Hyperactivity in preschool age is associated with higher fat-free mass and healthy lifestyle behaviours five years later: A longitudinal study of Swedish children

BACKGROUND

There is evidence for a link between hyperactivity and obesity, especially among older children. Both conditions seem to be multifactorial in origin and hypotheses of common underlying issues, such as emotional dysregulation, have been suggested. However, studies of the co-occurrence of the two conditions in younger age groups have been inconclusive.

OBJECTIVES

We aimed to study the longitudinal associations of psychological strengths and difficulties at 4 years of age with health behaviours, body composition, physical fitness, and cardiovascular disease (CVD) risk factors 5 years later.

METHODS

Parents of 226 4-year-old children filled out the Strengths and Difficulties Questionnaire (SDQ). At 9 years of age, we assessed health behaviours, physical fitness, body composition, and CVD risk factors. Associations were examined with linear regression models that were adjusted for sex, age of the child at 9, and maternal education.

RESULTS

In the adjusted models, hyperactivity at 4 was associated with higher fat-free mass (β = 0.18, p = 0.007) and lower levels of sedentary behaviour (β -0.14, p = 0.043) at 9 years. Furthermore, greater emotional problems at 4 were associated with lower intake of fruit and vegetables (β -0.14, p = 0.038) at 9 years. However, there were no statistically significant associations between psychological difficulties and fat-mass index.

CONCLUSIONS

Our novel data provide no evidence of an association between hyperactivity in preschool age and obesity or obesity-related behaviours in school age. Future studies examining how psychological factors relate to obesity development should consider a developmental perspective.

Mindfulness-Based Stress Reduction for Coronary Artery Disease Patients: Potential Improvements in Mastery and Depressive Symptoms

Depressive symptoms after coronary events are associated with a worse prognosis. When changing the focus from psychopathology towards a resilience framework, treatments such as mindfulness meditation could offer novel ways to address psychological distress among coronary artery disease (CAD) patients. We studied the feasibility of mindfulness-based stress reduction (MBSR) for CAD patients with depressive symptoms. Seventy-nine CAD patients with elevated depressive symptoms were invited to an 8-week MBSR course. Twenty-four patients (30%) accepted and 16 (20%) completed MBSR. Depressive symptoms decreased immediately after the course (p = .006). After 12 months, this improvement remained, and Mastery scores increased (p = .005). A reference group of 108 CAD patients did not show any significant changes in depressive symptoms or Mastery between 1 and 12 months after a coronary event. MBSR thus appears to be a feasible alternative for CAD patients with elevated depressive symptoms. Future studies are warranted to study if MBSR can improve psychological functioning in CAD patients.Clinicaltrials.gov (Registration Number: NCT03340948).

Digital multiple health behaviour change intervention targeting online help seekers: protocol for the COACH randomised factorial trial

INTRODUCTION

Unhealthy lifestyle behaviours continue to be highly prevalent, including alcohol consumption, unhealthy diets, insufficient physical activity and smoking. There is a lack of effective interventions which have a large enough reach into the community to improve public health. Additionally, the common co-occurrence of multiple unhealthy behaviours demands investigation of efforts which address more than single behaviours.

METHODS AND ANALYSIS

The effects of six components of a novel digital multiple health behaviour change intervention on alcohol consumption, diet, physical activity and smoking (coprimary outcomes) will be estimated in a factorial randomised trial. The components are designed to facilitate behaviour change, for example, through goal setting or increasing motivation, and are either present or absent depending on allocation (ie, six factors with two levels each). The study population will be those seeking help online, recruited through search engines, social media and lifestyle-related websites. Included will be those who are at least 18 years of age and have at least one unhealthy behaviour. An adaptive design will be used to periodically make decisions to continue or stop recruitment, with simulations suggesting a final sample size between 1500 and 2500 participants. Multilevel regression models will be used to analyse behavioural outcomes collected at 2 months and 4 months postrandomisation.

ETHICS AND DISSEMINATION

Approved by the Swedish Ethical Review Authority on 2021-08-11 (Dnr 2021-02855). Since participation is likely motivated by gaining access to novel support, the main concern is demotivation and opportunity cost if the intervention is found to only exert small effects. Recruitment began on 19 October 2021, with an anticipated recruitment period of 12 months.

TRIAL REGISTRATION NUMBER

ISRCTN16420548.

Multiple lifestyle behaviour mHealth intervention targeting Swedish college and university students: protocol for the Buddy randomised factorial trial

Introduction

The time during which many attend college or university is an important period for developing health behaviours, with potentially major implications for future health. Therefore, it is concerning that many Swedish students excessively consume alcohol, have unhealthy diets, are not physical active and smoke. The potential of digital interventions which integrate support for change of all of these behaviours is largely unexplored, as are the dismantled effects of the individual components that make up digital lifestyle behaviour interventions.

Methods and analysis

A factorial randomised trial (six factors with two levels each) will be employed to estimate the effects of the components of a novel mHealth multiple lifestyle intervention on alcohol consumption, diet, physical activity and smoking among Swedish college and university students. A Bayesian group sequential design will be employed to periodically make decisions to continue or stop recruitment, with simulations suggesting that between 1500 and 2500 participants will be required. Multilevel regression models will be used to analyse behavioural outcomes collected at 2 and 4 months postrandomisation.

Ethics and dissemination

The study was approved by the Swedish Ethical Review Authority on 2020-12-15 (Dnr 2020-05496). The main concern is the opportunity cost if the intervention is found to only have small effects. However, considering the lack of a generally available evidence-based multiple lifestyle behaviour support to university and college students, this risk was deemed acceptable given the potential benefits from the study.

Recruitment will begin in March 2021, and it is expected that recruitment will last no more than 24 months. A final data set will, therefore, be available in July 2023, and findings will be reported no later than December 2023.

Trial registration number

ISRCTN23310640; Pre-results.

Cultivating the Interpersonal Domain: Compassion in the Supervisor-Doctoral Student Relationship

The long-term and complex supervisor-doctoral student relationship is often characterised by tension and frictions. In higher education research, models, and interventions that take the potential beneficial interpersonal effects of compassion into account seem to be scarce. Hence, the aim of this study was to conceptualise the potential role compassion could have in the cultivation of an affiliative and sustainable supervisor-doctoral student relationship. The concept of compassion was investigated and analysed in relation to a contemporary model of supervisor behaviours. Furthermore, a systematic literature search in the scientific databases PubMed, PsychInfo, ScienceDirect, and Google Scholar was performed. The conceptual analysis revealed that the interpersonal domain, in which compassion could afford a shared sense of warmth, is neglected in previous definitions. Furthermore, the integration of compassion into a model of adaptive supervisor behaviour indicates a strong case for a salutary role for compassion in the supervisor-doctoral student relationship. However, the literature review showed that empirical data are lacking, and more studies are needed. The role of compassion deserves to be investigated empirically in this particular interpersonal context.

Hyperactivity is associated with higher fat-free mass and physical activity in Swedish preschoolers: A cross-sectional study

Aim

We investigated psychological strengths and difficulties in a Swedish population of preschool children and analysed how these behavioural variables were related to body composition, cardiorespiratory fitness, physical activity levels, sedentary behaviour and diet.

Methods

Three hundred and fifteen boys and girls were recruited during 2014‐2015. Body composition was measured using air‐displacement plethysmography, and anthropometric measures were taken. Parents responded to questions about age, sex and educational attainment, diet, physical activity levels and smoking habits, as well as the Strengths and Difficulties Questionnaire (SDQ). Regression models were created to analyse associations between psychological variables, body composition and health behaviours.

Results

Hyperactivity scores were positively related to fat‐free mass (β = 0.20, P = .001) and moderate‐to‐vigorous physical activity (β = 0.16, P = .003) and negatively associated with sedentary behaviours (β = 0.18, P = .001), but showed no statistically significant associations with fat mass.

Conclusion

Our findings suggest that the adverse health consequences of hyperactivity on obesity and obesity‐related health behaviours may be established after the preschool period. Questions about the time frame of contributing and modulating factors in obesity development are discussed.

Inverted items and validity: A psychobiological evaluation of two measures of psychological resources and one depression scale

Psychological resources and risk factors influence risk of coronary heart disease. We evaluated whether inverted items in the Self-esteem, Mastery, and Center for Epidemiological Studies Depression scales compromise validity in the context of coronary heart disease. In a population-based sample, validity was investigated by calculating correlations with other scales (n = 1004) and interleukin-6 (n = 374), and by analyzing the relationship with 8-year coronary heart disease risk (n = 1000). Negative items did not affect the validity of the resource scales. In contrast, positive items from Center for Epidemiological Studies Depression showed no significant relationships with biological variables. However, they had no major impact on the validity of the original scale.

Muscarinic receptor subtypes in the alimentary tract

Acetylcholine is a transmitter in preganglionic autonomic and postganglionic parasympathetic nerves and a non-neuronal paracrine mediator in the alimentary tract. Acetylcholine is involved in the control of almost any function within these organ systems, and almost every cell type expresses multiple muscarinic receptor subtypes. Although muscarinic receptors at non-neuronal effector cells commonly are of the M3 subtype, the population usually consists of a mixture of muscarinic receptor subtypes often co-acting postsynaptically. However, the pattern of heterogeneity of varies between different tissues. The population in gland parenchymal tissue often consists of a mixture of M1 and M3 receptors, smooth muscle tissue of the gut of M2 and M3, blood vessels of M1, M3, M4 and M5 and neuronal cells of M1 and M4. Nitric oxide production, effects on inflammation and proliferation may involve M1, M3 and M5 receptors. Muscarinic receptors expressed on nerve terminals may indirectly modulate the responses by inhibition or facilitation of neuronal transmission in the autonomic nervous system. The present review describes signalling mechanisms, expression and functional effects of muscarinic receptors in salivary glands and in the gastrointestinal tract.

Serotonin and vasoactive intestinal peptide antagonists attenuate rotavirus diarrhoea

BACKGROUND AND AIMS

The mechanisms underlying intestinal secretion in rotavirus diarrhoea remain to be established. We previously reported that rotavirus evokes intestinal fluid and electrolyte secretion by activation of the enteric nervous system. We now report that antagonists for the 5-hydroxytryptamine 3 receptor (5-HT(3)) and vasoactive intestinal peptide (VIP) receptor, but not antagonists for 5-hydroxytryptamine 4 receptor or the muscarinic receptor, attenuate rotavirus induced diarrhoea.

METHODS

Neurotransmitter antagonists were administered to wild-type or neurokinin 1 receptor knockout mice infected with homologous (EDIM) or heterologous (RRV) rotavirus.

RESULTS

While RRV infected mice had diarrhoea for 3.3 (0.2) days (95% confidence interval (CI) 3.04-3.56), the 5-HT(3) receptor antagonist (granisetron) and the VIP receptor antagonist (4Cl-D-Phe(6),Leu(17))-VIP both reduced the total number of days of RRV induced diarrhoea to 2.1 (0.3) (95% CI 1.31-2.9) (p<0.01). EDIM infected mice treated with granisetron had a significantly shorter duration of diarrhoea (5.6 (0.4) days) compared with untreated mice (8.0 (0.4) days; p<0.01). Experiments with neurokinin 1 receptor antagonists suggest that this receptor may possibly be involved in the secretory response to rotavirus. On the other hand, rotavirus diarrhoea was not attenuated in the neurokinin 1 receptor knockout mice.

CONCLUSIONS

Our results suggest that the neurotransmitters serotonin and VIP are involved in rotavirus diarrhoea; observations that could imply new principles for treatment of this disease with significant global impact.

Interface between the intestinal environment and the nervous system

Possible mechanisms by which the intestinal contents may influence afferent nerve fibres in the lamina propria of the intestinal mucosa are discussed in this brief review. After addressing intestinal epithelial permeability, endocrine and brush cells are discussed, as well as enterocytes, as sensors for luminal microbes.

Pathogenesis of rotavirus diarrhea

Rotavirus diarrhea is a major cause of infantile gastroenteritis worldwide. This review is mainly devoted to the effects of Rotavirus on intestinal epithelial transport and to the pathophysiological mechanisms proposed to underlie the intestinal fluid secretion caused by the virus.

Involvement of nerves and calcium channels in the intestinal response to Clostridium difficile toxin A: an experimental study in rats in vivo

BACKGROUND

The involvement of nerves and calcium channels in the intestinal response to Clostridium difficile toxin A (luminal concentration 1 or 15 microg/ml) was studied in the small intestine of rats in vivo.

METHODS

Inflammation was quantified by estimating myeloperoxidase (MPO) activity in the intestinal lumen, extravascular accumulation of Evan's blue (EB) in the intestine, and number of red blood cells (RBCs) in veins in histological sections. Intestinal damage was estimated using a histological grading system. In some experiments net fluid transport was recorded using a gravimetric technique.

RESULTS

In acutely denervated intestines, toxin A caused marked destruction of the villi, increased luminal release of MPO activity, and augmentation of intestinal content of EB and venous RBCs. Denervating the intestine 3-4 weeks prior to the actual experiment prevented the development of villus damage and significantly decreased the number of RBCs in intestinal veins in experiments with a low toxin concentration, whereas no effect was demonstrated on luminal MPO activity. Using a high toxin concentration, chronic denervation decreased only the number of RBCs. Pretreatment with hexamethonium (low toxin concentration; acute denervation) attenuated the effect of toxin A on morphology, luminal MPO activity, and number of RBCs. Pretreatment with nifedipine (low toxin concentration; acute denervation) significantly decreased intestinal MPO activity and number of RBCs. Tissue accumulation of EB was not influenced by experimental manipulation. Net fluid transport was measured in experiments exposing the intestinal mucosa to a high toxin concentration. Fluid secretion caused by the toxin was significantly attenuated by intravenous hexamethonium whereas no effect was observed after administration of nifedipine or granisetron.

CONCLUSIONS

At a low toxin concentration, intramural reflexes are involved in the inflammatory response whereas axon reflexes contribute to tissue damage. At a high toxin concentration no nervous involvement in the toxin A response was demonstrated except for fluid secretion evoked by the toxin.

Role of the enteric nervous system in the fluid and electrolyte secretion of rotavirus diarrhea

The mechanism underlying the intestinal fluid loss in rotavirus diarrhea, which often afflicts children in developing countries, is not known. One hypothesis is that the rotavirus evokes intestinal fluid and electrolyte secretion by activation of the nervous system in the intestinal wall, the enteric nervous system (ENS). Four different drugs that inhibit ENS functions were used to obtain experimental evidence for this hypothesis in mice in vitro and in vivo. The involvement of the ENS in rotavirus diarrhea indicates potential sites of action for drugs in the treatment of the disease.

Somatic nerve stimulation and cholera-induced net fluid secretion in the small intestine of the rat: evidence for an opioid effect

The effects of somatic nerve stimulation on cholera toxin induced secretion was investigated in vivo in anaesthetised rats. Small intestinal secretion was induced with cholera toxin and measured by a gravimetric technique. Afferent stimulation (pulse frequency within train; 100 Hz; train duration: 50 ms; train frequency: 3 Hz) of the sciatic nerve over 30 min significantly reduced the net fluid secretion both during (P < 0.05) and after cessation of the stimulation (P < 0.01). The greatest effect was obtained immediately after the termination of the nerve stimulation when the secretion was reversed to net fluid absorption. The opioid receptor antagonist naloxone (10 mg kg(-1) i.v.) administrated during the stimulation, significantly inhibited the antisecretory effect seen after the stimulation, thus no significant difference was seen between the control period and the periods after cessation of the stimulation. The opioid receptor antagonist naloxone methiodide (10 mg kg(-1) i.v.), which does not cross the blood-brain barrier, partly inhibited the antisecretory effects but not with the same magnitude as naloxone, thus the net fluid secretion was still significantly inhibited after the stimulation (P < 0.05). We conclude that afferent stimulation of the sciatic nerve strongly inhibits the cholera toxin induced secretion in the small intestine. This inhibition involves primarily a central opioid mechanism and to a lesser extent peripheral opioid mechanism.

Lithium evokes a more pronounced natriuresis when administered orally than when given intravenously to salt-depleted rats

The effects on renal sodium excretion of giving lithium chloride (LiCl; 0.75 mmol per kg body mass) by gavage or intravenously were investigated. The experiments were carried out on Wistar-Kyoto (WKY) or spontaneously hypertensive (SHR) rats in metabolic cages. The rats had been on a low-salt diet for 4 days. Urine excretion of water, sodium and potassium was followed before and for 24 h after giving LiCl. An oral dose of LiCl evoked a more pronounced renal sodium excretion in either strain of rat as compared to that following intravenous administration, in agreement with previous observations of the effects of giving sodium chloride. Choline chloride (1.5 mmol per kg body mass) given by gavage to WKY rats or SHR evoked no change in the renal excretion of sodium. Based on the results of the present study and on observations reported in the literature, we propose that the intestinal tract contains a sodium "sensor", which upon activation releases a natriuretic factor to cause renal sodium excretion. The present results indicate that the proposed "sensor" is sensitive to lithium but not chloride ions.

Involvement of serotonin and calcium channels in the intestinal fluid secretion evoked by bile salt and cholera toxin

1. The enteric nervous system (ENS) is activated when exposing the intestinal mucosa to cholera toxin or certain bile salts. Cholera toxin stimulates ENS, at least in part, by the release of 5-hydroxytryptamine (5-HT) from the enterochromaffin cells. Calcium channel blockers of the L-type markedly attenuate the fluid secretion and the luminal release of 5-HT caused by cholera toxin. 2. The objective of the present study was to elucidate if sodium deoxycholate activated ENS in a similar manner as cholera toxin. Furthermore, the effect of several calcium channel blockers was tested on the fluid secretion caused by cholera toxin or bile salt. 3. Sodium deoxycholate (4 mM) caused a release of 5-HT into the intestinal lumen, which was inhibited by calcium channel blockade. Granisetron, a 5-HT3 receptor blocker, partly inhibited the fluid secretion caused by bile salt. 4. The effects of nifedipine, felodipine, R-felodipine, H186/86 (t-butyl analogue of felodipine) on the fluid secretion caused by cholera toxin or sodium deoxycholate were studied. Both secretory states were markedly attenuated in a dose dependent manner by all calcium channel blockers tested regardless of their effects on arterial pressure. 5. It is concluded that both cholera toxin and bile salt activate ENS, at least in part, via a release of 5-HT from the enterochromaffin cells. The antisecretory effect calcium channel blockers is partly explained by an inhibition of this release of 5-HT.

The effects on net fluid transport of noxious stimulation of jejunal mucosa in anaesthetized rats

A major aim of the present study was to investigate whether exposing the jejunal mucosa to a noxious stimulus induces a net fluid secretion by activating the enteric nervous system (ENS) and, if so, to what extent an axon reflex was involved. Net fluid transport was measured in vivo with a gravimetric method. The intestinal mucosa was exposed to an isotonic solution with an unphysiologically low pH (1.0). This evoked a fluid secretion, which was markedly attenuated by giving hexamethonium (nicotinic receptor antagonist) i.v. or exposing the intestinal serosa to lidocaine (local anaesthetic). Atropine (muscarinic receptor antagonist) had no effect. Luminal acid evoked a fluid secretion of the same magnitude in acutely denervated segments and in segments denervated about 3 weeks prior to the experiments. Luminal capsaicin (1.6-16 mM) did not influence jejunal net fluid transport. A second aim of the study is to investigate the effect of nifedipine (Ca channel blocker of L-type) on the acid-induced fluid secretion. Nifedipine markedly attenuated acid-induced fluid secretion. In contrast to cholera toxin-evoked secretion, the nifedipine effect was not mediated via 5 hydroxytryptamine (5-HT) as judged by measurements of 5-HT release into the intestinal lumen and the lack of effect of granisetron (5-HT3 receptor antagonist). It is concluded that the net fluid secretion evoked by hydrochloric acid in the small intestine is mainly mediated via an intramural reflex in the ENS. No experimental evidence was obtained for the involvement of an axon reflex. The site of action of the calcium channel blocker is tentatively discussed.

Nervous control of alkaline secretion in the duodenum as studied by the use of cholera toxin in the anaesthetized rat

There is experimental evidence for an axon reflex control of alkaline secretion in the rat duodenum. We have investigated if there is also an intramural reflex control of alkaline secretion similar to that demonstrated with regard to the control of the fluid transport in the rat jejunum. Alkaline secretion in the duodenum of an anesthetized rat was continuously monitored using an in situ titration technique. The segment was extrinsically denervated. Exposing the duodenal segment to 80 microg cholera toxin markedly increased alkaline secretion. This response was abolished by hexamethonium (28 micromol (10 mg) kg(-1) body wt), a nicotinic receptor blocker, lidocaine (0.5 mL of a 1% solution on the serosal surface), a local anaesthetic, and nifedipine (5.75 micromol (2 mg) kg(-1) body wt i.v.), a calcium channel blocker. The response to cholera toxin was partially abolished by granisetron (0.11 micromol (40 microg) kg(-1) body wt i.v.), a 5-HT3 receptor blocker. Atropine (1.7 micromol (0.5 mg) kg(-1) body wt i.v.), a muscarinic receptor blocker, had no effect. We therefore conclude that the alkaline secretion in the rat jejunum evoked by cholera toxin exhibits the same pharmacological properties as the fluid secretion caused by the toxin in the jejunum. This suggests that the alkaline secretion in the rat duodenum is controlled not only by an axon reflex but also by an intramural secretory reflex similar to that controlling fluid transport in the rat jejunum.

The enteric nervous system and cholera toxin-induced secretion

This article reviews briefly some general aspects of the enteric nervous system (ENS). Furthermore, the ENS control of epithelial transport is exemplified by a description of the enteric nervous reflexes activated by cholera toxin.

Effects of calcium channel blockade on intestinal fluid secretion: sites of action

Most intestinal secretagogues, including cholera toxin, evoke fluid secretion in part by activating the enteric nervous system (ENS). The enterotoxins that, due to size, cannot pass the intestinal epithelial lining have been proposed to activate the ENS via the release of amines/peptides from the intestinal endocrine cells. It has been shown that calcium channel blockers of the L-type attenuate intestinal fluid secretion. This study was performed on rat jejunal segments to elucidate where calcium channel antagonists interact with the secretory nervous reflex(es) of the ENS. In vivo, net fluid transport, transmural potential difference (PD) and luminal release of serotonin from the enterochromaffin cells were monitored before and after exposing the intestinal mucosa to cholera toxin (20 microg/mL) or the calcium ionophore A23187 (0.5 mM). In vitro, the effects of transmural electrical field stimulation (EFS) on short circuit current (SCC) was investigated using the Ussing chamber method. Cholera toxin and A23187 evoked a net fluid secretion, an increased PD and an augmented luminal release of 5-HT. These effects were markedly attenuated by giving the calcium channel blocker nifedipine i.v. (5.75 micromol kg(-1) body wt). On the other hand, nifedipine (0.02 mM) had no significant effect on the increased SCC caused by EFS in vitro. The results obtained in the in vivo experiments suggest that the nifedipine markedly attenuates the initial event in cholera toxin- and A23187-induced secretion, the release of amines and probably also of peptides from the intestinal endocrine cells. The in vitro experiments seem to exclude an effect of the calcium channel blockade on the efferent part of the secretory nervous reflex.

Calcium channels and intestinal fluid secretion: an experimental study in vivo in rats

Several mechanisms involved in nervous secretory reflex(es) of the enteric nervous system may be dependent on the flux of calcium across the plasma membrane, which may be controlled by voltage-gated calcium channels. In this study, we investigated the importance of plasma membrane calcium channels for intestinal fluid secretion. Two types of studies were performed, in which intestinal net fluid transport in anaesthetized rats was followed with a gravimetric method. First, the effects on intestinal fluid transport of placing A23187, a calcium ionophore, in the intestinal lumen was studied. A23187 induced in a dose-dependent manner a net fluid secretion, which was abolished by giving hexamethonium (10 mg kg(-1) body wt) i.v. or placing lidocaine (1% solution) on the intestinal serosa. Nifedipine (5.75 micromol kg(-1) body wt i.v.) also abolished the fluid secretion caused by the ionophore. In the second study, the effects of various calcium channel blockers (gadolinium chloride, nifedipine, verapamil) were tested on the cholera toxin-induced secretion. It was attenuated by luminal application of gadolinium chloride (1-10 mM) or nifedipine (10-200 microM). Intravenously administered nifedipine (2.5-5.75 micromol kg(-1) body wt) abolished cholera toxin-evoked secretion dose-dependently, whereas verapamil (0.05-1 micromol kg(-1) body wt) was without consistent effect. It is concluded that the fluid secretion evoked by placing A23187 in the intestinal lumen in vivo was induced via an activation of the enteric nervous system. Cholera secretion was attenuated or abolished by calcium channel blockers of the L- or N-type.

The effects of enalapril on the natriuretic response evoked by an oral sodium load in sodium deprived normotensive and hypertensive rats

Previous studies have shown that an oral sodium load during sodium deprivation is excreted faster than an intravenous load. We wanted to study whether the renin-angiotensin-aldosterone system might be associated with this phenomenon and therefore the influence of the angiotensin converting enzyme (ACE) inhibitor enalapril was investigated. The experiments were performed on four strains of rat: spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY) rats, inbred hypertension-prone (SS/Jr) and hypertension-resistant (SR/Jr) Dahl rats. In SHR and WKY rats pretreated with enalapril it was observed that an intravenous sodium load induced a renal sodium excretion which was between two and five times larger than that seen after an oral load. In SR/Jr and SS/Jr rats the sodium excretion was the same regardless of the route of administration. In SS/Jr rats sodium excretion increased three- to fourfold upon sodium repletion, whereas no significant increase was observed in SR/Jr rats. Thus, the present results indicate that an intact renin-angiotensin system is necessary for the interplay between the gastrointestinal tract and kidney.

The intestinal tract and the pathophysiology of arterial hypertension: an experimental study on Dahl rats

Salt depleted rabbits and humans excrete an oral sodium load more quickly via the kidneys than an intravenous one. This has been ascribed to the presence of a sodium sensor in the gastrointestinal tract which in some way can influence renal function. The purpose of this study was to investigate this response in the Dahl rats. Renal and faecal sodium excretion was followed in the two strains of rats (normotensive, saltresistant (SR/Jr) and hypertensive, saltsensitive (SS/Jr) rats). After 4 days on a low salt diet they were given NaCl (1.5 mmol k(-1) body wt) either by gavage or intravenously. SR/Jr rats showed an increased renal sodium excretion both after oral and intravenous sodium repletion. The excretion was 2-3 times greater after th oral than after the intravenous administration. The SS/Jr rats augmented their renal sodium excretion only after the oral load, although the sodium excretion was significantly less than in SR/Jr rats. In fact, during the first 8 h after giving sodium orally the renal excretion of sodium was on an average eight times larger in the SR/Jr than in the SS/Jr rats. Renal excretion of sodium was similar in the two strains after intravenous administration. We conclude that the hypertensive SS/Jr rats have great difficulties in excreting an oral sodium load, a phenomenon that may be of importance in the pathophysiology of arterial hypertension in this strain of rats.

Substance P effects on blood flow, fluid transport and vasoactive intestinal polypeptide release in the feline small intestine

1. Substance P (SP) infusions were given close I.A. to the feline small intestine in vivo in a dose that produced plasma concentrations of 1-5 microM. This infusion regularly evoked a net fluid secretion measured with a gravimetric technique. Concomitantly, the release into blood of vasoactive intestinal polypeptide (VIP), a putative neurotransmitter of the enteric nervous system, increased. 2. The SP-induced fluid secretion was blocked by tetrodotoxin (7 micrograms close I.A.), a blocker of fast sodium channels in excitable tissues, and hexamethonium (10 mg (kg body wt)-1, I.V.), a nicotinic receptor antagonist, suggesting that the SP effect was mediated by the enteric nervous system. In line with this it was shown that the SP-evoked release of VIP was also significantly diminished by hexamethonium. 3. Close I.A. infusions of methionine enkephalin (Met-enkephalin; 7-23 nmol min-1) or electrical stimulation of the sympathetic nerve fibres (6 Hz) to the intestine markedly diminished net fluid secretion and the release of VIP caused by SP given close I.A. 4. The cyclo-oxygenase inhibitor diclofenac (5 mg (kg body wt)-1, I.V.) or the histamine-1 receptor antagonist pyrilamine (10 mg (kg body wt)-1, I.V.) did not influence the fluid secretion caused by SP, indicating that the effects of SP were not due to the actions of prostaglandins or histamine. 5. It is proposed that SP activates a nervous reflex arch that we have shown to be activated by various luminal stimuli, including cholera toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

The small intestine, salt intake and arterial hypertension

The possibility that the small intestine is of importance for the development of arterial hypertension is discussed in relation to the presence of an intestinal sodium sensor and an intestinal natriuretic factor. We propose that an intestinal sodium sensor upon activation releases a factor that evokes renal excretion of sodium. Based on observations made in the Dahl strain of hypertensive rats it is suggested that an attenuation of this mechanism may contribute to the development of arterial hypertension.

Partial purification of a factor from the feline small intestine causing natriuresis in vivo and inhibiting rubidium uptake into renal cells in vitro

Small intestine of cat was homogenized under denaturing condition (6.0 M guanidinium chloride) in the presence of protease inhibitors and molecules in the 500 to 10,000 Da mass range were obtained by sequential ultrafiltrations. This material was separated by gel chromatography (Sephadex G-25), where fractions eluted in the mass range of 500-1000 Da inhibited 86Rb uptake into kidney slices in vitro. Furthermore, the same fractions exhibited a natriuretic effect when given intravenously to anesthetized rats. The gel chromatography fractions were further purified by cation exchange chromatography (CM-Sephadex C-25). Fractions eluted with a NaCl solution of around 250 mM inhibited 86Rb uptake into renal cortical tissue in vitro and showed natriuretic activity when tested in vivo in rats. It is proposed that intestine contains a water soluble natriuretic factor with an apparent molecular mass of 500-1000 Da. This material evokes a natriuresis in vivo and inhibits 86Rb uptake in vitro.

Renal sodium excretion after oral or intravenous sodium loading in sodium-deprived normotensive and spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats that had been on a low sodium diet for 3 days were given 1.5 mmol sodium chloride kg-1 body weight either orally or intravenously. The rats receiving an oral sodium load showed a greater natriuresis than those receiving the same saline load intravenously. No increase of renal sodium excretion was observed when the rats received a hypertonic mannitol solution orally. The cumulative sodium excretion during the 8 h following oral loading was two to three times larger in SHR than in WKY, whereas no difference between strains could be demonstrated after giving saline intravenously. Furthermore, after switching from normal to low sodium diet the rate of decrease of renal sodium excretion was greater in SHR than in WKY rats. It is proposed that there exists a gastrointestinal sensory mechanism for sodium controlling the renal sodium excretion. Furthermore, it is suggested that the function of this mechanism differs between SHR and WKY.

Quantification of tissue damage in the feline small intestine during ischaemia-reperfusion: the importance of free radicals

Intestinal ischaemia is accompanied by characteristic mucosal lesions, which can be graded according to a six-grade system proposed by Chiu et al. (1970). This report describes a continuous grading system which makes it possible to quantify the intestinal damage in connection with ischaemia-reperfusion. The present morphometric method is based on quantitative histological analysis of intestinal biopsies performed on 200 histological sections from 44 cat experiments. Radical formation was quantified by infusing close i.a. a spin trap, OXANOH, which produces a secondary stable radical, OXANO., after reacting with radicals in the tissue. OXANO. concentration was determined in venous blood samples with electron spin resonance. We demonstrate a highly significant correlation between the grading system of Chiu et al. (1970) and the morphometric analysis of this study. The tissue damage was located exclusively in the intestinal villi. Comparing the mucosal damage that occurs during 60 min of intestinal ischaemia (superior mesenteric artery pressure 15-25 mmHg) with that seen during the first 30 min reperfusion this study shows that the villus damage occurring during ischaemia is at least twice as large as the aggravation seen upon reperfusion. Furthermore, the authors demonstrate a significant correlation between rate of radical formation and villus tissue damage particularly during the first 30 min after ischaemia. It is concluded that the proposed quantitative morphological method represents a non-discrete grading system for evaluating tissue damage in connection with ischaemia-reperfusion in the small intestine. The ischaemia itself inflicted a more severe damage to the intestine than reperfusion. A significant correlation between damage and radical formation was demonstrated during the reperfusion. However, the results suggest that factors other than radical formation are of importance in explaining the tissue damage upon reperfusion. The nature of these factors is presently unknown.

Free radicals and pathogenesis during ischemia and reperfusion of the cat small intestine

BACKGROUND/AIM

In spite of the interest in free radicals as mediators of ischemic damage, most information on these species in biological systems is derived from indirect measurements. Our aim was to obtain more direct information concerning sources of free radical production during ischemia and reperfusion.

METHODS

We have performed simultaneous measurement of radical generation, purine metabolites, reduced glutathione, neutrophil infiltration and morphological appearance in the cat small intestine in vivo during 60 minutes of ischemia followed by 60 minutes of reperfusion.

RESULTS

Radical formation increased abruptly on reperfusion and remained elevated in untreated animals. Inhibition by a monoclonal antibody (IB4) against the neutrophil and by allopurinol treatment was paralleled by improvement of biochemical and morphological parameters. The radicals detected during reperfusion could be divided into one component arising directly from the neutrophils, one due to the xanthine oxidase reaction, and one unknown source.

CONCLUSIONS

Neutrophils are a major source of radical production during reperfusion after ischemia. Radicals formed in the xanthine oxidase reaction seem to function as a primer for the neutrophils. The nonsignificant linear correlation between radical formation and morphological appearance suggests that factors other than free radicals are important for the development of intestinal damage after a period of ischemia.

Effects of luminal stimuli on polyamine metabolism in the small intestine of the rat: the role of enteric nerves

The aim of this study was to investigate to what extent polyamine metabolism in the small intestine of the rat is controlled by the enteric nervous system. Polyamine metabolism was followed by measuring the activity of ornithine decarboxylase (ODC) and in some instances also the content of polyamines (putrescine, spermidine and spermine). ODC activity in the intestine was increased when intraluminal pressure was increased and 3 h after placing cholera toxin in the intestinal lumen. Cholera toxin also increased the tissue putrescine content. Atropine or hexamethonium given i.v. did not influence the evoked changes of ODC activity. The pressure induced changes were not decreased by placing lidocaine on the serosal surface. On the other hand, the ODC activity of control segments were decreased by hexamethonium or atropine. The presence of glucose in the intestinal perfusate did not augment tissue ODC activity, neither did the heat stable enterotoxin from Escherichia coli (STa). It is concluded that the effect on polyamine metabolism evoked by luminal pressure or cholera toxin seems not to be mediated via nerves, while nerves seem to influence ODC activity during control conditions. The experiments with enterotoxins suggest that cAMP is the intracellular second messenger controlling intestinal ODC activity.

Involvement of the myenteric plexus in the cholera toxin-induced net fluid secretion in the rat small intestine

BACKGROUND

The enteric nervous system is responsible in vivo for most of the change in fluid transport induced by cholera toxin. The aim of the present study was to investigate the importance of the myenteric plexus in the Intramural reflex responsible for this secretion.

METHODS

Long-term ablation of the myenteric plexus was achieved by serosal application of benzalkonium chloride on jejunal segments in rats.

RESULTS

The treated segments without functioning myenteric plexus showed a normal net fluid absorption. Cholera toxin in this segment only induced a reduction of fluid absorption, whereas in a nontreated ileal segment it concomitantly induced a conspicuous net fluid secretion. Intravenous hexamethonium did not change the cholera toxin response in the treated jejunal segments, whereas vasoactive intestinal polypeptide elicited a marked secretion.

CONCLUSIONS

Benzalkonium chloride treatment eliminated the ability of cholera toxin to induce intestinal secretion. Thus, all afferent fibers in the intramural secretory reflex activated by cholera toxin are probably conveyed via the myenteric plexus, which functions as the integrating center in the enteric nervous system. The Ussing chamber technique using stripped intestinal preparations cannot be used when studying effects of luminal secretagogues.

Nerve involvement in fluid transport in the inflamed rat jejunum

Net fluid transport was measured in denervated jejunal segments of rats infected with larvae of Nippostrongylus brasiliensis. On days 6-9 after nematode inoculation, when the jejunal segment exhibited macroscopic and microscopic signs of inflammation, net fluid absorption was noticeably attenuated compared with control, and in eight of 26 experiments a net fluid secretion was seen. To determine whether enteric nerves participated in the response, intravenous hexamethonium (10 mg/kg body weight) was given or lidocaine (1% solution) was placed on the serosa of the intestinal segment. Both drugs significantly reduced fluid secretion or increased fluid absorption. The effect was more pronounced the lower the rate of fluid absorption or the higher the rate of fluid secretion. The inflammatory response influenced intestinal fluid transport partly via activation of the enteric nervous system. It was estimated that 50-60% of the change in fluid transport caused by the parasite could be ascribed to activation of intramural nervous reflexes. The effect of hexamethonium indicates that a cholinergic synapse is present in the secretory nervous reflux activated by inflammation. Experiments were also performed on animals on days 11-14 after infection when the nematodes had been expelled from the animal. A large net fluid absorption was then recorded.

On the involvement of tachykinin neurons in the secretory nervous reflex elicited by cholera toxin in the small intestine

The possible involvement of tachykinins in the nervous reflex activated by exposing the intestinal mucosa to cholera toxin was investigated in cats and rats. Three types of experiments were performed. In cats the release of tachykinins into blood was followed after placing cholera toxin in the intestinal lumen. In rat experiments a tachykinin receptor antagonist (Spantide II) was given close i.a. and its effect on cholera toxin-evoked fluid secretion was studied. Finally, in rats the effect of cholera toxin on the SP contents in the intestinal mucosa was studied. No release of tachykinins could be demonstrated. Spantide II did not change the rate of cholera toxin induced secretion. The SP content in the intestinal mucosa was not influenced by placing the toxin in the intestinal lumen. Hence, no experimental evidence was obtained for the involvement of a tachykinin neuron in the intestinal secretory nervous reflex activated by cholera toxin. Based on observations reported in the literature the involvement of an acetylcholine/tachykinin neuron in the reflex is tentatively discussed.

An intestinal natriuretic factor

In 1975, reports were published that suggested that the gastrointestinal tract can "taste" the intake of sodium and in some unknown way influence the kidneys to increase sodium excretion. To test whether the intestine contained a natriuretic factor, intestinal tissue from cats was homogenized and fractionated by ultrafiltration to a molecular range of approximately 500-10,000 Da and separated by gel chromatography (Sephadex G25). The fractions were pooled into four large fractions that were assayed for "natriuretic" activity on anesthetized rats. The fraction containing the material with an apparent molecular mass of 500-1,000 Da augmented renal excretion of sodium and water, whereas the other pooled fractions did not exhibit any consistent natriuretic effect. The "natriuretic" fractions from gel filtration were further purified by ion exchange chromatography using a cation exchanger. The natriuretic activity was eluted from the ion exchange chromatography column at a NaCl concentration of 250 mM. Preliminary experiments on Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) suggest that the intestinal influence on renal sodium excretion is more pronounced in SHR than in WKY rats.

Feline intestinal ischemia and reperfusion: relation between radical formation and tissue damage

Experimental ischemia of 15, 30, or 60 min length, followed by 30 min of reperfusion, was produced in situ in the cat small intestine by means of an adjustable arterial clamp. Arterial perfusion pressure was lowered to such an extent that intestinal blood flow decreased from about 25 to 3.5 ml x min-1 x 100 g-1. The rate of free radical formation was followed intermittently with ESR and a modified spin trapping technique in the control period prior to ischemia and at various times during reperfusion. Upon reperfusion radical formation increased above the preischemic control value in all three series of experiments. Cumulative radical production during the 30 min reperfusion period rose from about 3 mumol x 100 g-1 after 15 min ischemia to approximately 4.5 mumol x 100 g-1 after 30 min and 8-10 mumol x 100 g-1 after 60 or 120 min ischemia. At the same time mucosal damage became more pronounced, suggesting a causal connection between tissue damage and radical formation. More specifically, radical production was strongly correlated to histological damage occurring during reperfusion as seen when comparing radical production in animals not experiencing reperfusion damage to those who did. Radical formation in these two groups were 0.35 and 9.0 mumol x 100 g-1, respectively (p < 0.0005).

Actions of serotonin antagonists on cholera-toxininduced intestinal fluid secretion

The effects of several 5-hydroxytryptamine (5-HT) receptor antagonists were tested in rats in vivo on the intestinal fluid secretion evoked by cholera toxin. Five receptor antagonists were used, namely 2-bromolysergic acid diethylamine (2-bromo-LSD), granisetron, ketanserin, methysergide and ondansetron. The drugs were used in doses that inhibited the arterial hypertension and/or bradycardia evoked by 5-HT given i.v. Granisetron and ondansetron markedly diminished cholera-toxin-evoked secretion, whereas ketanserin was without any effect. Methysergide also diminished cholera-toxin-induced fluid secretion particularly when the drug was given as an i.v. infusion. The results are considered in relation to the pathophysiology of cholera secretion and to the current views of receptor subtypes for 5-HT. It is proposed that the receptor involved is a 5-HT3 receptor, possibly also a receptor of the 5-HT1 type. Results from experiments in which 5-HT (20 mM) was placed in the intestinal lumen to evoke an intestinal secretion suggest that the 5-HT3 receptor is located in the villus tissue. It was also demonstrated that zimeldine, an inhibitor of presynaptic 5-HT reuptake, diminished choleraic secretion, an effect that may be ascribed to a 5-HT tachyphylaxis caused by an accumulation of 5-HT in a synaptic cleft.

Tissue osmolality in intestinal villi of four mammals in vivo and in vitro

Using a freezing point depression method osmolality in the intestinal tissue of four mammals (gerbils, guinea-pigs, rabbits and rats) was estimated in vivo, during fluid transport from an isotonic electrolyte-glucose solution. Net fluid transport was also measured. In gerbils, guinea-pigs and rabbits tissue osmolality was also estimated during in vitro conditions. A marked hyperosmolality was observed in vivo in the upper parts of the villi of all four mammals studied. The tissue osmolality was significantly higher than that seen in the same species during in vitro conditions. A villus hyperosmolality was observed also in species which exhibited a net fluid secretion (guinea-pig, rabbit ileum), indicating that the fluid secretion emanated from the intestinal crypts. Based on the results of the present experiments and on observations made in earlier experiments performed on the cat, it is proposed that the villus hyperosmolality is created by a countercurrent multiplier present in the intestinal villus. The hyperosmolar compartment in the villus tissue creates the force that drives fluid from lumen to tissue.

Influence of fibre diameter and probe geometry on the measuring depth of laser Doppler flowmetry in the gastrointestinal application

The measuring depth of laser Doppler flowmetry (LDF) was studied in isolated segments of feline small intestine, using five probes having different fibre geometry, fibre core diameter and fibre centre separation. Recordings were made on the mucosal side at constant systemic blood pressure and venous outflow from the bowel segment. The insertion of a layer of unperfused intestine (average thickness 2.4 mm), between the probe and the perfused bowel wall, reduced the output signal from the flowmeter to an average of 42% of the initial value when a probe with large diameter fibres (700 microns) was used. No LD-signal was obtained through the unperfused tissue layer using the probes with small core diameter fibres (120 microns). Application of a mirror at the serosal surface opposite to the probe, resulted in an average increase of the output signal by 50% using the large fibre diameter probe, whereas no increase was observed with the small fibre probe. Probes based on intermediate fibre diameter and fibre centre separations, gave intermediate results in both experiments. It is concluded that the measuring depth of laser Doppler flowmetry in the gastrointestinal application is highly dependent on the fibre diameter and geometry of the probe. It is possible that, by taking into account these factors, probes may be constructed that are suitable for superficial and transmural measurements.