Dismantling structural racism in nursing research

Dismantling structural racism in nursing research is key to achieving health equity for populations that experience disproportionate burden of health disparities. Several nursing organizations have advocated for the nursing profession to address structural racism in the discipline and the Future of Nursing 2020 to 2030: Charting a Path to Achieve Health Equity specifically calls for research that addresses equity and social justice. Bold calls to conduct research to address structural racism notwithstanding, what remains less clear are the strategies needed. We propose key considerations for the design of research to address structural racism and offer examples from behavioral and biobehavioral research designed to dismantle structural racism.

Association of Acute Respiratory Failure in Early Childhood With Long-term Neurocognitive Outcomes

IMPORTANCE

Approximately 23 700 US children undergo invasive mechanical ventilation for acute respiratory failure annually, with unknown long-term effects on neurocognitive function.

OBJECTIVE

To evaluate neurocognitive outcomes of children who survive pediatric intensive care unit (PICU) hospitalization for acute respiratory failure compared with their biological siblings.

DESIGN, SETTING, AND PARTICIPANTS

Prospective sibling-matched cohort study conducted at 31 US PICUs and associated neuropsychology testing centers. Patients were 8 years or younger with a Pediatric Cerebral Performance Category score of 1 (normal) before PICU admission and less than or equal to 3 (no worse than moderate neurocognitive dysfunction) at PICU discharge, excluding patients with a history of neurocognitive deficits or who were readmitted and underwent mechanical ventilation. Biological siblings were aged 4 to 16 years at testing, with Pediatric Cerebral Performance Category score of 1 and no history of mechanical ventilation or general anesthesia. A total of 121 sibling pairs were enrolled from September 2, 2014, to December 13, 2017, and underwent neurocognitive testing starting March 14, 2015. The date of the final follow-up was November 6, 2018.

EXPOSURES

Critical illness and PICU treatment for acute respiratory failure.

MAIN OUTCOMES AND MEASURES

The primary outcome was IQ, estimated by the age-appropriate Vocabulary and Block Design subtests of the Wechsler Intelligence Scale. Secondary outcomes included measures of attention, processing speed, learning and memory, visuospatial skills, motor skills, language, and executive function. Evaluations occurred 3 to 8 years after hospital discharge.

RESULTS

Patients (n = 121; 55 [45%] female patients) underwent PICU care at a median (IQR) age of 1.0 (0.2-3.2) years, received a median (IQR) of 5.5 (3.1-7.7) days of invasive mechanical ventilation, and were tested at a median (IQR) age of 6.6 (5.4-9.1) years. Matched siblings (n = 121; 72 [60%] female siblings) were tested at a median (IQR) age of 8.4 (7.0-10.2) years. Patients had a lower mean estimated IQ than matched siblings (101.5 vs 104.3; mean difference, -2.8 [95% CI, -5.4 to -0.2]). Among secondary outcomes, patients had significantly lower scores than matched siblings on nonverbal memory (mean difference, -0.9 [95% CI, -1.6 to -0.3]), visuospatial skills (mean difference, -0.9 [95% CI, -1.8 to -0.1]), and fine motor control (mean difference, -3.1 [95% CI, -4.9 to -1.4]) and significantly higher scores on processing speed (mean difference, 4.4 [95% CI, 0.2-8.5]). There were no significant differences in the remaining secondary outcomes, including attention, verbal memory, expressive language, and executive function.

CONCLUSIONS AND RELEVANCE

Among children, survival of PICU hospitalization for respiratory failure and discharge without severe cognitive dysfunction was associated with significantly lower subsequent IQ scores compared with matched siblings. However, the magnitude of the difference was small and of uncertain clinical importance.

Bias in Musculoskeletal Pain Management and Bias-Targeted Interventions to Improve Pain Outcomes: A Scoping Review

Bias in healthcare negatively impacts disparities in care, treatment, and outcomes, especially among minority populations. A scoping review of the literature was performed to provide a deeper understanding of how bias influences musculoskeletal pain and potential effects of bias-targeted interventions on reducing pain disparities, as well as identify gaps and make suggestions for further research in this area. Publications from peer-reviewed journals were searched using the databases PubMed/MEDLINE, PsycINFO, CINAHL, and Scopus, with 18 studies identified. The literature review revealed that clinician-based bias and discrimination worsen pain and disability by reducing access to treatment and increasing patient pain-related injustice, catastrophizing, depression, and perceived stress. In contrast, clinician education and perspective-taking, patient decision tools, and community outreach interventions can help reduce bias and disparities in musculoskeletal pain outcomes. Increasing the diversity of the healthcare workforce should also be a priority. Models of care focused on health equity may provide an ideal framework to reduce bias and provide sustainable improvement in musculoskeletal pain management.

Characterizing Long COVID: Deep Phenotype of a Complex Condition

BACKGROUND

Numerous publications describe the clinical manifestations of post-acute sequelae of SARS-CoV-2 (PASC or "long COVID"), but they are difficult to integrate because of heterogeneous methods and the lack of a standard for denoting the many phenotypic manifestations. Patient-led studies are of particular importance for understanding the natural history of COVID-19, but integration is hampered because they often use different terms to describe the same symptom or condition. This significant disparity in patient versus clinical characterization motivated the proposed ontological approach to specifying manifestations, which will improve capture and integration of future long COVID studies.

METHODS

The Human Phenotype Ontology (HPO) is a widely used standard for exchange and analysis of phenotypic abnormalities in human disease but has not yet been applied to the analysis of COVID-19.

FUNDING

We identified 303 articles published before April 29, 2021, curated 59 relevant manuscripts that described clinical manifestations in 81 cohorts three weeks or more following acute COVID-19, and mapped 287 unique clinical findings to HPO terms. We present layperson synonyms and definitions that can be used to link patient self-report questionnaires to standard medical terminology. Long COVID clinical manifestations are not assessed consistently across studies, and most manifestations have been reported with a wide range of synonyms by different authors. Across at least 10 cohorts, authors reported 31 unique clinical features corresponding to HPO terms; the most commonly reported feature was Fatigue (median 45.1%) and the least commonly reported was Nausea (median 3.9%), but the reported percentages varied widely between studies.

INTERPRETATION

Translating long COVID manifestations into computable HPO terms will improve analysis, data capture, and classification of long COVID patients. If researchers, clinicians, and patients share a common language, then studies can be compared/pooled more effectively. Furthermore, mapping lay terminology to HPO will help patients assist clinicians and researchers in creating phenotypic characterizations that are computationally accessible, thereby improving the stratification, diagnosis, and treatment of long COVID.

FUNDING

U24TR002306; UL1TR001439; P30AG024832; GBMF4552; R01HG010067; UL1TR002535; K23HL128909; UL1TR002389; K99GM145411.

'I think there is nothing . . . that is really comprehensive': healthcare professionals' views on recommending online resources for pain self-management

Objectives

To explore healthcare professionals' views on, and attitudes, towards recommending online resources for persistent pain self-management.

Methods

This study was the qualitative phase of a two-phase mixed method study. Thirty-one New Zealand health professionals involved in the management of persistent pain were interviewed via focus groups and individual interviews. Data were analysed using the general inductive approach.

Results

The major themes were as follows: (1) risks and limits of online information outweigh benefits, (2) a blended model, of online resources with healthcare professional support, could work, (3) only trustworthy resources can be recommended, (4) need for personalisation and (5) perceived barriers to adoption.

Conclusion

Online resources were perceived as a useful adjunct to support pain self-management; however, due to potential risks of misinterpretation and misinformation, healthcare professionals proposed a 'blended model' where curated online resources introduced during face-to-face consultations could be used to support self-management. Participants needed 'trustworthy online resources' that provide evidence-based, updated information that is personalised to clients' health literacy and cultural beliefs.

Practice implications

Training for healthcare professionals on critical appraisal of online resources or curation of evidence-based online resources could increase recommendation of online resources to support pain self-management as an adjunct to in-person care.

Income-driven socioeconomic status and presenting illness severity in children with acute respiratory failure

Children living in low socioeconomic communities are vulnerable to poor health outcomes, especially when critically ill. The purpose of this study was to investigate the association between socioeconomic status (SES) and illness severity upon pediatric intensive care unit (PICU) admission in children with acute respiratory failure. This secondary analysis of the multicenter Randomized Evaluation of Sedation Titration for Respiratory Failure clinical trial includes children, 2 weeks to 17 years old, mechanically ventilated for acute respiratory failure; specifically, subjects who had parental consent for follow-up and residential addresses that could be matched with census tracts (n = 2006). Subjects were categorized into quartiles based on income, with a median income of $54,036 for the census tracts represented in the sample. Subjects in the highest income quartile were more likely to be older, non-Hispanic White, and hospitalized for pneumonia. Subjects in the lowest income quartile were more likely to be Black, younger, and hospitalized for asthma or bronchiolitis, to have age-appropriate baseline functional status, and history of prematurity and asthma. After controlling for age group, gender, race, and primary diagnosis, there were no associations between income quartile and either Pediatric Risk of Mortality scores or pediatric acute respiratory distress syndrome. As measured, income-based SES was not associated with illness severity upon PICU admission in this cohort of patients. More robust and reliable methods for measuring SES may help to better explain the mechanisms by which socioeconomic affect critical illness.

Study protocol for a two-center test of a nurse-implemented chronotherapeutic restoring bundle in critically ill children: RESTORE Resilience (R2)

Often, pediatric intensive care environments are not conducive to healing the sick. Critically ill children experience disruptions in their circadian rhythms, which can contribute to delayed recovery and poor outcomes. We aim to test the hypothesis that children managed via RESTORE Resilience (R2), a nurse-implemented chronotherapeutic bundle, will experience restorative circadian rhythms compared to children receiving usual care. In this two-phased, prospective cohort study, two separate pediatric intensive care units in the United Sates will enroll a total of 20 baseline subjects followed by 40 intervention subjects, 6 months to less than 18 years of age, requiring invasive mechanical ventilation. During the intervention phase, we will implement the R2 bundle, which includes: (1) a focused effort to replicate the child's pre-hospitalization daily routine, (2) cycled day-night lighting and sound modulation, (3) minimal yet effective sedation (RESTORE), (4) nighttime fasting with bolus enteral daytime feedings, (5) early progressive mobility (PICU Up!), (6) continuity in nursing care, and (7) parent diaries. Our primary outcome is circadian activity ratio post-extubation. We hypothesize that children receiving R2 will experience restored circadian rhythms as evidenced by decreased nighttime activity while in the PICU. Our exploratory outcomes include salivary melatonin levels; electroencephalogram (EEG) slow-wave activity; R2 feasibility, adherence, and system barriers; levels of patient comfort; exposure to sedative medications; time to physiological stability; and parent perception of being well cared for. This paper describes the design, rationale, and implementation of R2.

CLINICALTRIALSGOV IDENTIFIER

NCT04695392.

Racial, ethnic, and socioeconomic disparities in paediatric critical care in the USA

In an era of tremendous medical advancements, it is important to characterise and address inequities in the provision of health care and in outcomes. There is a large body of evidence describing such disparities by race or ethnicity and socioeconomic position in critically ill adults; however, this important issue has received less attention in children and adolescents (aged ≤21 years). This Review presents a summary of the available evidence on disparities in outcomes in paediatric critical illness in the USA as a result of racism and socioeconomic privilege. The majority of evidence of racial and socioeconomic disparities in paediatric critical care originates from the USA and is retrospective, with only one prospective intervention-based study. Although there is mixed evidence of disparities by race or ethnicity and socioeconomic position in general paediatric intensive care unit admissions and outcomes in the USA, there are striking trends within some disease processes. Notably, there is evidence of disparities in management and outcomes for out-of-hospital cardiac arrest, asthma, severe trauma, sepsis, and oncology, and in families' perceptions of care. Furthermore, there is clear evidence that critical care research is limited by under-enrolment of participants from minority race or ethnicity groups. We advocate for rigorous research standards and increases in the recruitment and enrolment of a diverse range of participants in paediatric critical care research to better understand the disparities observed, including the effects of racism and poverty. A clearer understanding of when, where, and how such disparities affect patients will better enable the development of effective strategies to inform practice, interventions, and policy.

Transmural gradient of leukocyte-endothelial interaction in the rat gastrointestinal tract

Gastrointestinal injury usually starts in the superficial mucosa. We investigated whether leukocyte-endothelial interactions were greater in the gastrointestinal mucosa than the submucosa and muscularis in control tissue and after upregulation of adhesion molecules with endotoxin and after chemical insult with nonsteroidal anti-inflammatory drugs. Inactin-anesthetized rats were given either endotoxin, flurbiprofen, or nitric oxide (NO)-flurbiprofen, after which ICAM-1 and P-selectin expression was measured with the dual-label antibody technique. Leukocyte-endothelial interactions in the different gastric layers were assessed after endotoxin using intravital microscopy. Endotoxin caused a two- to threefold increase in ICAM-1 expression in the stomach and duodenum. There was, however, a gradient in expression across the gut wall with the level of expression in the superficial mucosa (per g) being only 10-25% of that in the deeper layers in both control and endotoxin-treated animals. Constituitive expression of P-selectin in control animals was barely detectable. Endotoxin caused a modest increase in mucosal P-selectin but a very significant increase in the deeper layers. Flurbiprofen caused a slight upregulation of ICAM-1 in the gastric mucosa and duodenum, whereas NO-flurbiprofen had no affect on expression. Intravital microscopy revealed no adhesion and virtually no leukocyte rolling in the vessels of the gastric mucosa despite endotoxin treatment. There was, however, some adhesion and significant leukocyte rolling in the submucosa and muscularis. Thus the superficial gastric and duodenal mucosal microcirculations have a much lower density of ICAM-1 and P-selectin and less leukocyte-endothelial interactions than occurs in the deeper layers of the gut wall even during stimulated upregulation with endotoxin.

NMDA receptor involvement in the effects of low dose domoic acid in neonatal rats

We have previously reported that neonatal rats display enhanced sensitivity to domoic acid relative to adults, and that perinatal injections of low doses of domoic acid alter early associational learning in the newborn rat. The current study was designed to further investigate the effects of low dose domoic acid on neonatal odour conditioning and to determine if the observed effects are due in part to an action on NMDA receptors. Groups of rat pups were conditioned to a novel odour on postnatal day (PND) 8, injected with 20 microg/kg domoic acid either alone, or in combination with the NMDA antagonist CPP (or appropriate controls), daily from day 8-14, re-exposed to the conditioning odour or a novel odour on day 9, and tested for odour preference on day 13 using a standard 3-choice paradigm. Results indicated that rats treated with domoic acid spent significantly more time over the conditioning odour than did saline-treated rats when tested on PND 13. This effect was antagonized by concomitant injection of CPP, indicating an involvement of NMDA receptors in the actions of DOM in this paradigm. Rats injected with either saline or CPP alone showed the opposite effect, i.e. a preference for the alternate odour. The results indicate that a very low dose of DOM produces a conditioned odour preference in neonatal rats and that this effect is due in part to NMDA receptor involvement, thereby emphasizing a role for both kainate and NMDA glutamate receptors in implicit memory.

Low doses of domoic acid during postnatal development produce permanent changes in rat behaviour and hippocampal morphology

It is well established that the developing brain is a highly dynamic environment that is susceptible to toxicity produced by a number of pharmacological, chemical and environmental insults. We report herein on permanent behavioural and morphological changes produced by exposing newborn rats to very low (subconvulsive) doses of kainate receptor agonists during a critical window of brain development. Daily treatment of SD rat pups with either 5 or 20 microg/kg of domoic acid (DOM) from postnatal day 8-14 resulted in a permanent and reproducible seizure-like syndrome when animals were exposed to different tests of spatial cognition as adults. Similar results were obtained when animals were treated with equi-efficacious doses of kainic acid (KA; 25 or 100 microg/kg). Treated rats had significant increases in hippocampal mossy fiber staining and reductions in hippocampal cell counts consistent with effects seen in adult rats following acute injections of high doses of kainic acid. In situ hybridization also revealed an elevation in hippocampal brain derived neurotrophic factor (BDNF) mRNA in region CA1 without a corresponding increase in neuropeptide Y (NPY) mRNA. These results provide evidence of long-lasting behavioural and histochemical consequences arising from relatively subtle changes in glutamatergic activity during development, that may be relevant to understanding the aetiology of seizure disorders and other forms of neurological disease.

NO-flurbiprofen maintains duodenal blood flow, enhances mucus secretion contributing to lower mucosal injury

This study investigates possible mechanisms behind the reduced gastrointestinal ulcerogenicity of nitric oxide (NO)-flurbiprofen compared with flurbiprofen. The duodenal mucosa of Inactin-anaesthetised rats was exteriorized for intravital microscopy. Blood flow was measured with laser-Doppler flowmetry (LDF), mucus thickness with micropipettes, ICAM-1 and P-selectin expression with dual-labeled antibody technique, and mucosal integrity by (51)Cr-EDTA permeability. Exposure of the duodenum to flurbiprofen (1.0 mg/ml) for 90 min significantly reduced LDF to 70 +/- 4%, whereas NO-flurbiprofen (1.3 mg/ml) had no significant effect. Mucus accumulation after 60-min exposure was 75 +/- 23 microm (control), -1 +/- 17 microm (flurbiprofen), and 104 +/- 35 microm (NO-flurbiprofen). Mucosal permeability to (51)Cr-EDTA was unchanged in the control and NO-flurbiprofen groups but increased significantly from 1.0 +/- 0.2 to 3.7 +/- 0.7 microl x min(-1) x g(-1) after 90-min exposure to flurbiprofen. Expression of ICAM-1 was significantly increased after oral flurbiprofen but not by NO-flurbiprofen. Positive effects of NO-flurbiprofen compared with flurbiprofen on mucus formation, blood flow, and adhesion molecule expression likely contribute to the reduced mucosal injury observed with NO-flurbiprofen.

How can the uptake of cervical cytology screening be improved?

BACKGROUND

Cervical cancer remains a killer, despite a screening programme designed to detect cases in the early stages of development. A number of factors appear to influence a woman's decision to attend for a smear test. This literature review considers these factors, and whether nurses can play a part in reducing the death rate by dispelling the misapprehensions and misinformation that deter vulnerable women from attending.

CONCLUSION

There is a great need for modification and improvement of the present screening programme if all women who are at risk from cervical cancer are to be encouraged to attend for screening. The attitude of those who conduct smear tests is often crucial in gaining women's confidence--an unpleasant experience might deter a patient from attending again. Other barriers to attendance include administrative errors and lack of knowledge. Given the impact of mass advertising and health promotion campaigns in other areas, such as smoking cessation, there is clearly a need for a similar strategy to be applied to cervical screening.

Bufokinin: immunoreactivity, receptor localization and actions in toad intestine and mesenteric circulation

In this study, we have mapped the immunoreactivity and the binding sites for bufokinin, a tachykinin peptide from the toad intestine. Dense bufokinin-immunoreactive fibers were present at the myenteric plexus, but no cell bodies were stained, suggesting an extrinsic origin. Bufokinin nerve fibers were also associated with submucosal blood vessels and mesenteric arteries. Autoradiographic binding sites for [(125)I]Bolton-Hunter-bufokinin were densely localized over the intestinal circular and longitudinal muscle, submucosal blood vessels and the endothelium of mesenteric arteries. Mesenteric veins had minimal immunoreactivity and binding sites. In the anesthetized toad, topical application of bufokinin onto the mesentery caused a 2.7-fold increase in arterial blood flow, observed using intravital microscopy. This study supports a role for bufokinin as an endogenous spasmogen and hemodynamic regulator in the toad intestine.

Interrelations between plasma homocysteine and intracellular S-adenosylhomocysteine

S-Adenosylhomocysteine, a potent intracellular methylation inhibitor, is suggested as a potential mediator for hyperhomocysteinemia-related vascular changes. We investigated the effect of acute and chronic hyperhomocysteinemia on intracellular S-adenosylhomocysteine and S-adenosylmethionine in rats and humans. Elevated plasma homocysteine in rats infused with homocysteine produced an increase in S-adenosylhomocysteine (P < 0.001) but not S-adenosylmethionine levels (P > 0.05) in various rat tissues. However intraerythrocyte S-adenosylhomocysteine and S-adenosylmethionine levels were not changed in homocysteine-infused rats and human subjects with experimentally acute hyperhomocysteinemia by methionine loading test. In contrast, erythrocyte S-adenosylhomocysteine levels were significantly higher in chronic renal failure patients, who had chronically elevated plasma homocysteine levels, than in either vascular disease patients or healthy controls (P < 0.05). In conclusion, acute hyperhomocysteinemia can increase intracellular S-adenosylhomocysteine levels in tissues actively involved in homocysteine metabolism. The findings are relevant to homocysteine-related endothelial dysfunction since S-adenosylhomocysteine modulates endothelial cell apoptosis.

A combination of midazolam and ketamine for procedural sedation and analgesia in adult emergency department patients

OBJECTIVE

To describe the clinical characteristics of a combination of midazolam and ketamine for procedural sedation and analgesia in adult emergency department (ED) patients.

METHODS

This was a prospective, observational trial, conducted in the ED of an urban level II trauma center. Patients > or = 18 years of age requiring procedural sedation and analgesia were eligible, and enrolled patients received 0.07 mg/kg of intravenous midazolam followed by 2 mg/kg of intravenous ketamine. Vital signs were recorded at regular intervals. The adequacy of sedation, adverse effects, patient satisfaction, and time to reach discharge alertness were determined. Descriptive statistics were calculated using statistical analysis software.

RESULTS

Seventy-seven patients were enrolled. Three were excluded due to protocol violations, three due to lack of documentation, and one due to subcutaneous infiltration of ketamine, leaving 70 patients for analysis. The average age was 31 years, and 41 (59%) were female. Indications for procedural sedation and analgesia included abscess incision and drainage (66%), fracture/joint reduction (26%), and other (8%). The mean dose of midazolam was 5.6 +/- 1.4 mg and the mean dose of ketamine was 159 +/- 42 mg. The mean time to achieve discharge criteria was 64 +/- 24 minutes. Five patients experienced mild emergence reactions, but there were no episodes of hallucinations, delirium, or other serious emergence reactions. Eighteen (25%) patients recalled dreaming while sedated; twelve (17%) were described as pleasant, two (3%) unpleasant, three (4%) both pleasant and unpleasant, and one (1%) neither pleasant nor unpleasant. There were four (6%) cases of respiratory compromise, two (3%) episodes of emesis, and one (1%) case of myoclonia. All of these were transient and did not result in a change in the patient's disposition. Only one (1%) patient indicated that she was not satisfied with the sedation regimen.

CONCLUSIONS

The combination of midazolam and ketamine provides effective procedural sedation and analgesia in adult ED patients, and appears to be safe.

Reflections on intuition and expertise

Reflective practice now appears firmly established in the English speaking world of professional nursing practice and development. Outside this linguistic context, however, the concept seems less well-known. This paper describes an experience drawn from clinical practice and education in French-speaking Switzerland followed by explicit reflection grounded in questions generated by Johns' model for structured reflection. Thus, a concept well-described in the English-language literature underpins an innovative approach to a French-language clinical teaching situation. The professional implications of this situation are explored through meaningful reflection providing new insight into familiar circumstances as they relate to the nurse tutor's role. This exploration is followed by a critical approach to the experience and the subsequent structured reflection in order to address relationships between intuition and expertise and self-awareness through reflection. A hermeneutic perspective provides additional insight into the nurse-patient relationship where both come to the situation with their own 'pre-understandings'. Individual horizons thus endorse a new understanding going beyond taken-for-granted meanings.

Homocysteine enhances neutrophil-endothelial interactions in both cultured human cells and rats In vivo

Despite intense investigation, mechanisms linking the development of occlusive vascular disease with elevated levels of homocysteine (HCY) are still unclear. The vascular endothelium plays a key role in regulating thrombogenesis and thrombolysis. We hypothesized that vascular lesions in individuals with elevated plasma HCY may be related to a dysfunction of the endothelium triggered by HCY. We investigated the effect of HCY on human neutrophil adhesion to and migration through endothelial monolayers. We also examined the effect of HCY on leukocyte adhesion and migration in mesenteric venules of anesthetized rats. We found that pathophysiological concentrations of HCY in vitro induce increased adhesion between neutrophils and endothelial cells. This contact results in neutrophil migration across the endothelial layer, with concurrent damage and detachment of endothelial cells. In vivo, HCY infused in anesthetized rats caused parallel effects, increasing leukocyte adhesion to and extravasation from mesenteric venules. Our results suggest that extracellular H2O2, generated by adherent neutrophils and/or endothelial cells, is involved in the in vitro endothelial cell damage. The possibility exists that leukocyte-mediated changes in endothelial integrity and function may lead to the vascular disease seen in individuals with elevated plasma HCY.

Australian animal ethics committees: we have come a long way

Twenty years ago, Australian biomedical researchers took the first steps along a pathway toward common ground with opponents of the use of animals in science. Leaders of Australian medical research at that time saw the necessity of established science facing the ethical and political challenges that a revived antivivisectionist movement was mounting in the late 1970s and the 1980s.

Intercellular adhesion molecule-1 expression in adjuvant arthritis in rats: inhibition by kappa-opioid agonist but not by NSAID

OBJECTIVE

To quantify intercellular adhesion molecule-1 (ICAM-1) expression in normal and adjuvant arthritic rats and to determine the extent to which ICAM-1 expression in arthritic animals is altered by treatment with a prototype nonsteroidal antiinflammatory drug (NSAID) and a kappa-opioid agonist.

METHODS

Unilateral hind paw inflammation was induced by intradermal injection of Freund's complete adjuvant (FCA) into the right hind paw of female Lewis rats. Polyarthritis was induced by intradermal injection of FCA into the base of the tail of female dark Agouti rats. The NSAID naproxen [5 mg/kg intraperitoneally (ip)] or the kappa-opioid PD117302 (15 mg/kg ip) was administered twice daily throughout the experiment (21 days). ICAM-1 expression was quantified using monoclonal antibodies against rat ICAM-1 that bind to the endothelium in proportion to the degree of adhesion molecule expression.

RESULTS

ICAM-1 expression was significantly upregulated in the joints of affected limbs of animals with both unilateral hind paw inflammation and polyarthritis. In animals treated with PD 117302 and naproxen there was a significant attenuation of arthritis; however, only treatment with PD117302 was able to significantly inhibit the upregulation of ICAM-1 expression in arthritic joints.

CONCLUSION

ICAM-1 expression is upregulated in experimental arthritis. It appears that the kappa-opioid PD117302, but not the NSAID naproxen, inhibits the upregulation of ICAM-1 in arthritic joints, suggesting these agents act via different mechanisms. The ability of the kappa-agonist, PD117302, to inhibit both the inflammation and upregulation of ICAM-1 in arthritic joints emphasizes the potential of kappa-agonists as antiarthritic agents.

Role of neutrophils and mast cells in acute indomethacin-induced small bowel injury in the rat

The aim of this study was to determine whether the injury to the rat jejunum during the first 4.5 h exposure to indomethacin is due to an influx of neutrophils or degranulation of resident mast cells. Indomethacin and vehicle both caused changes in villous morphology (length, width, etc.) while only indomethacin injured the small bowel, as indicated by increased histological lesion score and 51Cr-ethylene diamine tetraacetate (EDTA) flux across the intestinal epithelium. Immunohistochemical staining showed the same small increase in neutrophil density (predominantly in the submucosa) following exposure to vehicle as following exposure to indomethacin. Chronic oral administration of indomethacin for 48 h did cause increased tissue neutrophil density compared to that in vehicle-fed controls. Mast cell depletion (using dexamethasone) did not alter either the indomethacin-induced increase in 51Cr-EDTA clearance or the increase in neutrophil density caused by the vehicle and by indomethacin. However, the lesion score following exposure to indomethacin was significantly lower in mast-cell-depleted animals than in control animals. We conclude that the acute phase of indomethacin-induced intestinal injury is not associated with neutrophil influx. Increased neutrophils seen after chronic indomethacin may result from injury rather than be causative. Mast cells appear to exacerbate the initial stages of indomethacin-induced intestinal injury.

Portal hypertension enhances endotoxin-induced intercellular adhesion molecule 1 up-regulation in the rat

BACKGROUND & AIMS

Liver disease or portosystemic shunting enhances th e sensitivity to endotoxin. The aim of this study was to investigate whether intercellular adhesion molecule 1 (ICAM-1) expression in response to endotoxin may be dysregulated in an animal model of portal hypertension.

METHODS

Portal hypertension was induced by partial portal vein ligation. Sham-operated animals served as controls. ICAM-1 expression was measured using radiolabeled antibodies under baseline conditions or 5 hours after treatment with either endotoxin or recombinant tumor necrosis factor (TNF). Immunoreactive plasma TNF was also measured.

RESULTS

Under baseline conditions, ICAM-1 expression in all organs studied was similar in portal-hypertensive and sham-operated rats. ICAM-1 up-regulation after a high dose of endotoxin (5 mg/kg) was similar in both groups of animals. However, portal-hypertensive animals showed a significantly higher ICAM-1 expression in response to low doses of endotoxin (0.1-10 microgram/kg). The response to a low (but not a high) dose of recombinant TNF was also significantly enhanced in portal-hypertensive animals. In addition, portal-hypertensive rats had higher plasma TNF levels after treatment with endotoxin or recombinant TNF.

CONCLUSIONS

Portal hypertension induces an exaggerated ICAM-1 up-regulation in response to endotoxin, which is related to an increased production and decreased clearance of the cytokine.

Regional differences in constitutive and induced ICAM-1 expression in vivo

The aim of the present study was to characterize and compare the expression of intercellular adhesion molecule 1 (ICAM-1) on unstimulated and endotoxin-challenged endothelial cells in different tissues of the rat. ICAM-1 expression was measured using 125I-labeled anti-rat ICAM-1 monoclonal antibody (MAb) and an isotype-matched control MAb labeled with 131I (to correct for nonspecific accumulation of the binding MAb). Under baseline conditions, ICAM-1 MAb binding was observed in all organs. The binding of 125I-ICAM-1 MAb varied widely among organs, with the largest accumulation (per g tissue) in the lung, followed by heart (1/30th of lung activity), splanchnic organs (1/50th of lung activity), thymus (1/100th of lung activity), testes (1/300th of lung activity), and skeletal muscle (1/800th of lung activity). Endotoxin induced an increase in ICAM-1 MAb binding in all organs except the spleen. Endotoxin-induced upregulation of ICAM-1 was greatest in heart and skeletal muscle (5- to 10-fold), whereas the remaining organs exhibited a two- to fourfold increase in ICAM-1 expression. Maximal upregulation of ICAM-1 occurred at 9-12 h after endotoxin administration. A dose-dependent increase in ICAM-1 expression was elicited by 0.1-10 microgram/kg, with higher doses (up to 5 mg/kg) producing no further increment. Induction of ICAM-1 mRNA after endotoxin was observed in all tissues examined (lung, heart, intestine), peaked at 3 h, and then rapidly returned to control levels. These findings indicate that ICAM-1 is constitutively expressed on vascular endothelium in all organs of the rat and that there are significant regional differences in the magnitude and time course of endotoxin-induced ICAM-1 expression.

Role of leukocytes in indomethacin-induced small bowel injury in the rat

This study assesses the role of neutrophils in indomethacin-induced small bowel injury and determines the influence of intestinal pH on the magnitude of this injury. Rat jejunum was perfused via the lumen with buffer, and mucosal injury was assessed by blood-to-lumen clearance of 51Cr-EDTA and quantitative histology. Reduction in luminal pH from 7.4 to 6.0 in the presence of indomethacin (1.0 mg/ml) increased 51Cr-EDTA clearance from 2.0 +/- 0.1 to 6.5 +/- 0.3 microliter.min-1.g-1. Indomethacin caused a reduction in villus length, an increase in villus width, and an increase in lesion score. Depletion of neutrophils with antiserum largely prevented the increase in 51Cr-EDTA clearance and morphological changes. Intravenous indomethacin given at a dose to mimic therapeutic plasma levels (1 mg/kg iv) had no significant effect on 51Cr-EDTA clearance but caused similar morphological changes to those observed following intraluminal administration. The data suggest that neutrophils play a role in acute indomethacin injury and that the drug given intravenously can cause morphological changes without necessarily altering mucosal permeability to 51Cr-EDTA.

Mechanisms of acute and chronic intestinal inflammation induced by indomethacin

The objective of this study was to characterize the mechanisms of acute and chronic intestinal mucosal injury and inflammation induced by subcutaneously injected indomethacin (Indo). One injection of Indo (7.5 mg/kg) produced acute injury and inflammation in the distal jejunum and proximal ileum that were maximal at three days and completely resolved within one week. Two daily subcutaneous injections of Indo produced a more extensive and chronic inflammation that lasted in an active form in more than 75% of the rats for at least two weeks. Epithelial injury, as measured by enhanced mucosal permeability, was significantly elevated only at one day in the acute model (one injection) but was persistently elevated in the chronic model (two injections). Bile duct ligation completely attenuated increased mucosal permeability in the acute model, however, depletion of circulating neutrophils had no effect. Neither Indo (0-0.1 mg/ml) nor normal bile was cytotoxic to cultured rat intestinal epithelial cells; however, they synergistically promoted significant cytotoxicity. Bile collected from rats treated with Indo was cytotoxic towards the epithelial cells in a dose-dependent manner. Sulfasalazine and metronidazole (100 mg/kg/day, both) attenuated enhanced mucosal permeability in the chronic model. Massive bacterial translocation into the mesenteric lymph nodes, liver, and spleen following two injections of Indo was significantly attenuated by metronidazole. We conclude that: (1) a single injection of Indo produces acute intestinal mucosal injury and inflammation that resolve completely within three to seven days, whereas two daily injections of Indo produce both acute and chronic injury and inflammation, (2) enterohepatic circulation of Indo is important in promoting the acute phases of injury and inflammation, (3) circulating neutrophils do not play a role in the pathogenesis of this model, and (4) endogenous bacteria play an important role in exacerbating and/or perpetuating the chronic phases of injury and inflammation.

Spatial and Temporal Variation in Competitive Effects on Soil Moisture and Pine Response

The effects of different plant life-forms, including a bunch grass species, Andropogon virginicus L. (broomsedge), and a sprouting deciduous tree species, Liquidambar styraciflua L. (sweetgum), on soil moisture and competitive responses of a transplanted coniferous tree seedling, Pinus taeda L. (loblolly pine), were investigated. Addition of the bunch grass and/or hardwood sprouts either had no effect or increased soil moisture in the surface soil (0-14 cm) depending on the time, while addition of sweetgum and/or broomsedge (greatest density alone) decreased soil moisture in deeper portions of the solum during the summer months. Soil moisture available to pine seedlings at various points in time was assessed by measuring predawn xylem pressure potential. Temporal variation in predawn xylem pressure potential was accounted for through a water stress integral approach. More than half of the variation in pine size after one growing season could be accounted for by the water stress integral.

Leukocyte--endothelial cell adhesion induced by ischemia and reperfusion

Reperfusion of ischemic tissues is associated with an enhanced production of inflammatory mediators, increased rolling, adherence, and emigration of leukocytes in postcapillary venules, and vascular protein leakage. There is a growing body of evidence that the leukocyte--endothelial cell interactions are largely responsible for the microvascular dysfunction induced by ischemia--reperfusion. Oxygen radicals, produced by xanthine oxidase and other enzymes, appear to play an important role in initiating and amplifying the inflammatory response elicited by ischemia--reperfusion, while neutrophilic proteases contribute significantly to the injury response. The magnitude of the inflammatory responses observed during ischemia and reperfusion is also influenced by adhesion forces generated by specific glycoproteins expressed on the surface of granulocytes and microvascular endothelium, as well as shear forces that are generated by the movement of blood within the microcirculation. Manipulation of free-radical production, leukocyte--endothelial cell adhesion, and (or) intravascular shear forces provides an effective means for attenuating the deleterious influences of ischemia--reperfusion on the microvasculature.

Leukocyte adhesion in local versus hemorrhage-induced ischemia

The objective of this study was to compare the leukocyte-endothelial cell adhesive interactions elicited in postcapillary venules by either local ischemia-reperfusion or hemorrhage-reperfusion. Leukocyte rolling, adherence, and emigration were monitored in cat mesenteric venules exposed to an 85% reduction in blood flow (induced by either hemorrhage or local restriction of arterial inflow) for 1 h, followed by 1 h reperfusion. Leukocyte-endothelial cell interactions, venular diameter, and red blood cell velocity were measured during baseline, ischemia, and reperfusion periods. Both local and hemorrhage-induced ischemia reperfusion caused a reduction in leukocyte rolling velocity and increases in leukocyte adherence and emigration. Quantitatively, the adherence and emigration responses in both ischemia models were nearly identical. However, the two models differed in their response to immunoneutralization of the leukocyte adhesion glycoprotein CD11/CD18 with monoclonal antibody (MAb) IB4. The MAb had a more profound effect in attenuating leukocyte adherence and emigration in the local ischemia model. These results indicate that different factors may contribute to leukocyte-endothelial cell adhesive interactions observed in local vs. systemic models of ischemia-reperfusion.

Effect of aspirin on ulcer site blood flow in cat stomachs

Radioactive microspheres were used to measure blood flow in the cat stomach during exposure to saline, 0.075 M HCl, and then 15 and 30 min after exposure to 20 or 40 mM aspirin in HCl. At the end of the experiment, the stomach wall was divided into ulcerated regions and adjacent nonulcerated areas. When exposed to saline, both regions had similar blood flow: 27 +/- 5 and 25 +/- 5 ml.min-1.100 g-1 (means +/- SE). Addition of acid caused a significant increase in blood flow to 41 +/- 7 ml.min-1.100 g-1 only at those sites that eventually ulcerated in the presence of aspirin. In the adjacent nonulcerated regions, blood flow was 31 +/- 5 ml.min-1.100 g-1 and was not significantly greater than the flow recorded during saline exposure. Aspirin caused ulcer site blood flow to increase dramatically to 89 +/- 12 and 122 +/- 18 ml.min-1.100 g-1 after 15 and 30 min, whereas the adjacent nonulcerated tissue rose to 40 +/- 6 and 44 +/- 5 ml.min-1.100 g-1, respectively. The ulcer site hyperemia with acid alone suggests higher mucosal permeability in these regions allowing back-diffusion of acid and injurious agents. The present data obtained in the cat do not support the notion that ischemia plays a role in initiating nonsteroidal anti-inflammatory drug (NSAID)-induced ulcers, but rather that acute NSAID ulcers are associated initially with a hyperemia.

Morphologic assessment of leukocyte-endothelial cell interactions in mesenteric venules subjected to ischemia and reperfusion

Intravital microscopic studies of the mesenteric microcirculation have demonstrated that leukocyte adherence and emigration in postcapillary venules are a characteristic feature of tissues exposed to ischemia-reperfusion. The objectives of this study were to determine whether: (1) neutrophils are the predominant leukocytes that adhere and emigrate in postischemic mesenteric venules, and (2) leukocyte adherence and/or emigration are a prerequisite for reperfusion-induced increases in venular permeability. Leukocyte kinetics in cat mesenteric venules (25-35 microns diameter) were evaluated using both intravital microscopy and quantitative morphometry. The intestine and mesentery were exposed to 60 min of ischemia, followed by 60 min reperfusion. Some animals were pretreated with a monoclonal antibody (MoAb IB4) against the leukocyte adhesion glycoprotein, CD11/CD18. Vessels observed by intravital microscopy and adjacent venules of similar diameter were excised and processed for light (LM) and electron microscopy (EM). Horseradish peroxidase (HRP), administered intravenously, was used to assess vascular permeability by EM. By LM, the control (nonischemic) mesentery is sparsely populated by plasma cells, mast cells, and leukocytes; 30-50% of the resident population is neutrophils. Ischemia-reperfusion led to a significant increase in the number of extravascular cells, with neutrophils accounting for greater than 80% of the total cell population. Control and ischemic venules demonstrated no leakage of HRP into the interstitium. However, venules exposed to ischemia and reperfusion demonstrated HRP leakage between endothelial cells and into the surrounding interstitium; neutrophils were adherent to the luminal surface of the endothelium, transmigrating the vessel wall, and in the surrounding interstitium. Animals pretreated with MoAb IB4 presented the same cell profile as nonischemic controls, with no adherent or transmigrating neutrophils. However, some HRP leakage was noted following reperfusion in venules treated with MoAb IB4. The results of this study indicate that: (1) neutrophils are the predominate leukocytes that adhere and emigrate in postischemic venules, and (2) inhibition of leukocyte adhesion does not completely prevent the venular dysfunction associated with ischemia-reperfusion.

Role of CD11/CD18 in shear rate-dependent leukocyte-endothelial cell interactions in cat mesenteric venules

In vivo microscopy was used to assess the relationships among shear rate (and shear stress), leukocyte rolling velocity, and leukocyte adherence in a cat mesentery preparation. Shear rate in individual venules and arterioles of 25-35 microns diameter were varied over a wide range by graded occlusion of an arterial loop. There was a linear decline in leukocyte rolling velocity (Vwbc) as red cell velocity (Vrbc) was reduced. The ratio Vwbc/Vrbc remained constant despite variations in shear stress from 5-25 dyn/cm2. A reduction in shear stress was associated with an increased leukocyte adherence, particularly when Vwbc was reduced below 50 microns/s. Reduction in wall shear rate below 500 s-1 in arterioles allowed 1-3 leukocytes to adhere per 100 microns length of vessel, while venules exposed to the same shear rates had 5-16 adherent leukocytes. In arterioles, leukocyte rolling was only observed at low shear rates. At shear rates less than 250 s-1 leukocyte rolling velocity was faster in arterioles than venules, and the ratio Vwbc/Vrbc for arterioles was 0.08 +/- 0.02, which was fourfold higher than the ratio obtained in venules at similar shear rates. Pretreatment with the CD18-specific antibody (mAb) IB4 increased leukocyte rolling velocity in venules by approximately 20 microns/s at red cell velocities below 2,000 microns/s. mAb IB4 largely prevented the leukocyte adherence to arterioles and venules, and increased the ratio Vwbc/Vrbc observed in venules at low shear elicit a CD18-dependent adhesive interaction between leukocytes and microvascular endothelium, and that differences in shear rates cannot explain the greater propensity for leukocyte rolling and adhesion in venules than arterioles.

Ethanol enhances leukocyte-endothelial cell interactions in mesenteric venules

In vivo studies have implicated neutrophils in the gastric mucosal injury produced by intraluminal administration of ethanol. However, in vitro studies indicate that ethanol inhibits various neutrophil functions such as adherence, chemotaxis, and degranulation. The aim of the present study was to assess whether ethanol, at clinically relevant concentrations, is proinflammatory in vivo. Ethanol (0.2, 1.0, 2.0, and 4.0%) was applied to the surface of the cat mesentery, and neutrophil adherence to venules (30 microns diam) and extravasation into the interstitium were quantitated using intravital microscopy. Hemodynamic parameters were also measured (venular diameter, red blood cell velocity, and leukocyte rolling velocity) or calculated (venular blood flow and wall shear stress). In this model ethanol produced a dose-dependent increase in neutrophil adherence and extravasation. The increase in leukocyte-endothelial cell interactions could not be attributed to alterations in hemodynamic factors. Pretreatment of animals with a monoclonal antibody (MoAb IB4) directed to the neutrophil CD11/CD18 adherence complex completely prevented the ethanol-induced neutrophil adherence and extravasation. Pretreatment with a leukotriene B4 (LTB4)-receptor antagonist (SC 41930) or a platelet-activating factor (PAF)-receptor antagonist (WEB 2170) did not alter the ethanol-induced neutrophil-endothelial interactions. We conclude that ethanol is proinflammatory at concentrations which may be achieved in the mucosal interstitium during acute alcohol intoxication. The ethanol-induced leukocyte adherence and extravasation is dependent on the expression of adhesive glycoproteins. The inflammatory mediators, PAF and LTB4, do not appear to play an important role in the leukocyte-endothelial cell interactions initiated by ethanol.

Role of blood flow in gastric acid secretion

The relationship between gastric acid secretion and blood flow has been investigated with a variety of different blood flow techniques including aminopyrine clearance, hydrogen gas clearance, intravital microscopy, laser-Doppler flowmetry, radioactive microspheres, and the elimination of inert gases. The most commonly used technique, aminopyrine clearance, predicts that increasing acid secretion is accompanied by a parallel increase in blood flow. However, the efficiency of clearance of aminopyrine is low in the nonsecreting stomach and increases as secretion rate increases. This precludes the use of aminopyrine clearance as a reliable measure of gastric mucosal blood flow at all but the highest steady-state level of acid secretion and casts doubt on the findings with this technique. Other methods for measuring blood flow indicate that there is no simple relationship between secretion and flow, with some studies finding that secretion and flow change in parallel and others finding that secretion varies quite independently of flow to the mucosa. One consistent finding is a strong correlation between stimulated acid secretion and gastric oxygen consumption. Both acid secretion and oxygen consumption fall if celiac blood flow is reduced below a critical value, which in the anesthetized dog stomach is approximately 30-40 ml.min-1.100 g-1. Driving blood flow above this value does not increase oxygen consumption and acid secretion, i.e., they reach a plateau. The shape of this relationship with its flow-dependent and flow-independent portions is used to explain the apparently contradictory findings in the literature regarding gastric acid secretion and blood flow.

Gradual reintroduction of oxygen reduces reperfusion injury in cat stomach

Recent studies have shown that oxygen-derived free radicals are responsible for a major portion of ischemia-reperfusion injury in the stomach. The oxygen radicals are produced during reperfusion when oxygen delivery to the tissue increases. In the present study we investigate the effect on mucosal injury of regulating the rate of reintroduction of oxygen to the stomach after ischemia. Local gastric ischemia was achieved by reducing celiac artery pressure to 30 mm Hg for 1 h. Ischemic injury was assessed by measuring the loss of 51Cr-labeled red blood cells across the gastric mucosa. Mucosal blood loss was negligible before and during the ischemia period but increased to 0.178 ml.min.-1.100 g-1 during reperfusion. When blood flow to the stomach was gradually returned to normal after ischemia by increasing celiac artery pressure by 10 mmHg every 10 min, the mucosal blood loss was reduced to 0.013 ml.min.-1.100 g-1. If the stomach was vascularly perfused with low PO2 (34 mmHg) blood for 1 h after ischemia before being returned to normal arterial perfusion, the mucosal blood loss was also reduced to 0.063 ml.min.-1.100 g-1. When the stomach was made hypoxemic for 1 h rather than ischemic by perfusing the vasculature with low PO2 (29 mmHg) blood then reperfused with normoxic blood, there was very little mucosal bleeding (0.014 ml.min.-1.100 g-1). The data indicate that gastric mucosal bleeding after ischemia is reduced if the tissue is returned slowly to a normal PO2. These findings support the concept that reperfusion injury is due largely to the production of oxygen radicals.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of neutrophils in hemorrhagic shock-induced gastric mucosal injury in the rat

Gastric mucosal clearance of 51Cr-labeled red blood cells (51Cr-RBC) was measured in rats during a 30-min control period, a 30-min ischemic period (hemorrhage to 27 mmHg arterial pressure), and a 60-min reperfusion period (reinfusion of shed blood). In untreated (control) rats, a dramatic rise in the leakage of 51Cr-labeled red blood cells into the gastric lumen was observed during the reperfusion period. Treatment with neutrophil antiserum attenuated 51Cr-labeled red blood cell flux into the gastric lumen. Using the radioactive microsphere technique, neutrophil-depleted animals were shown to have higher blood flows in the ischemic period than the untreated rats. Bleeding of untreated rats to a mean arterial pressure of 40 mmHg resulted in blood flows that were not different from those in antiserum-treated rats bled to 27 mmHg and leakage of 51Cr-labeled red blood cells similar to that measured in antiserum-treated rats. The results of this study indicate that neutrophils play an important role in hemorrhagic shock-induced gastric bleeding.

Gastric injury induced by hemorrhage, local ischemia, and oxygen radical generation

Gastric mucosal injury caused by local intra-arterial generation of oxygen-derived free radicals was compared with gastric injury caused by 30 min of hemorrhage-induced ischemia (systemic pressure of 30 mmHg) or local ischemia (celiac artery pressure of 30 mmHg). The index of injury was the loss of 51Cr-labeled red cells across the gastric mucosa. Generation of oxygen radicals in the celiac artery caused a rapid increase in mucosal blood loss during the period of radical generation (0.029 +/- 0.013 ml X min-1 X 100 g-1, mean +/- SE), and this loss was maintained after radical production ceased (0.041 +/- 0.018 ml X min-1 X 100 g-1). Local ischemia produced similar mucosal injury; however, this occurred after reperfusion of the stomach (0.038 +/- 0.006 ml X min-1 X 100 g-1) and not during the ischemic episode (0.001 +/- 0.0003 ml X min-1 X 100 g-1). Hemorrhage-induced ischemia produced a threefold greater mucosal blood loss (0.133 +/- 0.048 ml X min-1 X 100 g-1) than local ischemia. The results of this study indicate that oxygen radicals generated enzymatically in the blood supply to the stomach cause mucosal bleeding of similar magnitude to that observed after local ischemia and that gastric ischemia induced by systemic hypotension produces more severe gastric injury than the same level of local hypotension.

Proarrhythmic effects of an oxygen-derived free radical generating system on action potentials recorded from guinea pig ventricular myocardium: a possible cause of reperfusion-induced arrhythmias

Standard microelectrode techniques were used to study the effects of a free radical generating system on action potentials recorded from guinea pig ventricular myocardium. Free radicals were generated by mixing xanthine oxidase (0.02-0.04 mu/ml) with the superfusate-modified Locke's solution containing purine 2.3 mM. The system was validated by demonstrating that it could reduce cytochrome C at a rate of 15.9 +/- 1.5 mol/l/min. This rate was decreased to 3.0 +/- 0.3 (p less than 0.001) in the presence of superoxide dismutase (12 mg/100 ml), and the reaction was absent if xanthine oxidase and purine were premixed for 60 minutes prior to adding cytochrome C. Superfusion of guinea pig ventricular strips with the free radical generating system (20-30 minutes) resulted in a highly significant reduction in resting potential from -79.3 +/- 1.8 mV to -70.9 +/- 1.4 mV (p less than 0.0001, n = 6) and in action potential amplitude from 110.9 +/- 2.2 mV to 101.7 +/- 4.0 mV (p less than 0.0001). There was an accompanying fall in maximum rate of depolarization (Vmax) from 254.1 +/- 17.7 V/sec to 207.1 +/- 18.6 V/sec (p less than 0.01) and no significant change in action potential duration. These changes were accompanied by spontaneous activity in 3 of 6 preparations and reversed after 20-30 minutes washing in Locke's solution. They were largely abolished by adding superoxide dismutase (12 mg/100 ml) to the superfusate and completely absent if the xanthine oxidase and purine were premixed for 60 minutes before superfusing the myocardium. We conclude that the phenomena observed may contribute to the genesis of reperfusion arrhythmias.

Charge selectivity of rat intestinal capillaries. Influence of polycations

The role of fixed anionic sites on the intestinal capillary wall in transvascular protein exchange was assessed by neutralizing the negative charges with polycations. The studies were performed in anesthetized rats with an intestinal lymph cannula. Intestinal lymph flow and lymph and plasma total protein concentrations were measured at regular intervals before and after intravenous infusion of either protamine sulfate, poly-L-lysine, or poly-ethyleneimine. Protamine sulfate infusion produced an eightfold increase in lymph flow and a fivefold increase in lymph protein clearance. Lymph flow increased 4.6-fold and lymph protein clearance increased 3.6 times over control in rats receiving the poly-L-lysine infusion. Polyethyleneimine infusion produced results comparable in magnitude to protamine sulfate; however, the animals were unable to tolerate this agent. The enhanced transcapillary protein fluxes produced by the polycation infusions suggest that fixed anionic sites normally impede the egress of proteins from the intestinal vasculature.

Descending noradrenergic pathways involved in the A5 depressor response

The objective of the present study was to analyze the anatomical basis of the A5 depressor response and to test if the putative neurotransmitter noradrenaline is involved in the response. Two approaches were used; one was neuroanatomical and the other was pharmacological. First, the retrograde transport method in which two fluorescent markers (Fast blue and rhodamine microspheres) was used in combination with the indirect immunofluorescence technique to establish that A5 catecholamine neurons project to both the spinal cord and the region of the nucleus tractus solitarii (NTS). Second, we analyzed the effects of 6-hydroxydopamine (6-OHDA) lesions of the spinal cord and/or NTS area on the A5 depressor response. This response was elicited by a 80-nl microinjection of L-glutamate (500 mM) into the A5 region in pentobarbital anesthetized rats; it was characterized by a decrease in blood pressure and heart rate. After destruction of various noradrenergic terminal fields we have found that intraspinal injections of 6-OHDA caused a 30% reduction in the blood pressure component of the A5 depressor response and a transient depression of the bradycardic response. This result suggests that only a small portion of the A5 depressor response depends on the descending A5 spinal pathway. Injections of 6-OHDA into the NTS region caused a transient depression of the A5 depressor response, and by 7-14 days postinjection, the response returned to normal. After combined 6-OHDA injections into the spinal cord and NTS area, the blood pressure and heart rate components of the A5 depressor response were reduced to 80% of the control level at 3 days postinjection. By 14 days, even with severe depletion of noradrenaline in the spinal cord (96%) and a moderate depletion of noradrenaline in the NTS (50%), the A5 response was restored to about 80% of its original magnitude, suggesting some type of functional recovery occurs in this system. Third, the blood pressure decrease elicited by L-glutamate stimulation of the A5 cell group was unaffected by pharmacological blockade of the heart. In addition, this response appeared to be normal in rats that had both their autonomic supply to the heart blocked pharmacologically and their spinal cord noradrenaline levels depleted (14 days after intraspinal 6-OHDA injections). These data suggest that the major A5 depressor response operates mainly by inhibition of the sympathetic outflow involved in control of total peripheral resistance and that this system is controlled by a descending spinal pathway which probably does not use noradrenaline as a neurotransmitter.

Measurement of capillary pressure in humans using a venous occlusion method

The venous occlusion technique was used to measure capillary pressure in the forearm and foot of man over a wide range of venous pressures. In six recumbent subjects venous pressure (Pv) in the forearm (mean +/- SE) was 9.3 +/- 1.4 mmHg and the venous occlusion estimate of capillary pressure (Pc) was 17.0 +/- 1.6 mmHg, whereas in another six subjects Pv in the foot was 17.1 +/- 1.2 mmHg and Pc was 23.4 +/- 2.5 mmHg. Venous pressure in the limbs was increased either by changes in posture or by venous congestion with a sphygmomanometer cuff. On standing Pv in the foot increased to 95.2 +/- 1.5 mmHg and Pc rose to 112.8 +/- 3.1 mmHg. The relationship established between venous pressure and capillary pressure in the forearm is Pc = 1.16 Pv + 8.1, whereas in the foot the relationship is Pc = 1.2 Pv + 1.6. The magnitude and duration of the changes in capillary pressure were also recorded during reactive hyperemia. The venous occlusion method of measuring capillary pressure is simple and easily applied to studies in humans.

Role of oxygen radicals in ischemia-induced lesions in the cat stomach

Ischemia in a stomach that contains acid may produce severe gastric mucosal injury. The extent to which oxygen-derived free radicals are involved in the pathogenesis of this injury was investigated in the present study. Local gastric ischemia was achieved by reducing celiac artery pressure to 30 mmHg for 1 h. Ischemic injury was assessed by recording the loss of 125I-albumin and 51Cr-red cells across the gastric mucosa. Cats were treated with a xanthine oxidase inhibitor (allopurinol), a superoxide radical scavenging enzyme (superoxide dismutase), and a scavenger of hydroxyl radicals (dimethyl sulfoxide). The damage associated with ischemia only occurred during reperfusion of the stomach and was worst in the antrum. The level of xanthine oxidase in the antrum was twice that of the corpus. Treatment with allopurinol, superoxide dismutase, and dimethyl sulfoxide reduced 51Cr-red cell loss to 15%, 25%, and 21% of control (untreated) animals, respectively. The data indicate that oxygen-derived free radicals play a role in ischemic injury to the stomach and that the hydroxyl radical, a secondary radical produced from the superoxide anion, appears to be the major oxygen radical contributing to ischemic damage.

Relationship of blood flow and oxygen consumption to ischemic injury in the canine small intestine

The relationship of blood flow and oxygen uptake to ischemic intestinal injury was investigated by measuring the clearance of 131I-albumin from the blood to the lumen of isolated, perfused segments of canine jejunum. Reductions in blood flow for 2 h to various levels confirmed the previously demonstrated relationship of oxygen uptake to blood flow, i.e., oxygen uptake was flow-independent at blood flows above 30 ml/min X 100 g, and flow-dependent at levels below this. Blood flows above this threshold did not change the level of albumin clearance seen under control conditions (0.022 +/- 0.003 ml/min X 100 g). However, increases in the mucosal permeability to albumin were seen after blood flow was reduced to levels where oxygen uptake was decreased by more than 50%. These findings indicate that the ability of the small intestine to maintain oxygen consumption during low flow states may be an important factor in providing protection from ischemic injury, even during prolonged periods of hypoperfusion.

Regulation of capillary exchange capacity in the dog stomach

The capillary exchange capacity of the isolated, perfused dog stomach was investigated during vasoconstriction (norepinephrine) and vasodilation (isoproterenol) and compared with values obtained when blood flow to the stomach was decreased or increased mechanically. The capillary filtration coefficient (Kf,c) was used as an index of capillary exchange capacity. Under resting conditions, Kf,c in the isolated stomach was 0.20 +/- 0.02 ml . min-1 . mmHg-1 . 100 g-1. Vasoconstriction and mechanical reduction in blood flow caused Kf,c to fall to 68 and 58% of control, while vasodilation and mechanical increase in blood flow caused Kf,c to rise to 176 and 231% of control, respectively. Pentagastrin produced an increase in gastric oxygen consumption and a 50% increase in Kf,c. In all instances, capillary exchange capacity appeared to be correlated with gastric blood flow. The data suggest there is little local control of precapillary sphincter tone in the stomach and that capillary exchange capacity may be governed by local pressure within the microvasculature.

Effect of hypoxia on feline intestinal capillary permeability

The multiple-indicator dilution technique was used to investigate the permeability characteristics of capillaries in the cat small intestine during hypoxia. Reducing the arterial oxygen tension from 108 to 35 mmHg for 10 min increased the calculated equivalent pore radius of intestinal capillaries from 59 to 67 A. This effect was sustained for at least 15 min after the hypoxic episode. Hypoxia did not alter intestinal lymphatic protein clearance. Thus, the dimensions of the large pores did not change. This study demonstrates that 10 min of severe hypoxia increases vascular permeability in the small intestine and that this change occurs only in the small pores and is sustained, at least briefly, after restoration of normoxia. Hypoxia does not significantly change the permeability to macromolecules.

Permselectivity of the peritoneal membrane

To investigate the osmotic barrier characteristics of the peritoneal membrane during conditions similar to peritoneal dialysis in man, yet transperitoneal fluid movement was measured in 20 cats following intraabdominal placement of isotonic saline and hypertonic solutions of NaCl, glucose, raffinose, and inulin. Also, isooncotic solutions of hemoglobin and albumin and two sulfated high-molecular-weight dextrans were investigated. Transperitoneal fluid movement was measured by a volume recovery method. Oncotic pressures of test solutions and plasma were measured by osmometry. Peritoneal osmotic conductances were calculated from the rate of transperitoneal water movement and the difference in osmotic pressures between the test solution and isotonic saline. The average glucose osmotic conductance per unit body surface are was found to be 2.3 +/- 0.18 x 10(-3) ml . min-1 . mm Hg-1 . m-2, in good agreement with previous reports, and the glucose osmotic reflection coefficient (sigma) was estimated to be 0.02. All the osmotic conductances measured could be fitted to a peritoneal equivalent pore radius of approximately 6 nm according to current hydrodynamic theories. The peritoneal membrane filtration coefficient was estimated to be 0.12 ml . min-1 . mm Hg-1 . m-2, of which 0.5-1% was found to be due to transcellular water flow. In conclusion the results of this study indicate that the peritoneum is a highly selective membrane with restrictive properties comparable to those reported for continuous capillary beds.

Peritoneal dialysis solutions and feline splanchnic blood flow

Splanchnic blood flow is generally considered to be one of the major factors governing the efficiency of peritoneal dialysis; however, few direct measurements of blood flow have been made during peritoneal dialysis. The radioactive microsphere technique was used to assess the effects of 1.5 and 4.25 g/100 ml dextrose-Dianeal solutions on blood flow to various tissues in the abdominal cavity. The effects of dialysis solution on blood flow through the superior mesenteric and coeliac arteries were measured by electromagnetic flowmetry. The results indicate that the commercial peritoneal dialysis solutions dramatically increase blood flow to the mesentery, omentum, intestinal serosa and parietal peritoneum. These changes are not accompanied by significant alterations in blood perfusion in the major abdominal organs (liver, stomach, intestine, pancreas, spleen). Peritoneal dialysis solutions do not significantly alter blood flow through the coeliac and superior mesenteric arteries. These findings indicate that commercial dialysis solutions improve perfusion to the peritoneum without significantly altering splanchnic blood flow.

Capillary and interstitial forces during fluid absorption in the cat small intestine

A systematic steady-state analysis of the forces and membrane coefficients governing transcapillary and lymphatic fluid fluxes was performed in the cat ileum under absorptive and nonabsorptive conditions. Net transmucosal fluid flux, lymph flow, capillary pressure, blood flow, capillary filtration coefficient, and lymph and plasma oncotic pressures were measured before and during perfusion of the ileal lumen with a glucose (20 mM)--Tyrode's solution. Interstitial fluid pressure was calculated for the two conditions from measured parameters. Stimulation of mucosal fluid absorption resulted in an increase in lymph flow (which tripled), capillary filtration coefficient (which doubled), capillary pressure (which increased by 9%), interstitial fluid pressure (which doubled), and blood flow (which increased by 16%), whereas interstitial (lymph) oncotic pressure fell (by 20%). These changes converted filtering capillaries to absorbing capillaries, thereby allowing 82% of the absorbed fluid to be removed from the mucosal interstitium via the capillaries, while the lymphatics removed the remaining 18%. The results of this study indicate that hydrostatic and oncotic forces within the interstitium are primarily responsible for preventing interstitial fluid accumulation during periods of net fluid absorption in the small bowel.