Conscious Animal Model Research Articles

Brain activity studied with magnetic resonance imaging in awake rabbits.

We reviewed fMRI experiments from our previous work in conscious rabbits, an experimental preparation that is advantageous for measuring brain activation that is free of anesthetic modulation and which can address questions in a variety of areas in sensory, cognitive, and pharmacological neuroscience research. Rabbits do not struggle or move for several hours while sitting with their heads restrained inside the horizontal bore of a magnet. This greatly reduces movement artifacts in magnetic resonance (MR) images in comparison to other experimental animals such as rodents, cats, and monkeys. We have been able to acquire high-resolution anatomic as well as functional images that are free of movement artifacts during several hours of restraint. Results from conscious rabbit fMRI studies with whisker stimulation are provided to illustrate the feasibility of this conscious animal model for functional MRI and the reproducibility of data gained with it.

Activation of Cold‐Sensitive Afferents Inhibits Aberrant Irritant‐evoked Cardiopulmonary Reflexes in the Spontaneously Hypertensive (SH) Rat

Inhalation of irritants activates airway vagal afferent nerves, evoking cardiopulmonary reflexes. Evidence suggests that cardiopulmonary reflexes evoked by irritant/pollution inhalation are remodeled from bradycardia in normal subjects to tachycardia and ventricular arrhythmia in patients with pre‐existing cardiovascular disease. We have shown similar remodeling in the spontaneously hypertensive (SH) rat: selective activation of airway vagal afferent nerves via inhalation of the TRPA1‐specific agonist allyl isothiocyanate (AITC) evoked parasympathetic‐mediated reflex bradycardia in normotensive wistar‐kyoto rats but evoked sympathetically‐mediated tachycardia and premature ventricular contractions (PVCs) in spontaneously hypertensive (SH) rats.Activation of TRPA1‐expressing airway vagal afferents also evokes cough in some conscious animal models. Cough reflexes have been shown to be inhibited by nasal stimulation with L‐menthol via activation of TRPM8 ion channels expressed on cold‐sensitive trigeminal afferents which regulate brainstem respiratory networks. Here, we investigated the cardiopulmonary reflexes evoked by inhalation of L‐menthol (150mg/ml) alone and in combination with AITC (4.7mg/ml) in SH rats. L‐menthol inhalation alone had no effect on respiration/heart rate, but, when inhaled during AITC inhalation, L‐menthol selectively inhibited the AITC‐evoked tachyarrhythmia and tachypnea. Importantly, the inactive isomer D‐menthol (150mg/ml) failed to affect AITC‐evoked sympathoexcitatory reflexes. In another set of studies, the selective TRPM8 agonist WS‐12 (300mM) also inhibited the AITC‐evoked tachyarrhythmia. Therefore, we conclude that aberrant cardiopulmonary reflexes evoked by irritant inhalation are reduced by activation of menthol‐sensitive pathways within the airways. This data supports the therapeutic potential of menthol treatment against irritant‐evoked cardiopulmonary reflexes.

Multiscale entropy analysis of heart rate variability in heart failure, hypertensive, and sinoaortic-denervated rats: classical and refined approaches.

The analysis of heart rate variability (HRV) by nonlinear methods has been gaining increasing interest due to their ability to quantify the complexity of cardiovascular regulation. In this study, multiscale entropy (MSE) and refined MSE (RMSE) were applied to track the complexity of HRV as a function of time scale in three pathological conscious animal models: rats with heart failure (HF), spontaneously hypertensive rats (SHR), and rats with sinoaortic denervation (SAD). Results showed that HF did not change HRV complexity, although there was a tendency to decrease the entropy in HF animals. On the other hand, SHR group was characterized by reduced complexity at long time scales, whereas SAD animals exhibited a smaller short- and long-term irregularity. We propose that short time scales (1 to 4), accounting for fast oscillations, are more related to vagal and respiratory control, whereas long time scales (5 to 20), accounting for slow oscillations, are more related to sympathetic control. The increased sympathetic modulation is probably the main reason for the lower entropy observed at high scales for both SHR and SAD groups, acting as a negative factor for the cardiovascular complexity. This study highlights the contribution of the multiscale complexity analysis of HRV for understanding the physiological mechanisms involved in cardiovascular regulation.

Cortical and Medullary Tissue Perfusion and Oxygenation in Experimental Septic Acute Kidney Injury.

To determine whether there is a decrease in renal cortical or medullary perfusion and oxygenation in a conscious large animal model of hyperdynamic septic shock with acute kidney injury. Interventional animal study. University-affiliated research institute. Eight merino ewes. Sheep were surgically instrumented with pulmonary and renal artery flow probes in the renal cortex and medulla, combination fiber-optic probes comprising a fluorescence optode to measure tissue PO2, and a laser-Doppler probe to assess tissue perfusion. Sepsis was induced by infusion of live Escherichia coli for 24 hours followed by 24-hour recovery. In unanesthetized normal sheep, resting levels of cortical and medullary tissue PO2 were 29.5 ± 4.4 and 29.1 ± 4.3 mm Hg, respectively. During infusion of E. coli, hyperdynamic sepsis developed with hypotension, tachycardia, increased cardiac output, increased renal blood flow, oliguria, decreased creatinine clearance, and increased serum creatinine. Renal oxygen delivery increased while renal oxygen consumption was unchanged. During sepsis, cortical tissue PO2 increased from 29.4 ± 4.3 to 36.3 ± 3.5 mm Hg (p < 0.001), whereas medullary oxygenation decreased from 29.6 ± 4.7 to 13.1 ± 2.7 mm Hg (p < 0.001). Cortical perfusion was not significantly changed, but medullary perfusion decreased (671 BPU [500-900 BPU] to 480 BPU [349-661 BPU]; geometric mean [95% CI]; p < 0.001). In a large animal model of hyperdynamic sepsis, renal hyperemia was associated with preserved cortical oxygenation and perfusion, but decreased medullary oxygenation and perfusion. Medullary hypoxia due to intrarenal blood flow redistribution may be one of the factors causing acute kidney injury in sepsis.

Fabrication and Implantation of Miniature Dual-element Strain Gages for Measuring &lt;em&gt;In Vivo&lt;/em&gt; Gastrointestinal Contractions in Rodents.

Gastrointestinal dysfunction remains a major cause of morbidity and mortality. Indeed, gastrointestinal (GI) motility in health and disease remains an area of productive research with over 1,400 published animal studies in just the last 5 years. Numerous techniques have been developed for quantifying smooth muscle activity of the stomach, small intestine, and colon. In vitro and ex vivo techniques offer powerful tools for mechanistic studies of GI function, but outside the context of the integrated systems inherent to an intact organism. Typically, measuring in vivo smooth muscle contractions of the stomach has involved an anesthetized preparation coupled with the introduction of a surgically placed pressure sensor, a static pressure load such as a mildly inflated balloon or by distending the stomach with fluid under barostatically-controlled feedback. Yet many of these approaches present unique disadvantages regarding both the interpretation of results as well as applicability for in vivo use in conscious experimental animal models. The use of dual element strain gages that have been affixed to the serosal surface of the GI tract has offered numerous experimental advantages, which may continue to outweigh the disadvantages. Since these gages are not commercially available, this video presentation provides a detailed, step-by-step guide to the fabrication of the current design of these gages. The strain gage described in this protocol is a design for recording gastric motility in rats. This design has been modified for recording smooth muscle activity along the entire GI tract and requires only subtle variation in the overall fabrication. Representative data from the entire GI tract are included as well as discussion of analysis methods, data interpretation and presentation.

Fabrication and implantation of miniature dual-element strain gages for measuring in vivo gastrointestinal contractions in rodents.

Gastrointestinal dysfunction remains a major cause of morbidity and mortality. Indeed, gastrointestinal (GI) motility in health and disease remains an area of productive research with over 1,400 published animal studies in just the last 5 years. Numerous techniques have been developed for quantifying smooth muscle activity of the stomach, small intestine, and colon. In vitro and ex vivo techniques offer powerful tools for mechanistic studies of GI function, but outside the context of the integrated systems inherent to an intact organism. Typically, measuring in vivo smooth muscle contractions of the stomach has involved an anesthetized preparation coupled with the introduction of a surgically placed pressure sensor, a static pressure load such as a mildly inflated balloon or by distending the stomach with fluid under barostatically-controlled feedback. Yet many of these approaches present unique disadvantages regarding both the interpretation of results as well as applicability for in vivo use in conscious experimental animal models. The use of dual element strain gages that have been affixed to the serosal surface of the GI tract has offered numerous experimental advantages, which may continue to outweigh the disadvantages. Since these gages are not commercially available, this video presentation provides a detailed, step-by-step guide to the fabrication of the current design of these gages. The strain gage described in this protocol is a design for recording gastric motility in rats. This design has been modified for recording smooth muscle activity along the entire GI tract and requires only subtle variation in the overall fabrication. Representative data from the entire GI tract are included as well as discussion of analysis methods, data interpretation and presentation.

The effects of nasal irritant induced responses on breathing and cough in anaesthetized and conscious animal models

There is little evidence to support the down-regulation of coughing from the nose. The cough response to citric acid (CA) was studied in anesthetized and conscious guinea pigs after nasal pretreatment with saline, 1% DMSO, allylisothiocyanate (TRPA1 agonist) and allylisothiocyanate +AP-18 (TRPA1 antagonist). Cough was induced by adding citric acid (CA) to the tracheal perfusion in anaesthetized animals, or by inhaling 0.4M CA in conscious animals. The cough response was counted from the dose response curves, airflow traces and cough sound analysis.In conscious animals, nasal allylisothiocyanate induced reproducible, dose dependent nasal symptoms and a significant drop in respiratory rate. Cough induced by CA was suppressed after nasal allylisothiocyanate (p<0.05), and this effect was prevented by AP-18 (1mM). In anaesthetized animals, nasal allylisothiocyanate induced a significant drop in respiratory rate. Cough induced subsequently by CA was suppressed when compared to baseline and vehicle responses (p<0.05).The reasons for the suppression of CA induced cough by TRPA1 agonist applied to the nose are not clear and remain to be elucidated.

Predictive value of the anesthetized guinea pig model to conscious animal models and humans

Predictive value of the anesthetized guinea pig model to conscious animal models and humans

Alexander Leaf, MD (1920–2012)—A tribute to a life in physiology and medicine

EDITORIAL article Front. Physiol., 25 January 2013Sec. Cardiac Electrophysiology Volume 4 - 2013 | https://doi.org/10.3389/fphys.2013.00006

Visceral pain readouts in experimental medicine

Visceral pain is studied at the level of the primary afferent fiber, spinal cord, subcortical, and cortical levels electrophysiologically and using brain imaging, which provides an objective measure of excitation at each level. However, correlation of these with actual perception of pain in conscious animal models has been problematic, and we rely on indirect measures in most preclinical research. The main method is electromyographic recording of abdominal muscle contractions in response to colorectal distension (CRD), which may reflect reflexes set up at several levels of the above pathway. Several experimental treatments for visceral pain have failed in clinical trials, possibly because of failure to translate from preclinical observations on CRD responses in animals to perception of spontaneous events in patients. Therefore, we need more objective outcomes. In this NGM issue, Hultin et al. show feasibility of routine recordings of cortical evoked electrical potentials (CEP) using implanted cranial electrodes in response to graded CRD in rats. CEP comprised three temporal components with latencies of approximately 20-50 ms, 90-180 ms, and 300 ms, which were reproducible and graded in intensity and latency with distension pressure. From this basic study it is clear that colorectal evoked potentials can be recorded reliably in awake rats and may serve as an objective marker for centrally projecting visceral sensory signals in rodents. It remains to be seen how these responses are affected by drugs under development for clinical management of visceral pain, and if there is improved translation.

Myocardial ischemia, reperfusion, and infarction in chronically instrumented, intact, conscious, and unrestrained mice

In the United States alone, the National Heart, Lung, and Blood Institute (NHLBI) has invested several hundred million dollars in pursuit of myocardial infarct-sparing therapies. However, due largely to methodological limitations, this investment has not produced any notable clinical application or cardioprotective therapy. Among the major methodological limitations is the reliance on animal models that do not mimic the clinical situation. In this context, the limited use of conscious animal models is of major concern. In fact, whenever possible, studies of cardiovascular physiology and pathophysiology should be conducted in conscious, complex models to avoid the complications associated with the use of anesthesia and surgical trauma. The mouse has significant advantages over other experimental models for the investigation of infarct-sparing therapies. The mouse is inexpensive, has a high throughput, and presents the ability of one to create genetically modified models. However, successful infarct-sparing therapies in anesthetized mice or isolated mouse hearts may not be successful in more complex models, including conscious mice. Accordingly, a conscious mouse model of myocardial ischemia and reperfusion has the potential to be of major importance for advancing the concepts and methods that drive the development of infarct-sparing therapies. Therefore, we describe, for the first time, the use of an intact, conscious, and unrestrained mouse model of myocardial ischemia-reperfusion and infarction. The conscious mouse model permits occlusion and reperfusion of the left anterior descending coronary artery in an intact, complex model free of the confounding influences of anesthetics and surgical trauma. This methodology may be adopted for advancing the concepts and ideas that drive cardiovascular research.

Nandrolone decanoate's effects on biochemical blood parameters in rat

Accurate and chronic measurements of various parameters in conscious animals are fundamental for depicting pathological chronic conditions and their etiology in many experimental models, but they are often difficult to achieve. The aim of the present work was to develop and describe step-by-step a reproducible surgical procedure and daily manipulations for continuous, chronic use of conscious rats as models towards a better understanding of various cardiovascular and renal diseases and the testing of novel pharmacological drugs. The complete apparatus involved the use of a series of specialized devices (harness, rotating swivel, revolving arm) supporting a flexible, permanently implanted vascular catheter into the left femoral artery up to the abdominal aorta connected to a miniaturized individual peristaltic pump for delivering fluid at a constant rate. Such a set-up also enabled easy, quick, and reproducible daily blood sampling for the evaluation of more than 20 parameters, including the monitoring of heart rate (HR) and blood pressure in freely moving conscious rats. The overall success and survival rate reached 98% over 14 days and could be extended further. This model represents a much needed and valuable advance in surgical research techniques to evaluate the hemodynamic, hematological, biochemical, pharmacokinetic, and toxicological profile of any new drugs over time in conscious animal models such as rats. What makes this procedure satisfactory is the long-term reliable arterial access and reproducibility of the methodological approach for accurate and continuous measurements, minimizing the stress or invasiveness associated with the use of currently employed systems.

Vitreal Pharmacokinetics of Peptide-Transporter-Targeted Prodrugs of Ganciclovir in Conscious Animals

To delineate the vitreal pharmacokinetics of dipeptide monoester prodrugs of ganciclovir (GCV) with conscious rabbit model using ocular microdialysis and to compare with published results from anesthetized model. New Zealand albino male rabbit was selected as the animal model. Conscious animal ocular microdialysis technique with permanently implanted probes was employed to delineate the pharmacokinetics of GCV, L-valine-GCV (Val-GCV), and dipeptide monoester GCV prodrugs [val-val and L-glycine-val (Gly-Val)] after intravitreal administration. This work employs conscious model to evaluate vitreal pharmacokinetic parameters and compares the results with previously published data from anesthetized animal, thereby demonstrating the effect of anesthesia on the vitreal disposition of dipeptide prodrugs of GCV. Results have revealed that area under curve (AUC), clearance, and last measured plasma concentration (C(last)) for all 4 compounds were significantly altered in a conscious animal relative to the anesthetized model, while mean residence time (MRT) was significantly reduced. However, the AUCs of regenerated Val-GCV and GCV from Gly-Val-GCV and Val-Val-GCV were found to be unchanged, suggesting higher ocular metabolism in conscious animals. This study for the first time delineates the vitreal pharmacokinetics of a GCV prodrug in conscious animals and compares the data with anesthetized animals. Lower vitreal exposure levels were obtained in case of conscious animal model; however, the elimination rates were not influenced by anesthesia.

Drug–anaesthetic interaction in phMRI: the case of the psychotomimetic agent phencyclidine

Pharmacological magnetic resonance imaging (phMRI) provides a powerful means to map the effects of drugs on brain activity, with important applications in pharmacological research. However, phMRI studies in preclinical species are often conducted under general anaesthesia as a means to avoid head motion and to minimise the stress induced by the procedure. Under these conditions, the phMRI response to the drug of interest may be affected by interactions with the anaesthetic agent, with consequences for the interpretation of the data. Here, we have investigated the phMRI response to phencyclidine (PCP), an NMDA receptor blocker, in the halothane-anaesthetised rat for varying levels of anaesthesia and different PCP challenge doses. PCP induces psychotic-like symptoms in humans and laboratory animals and is widely applied as a pharmacological model of schizophrenia. However, PCP possesses anaesthetic properties per se, and its interactions with halothane might result in significant effects on the phMRI activation patterns. We observed two qualitatively different patterns of phMRI response. At 0.5 mg/kg iv PCP and 0.8% halothane maintenance anaesthesia, the lowest doses explored, an activation of discrete cortico-limbo-thalamic structures was observed, consistent with neuroimaging studies in humans and 2-deoxyglucose functional mapping in conscious animal models. However, higher anaesthetic concentrations or higher PCP challenge doses resulted in complete abolition of the positive response and in a widespread cortical deactivation (negative response). In the intermediate regime, we observed a dichotomic behaviour, with individual subjects showing one pattern or the other. These findings indicate a dose-dependent drug-anaesthetic interaction, with a complete reversal of the effects of PCP at higher challenge doses or HT concentrations.

Hemorrhagic Shock Data Mining Project: Poincare Plot Analysis

In this study, Poincare plot analysis predicts volume status in conscious animal models of hemorrhagic shock. We examine beat‐to‐beat systolic pressure variability as a function of volume status. Archived data from 10 conscious sheep that were hemorrhaged from a catheter in the aorta then volume resuscitated are examined. Hemorrhage and resuscitation were followed by equilibration periods. All subjects survived. A major/minor axis ratio of the Poincare plot that is greater than 5 is a useful index of shock.

Selective Role for TRPV4 Ion Channels in Visceral Sensory Pathways

Although there are many candidates as molecular mechanotransducers, so far there has been no evidence for molecular specialization of visceral afferents. Here, we show that colonic afferents express a specific molecular transducer that underlies their specialized mechanosensory function: the transient receptor potential channel, vanilloid 4 (TRPV4). We found TRPV4 mRNA is highly enriched in colonic sensory neurons compared with other visceral and somatic sensory neurons. TRPV4 protein was found in colonic nerve fibers from patients with inflammatory bowel disease, and it colocalized in a subset of fibers with the sensory neuropeptide CGRP in mice. We characterized the responses of 8 subtypes of vagal, splanchnic, and pelvic mechanoreceptors. Mechanosensory responses of colonic serosal and mesenteric afferents were enhanced by a TRPV4 agonist and dramatically reduced by targeted deletion of TRPV4 or by a TRP antagonist. Other subtypes of vagal and pelvic afferents, by contrast, were unaffected by these interventions. The behavioral responses to noxious colonic distention were also substantially reduced in mice lacking TRPV4. These data indicate that TRPV4 contributes to mechanically evoked visceral pain, with relevance to human disease. In view of its distribution in favor of specific populations of visceral afferents, we propose that TRPV4 may present a selective novel target for the reduction of visceral pain, which is an important opportunity in the absence of current treatments.

Utilizing Cross Correlation Coefficient for Estimation the Detection Range of Michigan Probe

Event Abstract Back to Event Utilizing Cross Correlation Coefficient for Estimation the Detection Range of Michigan Probe Yu-Chieh Kao1*, C.H.Y Wang1 and F.S Jaw1 1 National Taiwan University, Taiwan The technique of large-scale ensemble recording is a trend to explore neuronal network in conscious state. Thus, extracellular multi-channel electrodes and spike sorting algorithm are indispensable for ensemble recording. However, in such recording, the same action potential could be detected by more than one recording site yet determined as from different neurons. Since the collected spikes are in different waveforms and amplitudes apiece owing to different conductive distances and relatively poor selectivity of these electrodes, overestimation of neurons from different recording sites may occur. In this study, cross-correlation coefficient as a laconic method was introduced to determine multiple spikes of a single source recorded from different recording sites, likewise to estimate the detection range of the electrode. The characteristics of neural signal gathered from cross-correlation coefficient help us to strike a balance between the selectivity of electrode and collected spike amount, then modify and strengthen the efficiency of multi-channel spike-sorting algorithm. Therefore, this method enhances the practical utility of multi-channel electrodes in the analysis of neuronal activities in conscious animal model. Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Neuroinformatics of Cognition Citation: Kao Y, Wang C and Jaw F (2008). Utilizing Cross Correlation Coefficient for Estimation the Detection Range of Michigan Probe. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.358 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Dec 2008; Published Online: 15 Dec 2008. * Correspondence: Yu-Chieh Kao, National Taiwan University, Taipei, Taiwan, f95548021@ntu.edu.tw Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Yu-Chieh Kao C.H.Y Wang F.S Jaw Google Yu-Chieh Kao C.H.Y Wang F.S Jaw Google Scholar Yu-Chieh Kao C.H.Y Wang F.S Jaw PubMed Yu-Chieh Kao C.H.Y Wang F.S Jaw Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Cardiac sympathetic nerve activity and ventricular fibrillation during acute myocardial infarction in a conscious sheep model

The association between cardiac sympathetic nerve activity (CSNA) and ventricular fibrillation (VF) during acute myocardial infarction (MI) has not been assessed in conscious animal models. During the first 60 min post-MI, mean blood pressure (MBP), heart rate (HR), and CSNA were recorded continuously in 20 conscious sheep. Resistant sheep (group A, n = 10) were compared with susceptible sheep (group B, n = 10) who developed fatal VF (n = 7) or sustained ventricular tachycardia (VT, n = 3). The mean time to VF/VT was 28.1 +/- 3.3 min. In group B, MBP, HR, and CSNA were averaged at each consecutive minute from baseline at 14 min before the onset of VF/VT and compared with time-matched values in group A. When compared with those of group A, indexes of CSNA burst size increased before the onset of VF/VT: burst area/minute (F(13,208) = 2.17, P = 0.01) and burst area/100 beats (F(13,208) = 1.86, P = 0.04). By contrast, burst frequency indexes were not significantly different: burst frequency (F(13,208) = 1.6, P = 0.09) and burst incidence (F(13,208) = 1.48, P = 0.13). In group A, CSNA burst area/min and burst area/100 beats did not change across this time period (F(13,117) = 0.97, P = 0.5, F(13,117) = 0.96, P = 0.7) but increased with time in group B (F(13,91) = 2.3, P = 0.01; and F(13,91) = 2.25, P = 0.01). Between-group comparisons demonstrated no differences in time of onset of ventricular ectopic beats: 18.5 (range 12-24) in group A versus 15.0 min (range 7-22) in group B (Mann-Whitney U-test, P = 0.09). Pre-MI baroreflex slopes were similar: R-R slopes were 11.8 +/- 2 and 15.6 +/- 1.1 ms/mmHg (t(18) = -1.6, P = 0.14). CSNA slopes were -1.8 +/- 0.3 and -2.3 +/- 0.2%/mmHg (t(18) = -1.4, P = 0.2). An early increase in CSNA burst size indexes (before 60 min post-MI), mediated by an excitatory sympathetic reflex, is important in the genesis of VF/VT.

Cardiac sympathetic nerve activity and ventricular fibrillation during acute myocardial infarction in ambulent sheep

The association between cardiac sympathetic nerve activity (CSNA) and ventricular fibrillation (VF) following acute myocardial infarction (MI) has not been assessed in a conscious animal model. For 60 minutes post-MI, blood pressure (BP), heart rate (HR) and CSNA were recorded continuously. Resistant sheep (group A, n=10) were compared to susceptible sheep (group B, n-10) who developed fatal VF or sustained ventricular tachycardia VT. MI was induced under pethidine/diazepam analgesia by applying sustained tension to a coronary suture.

Glibenclamide Action on Myocardial Function and Arrhythmia Incidence in the Healthy and Diabetic Heart

Myocardial sarcolemmal ATP-dependent potassium (KATP) channels, which are normally closed by high ATP concentration, open during ischemia when ATP generation decreases favoring K(+) efflux. This reduces action potential duration (APD) decreasing the time of Ca(2+) influx and Ca(2+) overload. This behavior suggested that they might be involved in the protection against stunning and arrhythmias and in the mechanism of ischemic preconditioning. Sulfonylureas, used as hypoglycemic agents for the treatment of type 2 diabetes also block myocardial KATP channels prolonging APD during ischemia, which by allowing Ca(2+) entry for a longer period of time, is potentially harmful to the heart. Controversial findings have been reported regarding the protective effect of sulfonylureas. Due to their importance in the clinical setting, their action on the heart of large conscious animal models is relevant. The effect of glibenclamide, a representative sulfonylurea, has been studied in a conscious sheep model submitted to regional 12 min ischemia. Glibenclamide (0.4 mg/kg) completely blocked KATP channels, as assessed by monophasic APD, producing a deleterious effect on reperfusion-induced arrhythmias and myocardial recovery from stunning in normal animals. This adverse effect was more noticeable in alloxan-induced diabetic sheep, where a lower dose (0.1 mg/kg) inhibited KATP channel opening worsening mechanical recovery and arrhythmia incidence. However, glibenclamide did not abolish ischemic late preconditioning against stunning and arrhythmias in normal animals. Because diabetic sheep do not develop this cardioprotective phenomenon, probably due to KATP channel dysfunction, it was not possible to assess glibenclamide effect on preconditioning in this pathological condition. In conclusion, in large conscious animals, glibenclamide interferes with the beneficial action of KATP channel opening during acute ischemia-reperfusion events both in normal and diabetic animals. Therefore, despite some studies claiming no added cardiovascular risk due to glibenclamide treatment, this pharmacological agent should be further investigated to ensure its safe administration in patients with concurrent heart disease.