-stage renal failure undergoing haemodialysis (n=16) or automated peritoneal dialysis (n=14) were investigated. Endothelial function was determined using vascular ultrasound to measure flow-mediated dilatation of the brachial artery and was compared with the dilatation caused by sublingual glyceryl trinitrate. Endothelial function was assessed before and after a single dialysis treatment. Plasma concentrations of the inhibitors of endothelial function, asymmetric dimethyl-l-arginine and homocysteine were measured. Flow-mediated dilatation was expressed as percentage change from basal diameter and analysed using Student's t test.

RESULTS

The plasma concentration of circulating inhibitors of endothelial function was reduced after haemodialysis but not peritoneal dialysis. Haemodialysis increased flow-mediated dilatation from 4.0+/-1.0% to 5.8+/-1.2% (P<0.002). These changes persisted for 5 h but returned to baseline by 24 h. Automated peritoneal dialysis had no acute effect on flow-mediated dilatation (5.9+/-1.1% vs 5.4+/-0.8% after, P>0.5). There were no effects of either dialysis modality on dilatation to glyceryl trinitrate.

CONCLUSIONS

Short-term reduction of circulating inhibitors of endothelial function by haemodialysis is associated with increased flow-mediated dilatation. These data suggest that dialysable endothelial toxins have deleterious effects on endothelial function that are rapidly reversible.

Low dose dopamine infusion reduces renal tubular injury following cardiopulmonary bypass surgery

BACKGROUND

The use of dopamine to protect the kidneys against hypoperfusion injury remains controversial with little clinical evidence of benefit and increasing concerns regarding safety. In this double-blind, prospective, randomised study, we investigated the effect of dopamine infusion (2.5 microg/kg/min) on glomerular filtration rate (GFR) and tubular injury in patients undergoing routine cardiopulmonary bypass (CPB).

METHODS

Forty eight patients were randomly assigned to receive intravenous dopamine or saline from induction of anaesthesia until 48 hours post-operatively. There were no differences in mean age, bypass time or pre-op creatinine in the 36 patients (33 men) who completed the study. 51Cr-EDTA GFR (ml/min/1.73 m2) was measured pre-operatively and on day 5 only. Urinary markers of tubular injury (albumin, N-acetyl glucosaminidase, NAG; retinol binding protein, RBP) were measured pre-operatively, and on days 1, 2 and 5.

RESULTS

GFR was preserved equally in both groups. All patients demonstrated significant tubular injury but urinary levels of NAG and RBP were lower in the dopamine group (41%, p=0.057 and 41%, p=0.007, respectively) on the first post-operative day.

CONCLUSION

We conclude that low dose dopamine infusion may reduce renal tubular injury following CPB in patients with normal or near normal baseline renal function.

Outcome in patients with end-stage renal disease following heart or heart--lung transplantation receiving peritoneal dialysis

BACKGROUND

End-stage renal disease (ESRD) complicates 5--10% of heart and heart--lung transplant patients. We report our experience of peritoneal dialysis (PD) in 17 such patients.

METHODS

Between March 1995 and February 1999, 13 heart transplant and four heart--lung transplant patients (11 male, 6 female) joined our PD programme (10 continuous ambulatory PD, seven automated PD). Median time from heart or heart--lung transplantation to ESRD was 9 years (range 1--13 years), and median age at introduction of renal replacement therapy was 51 years (range 23--66 years). The frequency of exit-site infections, peritonitis, and PD survival (including technique failure and death) in the transplant group (TxP) was calculated retrospectively. These were compared with two contemporary control groups: PD patients immunosuppressed for other indications (ISP, n=19) and, all other patients recruited onto the PD programme (NISP, n=132).

RESULTS

Median follow-up was 10 months (range 2--27 months) for TxP, 7 months (range 2--29 months) for ISP, and 14 months (range 1--48 months) for NISP groups. The frequency of exit-site infections was similar in each group: 1 in 26 months for TxP; 1 in 30 months for ISP, and 1 in 27 months for NISP (P=NS). The frequency of peritonitis was greater in the TxP group at 1 in 15 months, compared with 1 in 20 months for ISP and 1 in 29 months for NISP (TxP vs NISP, P<0.05). PD failure following infection was 23.5% for TxP, 10.5% for ISP, and 12.9% for NISP. Actuarial PD survival at 24 months was only 25.2% in the TxP group compared with 79% in the NISP group. There were no deaths related to immediate complications of PD.

CONCLUSIONS

Increased risk of PD peritonitis and reduced PD survival is reported in this cohort of 17 heart and heart--lung recipients with ESRD. Nevertheless, for patients with severely impaired cardiac function, PD may still offer therapeutic advantage.

Community nephrology: audit of screening for renal insufficiency in a high risk population

BACKGROUND

The rate of acceptance onto dialysis programmes has doubled in the past 10 years and is steadily increasing. Early detection and treatment of renal failure slows the rate of progression. Is it feasible to screen for patients who are at increased risk of developing renal failure? We have audited primary care records of patients aged 50-75 years who have either hypertension or diabetes, and are therefore considered to be at high risk of developing renal insufficiency. Our aim was to see whether patients had had their blood pressure measured and urine tested for protein within 12 months, and plasma creatinine measured within 24 months.

METHODS

This was a retrospective study of case notes and computer records in 12 general practices from inner and greater London. A total of 16,855 patients were aged 50-75 years. From this age group, 2693 (15.5%) patients were identified as being either hypertensive or diabetic, or both.

RESULTS

Of the 2561 records audited, 1359 (53.1%) contained a plasma creatinine measured within 24 months, and 11% of these (150) had a value > 125 micromol/l. This equates to a prevalence of renal insufficiency of > 110,000 patients per million in this group. Forty two patients (28%) had been referred to a nephrologist. Of records audited, 73% contained a blood pressure measurement and 29% contained a test for proteinuria within 12 months.

CONCLUSIONS

There is a high prevalence of chronic renal insufficiency in hypertensive and diabetic patients. It is feasible to detect renal insufficiency at a primary care level, but an effective system will require computerized databases that code for age, ethnicity, measurement of blood pressure and renal function, as well as diagnoses.

Pseudo-proteinuria following gelofusine infusion

Transient massive proteinuria following cardiopulmonary bypass surgery was observed. It was characterized and attributed to post-operative gelofusine infusion. Gelofusine was found to interfere with dye binding but not immunochemical assays of proteinuria. Proteinuria following gelofusine infusion may not reflect underlying glomerular pathology.

Renal disease and the heart

Cardiovascular disease is responsible for significant morbidity and mortality in renal failure with increased prevalence of hypertension, left ventricular hypertrophy, ischaemic heart disease and valve disease. Optimum blood pressure control is fundamental to the management of these patients but the role of secondary prevention remains poorly defined.

Renal nuclear medicine: can it survive the millennium?

Much of the progress in renal nuclear medicine has been driven by technological development, but without rigorous assessment the value of some of these studies has been overestimated. The only tests to achieve gold standard status are the isotopic GFR, the DMSA renogram to detect cortical abnormalities and the captopril renogram when used to define those hypertensive patients who will not benefit from renovascular intervention. Consensus guidelines must be followed and routine protocols for combination tests must be developed, but even so isotopic renography is likely to be overtaken by competing technologies which can provide one test to give simultaneous information about both structure and function.

Management of bowel obstruction in patients with abdominal cancer

OBJECTIVE

To determine the value of operation in patients with bowel obstruction caused by recurrent abdominal cancer.

DESIGN

Retrospective case review.

SETTING

The University of Connecticut Health Center, Farmington.

PATIENTS

Ninety-eight patients admitted with a diagnosis of bowel obstruction and malignant neoplasm between November 1, 1987, and June 30, 1995.

RESULTS

Data for 75 patients who developed a bowel obstruction within 5 years of a malignant diagnosis were analyzed. Forty-six patients (61%) were treated operatively and 29 (39%) were treated nonoperatively. The operative group included 32 patients (70%) whose obstruction was caused by carcinomatosis; 6 (19%) of these 32 patients had had at least 1 episode of previous obstruction requiring hospitalization. They had a 22% in-hospital mortality, stayed an average of 21 days in the hospital, and survived 7 +/- 6 months (mean +/- SD) after discharge; 5 (16%) had at least 1 episode of postoperative obstruction that required hospitalization. After discharge from the hospital, 53% had an excellent or good quality of life (assessed retrospectively). Of the 29 patients in the nonoperative group, 16 (55%) had carcinomatosis. These 16 patients had a 38% in-hospital mortality (6 of 16), stayed an average of 10 days in the hospital, and survived a mean of 13 +/- 9 months; 3 (19%) had at least 1 episode of recurrent obstruction requiring hospitalization. After discharge from the hospital, 6 (37%) had an excellent or good quality of life.

CONCLUSION

The value of operative intervention for bowel obstruction in patients with cancer is derived from the possibility of a benign cause, not alleviation of the consequences of carcinomatosis.

Cyclosporin nephrotoxicity following cardiac transplantation

The greatest change in GFR in response to treatment with cyclosporin occurs in the first 3-6 months and the magnitude of the decrement in the first year (or perhaps the first few months) appears to be a vital indicator of future problems. However, the apparent stabilization of renal function, particularly when monitored only by plasma creatinine, can conceal progressive tubulointerstitial injury, and increasing proteinuria is an ominous sign. Although lower doses of cyclosporin and careful monitoring of renal function may be helpful, there is at present no pharmacological intervention to protect or reverse the reduction in GFR that occurs. We believe that the vascular lesion induced by cyclosporin is fundamental, with early and initially reversible cyclosporin-induced vasospasm leading to progressive vascular damage with activation of endothelial cells and increased platelet interactions. Amongst other determinants, the renal response to this vasculopathy will depend on the balance between the presence of vasoactive factors with the vasoconstrictors promoting interstitial fibrosis and the vasodilators inhibiting proliferation. It is likely that the kidneys of heart-transplant recipients are chronically ischaemic and as a consequence their renin-angiotensin systems massively activated, which may further sensitize their kidneys to cyclosporin. Overproduction of angiotensin II, associated with the DD ACE genotype, has already been associated with poor prognosis in diabetic and IgA nephropathy. It is interesting to speculate that this ACE genotype, which is associated with a poor outcome in non-ischaemic heart disease can influence renal sensitivity to cyclosporin and predict the development of morphological injury. Extension of these experimental findings into the clinical arena with a placebo-controlled trial of early introduction of ACE inhibitor therapy in recipients of cardiac transplants would be timely.

The true clinical significance of renography in nephro-urology

Isotopic renography is a non-invasive technique used routinely by the clinician to provide information about kidney structure and function. Whilst there is no doubt of its value in the accurate measurement of glomerular filtration rate and in the detection of parenchymal abnormalities, its role in the diagnosis of renovascular disease (especially in patients with renal insufficiency), the exclusion of obstruction and the evaluation of the patient with either acute renal failure or renal transplant dysfunction remains unproven. In part, this reflects a failure to standardise protocols and rigorously evaluate diagnostic techniques. Recent developments in ultrasound, computerised X-ray tomography and nuclear magnetic resonance now present the clinician with rival techniques and emphasise the need for the clinical development of isotopic renography.

Pre-conditioning with adenosine leads to concentration-dependent infarct size reduction in the isolated rabbit heart

Adenosine (ADO) has a cardioprotective effect in ischemia-reperfusion injury when administered both prior to ischemia and during reperfusion. ADO has also been implicated in the mechanism of ischemic pre-conditioning. The aim of this study was to investigate whether there was a concentration-response between the administration of ADO prior to ischemia-reperfusion and reduction in subsequent infarct size. Rabbit isolated perfused hearts were subjected to 45 min ischemia and 180 min reperfusion following pre-treatment with either Krebs Henseleit buffer alone or buffer containing ADO at a range of concentrations (3 micro M-100 micro M) for 5 min followed by 5 min perfusion with buffer. Infarct/risk ratios were significantly reduced in hearts pre-perfused with higher (> 3 micro M) concentrations of ADO (Control, 58.5 +/- 1.5%; 3 micro M ADO, 51.6 +/- 3.0% ; 6 micro M ADO, 44.1% +/- 2.0%; 10 micro M ADO, 33.3 +/- 1.9%; 20 micro M ADO, 26.6 +/- 0.9%; 50 micro M ADO, 21.6 +/- 3.5%; 100 micro M ADO, 23.0 +/- 0.6%). We conclude that pre-treatment with ADO leads to a concentration-dependent reduction in infarct size.

Nitric oxide contributes to tissue injury in mercuric chloride-induced autoimmunity

Recent data has suggested a role for nitric oxide (NO) both in the induction of immunity and as an effector of tissue injury in experimental models of inflammation. In this study, we have tested the efficacy of two inhibitors of NO synthase, NG-monomethyl-L-arginine (L-NMMA) and aminoguanidine (AG), to modify the autoimmune leucocytoclastic necrotizing vasculitis which develops following the administration of mercuric chloride (HgCl2) to the Brown Norway rat. Neither agent affected the induction of autoimmunity as judged by plasma IgE titres or the degree of tissue neutrophil infiltration; however, L-NMMA did significantly attenuate tissue injury scores. We conclude that inhibition of NO synthase does not influence the induction of autoimmunity by HgCl2, but that NO does contribute to the development of tissue injury in this experimental model.

Inhibition of nitric oxide synthesis reduces infarct size by an adenosine-dependent mechanism

BACKGROUND

Nitric oxide (NO) is both a potent endogenous vasodilator with potential to attenuate ischemia-reperfusion injury and a mediator of tissue injury. The aim of the present study was to investigate the mechanism by which prior inhibition of NO synthesis can lessen ischemia-reperfusion injury in the isolated rabbit heart.

METHODS AND RESULTS

We examined the effects of inhibition of NO synthesis on infarct size using a model of coronary artery ligation in isolated rabbit hearts perfused at a constant flow rate of 35 mL/min. Infarct size averaged 65% of the zone at risk after 45 minutes of ischemia and 180 minutes of reperfusion. The addition of 30 mumol/L NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis, to the perfusate reduced the infarct-to-risk (I/R) ratio to an average of 41% (P < .05 versus control). This effect was abolished by pretreatment with 75.5 mumol/L 8-p-sulfophenyl theophylline (SPT), an adenosine receptor antagonist (I/R ratio, 63%). Ischemic preconditioning (5 minutes of ischemia and 10 minutes of reperfusion) before 45 minutes of ischemia and 3 hours of reperfusion reduced the I/R ratio to an average of 21%, and this was not augmented by pretreatment with L-NAME (I/R ratio, 20%). However, all protection due to preconditioning and L-NAME was lost in hearts pretreated with SPT (I/R ratio, 59%). In a separate set of experiments, adenosine concentration in the coronary perfusate and myocardial lactate concentrations were measured. Treatment with L-NAME increased the average adenosine concentration in the perfusate from 5.7 mumol/L per 100 g of heart (control) to a peak of 24.0 mumol/L per 100 g of heart; however, there was no effect on average myocardial lactate concentration (control, 4.6 mumol/g dry wt; L-NAME, 5.5 mumol/g dry wt). In contrast, after 5 minutes of global ischemia, the average adenosine concentration peaked at 139.0 mumol/L per 100 g of heart, and the average myocardial lactate concentration increased to 27.1 mumol/g dry wt.

CONCLUSIONS

Infarct size limitation after inhibition of NO synthesis shares a common mechanism with that of ischemic preconditioning and is dependent on the release of adenosine. However, in this model, adenosine release after inhibition of NO synthesis is not secondary to myocardial ischemia. The protection of the heart against ischemic injury by adenosine appears to be concentration dependent.

Nephrotic syndrome, malignant thymoma, and myasthenia gravis. Case report and review of the literature

We describe a patient with nephrotic syndrome due to focal-segmental glomerulosclerosis, occurring 3 years after thymectomy and myasthenia gravis. Nine other cases of nephrotic syndrome associated with thymoma and myasthenia gravis reported in the literature are reviewed. The nephrotic syndrome may be due to T cell dysfunction associated with thymoma; however, animal models suggest that genetic factors may also be involved.

Evaluation of therapy for cast nephropathy: failure of colchicine to alter urinary Tamm Horsfall glycoprotein excretion in normal subjects

Tamm Horsfall glycoprotein (THG) is a major constituent of renal tubular casts including the light chain casts of myeloma. Animal studies suggest that the anti-inflammatory agent colchicine reduces urinary THG excretion and prevents light chain cast formation. Six normal male subjects were given therapeutic doses of colchicine (0.5 mg twice daily for 6 days) and excretion of THG, albumin, creatinine and N-acetyl glucosaminidase (NAG) was determined. Colchicine therapy had no effect on the urinary excretion of THG, albumin or NAG or on renal function as assessed by creatinine clearance. This suggests that colchicine will not be a useful therapeutic adjunct to the treatment of light-chain nephropathy.

Functional characteristics of small placental arteries

OBJECTIVES

The aim of this study was to investigate characteristics of placental arteries capable of influencing vasomotor tone in the fetoplacental vascular bed. Contractile characteristics and endothelium-dependent and endothelium-independent relaxation were examined.

STUDY DESIGN

By means of a small vessel myograph arteries of mean normalized internal diameter 353.22 +/- 13.14 microns were studied under isometric conditions. Contractile function was assessed with a variety of agonists, including angiotensin II, endothelin-1, the thromboxane mimetic U46619, prostaglandin E2, and prostaglandin F2 alpha. The effect of physiologic and supraphysiologic PO2 on vascular function was also examined. Relaxation was assessed in response to known endothelium-dependent vasodilators, including acetylcholine, bradykinin, histamine, and A23187 and to sodium nitroprusside (endothelium independent). The effect of indomethacin and the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester on contractile function was also evaluated.

RESULTS

Sensitivity to sodium nitroprusside was reduced by a high PO2. U46619 was the most potent constrictor agonist studied. The response of precontracted arteries to known endothelium-dependent vasodilators was minimal, other than for histamine, which led to modest relaxation. The constrictor response to U46619 was increased in the presence of NG-nitro-L-arginine methyl ester.

CONCLUSIONS

Oxygen tension may be an important determinant of relaxation in small placental arteries. Receptor-mediated release of endothelium-derived relaxing factor is not a major mechanism in the fetoplacental circulation.

Scintigraphic evidence of abnormal ureteric peristalsis following urological surgery

OBJECTIVE

To investigate the effect of urological surgery on ureteric peristaltic activity.

SUBJECTS AND METHODS

Ureteric peristalsis was assessed in a sample urological population (n = 29 patients) and the findings compared with a control population (n = 14 patients).

RESULTS

The incidence of disordered peristalsis was significantly increased (P < 0.05) following urological surgery and, in particular, the incidence of retrograde peristalsis was very significantly increased (P < 0.01) following ureteric division and re-anastomosis.

CONCLUSION

The results of this study are consistent with a central role for myogenic activity in the conduction of ureteric peristalsis in man.

Acute hypernatraemia during bicarbonate-buffered haemodialysis

Five patients on maintenance haemodialysis were exposed to varying degrees of hypernatric dialysate, leading to acute hypernatraemia (plasma sodium concentrations 158 mmol/l to 179 mmol/l). With the exception of one patient, who developed pulmonary oedema, symptoms were minimal and in each case hypernatraemia was corrected without residual complications. The hypernatric dialysate resulted from a granular and less soluble batch of sodium bicarbonate powder. The extra effort required to dissolve the powder caused CO2 to be shaken out of solution, producing sodium carbonate and raising the pH. Mixing calcium from the 'acid' concentrate with excess carbonate in the 'bicarbonate' concentrate led to rapid precipitation of calcium carbonate on the conductivity monitoring cells. Dialysate conductivity was incorrectly sensed as low by the coated conductivity cells, so that an increasing amount of 'acid' concentrate, with its accompanying electrolytes, was delivered to the patient. When the granular powder was ground to a fine powder, passed through a 125 microns sieve and gently dissolved, the machine operated normally. We recommend that sodium bicarbonate powder is supplied with a sieve size no greater than 125 microns, kept dry to prevent the formation of large crystals, and dissolved gently.

Ureteric peristalsis studies in loin pain and haematuria syndrome: another diagnostic disappointment

Although not a cause of progressive renal damage, loin pain and haematuria syndrome is nevertheless associated with significant morbidity. The management of pain often presents a formidable problem to urologists, physicians and general practitioners. An earlier study noted hold-up of urine in the renal pelvis and implicated this in the pathogenesis of pain. In this study we have failed to demonstrate an excess incidence of disordered urinary peristalsis in loin pain and haematuria syndrome.

Inhibition of nitric oxide limits infarct size in the in situ rabbit heart

Recent data has suggested a dual role for nitric oxide (NO) so that it can both attenuate myocardial injury during ischaemia and reperfusion as well as mediate reperfusion injury. In this study in the in situ rabbit heart, we have shown that pretreatment with intravenous NG-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthesis) significantly reduced infarct size following sustained coronary artery occlusion and reperfusion. L-NAME was also noted to increase myocardial lactate concentration. This study provides further evidence that protection against ischaemia-reperfusion injury can be derived from manipulation of the microcirculation.

Renal scintigraphy in acute scleroderma: report of three cases

Scintigraphic findings in acute renal failure secondary to scleroderma are reported. In three patients, we have demonstrated severe reduction of renal perfusion with little or no parenchymal uptake of tracer and absent excretion. These findings are compatible with the known histological process of occlusive vasculopathy, and such scintigraphic findings at presentation may reflect a poor prognosis for renal recovery.

Abnormal endothelial cell function of resistance arteries from women with preeclampsia

OBJECTIVE

There is substantial indirect evidence that the vascular endothelium may be dysfunctional in preeclampsia and that reduced production of endothelial-derived vasodilators may account for the increased vascular resistance and enhanced pressor sensitivity characteristic of this disorder. In this study we directly investigated endothelial function by examining acetylcholine-mediated relaxation in small arteries dissected from the subcutaneous fat layer examined at the time of cesarean section.

STUDY DESIGN

By means of a small vessel myograph we measured tension in resistance arteries of normal pregnant women (n = 12) and women with preeclampsia (n = 12) and assessed the contributions of vasodilatory prostanoids and endothelium-derived relaxing factor to endothelium-dependent relaxation, as elicited by acetylcholine, 1 nmol/L to 10 mumol/L, after precontraction with 3 mumol/L norepinephrine.

RESULTS

Endothelium-dependent relaxation was impaired in arteries of women with preeclampsia compared with arteries from normotensive pregnant women. Endothelium-independent relaxation as assessed by sodium nitroprusside was not altered in the arteries from preeclamptic women.

CONCLUSIONS

This study provides direct evidence of abnormal endothelial function in preeclampsia. No deficiency in endothelium-independent relaxation could be detected.

Effects of sodium-transport inhibition in human resistance arteries

It is hypothesized that endogenous inhibitors of active sodium transport may lead to an increase in peripheral vascular resistance. From studies in animal conduit arteries there is substantial evidence that cardiac glycosides may increase tension. A number of studies from our laboratory demonstrate that inhibition of active sodium transport may also increase tension in human resistance arteries, and that reduced Ca efflux via Na/Ca exchange could be a contributory mechanism. Further experiments also have suggested that endogenous inhibitors of sodium transport could lead to an increase in peripheral vascular resistance by reducing endothelium-dependent relaxation.

Effect of bufalin and pregnanes on vasoreactivity of human resistance arteries

Endogenous Na/K ATPase inhibitory activity has been implicated in salt and water homeostasis in mammals and amphibians. Recent interest has focused on endogenous cardiac glycosides, some progesterone derivatives (pregnanes) and the amphibian bufodienolides. This study has examined the effects of non-planar and planar pregnanes and the bufodienolide bufalin on vasoreactivity of human resistance arteries. Bufalin and a non-planar pregnane caused concentration-dependent potentiation of the tone of submaximally pre-contracted arteries and inhibited endothelium-dependent relaxation, whereas a planar pregnane affected neither response. The relative potency of the compounds studied suggest the results do not simply reflect degrees of Na/K ATPase inhibition. The active compounds may be important in the regulation of vascular tone.

Ouabain and responses to endothelium-dependent vasodilators in the human forearm

Ouabain inhibits endothelium-dependent vascular relaxation in vitro, but has not been studied in this regard in vivo. We have therefore measured blood flow responses to carbachol, bradykinin and sodium nitroprusside (endothelium-dependent and endothelium-independent vasodilators) infused into the brachial artery with and without co-infusion of ouabain (2 micrograms min-1). Six healthy male volunteers were each studied on two occasions. Ouabain reduced basal forearm blood flow, by 18.0 +/- 4.1% (mean +/- s.e. mean, 2P less than 0.05), but had no significant effect on responses to any of the three vasodilators. These results indicate that effects of ouabain on endothelium-dependent relaxation in vitro must be interpreted with caution.

Low-concentration ouabain does not inhibit noradrenaline-induced contraction of human resistance arteries

1. Using a Mulvany-Halpern myograph to measure changes in isometric tension, we have investigated the effect of ouabain on noradrenaline-induced contraction of human subcutaneous resistance arteries. 2. Low concentrations of ouabain (10 nmol/l or less) were shown not to alter vascular smooth muscle contractility or sensitivity to noradrenaline. 3. In contrast, higher concentrations of ouabain (100 nmol/l or more) were found to depress vascular smooth muscle contractility and to reduce the sensitivity of the noradrenaline concentration-response relationship. 4. These findings may have implications regarding the presence of an endogenous inhibitor of the sodium pump in essential hypertension and in pregnancy-associated hypertension.

Effect of ouabain on endothelium-dependent relaxation of human resistance arteries

Inhibition of active sodium transport by ouabain was found to cause concentration- and time-dependent impairment of acetylcholine-induced relaxation in human resistance arteries with a significant effect at 100 pM. The reduced acetylcholine response was attributable to inhibition of the NG-monomethyl L-arginine-sensitive but not the indomethacin-sensitive component of relaxation. Relaxation by sodium nitroprusside was not affected by ouabain, suggesting that inhibition of sodium transport, directly or indirectly, must affect synthesis or release of endothelium-derived relaxing factor rather than its effector pathway. These results do not support the existence of an additional endothelium-derived relaxing factor other than endothelium-derived relaxing factor, which is dependent on sodium pump activity. The finding that inhibition of sodium transport has a profound effect on vascular relaxation may have implications in the pathogenesis of certain forms of hypertension.

Effect of NG-monomethyl-L-arginine on endothelium-dependent relaxation of human subcutaneous resistance arteries

1. Using a myograph to measure isometric tension, we have looked at the action of NG-monomethyl-L-arginine on the endothelium-dependent relaxation of human subcutaneous resistance arteries. 2. NG-Monomethyl-L-arginine, the novel inhibitor of endothelium-derived relaxing factor synthesis, caused concentration-dependent but only partial inhibition of maximal relaxation induced by acetylcholine in human subcutaneous resistance arteries. 3. The inhibitory action of NG-monomethyl-L-arginine on acetylcholine-induced maximal relaxation was partially reversed by incubation of the arteries in equimolar concentrations of L-arginine and NG-monomethyl-L-arginine. Subsequent incubation in L-arginine led to further reversal, but this was no greater than with incubation in physiological saline. 4. A component of acetylcholine-induced relaxation was sensitive to indomethacin, suggesting that this response is mediated by prostanoids as well as by endothelium-derived relaxing factor. 5. NG-Monomethyl-L-arginine did not increase the tension of resting human subcutaneous resistance arteries. NG-Monomethyl-L-arginine did enhance the contractile response to noradrenaline, possibly due to inhibition of release of endothelium-derived relaxing factor resulting from stimulation of alpha 2-adrenoreceptors on the endothelial cells.

Effects of ouabain and low sodium on contractility of human resistance arteries

Earlier work with rat arteries has resulted in a widely held assumption that resistance artery smooth muscle will not contract on exposure to a reduced transplasmalemmal sodium gradient. In view of the well-recognized low sensitivity of rat tissue to cardiac glycosides, we have investigated the effects of altering the transplasmalemmal sodium gradient on vascular smooth muscle tone by using human resistance arteries. Incubation of arteries in low sodium or in ouabain to inhibit active sodium efflux for 1 hour increased the contractile response to caffeine stimulation; this finding indicated enhanced calcium buffering by the sarcoplasmic reticulum. Prolonged incubation in ouabain in the presence of phentolamine or diltiazem resulted in a concentration-dependent increase in the tone of resting human resistance arteries. Reduction of the transplasmalemmal sodium gradient by incubation in low sodium buffer effected an increase in tone similar to that obtained in the presence of ouabain. These results suggest that alteration of the transplasmalemmal sodium gradient may increase the vascular smooth muscle tone of human resistance arteries by altering intracellular calcium handling. This is a new finding in human resistance arteries and may involve inhibition and, indeed, reversal of sodium-dependent calcium efflux. A concentration-dependent potentiation of tone was found after the addition of ouabain to submaximally activated arteries. Sodium-calcium exchange may also play a pivotal role in this mechanism.