Intravenous iron versus blood transfusion for postpartum anemia: a systematic review and meta-analysis

BACKGROUND

Intravenous iron (IV-iron) is used as an alternative to, or alongside, red blood cell transfusion (RBC-T) to treat more severe postpartum anemia (PPA), although optimal treatment options remain unclear. No previous systematic reviews have examined IV-iron and RBC-T, including patient-reported outcomes and hematological responses.

METHODS

A systematic review and meta-analysis of randomized trials comparing IV-iron and RBC-T with each other, oral iron, no treatment, and placebo for the treatment of PPA. Key inclusion criteria were PPA (hemoglobin < 12 g/dL) and IV-iron or RBC-T as interventions. Key exclusion criteria were antenatal IV-iron or RBC-T. Fatigue was the primary outcome. Secondary outcomes included hemoglobin and ferritin concentrations, and adverse events. From 27th August 2020 to 26th September 2022, databases, registries, and hand searches identified studies. A fixed-effect meta-analysis was undertaken using RevMan (5.4) software. The quality of the studies and the evidence was assessed using the Cochrane Risk of Bias table, and Grading of Recommendations, Assessment, Development, and Evaluation. This review is registered with the Prospective Register of Systematic Reviews (CRD42020201115).

RESULTS

Twenty studies and 4196 participants were included: 1834 assigned IV-iron, 1771 assigned oral iron, 330 assigned RBC-T, and 261 assigned non-intervention. Six studies reported the primary outcome of fatigue (1251 participants). Only studies of IV-iron vs. oral iron (15 studies) were available for meta-analysis. Of these, three reported on fatigue using different scales; two were available for meta-analysis. There was a significant reduction in fatigue with IV-iron compared to oral iron (standardized mean difference - 0.40, 95% confidence interval (CI) - 0.62, - 0.18, I2 = 0%). The direction of effect also favored IV-iron for hemoglobin (mean difference (MD) 0.54 g/dL, 95% confidence interval (CI) 0.47, 0.61, I2 = 91%), ferritin, (MD 58.07 mcg/L, 95% CI 55.74, 60.41, I2 = 99%), and total adverse events (risk-ratio 0.63, 95% CI 0.52, 0.77, I2 = 84%). The overall quality of the evidence was low-moderate.

DISCUSSION

For all outcomes, the evidence for RBC-T, compared to IV-iron, non-intervention, or dose effects of RBC-T is very limited. Further research is needed to determine whether RBC-T or IV-iron for the treatment of PPA is superior for fatigue and hematological outcomes.

Updating the U.S. Life Cycle GHG Petroleum Baseline to 2014 with Projections to 2040 Using Open-Source Engineering-Based Models

The National Energy Technology Laboratory produced a well-to-wheels (WTW) life cycle greenhouse gas analysis of petroleum-based fuels consumed in the U.S. in 2005, known as the NETL 2005 Petroleum Baseline. This study uses a set of engineering-based, open-source models combined with publicly available data to calculate baseline results for 2014. An increase between the 2005 baseline and the 2014 results presented here (e.g., 92.4 vs 96.2 g CO₂e/MJ gasoline, + 4.1%) are due to changes both in modeling platform and in the U.S. petroleum sector. An updated result for 2005 was calculated to minimize the effect of the change in modeling platform, and emissions for gasoline in 2014 were about 2% lower than in 2005 (98.1 vs 96.2 g CO₂e/MJ gasoline). The same methods were utilized to forecast emissions from fuels out to 2040, indicating maximum changes from the 2014 gasoline result between +2.1% and -1.4%. The changing baseline values lead to potential compliance challenges with frameworks such as the Energy Independence and Security Act (EISA) Section 526, which states that Federal agencies should not purchase alternative fuels unless their life cycle GHG emissions are less than those of conventionally produced, petroleum-derived fuels.

Medicine-taking experiences and associated factors: comparison between Arabic-speaking and Caucasian English-speaking patients with Type 2 diabetes

AIM

The aim of this study was to explore and compare medication-taking experiences and associated issues in Arabic-speaking and Caucasian English-speaking patients with Type 2 diabetes in Australia.

METHODS

Various healthcare settings in metropolitan Melbourne, Australia, were purposefully selected to obtain a diverse group of participants with Type 2 diabetes. Recruitment occurred at diabetes outpatient clinics in two tertiary referral hospitals, six primary care practices and ten community centres. Face-to-face semi-structured individual interviews and group interviews were employed. All interviews were audiotaped, transcribed and coded thematically. Data collection continued until saturation was reached.

RESULTS

In total, 100 participants were recruited into two groups: 60 were Arabic-speaking and 40 were Caucasian English-speaking. Both groups had similar demographic and clinical characteristics. Only 5% of the Arabic-speaking participants had well-controlled diabetes compared with 17.5% of the participants in the English-speaking group. Arabic-speaking participants actively changed medication regimens on their own without informing their healthcare professionals. Arabic-speaking patients had more knowledge gaps about their prescribed treatments, compared with the English-speaking group. Their use of diabetes medicines was heavily influenced by peers with diabetes and family members; conversely, they feared revealing their diagnosis within the wider Arabic community due to stigma and collective negative social labelling of diabetes. Confidence in non-Arabic-speaking healthcare providers was lacking.

CONCLUSIONS

Findings yielded new insights into medication-taking practices and associated factors in Arabic-speaking patients with diabetes. It is vital that healthcare professionals working with Arabic-speaking patients adapt their treatment approaches to accommodate different beliefs and views about medicines.

Barriers and enablers to healthcare access and use among Arabic-speaking and Caucasian English-speaking patients with type 2 diabetes mellitus: a qualitative comparative study

OBJECTIVE

The objective of this study was to explore the decision-making processes and associated barriers and enablers that determine access and use of healthcare services in Arabic-speaking and English-speaking Caucasian patients with diabetes in Australia.

STUDY SETTING AND DESIGN

Face-to-face semistructured individual interviews and group interviews were conducted at various healthcare settings-diabetes outpatient clinics in 2 tertiary referral hospitals, 6 primary care practices and 10 community centres in Melbourne, Australia.

PARTICIPANTS

A total of 100 participants with type 2 diabetes mellitus were recruited into 2 groups: 60 Arabic-speaking and 40 English-speaking Caucasian.

DATA COLLECTION

Interviews were audio-taped, translated into English when necessary, transcribed and coded thematically. Sociodemographic and clinical information was gathered using a self-completed questionnaire and medical records.

PRINCIPAL FINDINGS

Only Arabic-speaking migrants intentionally delayed access to healthcare services when obvious signs of diabetes were experienced, missing opportunities to detect diabetes at an early stage. Four major barriers and enablers to healthcare access and use were identified: influence of significant other(s), unique sociocultural and religious beliefs, experiences with healthcare providers and lack of knowledge about healthcare services. Compared with Arabic-speaking migrants, English-speaking participants had no reluctance to access and use medical services when signs of ill-health appeared; their treatment-seeking behaviours were straightforward.

CONCLUSIONS

Arabic-speaking migrants appear to intentionally delay access to medical services even when symptomatic. Four barriers to health services access have been identified. Tailored interventions must be developed for Arabic-speaking migrants to improve access to available health services, facilitate timely diagnosis of diabetes and ultimately to improve glycaemic control.

Identifying/Quantifying Environmental Trade-offs Inherent in GHG Reduction Strategies for Coal-Fired Power

Improvements to coal power plant technology and the cofired combustion of biomass promise direct greenhouse gas (GHG) reductions for existing coal-fired power plants. Questions remain as to what the reduction potentials are from a life cycle perspective and if it will result in unintended increases in impacts to air and water quality and human health. This study provides a unique analysis of the potential environmental impact reductions from upgrading existing subcritical pulverized coal power plants to increase their efficiency, improving environmental controls, cofiring biomass, and exporting steam for industrial use. The climate impacts are examined in both a traditional-100 year GWP-method and a time series analysis that accounts for emission and uptake timing over the life of the power plant. Compared to fleet average pulverized bed boilers (33% efficiency), we find that circulating fluidized bed boilers (39% efficiency) may provide GHG reductions of about 13% when using 100% coal and reductions of about 20-37% when cofiring with 30% biomass. Additional greenhouse gas reductions from combined heat and power are minimal if the steam coproduct displaces steam from an efficient natural gas boiler. These upgrades and cofiring biomass can also reduce other life cycle impacts, although there may be increased impacts to water quality (eutrophication) when using biomass from an intensely cultivated source. Climate change impacts are sensitive to the timing of emissions and carbon sequestration as well as the time horizon over which impacts are considered, particularly for long growth woody biomass.

Evaluating the climate benefits of CO2-enhanced oil recovery using life cycle analysis

This study uses life cycle analysis (LCA) to evaluate the greenhouse gas (GHG) performance of carbon dioxide (CO2) enhanced oil recovery (EOR) systems. A detailed gate-to-gate LCA model of EOR was developed and incorporated into a cradle-to-grave boundary with a functional unit of 1 MJ of combusted gasoline. The cradle-to-grave model includes two sources of CO2: natural domes and anthropogenic (fossil power equipped with carbon capture). A critical parameter is the crude recovery ratio, which describes how much crude is recovered for a fixed amount of purchased CO2. When CO2 is sourced from a natural dome, increasing the crude recovery ratio decreases emissions, the opposite is true for anthropogenic CO2. When the CO2 is sourced from a power plant, the electricity coproduct is assumed to displace existing power. With anthropogenic CO2, increasing the crude recovery ratio reduces the amount of CO2 required, thereby reducing the amount of power displaced and the corresponding credit. Only the anthropogenic EOR cases result in emissions lower than conventionally produced crude. This is not specific to EOR, rather the fact that carbon-intensive electricity is being displaced with captured electricity, and the fuel produced from that system receives a credit for this displacement.

Application and a proposed modification of the 2010 McDonald criteria for the diagnosis of multiple sclerosis in a Canadian cohort of patients with clinically isolated syndromes

Background:

The 2005 and 2010 McDonald criteria utilize magnetic resonance imaging (MRI) to provide evidence of disease dissemination in space (DIS) and time (DIT) for the diagnosis of multiple sclerosis (MS) in patients who have clinically isolated syndromes (CIS).

Methods:

Data from 109 CIS patients not satisfying the 2005 criteria at entry into a randomized controlled minocycline trial were analyzed to determine the proportion who would have been diagnosed with MS at screening based on 2010 criteria. The impact of including symptomatic, as well as asymptomatic, MRI lesions to confirm DIT was also explored.

Results:

Thirty percent (33/109) of patients, retrospectively, met the 2010 criteria for a diagnosis of MS at baseline. When both symptomatic and asymptomatic lesions were used to confirm DIT, three additional patients met the 2010 criteria. There was a significant 10.1% increase in the proportion of patients who met the 2010 DIS criteria, compared with the 2005 DIS criteria; however, two patients satisfied the 2005 DIS but not 2010 DIS criteria.

Conclusion:

Using 2010 McDonald criteria, 30% of the CIS patients could be diagnosed with MS using a single MRI scan. Inclusion of symptomatic lesions in the DIT criteria further increases this proportion to 33%.

Prospective observational study to evaluate NOTSS (Non-Technical Skills for Surgeons) for assessing trainees' non-technical performance in the operating theatre

BACKGROUND

Most surgical assessment has been aimed at technical proficiency. However, non-technical skills also affect patient safety and clinical effectiveness. The NOTSS (Non-Technical Skills for Surgeons) assessment instrument was developed specifically to assess the non-technical skills of individual surgeons in the operating theatre. This study evaluated NOTSS as a real-world assessment, with a mix of minimally trained assessors. The evaluation criteria were feasibility, validity and psychometric reliability.

METHODS

In a standard evaluation of NOTSS, 56 anaesthetists, 39 scrub nurses, two surgical care practitioners and three independent assessors provided 715 assessments of 404 surgical cases of 15 index procedures across six specialties performed by 85 surgical trainees.

RESULTS

The assessment was feasible, but important implementation challenges were highlighted. Most respondents considered the method valid, but with reservations about assessing cognition. The factor structure of scores, and their positive relationships with other measures of experience and performance, supported validity. Trainees' non-technical skill scores were relatively procedure-independent and achieved good reliability (generalizability coefficient 0·8 or more) when six to eight assessors observed one case each.

CONCLUSION

Minimally trained assessors, who are typically present in operating theatres, were sufficiently discriminating and consistent in their judgements of trainee surgeons' non-technical skills to provide reliable scores based on an achievable number of observations.

Evaluation of procedure-based assessment for assessing trainees' skills in the operating theatre

BACKGROUND

Procedure-based assessment (PBA) is used within most UK surgical training programmes for assessing trainees' procedural skills in the operating theatre. All postgraduate assessment methods require evidence to support their implementation. The aims were to evaluate the validity, reliability and acceptability of PBA.

METHODS

Eighty-one trainees in six surgical specialties were assessed performing common procedures; 749 PBAs were provided across 348 operations by 57 clinical supervisors and four independent assessors.

RESULTS

Construct validity was demonstrated by correlation of PBA scores with measures of surgical training and experience. Reliability (G exceeding 0·8) of the adjusted total item score and global summary score for a given procedure was achieved using four and three assessor judgements respectively; assessing a mix of procedures required more cases/assessors because performance is procedure specific. The acceptability of PBA for assessment and feedback within surgical training was predominantly positive among clinical supervisors and trainees.

CONCLUSION

PBA demonstrated good overall validity and acceptability, and exceptionally high reliability. Trainees should be assessed adequately for each given procedure.

Life cycle assessment and grid electricity: what do we know and what can we know?

The generation and distribution of electricity comprises nearly 40% of U.S. CO(2), emissions, as well as large shares of SO(2), NO(x), small particulates, and other toxins. Thus, correctly accounting for these electricity-related environmental releases is of great importance in life cycle assessment of products and processes. Unfortunately, there is no agreed-upon protocol for accounting for the environmental emissions associated with electricity, as well as significant uncertainty in the estimates. Here, we explore the limits of current knowledge about grid electricity in LCA and carbon footprinting for the U.S. electrical grid, and show that differences in standards, protocols, and reporting organizations can lead to important differences in estimates of CO(2) SO(2), and NO(x) emissions factors. We find a considerable divergence in published values for grid emissions factor in the U.S. We discuss the implications of this divergence and list recommendations for a standardized approach to accounting for air pollution emissions in life cycle assessment and policy analyses in a world with incomplete and uncertain information.

Environmental effects of interstate power trading on electricity consumption mixes

Although many studies of electricity generation use national or state average generation mix assumptions, in reality a great deal of electricity is transferred between states with very different mixes of fossil and renewable fuels, and using the average numbers could result in incorrect conclusions in these studies. We create electricity consumption profiles for each state and for key industry sectors in the U.S. based on existing state generation profiles, net state power imports, industry presence by state, and an optimization model to estimate interstate electricity trading. Using these "consumption mixes" can provide a more accurate assessment of electricity use in life-cycle analyses. We conclude that the published generation mixes for states that import power are misleading, since the power consumed in-state has a different makeup than the power that was generated. And, while most industry sectors have consumption mixes similar to the U.S. average, some of the most critical sectors of the economy--such as resource extraction and material processing sectors--are very different. This result does validate the average mix assumption made in many environmental assessments, but it is important to accurately quantify the generation methods for electricity used when doing life-cycle analyses.

Development and application of a micro-capillary rheometer for in-vitro evaluation of parenteral injectability

A micro-capillary rheometer was developed to determine the rheology and injectability of parenteral formulations. The rheometer consisted of a micro-capillary and a glass syringe attached to an Instron that drove the syringe plunger at predetermined speeds and measured resulting forces on the plunger. The cross-head speed and the measured force were used to calculate the shear rate and the shear stress respectively, according to the Hagen-Poiseuille equation. The resulting rheograms of several Newtonian standards showed excellent linearity over a broad range of about 10 x 10(3) to 160 x 10(3) s(-1) and produced accurate and reproducible viscosity determinations over the viscosity range of about 10 x 10(-3) to 100 x 10(-3) Pa.s. The developed methodology focussed primarily on the minimization of errors associated with the determination of the wall frictional force using both direct measurement and linear regression to determine this parameter from the data. The effect of micro-capillary diameter, syringe cross-sectional area and micro-capillary length was explored in an effort to increase the measured force so that wall frictional force errors could be minimized. The micro-capillary rheometer gave reproducible and accurate rheograms over a range of shear rates consistent with the shear rate range used in clinical practice, and showed that Newtonian and non-Newtonian rheological behaviours could be evaluated quantitatively.

Differential display polymerase chain reaction reveals increased expression of striatal rat glia-derived nexin following chronic clozapine treatment

Clozapine is considered a prototype of the 'so-called' atypical antipsychotic drug class. It has affinity for a broad range of receptors and, in comparison to typical antipsychotic drugs, produces less extrapyramidal side effects. However, its mechanism of action remains unclear. Differential display polymerase chain reaction (ddPCR) was implemented in this study to contribute to the current understanding of this mechanism at the genetic level and to identify novel genes regulated by clozapine. This technique generated approximately 2400 gene sequences that were analyzed for differential gene expression following protracted clozapine treatment. One of these sequences, originally termed Clozapine Regulated Gene (CRG), was shown to be significantly upregulated following the treatment. Northern hybridization confirmation of this finding revealed that chronic clozapine administration caused a five-fold increase in CRG mRNA. Elongation of the 5'- and 3'-ends of CRG indicated that the fragment was in fact rat glia-derived nexin mRNA. Western blotting demonstrated that levels of the mRNA's associated protein also increased comparably (three-fold) following chronic treatment with the antipsychotic drug. This study presents a possible neuroprotective role of nexin in clozapine treatment, particularly in the prevention of neuronal proteolytic degradation, since nexin has been shown to be a protease inhibitor.

First year RNs' actual and self-rated pharmacology knowledge

A questionnaire survey was conducted of first year registered nurses whose postal details were recorded on the Victorian Nursing Council's 1994 mailing list. The nurses were asked to self-rate their knowledge of five categories of pharmacology and to answer questions that tested their knowledge of the same categories. The survey also obtained data related to aspects of the nurses' pharmacology education. The mean test score of the 363 respondents to the survey was 55.8%. The number of months worked as an RN and participation in a graduate year program were significantly correlated with test scores, i.e. longer experience as an RN and participation in a graduate program were associated with higher scores. There was a significant correlation between the groups' overall self-rating of their knowledge and their total test scores but the RNs' self-ratings overestimated their knowledge of drug administration and legal aspects of drug use. The study indicates that many newly registered nurses have an inadequate knowledge of pharmacology. Recommendations for improving the teaching and learning of the subject are drawn from the nurses' evaluation of aspects of their undergraduate and post-registration experience.

Bananas--physiology and biochemistry of storage and ripening for optimum quality

Bananas (Musa spp.) are a major food crop of the humid tropics, and although edible cultivars are diverse and numerous, most of our knowledge of the physiology and biochemistry of these fruits relates to a few dessert cultivars of the AAA type, mainly of the Cavendish subgroup, which dominate the export trade between tropical and temperate zones. The preclimacteric period of banana fruits after harvest determines their transportability, and its duration is very sensitive to changes in fruit maturity, storage temperature, ethylene concentration, and other factors; progress in measurement and resolution of each of these effects is described. Changes in composition of the ripening fruits, especially in the development of flavor volatiles, are reviewed. Progress in understanding the integration of the biochemical changes controlling ripening in banana fruits is discussed. Recent work on storage, ripening, and factors relating to sensory assessment of fruit quality is discussed for cultivars of Musa types not used in major export trades.

The value of mechanical cell harvesting in diagnosis and prognosis of bladder tumor recurrence

Specimens obtained after scraping the bladder mucosa were found to be of excellent quality because of the large cell harvest and the minimal inflammatory exudate. In addition, tumor recurrence could be predicted in a significant number of cases with this technique.

Sodium transport and short-circuit current in rat colon in vivo and the effect of aldosterone

1. A method for measurement of short-circuit current and for applying a voltage clamp to segments of rat colon in vivo is described.2. The mucosa behaved as an ohmic resistor of average resistance 154 Omega/cm(2) although brief transient effects were frequently observed. Tissue resistance was independent of considerable changes in ionic strength and composition of the luminal solution.3. The short-circuit current averaged 120 muA/cm(2) in normal rats. Aldosterone intravenously raised the p.d., short-circuit current rising proportionately and tissue resistance being unchanged. The effects of various modifications of the intraluminal solution in respect to composition, hydrostatic pressure and pH were examined. An increase in the osmolality of the luminal solution sufficient to abolish water absorption did not affect p.d. or short-circuit current.4. The short-circuit current measured with 150 mM-NaCl in the lumen was almost completely accounted for by active Na absorption both in normal and aldosterone-treated rats. The changes in Na efflux rate produced by voltage clamping suggested that only part of Na efflux was due to simple diffusion. With lower [NaCl] in the lumen, the short-circuit current exceeded that atributable to active Na absorption, the discrepancy increasing with reduction of [NaCl].5. The luminal [Na] at which Na efflux and influx rates were equal was reduced by aldosterone, an effect which is probably responsible for the low stool [Na] of aldosterone treated animals. The significance of this finding in terms of the mode of action of aldosterone is discussed.

Interrelationship of the effects of aldosterone and thyroid hormones on sodium transport and electrical properties of rat colon

Transmucosal electrical potential difference (p.d.), short-circuit current, electrical resistance and Na+ influx rate of the descending colon were similar in euthyroid and hypothyroid rats, the latter having been treated earlier with an ablation dose of 131I. However, in contrast to the considerable p.d. increase found in normal rats, little change of p.d. was found in hypothyroid rats when they were Na+ depleted or given an intravenous aldosterone infusion. A single small dose of tri-iodothyronine (T3) (1 μg/100g body weight) or a larger dose of thyroxine given to hypothyroid rats 10–16 h before aldosterone, restored the p.d. response to normal, although these doses did not influence the animal's oxygen consumption. Fasting for 3 days or giving actinomycin D (8 μg/100 g body weight) abolished the effect of T3 but this did not influence the action of aldosterone in euthyroid animals.

Activation of delta-aminolaevulate synthetase in extracts of Rhodopseudomonas spheroides

1. The spontaneous activation of delta-aminolaevulate synthetase in extracts from Rhodopseudomonas spheroides grown semi-anaerobically in the light requires oxygen and does not take place anaerobically in the dark. 2. Activation is completely prevented by azide or cyanide and is partially inhibited by chlorpromazine. These compounds inhibit markedly the succinoxidase activity of extracts. 3. NADH delays activation, but when it has been oxidized by the extract activation begins at the normal rate and complete activation occurs. By contrast both the rate and the extent of activation are markedly decreased by even small amounts of carboxylic acids. 4. The inhibitory effects of succinate and citrate on activation can be prevented by malonate and fluorocitrate respectively. 5. These results suggest that for activation to occur some endogenous compound has to be oxidized via the electron transport chain. 6. Activation occurs under anaerobic conditions in the light, probably by photo-oxidation.

Control of delta-aminolaevulate synthetase activity in Rhodopseudomonas spheroides

1. delta-Aminolaevulate synthetase from Rhodopseudomonas spheroides grown semi-anaerobically undergoes a spontaneous activation during the first hour after the disruption of cells when homogenates are stored at 4 degrees . 2. After cultures of R. spheroides growing semi-anaerobically are oxygenated no activation of delta-aminolaevulate synthetase occurs in cell extracts. Cessation of activation in extracts is almost complete 10min. after oxygenation of cells has begun. 3. A heat-stable fraction of low molecular weight from semi-anaerobic cells reactivates delta-aminolaevulate synthetase in extracts of oxygenated cells and appears to contain a compound responsible for the spontaneous activation. 4. A heat-stable fraction of low molecular weight from oxygenated cells inhibits the spontaneous activation in extracts of semi-anaerobic cells. 5. The effect of oxygen on the rate of bacteriochlorophyll synthesis in R. spheroides may be mediated through alterations in the concentrations of a low-molecular-weight activator and inhibitor of delta-aminolaevulate synthetase.

Electrical potential and short circuit current of an in vitro preparation of rat colon mucosa

1. Using a preparation of rat colon mucosa mounted in vitro in small chambers, some factors which influence the electrical properties of the mucosa have been investigated.2. The mucosa behaved mainly as an ohmic resistance although a very brief transient occurred on first passing current. At 32 degrees C, the fresh preparation had a mean resistance of 108Omega/cm(2) and a mean short circuit current (s.c.c.) of 143 muA/cm(2). Tissues taken from Na-depleted and adrenalectomized rats differed little from normal tissues in electrical resistance but those from Na-depleted rats had higher potential difference (p.d.) and s.c.c.3. Increase of temperature led to a rise of conductance of similar order to that found for ions in aqueous solution. S.c.c. also rose with increase of temperature but the effect was relatively greater consistent with its being dependent on metabolic processes.4. Anoxia or the addition of cyanide, iodoacetate or 2,4-dinitrophenol to the bath fluid caused considerable fall in the p.d. and s.c.c.5. Ouabain decreased the p.d. and s.c.c. when added to the serosal side but had no effect when on the luminal side.6. Aldosterone and acetazolamide had no effect.7. Varying serosal side [K] produced only minor changes in p.d.8. Reducing [Na] of the luminal solution caused a considerable fall of p.d. but similar reduction of [Na] on the serosal side had little effect.9. The frequently employed model which represents the transepithelial p.d. as the sum of diffusion potentials originating at the luminal and serosal sides of the cell layer is not consistent with the present results. The colonic transmucosal p.d. probably originates in the electrogenic transport of Na by a mechanism located on the serosal side of the epithelium.

Factors influencing the electrical potential across the mucosa of rat colon

1. An investigation has been carried out into various factors which influence the transmucosal potential difference (p.d.) of rat colon in vivo when the p.d. is either high (> 30 mV) or low (< 20 mV).2. The p.d. was uninfluenced by short duration anaesthesia with ether or pentobarbitone. When anaesthesia was prolonged for several hours, p.d. rose steadily. The gradient of p.d. along the descending colon which developed and its elimination by adrenalectomy suggested that the rise was due to increased secretion of adrenal steroids.3. P.d. was increased by Na depletion after a delay of about 18 hr and fell again following Na repletion with a similar time delay. A characteristic gradient of p.d. along the descending colon was seen.4. Both haemorrhage and anoxia caused a rapid fall of p.d. P.d. was restored rapidly to its previous level when anoxia was corrected.5. Vasopressin (I.V.) in low dose was without effect; in high dose it caused a transient fall of p.d. associated with intense vasoconstriction of gut blood vessels.6. The following factors studied were without effect on p.d.: presence of glucose within the lumen; considerable osmotic gradients across the mucosa; variation of luminal pH over the range 5.2-9.8; intravenous administration of acetazolamide, chlorothiazide, frusemide, triamterene, ethacrynic acid or ouabain. Ouabain in the luminal solution also had no effect in all but two rats in which a small fall of p.d. was seen.7. 2,4-dinitrophenol, 10(-2)M, in the lumen caused a small fall of p.d. only if the p.d. was high.8. Experiments were done to determine the effect on p.d. of altering the ionic composition of the luminal solution. When the p.d. was low (< 20 mV) alteration of [Na], [K] or [Cl] produced small absolute changes of the p.d., all of comparable magnitude. The changes could be interpreted as due to diffusion potentials resulting from the ionic gradients across the mucosa. When the p.d. was high (> 30 mV), it showed a striking dependence on the luminal [Na] only, consistent with the presence of a large p.d. due to active Na transport.