Generative Artificial Intelligence as a Tool for Teaching Communication in Nutrition and Dietetics Education-A Novel Education Innovation

Although effective communication is fundamental to nutrition and dietetics practice, providing novice practitioners with efficacious training remains a challenge. Traditionally, human simulated patients have been utilised in health professions training, however their use and development can be cost and time prohibitive. Presented here is a platform the authors have created that allows students to interact with virtual simulated patients to practise and develop their communication skills. Leveraging the structured incorporation of large language models, it is designed by pedagogical content experts and comprises individual cases based on curricula and student needs. It is targeted towards the practice of rapport building, asking of difficult questions, paraphrasing and mistake making, all of which are essential to learning. Students appreciate the individualised and immediate feedback based on validated communication tools that encourage self-reflection and improvement. Early trials have shown students are enthusiastic about this platform, however further investigations are required to determine its impact as an experiential communication skills tool. This platform harnesses the power of artificial intelligence to bridge the gap between theory and practice in communication skills training, requiring significantly reduced costs and resources than traditional simulated patient encounters.

Oral interview in place of traditional objective structured clinical examinations for assessing placement readiness in nutrition and dietetics education

AIM

Objective structured clinical examinations have long been used in dietetics education. This observational study aims to describe the development, deployment, feasibility and validity of assessment using an oral interview in place of traditional objective structured clinical examinations, and to determine the ability of this assessment to identify students who are either not ready for placement or may require early support and/or remediation.

METHODS

Student assessment data were collected over a two-and-a-half-year period and used to test the predictive ability of an oral interview to determine dietetic placement outcomes and highlight a need for early remediation. Descriptive statistics as well as a between-group one-way ANOVA was used to describe results.

RESULTS

A total of 169 students participated in the oral interview and subsequent medical nutrition therapy placement over the study period. Significant differences in oral interview score were seen between students who passed placement and students who passed with remediation or those who failed. Oral interview performance was able to predict placement outcome, yet required less resources than traditional objective structured clinical examinations.

CONCLUSION

An oral interview may provide the same utility as the objective structured clinical examination in dietetics education .

Prevalence, risk factors, and clinical outcomes of vitamin C deficiency in adult hospitalized patients in high-income countries: a scoping review

BACKGROUND

Assessment for vitamin C deficiency (VCD) is rarely undertaken in an acute hospital setting in high-income countries. However, with growing interest in VCD in community settings, there is emerging evidence investigating the prevalence and impact of VCD during hospitalization.

OBJECTIVES

In this scoping review, the prevalence of VCD in adult hospitalized patients is explored, patient characteristics are described, and risk factors and clinical outcomes associated with VCD are identified.

METHODS

A systematic scoping review was conducted in accordance with the PRISMA-ScR framework. The Ovid MEDLINE, Ovid Embase, Scopus, CINAHL Plus, Allied and Complementary Medicine Database, and the Cochrane Library databases were searched for interventional, comparative, and case-series studies that met eligibility criteria, including adult hospital inpatients in high-income countries, as defined by the Organization for Economic Co-operation and Development, that reported VCD prevalence using World Health Organization reference standards. These standards define VCD deficiency as plasma or serum vitamin C level <11.4 µmol/L, wholeblood level <17 µmol/L, or leukocytes <57 nmol/108 cells.

RESULTS

Twenty-three articles were included, representing 22 studies. The cumulative prevalence of VCD was 27.7% (n = 2494; 95% confidence interval [CI], 21.3-34.0). High prevalence of VCD was observed in patients with severe acute illness and poor nutritional status. Scurvy was present in 48% to 62% of patients with VCD assessed in 2 studies (n = 71). Being retired (P = 0.015) and using excessive amounts of alcohol and tobacco (P = 0.0003) were independent risk factors for VCD (n = 184). Age was not conclusively associated with VCD (n = 631). Two studies examined nutrition associations (n = 309); results were inconsistent. Clinical outcomes for VCD included increased risk of frailty (adjusted odds ratio, 4.3; 95%CI, 1.33-13.86; P = 0.015) and cognitive impairment (adjusted odds ratio, 2.93; 95%CI, 1.05-8.19, P = 0.031) (n = 160).

CONCLUSIONS

VCD is a nutritional challenge facing the healthcare systems of high-income countries. Research focused on early identification and treatment of patients with VCD is warranted.

SYSTEMATIC REVIEW REGISTRATION

Open Science Framework ( https://doi.org/10.17605/OSF.IO/AJGHX ).

Packaged hospital food appears safe and feasible to reuse

AIM

To determine the safety, operational feasibility and environmental impact of collecting unopened non-perishable packaged hospital food items for reuse.

METHODS

This pilot study tested packaged foods from an Australian hospital for bacterial species, and compared this to acceptable safe limits. A waste management strategy was trialled (n = 10 days) where non-perishable packaged foods returning to the hospital kitchen were collected off trays, and the time taken to do this and the number and weight of packaged foods collected was measured. Data were extrapolated to estimate the greenhouse gasses produced if they were disposed of in a landfill.

RESULTS

Microbiological testing (n = 66 samples) found bacteria (total colony forming units and five common species) on packaging appeared to be within acceptable limits. It took an average of 5.1 ± 10.1 sec/tray to remove packaged food items from trays returning to the kitchen, and an average of 1768 ± 19 packaged food items were per collected per day, equating to 6613 ± 78 kg/year of waste which would produce 19 tonnes/year of greenhouse gasses in landfill.

CONCLUSIONS

A substantial volume of food items can be collected from trays without significantly disrupting current processes. Collecting and reusing or donating non-perishable packaged food items that are served but not used within hospitals is a potential strategy to divert food waste from landfill. This pilot study provides initial data addressing infection control and feasibility concerns. While food packages in this hospital appear safe, further research with larger samples and testing additional microbial species is recommended.

Emotion recognition and eye tracking of static and dynamic facial affect: Acomparison of individuals with and without traumatic brain injury

Diminished social functioning is often seen after traumatic brain injury (TBI). Mechanisms contributing to these deficits are poorly understood but thought to relate to impaired ability to recognize facial expressions. Static stimuli are often used to investigate ability post-TBI, and there is less evidence using more real-life dynamic stimuli. In addition, most studies rely on behavioral responses alone. The present study investigated the performance of a TBI group and matched non-TBI group on static and dynamic tasks using eye-tracking technology alongside behavioral measures. This is the first study to use eye tracking methodology alongside behavioral measures in emotion recognition tasks in people with brain injury. Eighteen individuals with heterogeneous TBI and 18 matched non-TBI participants were recruited. Stimuli representing six core emotions (Anger, Disgust, Fear, Happy, Sad, and Surprise faces) were selected from the Amsterdam Dynamic Facial Expression Set (ADFES). Participants were instructed to identify the emotion displayed correctly whilst eye movement metrics were recorded.

RESULTS

Results of analyses showed that TBI patients had First Fixation to nose for all emotion stimuli, shorter Fixation Duration and lower Fixation Count to eyes, were generally slower to classify stimuli, and less accurate than non-TBI group for the static task. Those with TBI were also less accurate at identifying Angry, Disgust, and Fear stimulus faces compared to the non-TBI group during the dynamic unfolding of an emotion.

CONCLUSION

In the present study, those with TBI had atypical eye scan patterns during emotion identification in the static emotion recognition task compared to the non-TBI group and were associated with lower identification accuracy on behavioral measures in both static and dynamic tasks. Findings suggest potential disruption to oculomotor systems vital for first stage perceptual processing. Arguably, these impairments may contribute to diminished social functioning.

The Clinical Use of Monolaurin as a Dietary Supplement: A Review of the Literature

Objective

The purpose of this study was to determine what the peer-reviewed literature says about the clinical applications, therapeutic dosages, bioavailability, efficacy, and safety of monolaurin as a dietary supplement.

Methods

This was a narrative review using the PubMed database and the terms "monolaurin" and its chemical synonyms. Commercial websites that sell monolaurin were also searched for pertinent references. The reference sections of the newer articles were searched for any other relevant articles. Consensus was reached among the authors as to what articles had clinical relevance.

Results

Twenty-eight articles were found that appeared to address the clinical use of monolaurin.

Conclusion

There are many articles that address the antimicrobial effects of monolaurin in vitro. Only 3 peer-reviewed papers that evidence in vivo antimicrobial effects of monolaurin in humans were located, and these were only for intravaginal and intraoral-that is, topical-use. No peer-reviewed evidence was found for the clinical use of monolaurin as a human dietary supplement other than as a nutrient.

The cooking task: making a meal of executive functions

Current standardized neuropsychological tests may fail to accurately capture real-world executive deficits. We developed a computer-based Cooking Task (CT) assessment of executive functions and trialed the measure with a normative group before use with a head-injured population. Forty-six participants completed the computerized CT and subtests from standardized neuropsychological tasks, including the Tower and Sorting Tests of executive function from the Delis-Kaplan Executive Function System (D-KEFS) and the Cambridge prospective memory test (CAMPROMPT), in order to examine whether standardized executive function tasks, predicted performance on measurement indices from the CT. Findings showed that verbal comprehension, rule detection and prospective memory contributed to measures of prospective planning accuracy and strategy implementation of the CT. Results also showed that functions necessary for cooking efficacy differ as an effect of task demands (difficulty levels). Performance on rule detection, strategy implementation and flexible thinking executive function measures contributed to accuracy on the CT. These findings raise questions about the functions captured by present standardized tasks particularly at varying levels of difficulty and during dual-task performance. Our preliminary findings also indicate that CT measures can effectively distinguish between executive function and Full Scale IQ abilities. Results of the present study indicate that the CT shows promise as an ecologically valid measure of executive function for future use with a head-injured population and indexes selective executive function’s captured by standardized tests.

Preoperative immunonutrition and its effect on postoperative outcomes in well-nourished and malnourished gastrointestinal surgery patients: a randomised controlled trial

BACKGROUND/OBJECTIVES

Invasive procedures such as surgery cause immunosuppression, leading to increased risk of complications, infections and extended hospital stay. Emerging research around immune-enhancing nutrition supplements and their ability to reduce postoperative complications and reduce treatment costs is promising. This randomised controlled trial aims to examine the effect of preoperative immunonutrition supplementation on length of hospital stay (LOS), complications and treatment costs in both well-nourished and malnourished gastrointestinal surgery patients.

SUBJECTS/METHODS

Ninety-five patients undergoing elective upper and lower gastrointestinal surgery were recruited. The treatment group (n=46) received a commercial immuno-enhancing supplement 5 days preoperatively. The control group (n=49) received no supplements. The primary outcome measure was LOS, and secondary outcome measures included complications and cost.

RESULTS

A nonsignificant trend towards a shorter LOS within the treatment group was observed (7.1 ± 4.1 compared with 8.8 ± 6.5 days; P=0.11). For malnourished patients, this trend was greater with hospital stay reduced by 4 days (8.3 ± 3.5 vs 12.3 ± 9.5 days; P=0.21). Complications and unplanned intensive care admission rates were very low in both the groups. The average admission cost was reduced by AUD1576 in the treatment group compared with the control group (P=0.37).

CONCLUSIONS

Preoperative immunonutrition therapy in gastrointestinal surgery has the potential to reduce the LOS and cost, with greater treatment benefit seen in malnourished patients; however, there is a need for additional research with greater patient numbers.

Hospital malnutrition: prevalence, identification and impact on patients and the healthcare system

Malnutrition is a debilitating and highly prevalent condition in the acute hospital setting, with Australian and international studies reporting rates of approximately 40%. Malnutrition is associated with many adverse outcomes including depression of the immune system, impaired wound healing, muscle wasting, longer lengths of hospital stay, higher treatment costs and increased mortality. Referral rates for dietetic assessment and treatment of malnourished patients have proven to be suboptimal, thereby increasing the likelihood of developing such aforementioned complications. Nutrition risk screening using a validated tool is a simple technique to rapidly identify patients at risk of malnutrition, and provides a basis for prompt dietetic referrals. In Australia, nutrition screening upon hospital admission is not mandatory, which is of concern knowing that malnutrition remains under-reported and often poorly documented. Unidentified malnutrition not only heightens the risk of adverse complications for patients, but can potentially result in foregone reimbursements to the hospital through casemix-based funding schemes. It is strongly recommended that mandatory nutrition screening be widely adopted in line with published best-practice guidelines to effectively target and reduce the incidence of hospital malnutrition.

Investigating the 'latent' deficit hypothesis: age at time of head injury, implicit and executive functions and behavioral insight

This study investigated the 'latent deficit' hypothesis in two groups of head-injured patients with predominantly frontal lesions, those injured prior to steep morphological and corresponding functional maturational periods for frontal networks (<or=age 25), and those injured>28 years. The latent deficit hypothesis proposes that early injuries produce enduring cognitive deficits manifest later in the lifespan with graver consequences for behavior than adult injuries, particularly after frontal pathology (Eslinger, Grattan, Damasio & Damasio, 1992). Implicit and executive deficits both contribute to behavioral insight after frontal head injury (Barker, Andrade, Romanowski, Morton, & Wasti, 2006). On the basis of morphological and behavioral data, we hypothesized that early injury would confer greater vulnerability to impairment on tasks associated with frontal regions than later injury. Patients completed experimental tasks of implicit cognition, executive function measures and the DEX measure of behavioral insight (Behavioral Assessment of the Dysexecutive Syndrome: Wilson, Alderman, Burgess, Emslie, & Evans, 1996). The Early Injury group were more impaired on implicit cognition tasks compared to controls that Late Injury patients. There were no marked group differences on most executive function measures. Executive ability only contributed to behavioral awareness in the Early Injury Group. Findings showed that age at injury moderates the relationship between executive and implicit cognition and behavioral insight and that early injuries result in long-standing deficits to functions associated with frontal regions partially supporting the latent deficit hypothesis.

Implicit cognition is impaired and dissociable in a head-injured group with executive deficits

Implicit or non-conscious cognition is traditionally assumed to be robust to pathology but Gomez-Beldarrain et al. recently showed deficits on a single implicit task after head injury. Laboratory research suggests that implicit processes dissociate. This study therefore examined implicit cognition in 20 head-injured patients and age- and IQ-matched controls using a battery of four implicit cognition tasks: a serial reaction time task (SRT), mere exposure effect task, automatic stereotype activation and hidden co-variation detection. Patients were assessed on an extensive neuropsychological battery, and MRI scanned. Inclusion criteria included impairment on at least one measure of executive function. The patient group was impaired relative to the control group on all the implicit cognition tasks except automatic stereotype activation. Effect size analyses using the control mean and standard deviation for reference showed further dissociations across patients and across implicit tasks. Patients impaired on implicit tasks had more cognitive deficits overall than those unimpaired, and a larger dysexecutive self/other discrepancy (DEX) score suggesting greater behavioural problems. Performance on the SRT task correlated with a composite measure of executive function. Head injury thus produced heterogeneous impairments in the implicit acquisition of new information. Implicit activation of existing knowledge structures appeared intact. Impairments in implicit cognition and executive function may interact to produce dysfunctional behaviour after head injury. Future comparisons of implicit and explicit cognition should use several measures of each function, to ensure that they measure the latent variable of interest.

Impaired implicit cognition with intact executive function after extensive bilateral prefrontal pathology: a case study

LR has extensive bilateral pathology to prefrontal cortices after head injury and marked changes to interpersonal and social behavior relative to his premorbid state. WAIS scores revealed intact IQ at superior levels, equivalent to premorbid ability as measured by the NART. LR performed at normal levels on a battery of executive function tasks, as did eight age- and IQ-matched controls. However, he showed impaired implicit learning on a serial reaction time task, and performed differently from controls on a mere exposure effect task. This case supports claims that implicit cognition may underpin some aspects of normal social functioning.

Quality of relationships and structural properties of social support networks of female survivors of abuse

The purposes of this study were to examine the structural properties of the social support networks of female survivors of violence and abuse and to investigate the quality of the relationship, and specific level of satisfaction, survivors have with their social support networks. Participants averaged 5.8 persons in their social support networks. Their levels of satisfaction with the emotional, practical, financial, guidance, and socializing support they received from members of their social support networks were higher with respect to close friends and coworkers than with respect to family members and professionals (e.g., attorneys and social workers). The most common type of support provided by close friends who were themselves victims of abuse was emotional, guidance, and socializing support, and the most satisfying support was the financial and practical help that came from parents or family. An interesting finding was the significant presence of men in the survivors' social support networks. Overall satisfaction with the quality of support from the social support networks was high, and satisfaction with support from men was comparable, if not higher, than support from women. Multiple regression models revealed that satisfaction with support networks was a potent predictor of self-esteem, emotional health, and loneliness. Intimacy, especially in terms of exclusiveness and trust or loyalty, with at least a few members of the support network contributed significantly to the variance in self-esteem, emotional health, and loneliness among the abused women. The size of the support network also emerged as a limited contributor to well-being. Implications and applications are discussed for professionals working with female survivors of abuse.

Sex hormone modulation of serotonin-induced coronary vasodilation in isolated heart

The present study was designed to evaluate the differences in the coronary vasodilator actions of serotonin (5-HT) in isolated heart obtained from naive or castrated male and female rats that were treated with either estrogen or testosterone. Hearts from 12 groups of rats were used: male and female naive animals, castrated, castrated and treated with 17beta-estradiol (0.5 microg kg(-1) day(-1)) for 7 or 30 days, and castrated and treated with testosterone (0.5 mg kg(-1) day(-1)) for 7 or 30 days. After treatment, the vascular reactivity of the coronary bed was evaluated. Baseline coronary perfusion pressure (CPP) was determined and dose-response curves to 5-HT were generated. Baseline CPP differed between male (70 +/- 6 mmHg, N = 10) and female (115 +/- 6 mmHg, N = 12) naive rats. Maximal 5-HT-induced coronary vasodilation was higher (P<0.05) in naive female than in naive male rats. In both sexes, 5-HT produced endothelium-dependent coronary vasodilation. After castration, there was no significant difference in baseline CPP between hearts obtained from male and female rats (75 +/- 7 mmHg, N = 8, and 83 +/- 5 mmHg, N = 8, respectively). Castration reduced the 5-HT-induced maximal vasodilation in female and male rats (P<0.05). Estrogen treatment of castrated female rats restored (P<0.05) the vascular reactivity. In castrated male rats, 30 days of estrogen treatment increased (P<0.05) the responsiveness to 5-HT. The endothelium-dependent coronary vasodilator actions of 5-HT are greater in female rats and are modulated by estrogen. A knowledge of the mechanism of action of estrogen on coronary arteries could aid in the development of new therapeutic strategies and potentially decrease the incidence of cardiovascular disease in both sexes.

Acute pressor actions of ouabain do not enhance the actions of phenylephrine or norepinephrine in anesthetized rats

The inhibition of high-affinity isoforms of the Na+,K+-ATPase by nanomolar levels of ouabain has been proposed to enhance the actions of vasoconstrictor agents that act via a Ca+2-dependent mechanism. The present study tested this hypothesis by evaluating the effects of ouabain (6 and 18 microg/kg, i.v.) on the vasopressor actions of phenylephrine and norepinephrine in anesthetized, reflex-blocked rats. In separate groups of animals, dose-response curves for increases in diastolic pressure produced by phenylephrine were generated after the administration of saline (control), ouabain (18 microg/kg), L-omega-N-nitro arginine methyl ester (L-NAME, 3 micromol/kg) and angiotensin II (15 ng/kg per min). Treatment with ouabain (18 microg/kg) produced an increase in diastolic pressure of 19+/-3 mm Hg but did not significantly alter the potency or maximal response produced by phenylephrine. In contrast, treatment with angiotensin II and L-NAME, agents known to enhance the actions of alpha-adrenoceptor agonists, increased the potency of phenylephrine. In animals in which the pressor actions of norepinephrine were evaluated before and after the administration of ouabain (6 microg/kg), ouabain did not alter the pressor response to norepinephrine. Blockade of alpha-adrenoceptors with phentolamine was found to attenuate as well as partially reverse the increase in diastolic pressure produced by ouabain. These observations suggest that ouabain produces a pressor response by actions on sympathetic nerve endings as well as on vascular smooth muscle and that these actions do not alter the sensitivity to phenylephrine or norepinephrine.

The effect of acute ethanol exposure on the chronotropic and inotropic function of the rat right atrium

Consumption of ethanol (CH2CH3OH), both acutely and chronically, is known to affect cardiac function and may alter the autonomic control of the heart. This study investigated the effects of two modes of acute exposure to ethanol on the chronotropy and inotropy of the rat right atrium with emphasis on alterations in the adrenergic responses. Atria from rats infused with an anesthetizing level of ethanol for 21 h showed a tendency for a greater increase of the unstimulated beating rate with isoproterenol (ISO), while both unstimulated inotropy and the inotropic response to ISO were significantly decreased compared with the control. Right atria in the presence of ethanol in-vitro demonstrated decreased basal active tension development and decreased inotropic responses to ISO. No alteration of the chronotropic response to ISO was evident with any concentration of ethanol. These results demonstrate both an immediate as well as a persistent effect of ethanol on right atrial chronotropy and inotropy. Alterations in the G-stimulatory subunit of the adenylate cyclase system and alterations in myofilament binding of Ca2+ are consistent with these observed ethanol effects.

Cocaine metabolism in hyperthermic patients with excited delirium

The half-life of cocaine in clinical experiments has been reported to range from 60 to 90 min. It has been previously suggested that elevated temperature may accelerate the metabolism of cocaine. However, there is no clinical data to indicate the presence of hyperthermia like that seen in excited delirium alters the half-life of cocaine. We report the results of half-life determinations from serial cocaine concentrations in two patients with excited delirium. Both patients presented to the emergency department with classic findings of excited delirium that included hyperthermia, agitation, and cardiovascular aberrations. One patient died despite aggressive therapeutic intervention. Cocaine and metabolite concentrations were determined by an extractive alkylation mass spectrometry procedure. Presenting cocaine concentrations in patient 1 and patient 2 were 0.387 and 0.266 mg/L respectively. Results from pharmacokinetic modeling of the serial concentrations show that the half-life of cocaine was not significantly accelerated, despite the presence of hyperthermia. Data from these two cases provide further evidence that catastrophic reactions to cocaine are independent of amount or route of administration, and that the metabolism of cocaine, at least in these patients, was not altered by hyperthermia.

Long-term nitric oxide inhibition and chronotropic responses in rat isolated right atria

The long-term administration of nitric oxide synthesis inhibitors induces arterial hypertension accompanied by left ventricular hypertrophy and myocardial ischemic lesions. Because the enhancement of sympathetic drive has been implicated in these phenomena, the current study was performed to determine the potency of beta-adrenoceptor agonists and muscarinic agonists on the spontaneous rate of isolated right atria from rats given long-term treatment with the nitric oxide inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). Atrial lesions induced by long-term treatment with L-NAME were also evaluated. Long-term L-NAME treatment caused a time-dependent, significant (P<0.05) increase in tail-cuff pressure compared with control animals. Our results showed that the potency of isoproterenol, norepinephrine, carbachol, and pilocarpine in isolated right atria from rats given long-term treatment with L-NAME for 7, 15, 30, and 60 days was not affected as compared with control animals. Addition of L-NAME in vitro (100 microl/L) affected neither basal rate nor chronotropic response for isoproterenol and norepinephrine in rat heart. Stereological analysis of the right atria at 15 and 30 days revealed a significant increase on amount of fibrous tissues in L-NAME-treated groups (27+/-2.3% and 28+/-1.3% for 15 and 30 days, respectively; P<0.05) as compared with the control group (22+/-1.1%). Our results indicate that nitric oxide does not to interfere with beta-adrenoceptor-mediated and muscarinic receptor-mediated chronotropic responses.

Inhibition of nitric oxide synthase causes profound enhancement of the Bezold-Jarisch reflex

The Bezold-Jarisch reflex function was evaluated in rats made hypertensive by the chronic oral intake of a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, averaging 35 mg/kg/day), for 3, 6, and 12 days (n = 9/group) and in untreated control rats (CR, n = 9/group). L-NAME-treated rats showed a marked hypertension (MAP: 148 +/- 3, 182 +/- 4, and 179 +/- 4 mm Hg, respectively) compared with CR (110 +/- 2 mm Hg). The 6- and 12-day groups showed tachycardia (447 +/- 20 and 466 +/- 13 beats/min, respectively) when compared with CR (355 +/- 10 beats/min). When compared with CR, left ventricular hypertrophy was observed in rats treated with L-NAME for 6 and 12 days. The Bezold-Jarisch reflex, a decrease in heart rate (HR) accompanied by a decrease in diastolic arterial pressure (DAP), was evoked in a dose dependent manner by the intravenous injection of 5-hydroxytryptamine (5-HT, 5 to 10 microg/kg). Relative to responses observed in CR, 5-HT at 10 microg/kg caused a four- to fivefold greater decrease in HR and a two- to threefold greater decrease in DAP in all the L-NAME treatment groups. Using a Langendorff technique, we observed a significant increase in the responsiveness of the pacemaker to acetylcholine (1.25 to 80 microg/mL). These data suggest that the pharmacological inhibition of the nitric oxide synthase causes profound changes in the mechanisms of cardiovascular regulation as shown by a marked enhancement of the Bezold-Jarisch reflex in L-NAME-treated rats. The enhancement of this reflex seems to be in great part due to the hyperresponsiveness of the cardiac pacemaker to cholinergic stimulation.

Sino-aortic denervation causes right atrial beta adrenoceptor down-regulation

Rat isolated right atria obtained 1 wk after sinoaortic denervation were less sensitive to the chronotropic actions of beta-agonists than were tissues obtained from animals that underwent sham surgery or no surgery at all. The potencies, but not the maximal responses for two high efficacy agonists, norepinephrine and isoproterenol, were reduced about 3- to 4-fold. Sino-aortic denervation (SAD) caused about a 3-fold decrease in potency and about a 60% decrease in maximal response for a low efficacy agonist, prenalterol. The changes in the actions of these agonists occurred in the absence of any changes in the subtype of beta receptor mediating the chronotropic response. The results of analyses of the data for prenalterol showed that SAD caused a decrease in the operational efficacy of this agonist without any changes in its KD value for beta-1 adrenoceptors. SAD had no effect on the responses of the tissue to blockade of uptake 1 and uptake 2, suggesting no compensatory changes in the removal processes caused the decreased potency. The results of radioligand binding assays showed that SAD caused a decrease in the maximal binding of 125I-cyanopindolol without altering its KD. Also, the results of competition binding assays confirmed the lack of effect of SAD on the KD for prenalterol. The SAD-induced changes in the actions of agonists acting at right atrial beta-1 receptors were caused by a down-regulation of beta-1 adrenoceptors, which probably occurred in response to SAD-induced increases in sympathetic tone.

Characterization of the antinociceptive properties of cimetidine and a structural analog

The antinociceptive and pharmacological properties of the H2 receptor antagonist cimetidine and a novel cimetidine analog, SKF92374, were characterized. On both the hot-plate and tail-flick nociceptive tests, cimetidine and SKF92374 induced complete, dose-related analgesic responses when injected into the lateral ventricle of rats. SKF92374 showed strong similarities to cimetidine in analgesic efficacy, slope of dose-response curves and chemical structure, suggesting that these compounds share a common analgesic mechanism. In contrast, histamine induced submaximal antinociceptive effects, and the H3 antagonist thioperamide, a known HA-releasing drug, had little or no analgesic effects. Compared with cimetidine, SKF92374 showed very weak activity (400-fold lower affinity) on H2 receptors in vitro (isolated guinea pig atrium) and in vivo (rat gastric secretion). In addition, SKF92374 (100 microM) had neither agonist nor antagonist action on guinea pig ileum H1 receptors. SKF92374 was also a weak competitive antagonist of N alpha-methylhistamine-induced inhibition of electrically induced contractions of the guinea pig ileum (Kd = 5.2 microM), an H3 receptor-mediated response. Autoradiographic binding assays in guinea pig brain confirmed a weak antagonism of H3 receptors by SKF92374. The compound (up to 10 microM) also had no effect on unpurified rat brain histamine N-methyltransferase activity. These results support the hypothesis that cimetidine induces analgesia by a novel brain mechanism unrelated to H1, H2 or H3 receptors.

Effect of short-term treatment with gastrin and related peptides on gastrointestinal histamine H2-receptors

The effects of short-term, 7-day, treatment with synthetic 15-leucine human gastrin I, pentagastrin or sulfated cholecystokinin-8 on the activity of histamine (HA)-stimulated adenylate cyclase in membranes isolated from guinea pig gastric mucosa and H2-receptor-mediated contractions of isolated ilea were evaluated. Treatment with each of the peptides produced a decrease in the maximal rate of HA-stimulated adenylate cyclase. The decreases in the maximal rate occurred without any effect on the potency of HA or any effect on basal rates of activity. In animals treated with pentagastrin, but not with cholecystokinin octapeptide sulfate, the contractile activity of dimaprit, a selective H2-agonist, was decreased. In animals treated with pentagastrin, the contractile actions of pentagastrin on isolated ileal preparations were increased. A 7-day treatment with the H2-antagonist, tiotidine, did not alter the potency of or the maximal response for HA-stimulated adenylate cyclase activity. Co-treatment with tiotidine prevented the effects of pentagastrin on gastric mucosal HA-stimulated adenylate cyclase. Treatment with pentagastrin did not alter the sensitivity of the gastric mucosal H2-receptor to inhibition by tiotidine. The effects of treatment with gastrin on NaF-stimulated adenylate cyclase activity also were determined. Treatment with gastrin did not alter the actions of NaF, suggesting that the coupling between the Gs subunit and the catalytic subunit of adenylate cyclase was not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Supersensitivity and changes in the active population of beta adrenoceptors in rat right atria in early sepsis

We have investigated the effect of sepsis induced by cecal ligation and puncture on the chronotropic actions of beta adrenoceptor agonists on isolated right atria. The present findings show that right atria obtained from rats in an early stage of sepsis were supersensitive to the chronotropic actions of the beta-agonists, isoproterenol (ISO), fenoterol (FEN) and prenalterol (PREN). The supersensitivity to the chronotropic actions of ISO and FEN was much greater than that which developed to PREN. The positive chronotropic actions of isobutylmethylxanthine and forskolin were not affected by sepsis. The receptor subtypes mediating the responses to ISO, FEN and PREN by control and septic right atria were characterized by functional assays using selective beta-1 and beta-2 antagonists. The results showed that the chronotropic response produced by all three agonists on right atria obtained from control rats were mediated by beta-1 receptors. In contrast, the chronotropic actions of ISO and FEN on atria from septic rats were mediated by what appears to be beta-2 receptors and those of PREN by beta-1 receptors.

Cardiac function and chronotropic sensitivity to beta-adrenergic stimulation in sepsis

An organism's cardiovascular response to sepsis is at least partly dependent on hormonal and neural modulation of myocardial function. We have investigated both intrinsic myocardial performance and one aspect of myocardial sensitivity to beta-adrenergic stimulation in a model of sepsis in which animals, at the time studied, exhibited bacteremia, normal arterial blood pressure and cardiac output, elevated heart rate, and elevated plasma catecholamines. Intrinsic myocardial contractile function, studied with the isolated, perfused working heart preparation, was depressed over a range of preloads in septic animals, whereas heart rate was elevated. To determine whether hearts from septic animals could respond normally to beta-adrenergic stimulation, we studied chronotropic responses to isoproterenol in both Langendorff perfused hearts and in isolated right atria. In langendorff perfused hearts from septic animals, basal rates were significantly increased and lower concentrations of isoproterenol elicited greater increases in heart rate. In isolated right atria from septic animals, basal rates were also elevated and the EC50 for the chronotropic response to isoproterenol was significantly less than in atria from control animals. The maximal heart rate response to isoproterenol was not significantly different from control. These results indicate that in sepsis, despite apparently adequate in vivo cardiac performance, intrinsic myocardial function is depressed, but chronotropic sensitivity to beta-adrenergic stimulation is increased.

Metronidazole and 5-aminosalicylic acid enhance the contractile activity of histaminergic agonists on the guinea-pig isolated ileum

The effects of metronidazole and 5-aminosalicylic acid (5-ASA) on histamine receptor-effector systems in the small intestine and right atrium of the guinea pig were studied. In an apparently all-or-none manner, both caused a sinistral shift in dose-response curves for the phasic component of the contractile response to histamine at H1 receptors on the ileum. In the presence of either, the EC50 value for histamine was reduced from 0.07 to about 0.03 microM. Similarly, in an apparently all-or-none fashion, both produced an elevation in the dose-response curve for the actions of dimaprit at H2-receptors in the ileum; the response to all doses was increased about 30% with no significant change in the EC50 value. Metronidazole and 5-ASA did not alter dose-response curves for the tonic contractile response to histamine or curves generated by the cumulative addition of histamine. Also, neither altered the positive chronotropic response on isolated right atria or the phasic contractile response on isolated segments of jejunum and duodenum to histamine or dimaprit. Likewise, neither altered dose-response curves for the direct action of carbamylcholine at muscarinic receptors or for the indirect actions of dimethylphenylpiperazinium on the ileum. The effects of 5-ASA or metronidazole on the response to histamine could be prevented as well as reversed by scopolamine or tetrodotoxin. The results suggest that metronidazole and 5-ASA enhance the actions of histamine and dimaprit on the ileum by an action on myenteric plexus neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional variation in the sensitivity of longitudinal smooth muscle to histamine at H1-receptors in guinea-pig ileum and colon

The sensitivity of the distal ileum, proximal colon, medial colon, and distal colon of the guinea-pig to histamine has been evaluated. The rank order of sensitivity was ileum greater than medial colon greater than proximal colon approximately equal to distal colon. The mean -logEC50 values at receptors in the ileum, medial, proximal, and distal colon were 6.74, 6.18, 5.79, and 5.72, respectively. The apparent dissociation constant for the interaction of histamine with receptors in the various regions was determined. The -log Kd values at receptors in the ileum, proximal colon, medial colon, and distal colon were 4.68, 4.65, 4.62, and 4.44, respectively. The mean apparent -log Kd values for the antagonism of histamine by mepyramine were 9.0, 9.0, 9.1, and 8.9 for receptors on the ileum, proximal, medial, and distal colon, respectively. The results of these experiments provide no evidence that histamine receptors in the colon are distinguishable from H1-receptors as characterized on the ileum. The differences in sensitivity to histamine in the various regions of the intestine may be due to differences in the density of H1-receptors.

Enzymatic and nonenzymatic hydrolysis of D,L-dipivefrin

D,L-dipivefrin hydrochloride was administered bilaterally to rabbit eyes five or 150 minutes after unilateral application of a cholinesterase inhibitor. Aqueous humor levels of D,L-epinephrine, measured 30 minutes later by high-performance liquid chromatography, were not significantly different in the two eyes. Nonenzymatic conversion of D,L-dipivefrin to D,L-epinephrine was measured in tissue-free (pH 7.4) solutions; after three hours less than 1% of D,L-dipivefrin became D,L-epinephrine. Homogenates of corneal epithelium were 16 times more effective in converting D,L-dipivefrin to D,L-epinephrine than after heat-inactivation. The ocular hypotension produced by 0.25% D,L-dipivefrin eyedrops was unaffected by prior administration of 0.25% echothiophate iodide eyedrops provided the D,L-dipivefrin was administered after the echothiophate-induced ocular hypertensive phase. It was concluded that D,L-dipivefrin was converted to D,L-epinephrine in vivo primarily by enzymatic hydrolysis and that cholinesterase inhibitors did not affect this conversion.

Evaluation of presynaptic histamine receptors in the canine renal vascular bed

Histamine has been shown to increase renal blood flow via H1- and H2-receptors. Furthermore, H2-receptors have been demonstrated to attenuate stimulation-induced release of norepinephrine. The present studies examined whether histamine has a presynaptic effect on sympathetic nerves in the canine renal vascular bed. Renal blood flow was measured in anesthetized dogs, and vasoconstrictor responses to renal nerve stimulation and i.a. injections of norepinephrine were compared before and during i.a. infusions of histamine. Histamine increased renal blood flow and decreased stimulation-induced vasoconstriction to a greater degree than norepinephrine responses. 2-(2-pyridyl)ethylamine, an H1-agonist, did not produce consistent effects. Dimaprit, an H2-agonist, produced responses similar to histamine but to a lesser extent. The H1-antagonist tripelennamine and the H2-antagonist cimetidine each minimally antagonized the effect of histamine on nerve stimulation. When both blocking agents were infused together, maximum antagonism of histamine occurred. Thus, it appears that histamine will produce a neuroinhibitory effect in the canine renal vascular bed and this effect appears to be mediated by both H1- and H2-receptors because both receptor antagonists are necessary to block this effect.

Selectivity of 4-methylhistamine at H1- and H2-receptors in the guinea-pig isolated ileum

The selectivity of 4-methylhistamine (4-MH) as an agonist at histamine H1- and H2-receptors has been evaluated in the guinea-pig isolated ileum. The EC50 values of 4-MH on H1- and H2-receptors that mediate contractile responses were determined. The EC50 at H1-receptors was estimated after selective blockade of H2-receptors by tiotidine and the EC50 at H2-receptors estimated after selective blockade of H1-receptors by mepyramine. The -log EC50 values at H1- and at H2-receptors were 4.57 and 5.23, respectively. The dissociation constants for the interaction of 4-MH with H1- and H2-receptors were determined. The -log KD values at H1- and H2-receptors were 3.55 and 4.27, respectively. These results suggest that 4-MH is only about 5 times as potent at H2- as it is at H1-receptors in the guinea-pig ileum and that 4-MH should be used with caution to discriminate between H1- and H2-receptors.

Histamine H2-receptors on guinea-pig ileum myenteric plexus neurons mediate the release of contractile agents

Dimaprit, a highly selective H2-agonist, caused a multiphasic contraction of guinea-pig ileal segments and ileal myenteric plexus-longitudinal muscle preparations. The initial phase was characterized by a twitch which reached a maximum in 15 to 30 sec and was followed by a partial relaxation. The later phase was variable and consisted of a series of twitch responses or of a slowly developing contracture which sometimes was accompanied by oscillatory changes in tension. dose-response curves were generated for the initial response; for isolated ileal segments the EC50 was 5.1 +/- 1.8 micrometers (mean +/- S.D., N = 7) and the Hill coefficient was 1.1 +/- 0.2 and for longitudinal muscle strips the EC50 was 5.8 +/- 1.2 micrometer and the Hill coefficient was 1.2 +/- 0.1 (N = 7). Both the initial and secondary components of the contractile responses to dimaprit were prevented by 0.2 micron tetrodotoxin or 10 microns mefenamic acid and by the production of tachphylaxis to either substance P or serotonin. Scopolamine, 0.001 to 0.1 micron, insurmountably antagonized only the initial component of the response. Mepyramine (1.0 micrometer), hexamethonium (100 microns), bromolysergic acid (0.25 microns) and p-(imidazol-1-yl)phenyl (10 microns) were without effect on the response to dimaprit. The histamine H2-receptor antagonist, tiotidine, produced parallel dextral shifts in the dose-response curve for dimaprit. The apparent pA2 value for tiotidine was 7.65. The results suggest that dimaprit acts on H2-receptors located on myenteric plexus neurons to cause the release of contractile substances. The mediators of the contractile response are tentatively identified as acetylcholine, substance P, serotonin and a product(s) of the arachadonic acid cascade.

Subcellular distribution of prolyl endopeptidase and cation-sensitive neutral endopeptidase in rabbit brain

The subcellular distribution of prolyl endopeptidase, and of cation-sensitive neutral endopeptidase, two enzymes actively metabolizing many neuropeptides, was determined in homogenates of rabbit brain. The subcellular distribution of both enzymes was more similar to lactate dehydrogenase, a cytoplasmic enzyme marker, than to choline acetyltransferase, a synaptosomal marker. Only 35% of the activity of these two neutral endopeptidases was found in the crude mitochondrial fraction (P2), the bulk of the remaining activity being associated with the high-speed supernatant. Prolyl endopeptidase and cation-sensitive neutral endopeptidase thus can be regarded as mainly cytoplasmic enzymes in the rabbit brain.

Acetylcholine metabolism in the rat hippocampus and striatum following one-trial passive training

The steady state levels of acetylcholine and choline and the synthesis of acetylcholine in the hippocampus and striatum of rat brain have been determined after one-trial passive avoidance training. Steady state levels of acetylcholine and choline were not altered, but the rate of acetylcholine synthesis was significantly elevated in the striatum but not significantly elevated in the hippocampus at one hour after training.

Simultaneous measurement of acetylcholine and choline in brain by pyrolysis-gas chromatography-mass spectrometry

Pyrolysis-gas chromatography and chemical ionization mass fragmentography were combined to develop a specific, simple and rapid method for simultaneously measuring endogenous and stable isotopic variants of acetylcholine and choline with a detection limit of approximately 10(-12) mol. The recovery and reproducibility of the method are excellent, and the method is suitable for measuring acetylcholine and choline in discrete regions of rat brain and to measure incorporation of choline into acetylcholine, both of which uses are demonstrated. This method affords easy analysis of 40 samples in a working day. The new technique used to extract compounds from tissues and the modified gas flow arrangement may be useful to measure other compounds as well.

Histamine H1- and muscarinic receptor antagonist activity of cimetidine and tiotidine in the guinea pig isolated ileum

The histamine H2-receptor antagonists cimetidine and tiotidine were compared as antagonists for H1- and muscarinic receptors in the guinea pig isolated ileum. Their interactions with histamine were evaluated on the phasic and tonic components of the histamine response. For carbachol, only the phasic component of the response was monitored. For their interactions with histamine, the type of antagonism, surmountable or nonsurmountable, depended upon the choice of response metameter. Evaluation of the antagonism produced by either tiotidine or cimetidine for histamine concentration-response curves based on the phasic response metameter showed an initial dextral shift with surmountable antagonism. With increasing antagonist concentrations the concentration-response curves were further shifted to the right and the maximum response was depressed. When this antagonism was evaluated for histamine concentration-response curves based on the tonic response metameter, cimetidine produced dextral shifts and nonsurmountable antagonism, and tiotidine exhibited only nonsurmountable antagonist activity. pA2 values for cimetidine antagonism of the phasic and tonic components of the histamine response were 3.2 and 3.7 respectively, and pD'2 values for the phasic and tonic components were 1.8 and 2.3 respectively. The pA2 value for tiotidine antagonism of the phasic component was 3.9 and the pD'2 values for the phasic and tonic components were 2.6 and 3.3 respectively. Cimetidine and tiotidine at concentrations which did not depress the phasic component of the histamine response produced surmountable antagonism to the contractile action of carbachol. The pA2 values for cimetidine and tiotidine antagonism of carbachol were 3.8 and 3.6 respectively.

Histamine H2-receptor antagonism by propantheline and derivatives

The histamine H2-antagonist properties of propantheline and its tertiary amine derivatives were investigated. Propantheline and methantheline inhibited the histamine-activated cyclase of guinea-pig brain homogenates, a well characterized H2-receptor preparation; the inhibition was not competitive. Tertiary amine derivatives were competitive H2-antagonist in this system, one such derivative exhibiting greater potency than cimetidine. In concentrations blocking the brain H2-receptors, these derivatives had no effect on atrial histamine dose-response curves, but evidence for their antagonism on peripheral H2-receptors was obtained with papillary muscle preparations. The results suggest that the guinea-pig brain H2-linked cyclase of homogenates is a sensitive predictor of peripheral H2-antagonist activity. These drugs may also be effective inhibitors of gastric secretion.

Effect of sodium chloride on changing the rate-limiting step in the human placental choline acetyltransferase reaction

The kinetic constants, Km and Vmax, for the choline acetyltransferase reaction were determined for choline and eight choline analogs under conditions of high (0.3 M) and low (approximately 0.01 M) sodium chloride. At high sodium chloride, the maximal velocities of the different substrates varied over 27-fold, while at low sodium chloride, less than a 5-fold variation was observed. Dead-end inhibition studies using acetylaminocholine as the inhibitor showed that under conditions of high sodium chloride, inhibition changes from noncompetitive to competitive as the reactivity of the substrate decreases. Under conditions of low sodium chloride, acetylaminocholine inhibition is nonlinear and noncompetitive with respect to all substrates tested. These results suggest that increased ionic strength increases the rate of coenzyme A dissociation from the enzyme. The rate-determining step of the reaction can be ternary complex interconversion, coenzyme A release, or both, depending on the ionic strength and the substrate employed.

Comparative studies of substrates and inhibitors of choline transport and choline acetyltransferase

Analogs of choline and three hemicholinium derivatives were studied as substrates for choline acetyltransferase (ChAc) and as substrates or inhibitors of the high-affinity choline transport system in rat brain synaptosomes. Hemicholiniums-3 and -15, but not terphenylhemicholinium-3, were substrates of ChAc. All three inhibit the high-affinity choline transport system, with I50 values of 0.08, 8.0 and 0.08 muM, respectively. Simple choline analogs with substituents on the beta-carbon atom were found to be very poor substrates for ChAc. N-alkyl analogs, mono-, di- and triethyl choline and N-hydroxyethyl pyrrolidinium methiodide (pyrrolcholine), and DL-alpha-methyl choline are substrates for ChAc and also inhibit choline transport, with I50 values between 2 to 6 muM.[3-H] choline, [3-H] monoethycholine and [3-H] pyrrolcholine were transported into synaptosomes by the choline high affinity system and metabolized to acetyl derivatives. The results indicated that choline transport is the rate-limiting step in the biosynthesis of acetylcholine and provide the basis for the development of a group of cholinergic false transmitters.

Choline metabolism in the cerebral cortex of guinea pigs. Phosphorylcholine and lipid choline

1. The labelling of phosphorylcholine and choline-containing phospholipids in the subcellular fractions of guinea-pig cerebral cortex after the intraventricular injection of [N-Me-(3)H]choline into conscious animals has been studied. Special emphasis was placed upon the synaptosome fraction and early time-periods after administration. 2. The labelling of phosphorylcholine was rapid compared with that of phospholipid and was confined to two distinct subcellular fractions: the soluble cytoplasmic fraction and the synaptosome fraction. Most of the labelled phosphorylcholine of the synaptosome fraction was readily released by osmotic rupture indicating location in the nerve-ending cytoplasm. The two pools of phosphorylcholine had similar specific radioactivities at all observed times. 3. (3)H-labelled phospholipid was found in all membranous fractions. The labelling was confined to choline-containing phospholipids, notably phosphatidylcholine. 4. The labelling of the different membranous fractions was similar. 5. The half-life of the choline-containing phospholipids in the synaptic vesicle fraction was very much greater than the acetylcholine in this fraction. 6. Evidence is presented that synthesis de novo of phosphatidylcholine at nerve terminals occurs in vivo.

Choline metabolism in the cerebral cortex of guinea pigs. Stable-bound acetylcholine

1. The turnover of synaptosomal (vesicular-cytoplasmic) and stable-bound (vesicular) acetylcholine isolated from cortical tissue was investigated after the administration, under local anaesthesia, of [N-Me-(3)H]choline into the lateral ventricles of guinea pigs. 2. Radioactive acetylcholine and choline present in acid extracts of subcellular fractions were separated by a combination of liquid and column ion-exchange and thin-layer chromatography. 3. The specific radioactivity and pattern of labelling of acetylcholine present in a fraction of monodisperse synaptic vesicles was found to be essentially the same as that of synaptosomal acetylcholine. 4. The specific radioactivity of stable-bound acetylcholine present in partially disrupted synaptosomes (fraction H) at short times (10-20min) after the injection of [N-Me-(3)H]choline was very variable and inversely related to the yield of acetylcholine in that fraction. 5. Evidence was found for the existence of two small, but highly labelled pools of acetylcholine, one which could be isolated in fraction H and the other which was lost when synaptosomes, after isolation by gradient centrifugation, were left at 0 degrees C or pelleted. 6. It is concluded that the results are best explained by metabolic differences among the nerve-ending compartments (thought to be vesicles) which contain stable-bound acetylcholine. Computer simulation of our experiments supports this possibility and suggests that the highly labelled pool in fraction H is present in vesicles close to the external membrane.