Identification of human intestinal parasites affecting an asymptomatic peri-urban Argentinian population using multi-parallel quantitative real-time polymerase chain reaction

Background

In resource-limited countries, stool microscopy is the diagnostic test of choice for intestinal parasites (soil-transmitted helminths and/or intestinal protozoa). However, sensitivity and specificity is low. Improved diagnosis of intestinal parasites is especially important for accurate measurements of prevalence and intensity of infections in endemic areas.

Methods

The study was carried out in Orán, Argentina. A total of 99 stool samples from a local surveillance campaign were analyzed by concentration microscopy and McMaster egg counting technique compared to the analysis by multi-parallel quantitative real-time polymerase chain reaction (qPCR). This study compared the performance of qPCR assay and stool microscopy for 8 common intestinal parasites that infect humans including the helminths Ascaris lumbricoides, Ancylostoma duodenale, Necator americanus, Strongyloides stercoralis, Trichuris trichiura, and the protozoa Giardia lamblia, Cryptosporidium parvum/hominis, and Entamoeba histolytica, and investigated the prevalence of polyparasitism in an endemic area.

Results

qPCR showed higher detection rates for all parasites as compared to stool microscopy except T. trichiura. Species-specific primers and probes were able to distinguish between A. duodenale (19.1 %) and N. americanus (36.4 %) infections. There were 48.6 % of subjects co-infected with both hookworms, and a significant increase in hookworm DNA for A. duodenale versus N. americanus (119.6 fg/μL: 0.63 fg/μL, P < 0.001) respectively. qPCR outperformed microscopy by the largest margin in G. lamblia infections (63.6 % versus 8.1 %, P < 0.05). Polyparasitism was detected more often by qPCR compared to microscopy (64.7 % versus 24.2 %, P < 0.05).

Conclusions

Multi-parallel qPCR is a quantitative molecular diagnostic method for common intestinal parasites in an endemic area that has improved diagnostic accuracy compared to stool microscopy. This first time use of multi-parallel qPCR in Argentina has demonstrated the high prevalence of intestinal parasites in a peri-urban area. These results will contribute to more accurate epidemiological survey, refined treatment strategies on a public scale, and better health outcomes in endemic settings.

Intraventricular Taenia solium cysts presenting with Bruns syndrome and indications for emergent neurosurgery

Bruns syndrome is an unusual phenomenon, characterized by attacks of sudden and severe headache, vomiting, and vertigo, triggered by abrupt movement of the head. The presumptive cause of Bruns syndrome is a mobile deformable intraventricular mass leading to an episodic obstructive hydrocephalus. Intraventricular tumors have been associated with Bruns syndrome; however, few cases of intraventricular neurocysticercosis have been reported to present with Bruns syndrome. We report the first series of fourth ventricular neurocysticercosis presenting with Bruns syndrome in the United States and review the other published cases where surgery was indicated.

Accuracy of five serologic tests for the follow up of Strongyloides stercoralis infection

Background

Traditional faecal-based methods have poor sensitivity for the detection of S. stercoralis, therefore are inadequate for post-treatment evaluation of infected patients who should be carefully monitored to exclude the persistence of the infection. In a previous study, we demonstrated high accuracy of five serology tests for the screening and diagnosis of strongyloidiasis. Aim of this study is to evaluate the performance of the same five tests for the follow up of patients infected with S. stercoralis.

Methods

Retrospective study on anonymized, cryo-preserved samples available at the Centre for Tropical Diseases (Negrar, Verona, Italy). Samples were collected before and from 3 to 12 months after treatment. The samples were tested with two commercially-available ELISA tests (IVD, Bordier), two techniques based on a recombinant antigen (NIE-ELISA and NIE-LIPS) and one in-house IFAT. The results of each test were evaluated both in relation to the results of fecal examination and to those of a composite reference standard (classifying as positive a sample with positive stools and/or at least three positive serology tests). The associations between the independent variables age and time and the dependent variable value of serological test (for all five tests), were analyzed by linear mixed-effects regression model.

Results

A high proportion of samples demonstrated for each test a seroreversion or a relevant decline (optical density/relative light units halved or decrease of at least two titers for IFAT) at follow up, results confirmed by the linear mixed effects model that showed a trend to seroreversion over time for all tests. In particular, IVD-ELISA (almost 90% samples demonstrated relevant decline) and IFAT (almost 87%) had the best performance. Considering only samples with a complete negativization, NIE-ELISA showed the best performance (72.5% seroreversion).

Conclusions

Serology is useful for the follow up of patients infected with S. stercoralis and determining test of cure.

Patients infected by S. stercoralis are at risk of fatal complications. It is therefore mandatory to demonstrate complete response to therapy. Post treatment evaluation should be done with highly sensitive diagnostic methods, which can exclude the persistence of the infection. Serology is more sensitive than fecal examination and coproculture. In this study, we compare the post-treatment performance of five serology tests, and suggest that they can be useful for the follow up of patients with S. stercoralis infection, especially in non-endemic areas, where there is no risk of reinfection. In fact, the results of the tests show a progressive decrease, towards negativization, of the values (expressed in different units, depending on the specific test) through time.

Corticosteroid withdrawal precipitates perilesional edema around calcified Taenia solium cysts

Calcified Taenia solium granulomas are the focus of repeated episodes of perilesional edema and seizures in 50% of persons with calcifications, history of seizures, and a positive serology for cysticercosis. The pathophysiology is unclear but recent studies suggest the edema is caused by inflammation. We report two new cases and four other published cases where cessation of corticosteroids appeared to result in recurrence or new appearance of perilesional edema around calcifications. This suggests that perilesional edema is an immune-mediated phenomenon.

Prevalence of Strongyloides stercoralis in an urban US AIDS cohort

OBJECTIVES

We examined the prevalence of Strongyloides stercoralis (Ss) infection in a cohort of AIDS patients from a US urban centre. We monitored our cohort for possible cases of dissemination or immune reconstitution inflammatory syndrome after antiretroviral therapy (ART) initiation.

METHODS

One hundred and three HIV-infected participants were prospectively sampled from a cohort observational study of ART-naive HIV-1-infected patients with CD4 ≤100 T cells/μl. Clinical symptoms, corticosteroid therapy, eosinophilia, CD4 count, and plasma HIV-RNA were reviewed. Sera were tested by an enzyme-linked immunosorbent assay (CrAg-ELISA) to crude Ss extract or to an Ss-specific recombinant protein (NIE) and by luciferase immunoprecipitation system assay (LIPS) for Ss-specific antibodies.

RESULTS

Twenty-five per cent of study participants were Strongyloides seropositive by CrAg-ELISA and 62% had emigrated from Strongyloides-endemic areas. The remaining 38% of the seropositives were US born and tested negative by NIE and LIPS. CrAg-ELISA-positive participants had a median CD4 count of 22 T cells/μl and a median HIV-RNA of 4·87 log(10) copies/ml. They presented with diarrhea (27%), abdominal pain (23%), and skin manifestations (35%) that did not differ from seronegative patients. Peripheral blood eosinophilia was common among seropositive patients (prevalence of 62% compared to 29% in seronegatives, P = 0·004). Seropositive patients were treated with ivermectin. There were no cases of hyperinfection syndrome.

DISCUSSION

Strongyloidiasis may be prevalent in AIDS patients in the USA who emigrated from Ss-endemic countries, but serology can be inconclusive, suggesting that empiric ivermectin therapy is a reasonable approach in AIDS patients originating from Strongyloides endemic areas.

A novel, multi-parallel, real-time polymerase chain reaction approach for eight gastrointestinal parasites provides improved diagnostic capabilities to resource-limited at-risk populations

Diagnosis of gastrointestinal parasites has traditionally relied on stool microscopy, which has low diagnostic sensitivity and specificity. We have developed a novel, rapid, high-throughput quantitative multi-parallel real-time polymerase chain reaction (qPCR) platform. Species-specific primers/probes were used for eight common gastrointestinal parasite pathogens: Ascaris lumbricoides, Necator americanus, Ancylostoma duodenale, Giardia lamblia, Cryptosporidium spp., Entamoeba histolytica, Trichuris trichiura, and Strongyloides stercoralis. Stool samples from 400 13-month-old children in rural Ecuador were analyzed and the qPCR was compared with a standard direct wet mount slide for stool microscopy, as were 125 8-14-year-old children before and after anthelmintic treatment. The qPCR showed higher detection rates for all parasites compared with direct microscopy, Ascaris (7.0% versus 5.5%) and for Giardia (31.5% versus 5.8%). Using an enhanced DNA extraction method, we were able to detect T. trichiura DNA. These assays will be useful to refine treatment options for affected populations, ultimately leading to better health outcomes.

Evaluation and differential diagnosis of marked, persistent eosinophilia

High-grade eosinophilia can be a diagnostic dilemma, as the etiologies are extensive and varied. Hypereosinophilic syndromes (HES) are a group of heterogeneous disorders, many of which remain poorly defined. By definition, HES must be distinguished from other disorders with persistently elevated eosinophilia with a defined cause. Although marked eosinophilia worldwide is most commonly caused by helminth (worm) infections, non-infectious causes must be considered, and include drug reactions, malignancies, and immunologic, inflammatory and allergic diseases.

Peripheral blood stem cell transplant-related Plasmodium falciparum infection in a patient with sickle cell disease

BACKGROUND

Although transmission of Plasmodium falciparum (Pf) infection during red blood cell (RBC) transfusion from an infected donor has been well documented, malaria parasites are not known to infect hematopoietic stem cells. We report a case of Pf infection in a patient 11 days after peripheral blood stem cell transplant for sickle cell disease.

STUDY DESIGN AND METHODS

Malaria parasites were detected in thick blood smears by Giemsa staining. Pf HRP2 antigen was measured by enzyme-linked immunosorbent assay on whole blood and plasma. Pf DNA was detected in whole blood and stem cell retention samples by real-time polymerase chain reaction using Pf species-specific primers and probes. Genotyping of eight Pf microsatellites was performed on genomic DNA extracted from whole blood.

RESULTS

Pf was not detected by molecular, serologic, or parasitologic means in samples from the recipient until Day 11 posttransplant, coincident with the onset of symptoms. In contrast, Pf antigen was retrospectively detected in stored plasma collected 3 months before transplant from the asymptomatic donor. Pf DNA was detected in whole blood from both the donor and the recipient after transplant, and genotyping confirmed shared markers between donor and recipient Pf strains. Lookback analysis of RBC donors was negative for Pf infection.

CONCLUSIONS

These findings are consistent with transmission by the stem cell product and have profound implications with respect to the screening of potential stem cell donors and recipients from malaria-endemic regions.

Immunization with the recombinant antigen Ss-IR induces protective immunity to infection with Strongyloides stercoralis in mice

Human intestinal infections with the nematode Strongyloides stercoralis remain a significant problem worldwide and a vaccine would be a useful addition to the tools available to prevent and control this infection. The goal of this study was to test single antigens for their efficacy in a vaccine against S. stercoralis larvae in mice. Alum was used as the adjuvant in these studies and antigens selected for analysis were either recognized by protective human IgG (Ss-TMY-1, Ss-EAT-6, and Ss-LEC-5) or were known to be highly immunogenic in humans (Ss-NIE-1 and Ss-IR). Only mice immunized with the Ss-IR antigen demonstrated a significant decrease of approximately 80% in the survival of larval parasites in the challenge infection. Antibodies, recovered from mice with protective immunity to S. stercoralis after immunization with Ss-IR, were used to locate the antigen in the larvae. Confocal microscopy revealed that IgG from mice immunized with Ss-IR bound to the surface of the parasites and observations by electron microscopy indicated that IgG bound to granules in the glandular esophagus. Serum collected from mice immunized with Ss-IR passively transferred immunity to naïve mice. These studies demonstrate that Ss-IR, in combination with alum, induces high levels of protective immunity through an antibody dependent mechanism and may therefore be suitable for further development as a vaccine against human strongyloidiasis.

Oestrogens for preventing recurrent urinary tract infection in postmenopausal women

BACKGROUND

Recurrent urinary tract infection (RUTI) is defined as three episodes of urinary tract infection (UTI) in the previous 12 months or two episodes in the last six months. The main factors associated with RUTI in postmenopausal women are vesical prolapse, cystocoele, post-voidal residue and urinary incontinence, all associated with a decrease in oestrogen. The use of oestrogens to prevent RUTI has been proposed.

OBJECTIVES

To estimate the efficacy and safety of oral or vaginal oestrogens for preventing RUTI in postmenopausal women.

SEARCH STRATEGY

We searched the Cochrane Renal Group's specialised register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1950), EMBASE (from 1980), reference lists of articles without language restriction. Date of last search: February 2007.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in which postmenopausal women (more than 12 months since last menstrual period) diagnosed with RUTI received any type of oestrogen (oral , vaginal) versus placebo or any other intervention were included.

DATA COLLECTION AND ANALYSIS

Authors extracted data and assessed quality. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes or mean difference (WMD) for continuous data with 95% confidence intervals (CI).

MAIN RESULTS

Nine studies (3345 women) were included. Oral oestrogens did not reduce UTI compared to placebo (4 studies, 2798 women: RR 1.08, 95% CI 0.88 to 1.33). Vaginal oestrogens versus placebo reduced the number of women with UTIs in two small studies using different application methods. The RR for one was 0.25 (95% CI 0.13 to 0.50) and 0.64 (95% CI 0.47 to 0.86) in the second. Two studies compared oral antibiotics versus vaginal oestrogens (cream (1), pessaries (1)). There was very significant heterogeneity and the results could not be pooled. Vaginal cream reduced the proportion of UTIs compared to antibiotics in one study and in the second study antibiotics were superior to vaginal pessaries. Adverse events for vaginal oestrogens were breast tenderness, vaginal bleeding or spotting, nonphysiologic discharge, vaginal irritation, burning and itching.

AUTHORS' CONCLUSIONS

Based on only two studies comparing vaginal oestrogens to placebo, vaginal oestrogens reduced the number of UTIs in postmenopausal women with RUTI, however this varied according to the type of oestrogen used and the treatment duration.

Tobacco industry targeting youth in Argentina

BACKGROUND/AIM

Argentina has one of the highest cigarette smoking rates among both men and women in the Americas and no legislated restrictions on tobacco industry advertising. The tobacco industry has traditionally expanded markets by targeting adolescents and young adults. The objective of this study was to determine whether and how the tobacco industry promotes cigarettes to adolescents in Argentina.

METHODS

We conducted a systematic search of tobacco industry documents available through the internet dated between 1995 and 2004 using standard search terms to identify marketing strategies in Argentina. A selected review of the four leading newspapers and nine magazines with reported high readership among adolescents was completed. The selected print media were searched for tobacco images and these were classified as advertisements if associated with a commercial product or as a story if not.

RESULTS

The tobacco industry used market segmentation as a strategy to target Argentinean consumers. British American Tobacco (BAT) undertook a young adult psychographic study and classified them as "progressives", "Jurassics" or "conservatives" and "crudos" or "spoiled brats". BAT marketed Lucky Strike to the "progressives" using Hollywood movies as a vehicle. The tobacco industry also targeted their national brands to the conservatives and linked these brands with "nationalistic values" in advertising campaigns. Philip Morris promoted Marlboro by sponsoring activities directed at young people and they launched the 10 cigarettes packet as a starter vehicle.

CONCLUSIONS

The tobacco industry used psychographic segmentation of the population and developed advertising strategies focused on youth. Tobacco control researchers and advocates must be able to address these strategies in counter-marketing interventions.

Litigation in Argentina: challenging the tobacco industry

OBJECTIVE

To evaluate the processes and outcomes of tobacco litigation in Argentina and to analyse the strategies of the tobacco industry to oppose litigation using tobacco industry documents.

METHODS

A systematic search of tobacco industry documents on the internet dating from 1978 to 2002. Law library searches using Argentinean official and unofficial reports systems were combined with computerised online searches.

RESULTS

There have been at least 15 failed litigation cases in Argentina and the tobacco industry presented a concerted defence in every claim regardless of cost. We categorised 11 cases as product liability and nicotine addiction, two as health care reimbursement, and two as criminal law and secondhand smoke. Industry strategies included hiring legal consultants from prestigious international and Argentinean law firms and developing litigation prevention programmes. Industry monitored legal academic meetings, controlled the development of new product liability legislation, obtained favourable opinions from experts, and closely observed the development of litigation in Argentina.

CONCLUSION

The strategies used by the industry have been successful in preventing recovery for tobacco injuries through litigation. Argentinean health advocates and lawyers need to be aware of the roles and strategies of the tobacco industry in order to develop effective litigation in Argentina.

Effectiveness of salmeterol versus ipratropium bromide on exertional dyspnoea in COPD

The hypothesis of the study was that salmeterol and ipratropium would have similar dyspnoea ratings during steady-state cycle ergometry at 1 h, but that salmeterol would reduce dyspnoea at 6 h after administration in patients with chronic obstructive pulmonary disease (COPD). The study design was a randomized, double-blind trial in 16 patients (aged 63 +/- 11 yrs) with symptomatic COPD. Two days after familiarization with testing procedures, patients were randomly assigned to receive either two puffs (42 microg) of salmeterol and two puffs of placebo inhaler, or two puffs (36 microg) of ipratropium from each of two inhalers (total, 72 microg). Two days later, patients received the alternative medication. During exercise at 60% of peak oxygen consumption patients rated dyspnoea and performed inspiratory capacity manoeuvres each minute. Forced expiratory volume in one second was 1.13+/-0.48 L (37+/-13% predicted). Dyspnoea ratings were similar for salmeterol and ipratropium at 1 and 6 h. Inspiratory capacity was similar for salmeterol and ipratropium at 1 h, but significantly higher for salmeterol at 6 h (delta = 120 mL; p = 0.03). It is concluded that with the doses used, salmeterol and ipratropium provided similar dyspnoea ratings during exercise at 1 and 6 h after administration.

[Awareness and detection of domestic violence by clinical physicians]

Despite the fact that approximately 50% of Argentine women are estimated to experience domestic violence (DV) at some point in their lives, clinicians have historically not been formally trained in detecting and evaluating women at risk for DV. We surveyed general practitioners to assess their level of knowledge and practice styles regarding DV and their perception of need for training in this area. We surveyed 291 internists from 11 medical centers in 4 regions of the country. We used a 10 point scale to asses their knowledge of DV. Knowledge items were derived from McCauley's article on Battering Syndrome. We asked them about the frequency with which they discuss DV with their patients and had them rate their need for further training. A total of 175 surveys were completed (60% response), 66% were men, mean age was 46 yr and the average number of women patients seen per month was 143. The mean knowledge score was 4.6 (+/- 1.8)/10. On average, the respondents had discussed DV during the last month in 1.2 (+/- 0.22) opportunities and DV was diagnosed in 0.8 (+/- 0.18). 78% of physicians reported no previous training about DV; 65% considered themselves not properly equipped to diagnose or treat DV victims; 47% showed an interest in undergoing some type of formal training and 70% wanted written material. In conclusion, practicing clinicians in Argentina score poorly on knowledge assessment of domestic violence and perceive a need for additional training in this area.

Recruitment experience in the first phase of the African American Hereditary Prostate Cancer (AAHPC) study

The African American Hereditary Prostate Cancer (AAHPC) Study is an ongoing multicenter genetic linkage study organized by Howard University and the National Human Genome Research Institute (NHGRI), with support from the Office for Research on Minority Health and the National Cancer Institute. The goals of the study are to: (i) look for evidence of involvement of chromosome 1q24-25 (HPC1) in African American men with hereditary prostate cancer (HPC) and (ii) conduct a genome-wide search for other loci associated with HPC in African American men. To accomplish these goals, a network has been established including Howard University, the NHGRI, and six Collaborative Recruitment Centers (CRCs). The CRCs are responsible for the identification and enrollment of 100 African American families. To date, 43 families have been enrolled. Recruitment strategies have included mass media campaigns, physician referrals, community health-fairs/prostate cancer screenings, support groups, tumor registries, as well as visits to churches, barber shops, and universities. By far, the most productive recruitment mechanisms have been physician referrals and tumor registries, yielding a total of 35 (81%) families. Approximately 41% (n = 3400) of probands initially contacted by phone or mail expressed interest in participating; the families of 2% of these met the eligibility criteria, and 75% of those families have been enrolled in the study, indicating a 0.5% recruitment yield (ratio of participants to contacts). As the first large-scale genetic linkage study of African Americans, on a common disease, the challenges and successes of the recruitment process for the AAHPC Study should serve to inform future efforts to involve this population in similar studies.

Marginal fit of metal ceramic restorations subjected to a standardized postsoldering technique

The fit of a fixed partial denture (FPD) is fundamental for the clinical success of a restoration. When a postsoldering procedure is needed, a high-precision laboratory technique is necessary to not affect the fit of the FPD. This article evaluates whether a standardized postsoldering technique affected the marginal fit of a 3-unit high palladium alloy FPD. One hundred and eight measurements were made of 3-unit FPDs, fabricated in a high palladium alloy (2% Au-79% Pd-10% Cu-8% Ga) and constructed on 9 tin dies in vitro. After the castings were fabricated, specimens were measured at 3 specific points per abutment (distal, labial, lingual) before and after soldering. Differences were found in the marginal opening of both copings, before soldering (49.9 microm) and after soldering (48. 3 microm). There was no significant difference in the adaptation of the copings after the soldering procedure (P<.05).

Target dyspnea ratings predict expected oxygen consumption as well as target heart rate values

A target heart rate (THR) is the traditional method to prescribe and monitor exercise training intensity in healthy individuals. However, patients with chronic obstructive pulmonary disease (COPD) are limited by ventilatory impairment and dyspnea rather than cardiovascular factors. An alternative approach is to use dyspnea ratings as a target for exercise training in patients with respiratory disease just as ratings of perceived exertion have been used in healthy individuals. The study was a randomized, parallel group trial comparing the ability of patients with COPD to accurately and reliably produce an exercise intensity using a target dyspnea rating (TDR) versus a THR. At Visit 1 patients performed an incremental exercise test on the cycle ergometer, and target values were calculated at approximately 75% of maximal oxygen consumption (V O2). At Visits 2 (3 to 5 d later) and 3 (2 wk later) each patient was instructed to produce a TDR or a THR for 10 min of submaximal exertion. Anthropometric characteristics, lung function, and exercise performance were similar for the 22 patients in each group at Visit 1. For the TDR group the dyspnea target was 2.5 +/- 1.5 at an expected V O2 of 0.88 +/- 0.28 L/min; for the THR group the heart rate (HR) target was 114 +/- 15 beats/min at an expected V O2 of 0.76 +/- 0.29 L/min (p = 0.18 for V O2 between groups). Compared with the expected V O2 from Visit 1, the individual percent differences in V O2 at Visit 2 were -3.9 +/- 18.1% (TDR) and -0.5 +/- 23.2% (THR) (p = 0.58); at Visit 3 the individual percent differences in V O2 were -2.3 +/- 17.0% (TDR) and 2.6 +/- 30.6% (THR) (p = 0.52). The number of patients < 10% and >/= 10% of the expected V O2 were similar for the two groups at Visits 2 (p = 0.38) and 3 (p = 0.27). There were no significant differences for V O2 values (absolute or individual percent) at Visits 2 and 3 for each group and between the groups (p = 0.79). In conclusion, patients with symptomatic COPD demonstrated a comparable ability to use dyspnea ratings and HR as a target to accurately and reliably produce an expected exercise intensity (approximately 75% of V O2max) for 10 min of submaximal exertion.

Langerhans' cell histiocytosis in adults

Three cases of Langerhans' cell histiocytosis with unusual clinical and histopathologic features are described. The first two cases illustrate diagnostic pitfalls that underscore the importance of considering Langerhans' cell histiocytosis in the differential diagnosis of purpuric papular eruptions of the scalp and intertriginous areas, particularly in association with hypothalamic, pituitary, or liver disease. The third case is the first report of Langerhans' cell histiocytosis presenting as a vesicular eruption.

Oxytocin as an antidiuretic hormone. I. Concentration dependence of action

Circulating concentrations of oxytocin increase to 10-40 pM in rats in response to osmotic stimuli, suggesting that oxytocin could play a role in regulation of water balance. The present studies tested whether oxytocin at such concentrations increases osmotic water permeability (Pf) in isolated perfused terminal inner medullary collecting ducts (IMCD). In IMCD segments from Sprague-Dawley rats, 20 pM oxytocin added to the peritubular bath caused a two- to threefold increase in Pf, whereas 200 pM oxytocin increased Pf by five- to sixfold (n = 8, P < 0.01). IMCD from Brattleboro rats, which manifest central diabetes insipidus, exhibited a 2.8-fold increase in Pf in response to 20 pM oxytocin and a 4.7-fold increase in response to 200 pM oxytocin. However, in Brattleboro rats, the response to 20 pM oxytocin was dependent on prior water restriction of the rats. Immunoblotting showed no change in the expression of the aquaporin-CD water channel in Brattleboro rats in response to water restriction. Nevertheless, immunofluorescence studies of inner medullary tissue from Brattleboro rats revealed a marked redistribution of the aquaporin-CD water channels to a predominantly apical and subapical localization in IMCD cells in response to water restriction, similar to the redistribution seen in response to vasopressin. Mathematical modeling studies revealed that the measured increase in Pf in response to oxytocin is sufficient to generate a concentrated urine. We conclude that oxytocin can function physiologically as an antidiuretic hormone, mimicking the short-term action of vasopressin on water permeability, albeit with somewhat lower potency.

Catheter-related thrombosis in critically ill children: comparison of catheters with and without heparin bonding

OBJECTIVE

To compare the incidence of and factors associated with vascular thrombosis after placement of heparin-bonded and standard femoral venous catheters.

DESIGN

Prospective, masked, clinical study.

SETTING

Multidisciplinary, tertiary, pediatric intensive care unit.

PATIENTS

Consecutive cases (n = 50) of critically ill children admitted to a pediatric intensive care unit in whom either a heparin-bonded (n = 25) or a standard (n = 25) femoral venous catheter was placed.

MEASUREMENTS AND MAIN RESULTS

Patients were examined by ultrasonography within 3 days of catheter insertion, weekly while the catheter was in place, and after catheter removal for evidence of vascular thrombosis. Data were collected prospectively regarding clinical evidence of catheter thrombosis, infusate composition, and positive blood culture results. Of 50 patients, 13 (26%) had thrombotic complications, 11 (44%) of the 25 patients in the standard-catheter group, in comparison with 2 (8%) of the 25 patients in the heparin-bonded catheter group (p = 0.004). In addition, there was a significantly higher incidence of positive blood culture results among patients in the standard-catheter group (24% vs 0%; p = 0.009). Positive catheter blood culture results were obtained in 38% of patients with thrombosis versus 3% without thrombosis (p = 0.001). Clinical evidence of thrombosis was found in 69% of patients with, versus 27% of patients without, ultrasound-proved thrombosis (p = 0.007).

CONCLUSION

Heparin bonding of catheters is associated with significantly fewer thrombotic complications. A reduced incidence of positive catheter-related blood culture results may be associated with the absence of thrombosis.

Model of ammonium and bicarbonate transport along LDL: implications for alkalinization of luminal fluid

Luminal fluid exiting the proximal convoluted tubule of a juxtamedullary nephron is alkalinized as it passes through the long-loop thin descending limb of Henle (LDL). Three potential mechanisms of alkalinization are: 1) concentration of bicarbonate by water abstraction, 2) direct bicarbonate entry, and 3) NH3 entry. We have used a mathematical model of the LDL to investigate these mechanisms. With permeabilities of HCO3-, NH3, and NH4+ measured for subsegments of the chinchilla LDL [M. F. Flessner, R. Mejia, and M. A. Knepper. Am. J. Physiol. 264 (Renal Fluid Electrolyte Physiol. 33):F388-F396, 1993], the osmotic water permeability of each segment [C.-L. Chou and M. A. Knepper. Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32):F417-F426, 1992], and appropriate parameters from the literature, we have used the model to calculate hypothetical pH, HCO3- concentration, and NH3 concentration of the luminal fluid as it descends the LDL within an assumed interstitium. After eliminating each mechanism in turn by setting the appropriate permeability to zero, we recalculated the axial profiles. Our results suggest that, although all three mechanisms individually contribute to LDL alkalinization, NH3 entry likely plays the dominant role.

Ammonium and bicarbonate transport in isolated perfused rodent long-loop thin descending limbs

Ammonium accumulates in the renal medullas of antidiuretic mammals. The accumulation process is thought to involve countercurrent multiplication, energy-dependent recycling between the ascending and descending limbs of Henle's loop. To investigate the role of the long-loop thin descending limb (LDL) in countercurrent multiplication of ammonium, we have perfused outer medullary and inner medullary subsegments of the chinchilla LDL (and inner medullary subsegments of rat LDL) in vitro and measured the fluxes of total ammonia and total CO2. No spontaneous fluxes of total ammonia or total CO2 occurred in the absence of imposed concentration gradients. When transepithelial concentration gradients were imposed, passive total ammonia and total CO2 transport were observed in all subsegments, although the permeabilities varied with distance along the descending limb. Passive total ammonia transport occurred through a combination of NH3 and direct NH4+ permeation. The outer medullary segment was the most permeable to NH4+. The deep inner medullary segment was the most permeable to bicarbonate. Addition of carbonic anhydrase to the lumen accelerated passive NH3 entry in the outer medullary LDL, indicating that little or no luminal carbonic anhydrase is endogenously present. The passive secretion of NH4+ and NH3 into the LDL may contribute to the countercurrent multiplication of ammonium in the rodent renal medulla.

Renal actions of atrial natriuretic factor: a mathematical modeling study

Atrial natriuretic factor (ANF) is a peptide hormone that increases renal NaCl and water excretion. Several renal sites of ANF action have been identified, but general agreement has not been reached concerning the quantitative contribution of each action to the natriuresis and diuresis. Using a five-nephron central core model of NaCl, urea, KCl, and water transport in the rat kidney, we have quantitatively evaluated the hypothetical effects on whole kidney function of three experimentally observed ANF actions: 1) inhibition of active NaCl absorption in the collecting duct, 2) inhibition of osmotic water permeability in the collecting duct, and 3) increased NaCl and water delivery out of the proximal convoluted tubule simulating an increase in glomerular filtration rate. The simulations show that inhibition of collecting duct active NaCl absorption by greater than or equal to 50% can increase NaCl and water excretion to levels that match experimental values. In addition, the model predicted that the urinary sodium concentration will increase to greater than plasma levels as observed experimentally. Simulated decreases in collecting duct water permeability predicted an increase in water excretion with little change in NaCl excretion. Simulated 2.5-5% increases in glomerular filtration rate also increased simulated NaCl and water excretion rates to experimentally observed levels in response to ANF. However, this action was less effective than inhibition of collecting duct active NaCl absorption in increasing the urinary NaCl concentration. We conclude that a combination of several actions are likely to account for the overall renal effect of ANF.

Disequilibrium pH and ammonia transport in isolated perfused cortical collecting ducts

The present study was carried out to test directly whether isolated perfused rabbit cortical collecting ducts (CCDs) spontaneously generate a luminal disequilibrium pH. We determined disequilibrium pH as the difference between 1) the actual luminal pH measured by perfusing the lumen with a membrane-impermeant pH-sensitive dye [1,4-dihydroxyphthalonitrile (1,4-DHPN)] and 2) equilibrium pH calculated from the measured total CO2 concentration in fluid collected at the end of the tubule. When the peritubular bath and perfusate had the same composition, a statistically significant acidic disequilibrium pH was found (mean -0.14 units). To determine whether the disequilibrium pH is due to an absolute lack of luminal carbonic anhydrase, we measured the effective rate constant for carbonic acid dehydration in the lumen (k-1). To do this, a lumen-to-bath NH3 concentration gradient was imposed, and the luminal pH was measured along the tubule with 1,4-DHPN. NH3 absorption caused a luminal disequilibrium pH (due to dissociation of NH+4 to NH3 and H+), whose profile along the lumen is dependent on k-1 and NH3 permeability (PNH3). PNH3 and k-1 were estimated from the luminal pH profiles using a mathematical model of proton and buffer transport. The measured k-1 (37 s-1) is within the reported range of values for uncatalyzed H2CO3 dehydration. Calculations demonstrate that the measured PNH3 (2 X 10(-3) cm/s) is high enough and the measured k-1 is low enough to explain ammonia secretion rates seen in previous studies. We conclude that proton secretion in the CCD generates an acidic luminal disequilibrium pH, associated with an absolute lack of luminal carbonic anhydrase, which enhances the net rate of NH3 secretion.

Model of solute and water movement in the kidney

Finite difference equations describing salt and water movement in a model of the mammalian kidney have been solved numerically by an extension of the Newton-Raphson method used for the medullary counterflow system. The method permits both steady-state and transient solutions. It has been possible to simulate behavior of the whole kidney as a function of hydrostatic pressures in renal artery, vein, and pelvis; protein and other solute concentrations in arterial blood; and phenomenological equations describing transport of solute and water across nephron and capillary walls. With the model it has been possible to compute concentrations, flows, and hydrostatic pressures in the various nephron segments and in cortical and medullary capillaries and interstitium. In a general way, calculations on the model have met intuitive expectations. In addition, they have reemphasized the critical dependence of renal function on the hydraulic and solute permeabilities of glomerular, postglomerular, and medullary capillaries. These studies provide additional support for our thesis that the functional unit of the kidney is not the single nephron, but a nephrovascular unit consisting of a group of nephrons and their tightly coupled vasculature.

Quantitative analysis of mass and energy balance in non-ideal models of the renal counterflow system

A modified Newton-Raphson method for solving finite difference equations for the renal counterflow system is described. The method has proved generally stable and efficient, and has given significant computational results for a variety of models: calculations on single solute models of the coupled vasa recta nephron counterflow system have shown that for large water and solute permeabilities of the exchanging membranes, behavior of the non-ideal system approaches that of the previously described ideal central core model. Concentration by salt and urea mixing in two solute models has been analyzed and previous conclusions from central core models have been found to remain valid in non-ideal systems. The numerical solutions have set some order of magnitude bounds on permeability requirements for concentration in different types of non-ideal systems. Finally, from the detailed concentration profiles it has been possible to relate the rate of free energy creation and dissipation from transmembrane transport of solutes and water to the net rate of free energy efflux from the counterflow system, and so to compute in a given model the fraction of power used for solute concentration.