Anesthetized Rabbit Model Research Articles

Preclinical Safety and Pharmacokinetics of Heat Stable Oxytocin in Sublingual Fast-Dissolving Tablet Formulation.

The work reported here focuses on an evaluation of a novel heat stable formulation of a uterotonic peptide drug oxytocin involving stability testing under elevated temperatures and toxicokinetic response generated by sublingual (SL) administration in rabbits. The formulation was thermotolerant, maintaining the potency of oxytocin in the form of a fast-dissolving tablet at the end of 2-year storage at 30 °C/65% relative humidity with less than 5% loss in oxytocin content based on analytical high performance liquid chromatography (HPLC). The toxicokinetic results in rabbits showed that the fast-dissolving tablet was safe without any reactogenicity or toxicity associated with SL administration or the excipients present in the formulation. The SL route elicited rapid absorption of oxytocin in plasma within 5 min of administration although lower than intramuscular (IM) administration. IM resulted in area under the curve (AUC) values approximately 5 times higher than SL oxytocin. However, due to the limitations encountered during SL administration in an anesthetized rabbit model, the relevance of heat stable oxytocin formulation that has the flexibility to be adapted in different formats may warrant a human clinical study to determine whether therapeutically relevant plasma levels for treating postpartum hemorrhage can be generated via alternate non-injectable routes of administration.

Sciatic nerve stimulation and its effects on upper airway resistance in the anesthetized rabbit model relevant to sleep apnea.

Obstructive sleep apnea (OSA) is a disorder characterized by collapse of the velopharynx and/or oropharynx during sleep when drive to the upper airway is reduced. Here, we explore an indirect approach for activation of upper airway muscles that might affect airway dynamics, namely, unilateral electrical stimulation of the afferent fibers of the sciatic nerve, in an anesthetized rabbit model. A nerve cuff electrode was placed around the sciatic and hypoglossal nerves to deliver stimulus while airflow, air pressure, and alae nasi electromyogram (EMG) were monitored both before and after sciatic transection. Sciatic nerve stimulation increased respiratory effort, rate, and alae nasi EMG, which persisted for seconds after stimulation; however, upper airway resistance was unchanged. Hypoglossal stimulation reduced resistance without altering drive. Although sciatic nerve stimulation is not ideal for treating OSA, it remains a target for altering respiratory drive. NEW & NOTEWORTHY Previously, sciatic nerve stimulation has been shown to activate upper airway and chest wall muscles. The supposition that resistance through the upper airway would be reduced with this afferent reflex was disproven. Findings were in contrast with the effect of hypoglossal nerve stimulation, which was shown to decrease resistance without changing muscle activation or ventilatory drive.

Hypoglossal nerve stimulation in a pre-clinical anesthetized rabbit model relevant to OSA

We tested the functional effects of hypoglossal (CNXII) stimulation in the anesthetized rabbit before and after injections of saline into the tongue base to obstruct the airway. Data (n = 6) show little or no effect of CN XII trunk stimulation; however, medial branch stimulation (20–100 Hz; 50–500 μs pulse width, and incremental increases from 10 μA) reduced upper airway resistance. Medial branch stimulation was less effective in reducing resistance than anterior advancement of the hyoid. Endoscopic viewing (n-3) of the retropalate showed this region as the narrowest and dynamically changed by anterior hyoid displacement, with less evident effects than CNXII stimulation. We conclude that under these conditions CNXII medial branch stimulation reduces airway resistance, especially after induced obstruction.

An increasing electromechanical window is a predictive marker of ventricular fibrillation in anesthetized rabbit with ischemic heart.

The QTc interval is widely used in Safety Pharmacological studies to predict arrhythmia risk, and the electromechanical window (EMW) and short-term variability of QT intervals (STVQT) have been studied as new biomarkers for drug-induced Torsades de Pointes (TdP). However, the use of EMW and STVQT to predict ventricular fibrillation (VF) has not been elucidated. This study aimed to evaluate EMW and STVQT to predict VF in anesthetized rabbit model of VF. VF was induced by ligation of the left anterior descending and a descending branch of the left circumflex coronary arteries in a sample population of rabbits (n=18). VF was developed 55.6% (10/18). In rabbit with VF, the EMW was significantly higher than in rabbits without VF (96.3 ± 15.6 ms and 49.5 ± 5.6 ms, respectively, P<0.05). STVQT had significantly increased before the onset of VF in rabbits that experienced VF, but not in rabbits that did not experience VF (11.7 ± 1.8 ms and 3.7 ± 0.4 ms, respectively, P<0.05). The EMW and STVQT had better predictive power for VF with higher sensitivity and specificity than the QTc measure. The result suggested that the increasing of EMW, as well as the elevation of STVQT, can potentially be used as biomarkers for predicting of VF.

Evaluation of Index of Cardio-electrophysiological Balance (iCEB) and Short-term Variability of QT Intervals (STV) to Predict the Risk of Ventricular Fibrillation in Anesthetized Rabbit Model of Ischemia/Reperfusion

Evaluation of Index of Cardio-electrophysiological Balance (iCEB) and Short-term Variability of QT Intervals (STV) to Predict the Risk of Ventricular Fibrillation in Anesthetized Rabbit Model of Ischemia/Reperfusion

Characteristics of electromechanical window in anesthetized rabbit models of short QT and long QT syndromes.

The current regulatory guidelines recommend the use of QT interval to assess the risk of arrhythmogenic potential of new chemical entities. Recently, the electromechanical window (EMW), the difference in duration between electrical and mechanical systole, has been proposed as markers for drug-induced torsades de pointes (TdP); however, data of EMW in short QT model are not available. This study aimed to characterize the EMW as a marker for drug-induced ventricular arrhythmias in anesthetized rabbit model of long QT syndrome type 2 (LQT2) and short QT syndrome (SQTS) infused with reference compounds known to lengthen or shorten QT intervals. After rabbits were anesthetized with isoflurane, body surface electrocardiograms and left ventricular pressure were recorded. The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5). The EMW in anesthetized rabbits ranged from 1.3 to 53.3 msec. All three drugs known to lengthen QT intervals prolonged QT and QTcF interval while the EMW was markedly decreased to negative values. Pinacidil significantly produced QT and QTcF shortening and significantly abbreviated the EMW (p < 0.05). This study demonstrated that the EMW is associated with QT intervals (p < 0.001). It is negative in the presence of QT-prolonging drugs while it is more positive in the presence of QT-shortening drugs. The results suggest that the EMW in anesthetized rabbits can be used in drug safety evaluation in addition to the QT interval.

Development and validation of a computational finite element model of the rabbit upper airway: simulations of mandibular advancement and tracheal displacement.

The mechanisms leading to upper airway (UA) collapse during sleep are complex and poorly understood. We previously developed an anesthetized rabbit model for studying UA physiology. On the basis of this body of physiological data, we aimed to develop and validate a two-dimensional (2D) computational finite element model (FEM) of the passive rabbit UA and peripharyngeal tissues. Model geometry was reconstructed from a midsagittal computed tomographic image of a representative New Zealand White rabbit, which included major soft (tongue, soft palate, constrictor muscles), cartilaginous (epiglottis, thyroid cartilage), and bony pharyngeal tissues (mandible, hard palate, hyoid bone). Other UA muscles were modeled as linear elastic connections. Initial boundary and contact definitions were defined from anatomy and material properties derived from the literature. Model parameters were optimized to physiological data sets associated with mandibular advancement (MA) and caudal tracheal displacement (TD), including hyoid displacement, which featured with both applied loads. The model was then validated against independent data sets involving combined MA and TD. Model outputs included UA lumen geometry, peripharyngeal tissue displacement, and stress and strain distributions. Simulated MA and TD resulted in UA enlargement and nonuniform increases in tissue displacement, and stress and strain. Model predictions closely agreed with experimental data for individually applied MA, TD, and their combination. We have developed and validated an FEM of the rabbit UA that predicts UA geometry and peripharyngeal tissue mechanical changes associated with interventions known to improve UA patency. The model has the potential to advance our understanding of UA physiology and peripharyngeal tissue mechanics.

A threshold lung volume for optimal mechanical effects on upper airway airflow dynamics: studies in an anesthetized rabbit model

Increasing lung volume improves upper airway airflow dynamics via passive mechanisms such as reducing upper airway extraluminal tissue pressures (ETP) and increasing longitudinal tension via tracheal displacement. We hypothesized a threshold lung volume for optimal mechanical effects on upper airway airflow dynamics. Seven supine, anesthetized, spontaneously breathing New Zealand White rabbits were studied. Extrathoracic pressure was altered, and lung volume change, airflow, pharyngeal pressure, ETP laterally (ETPlat) and anteriorly (ETPant), tracheal displacement, and sternohyoid muscle activity (EMG%max) monitored. Airflow dynamics were quantified via peak inspiratory airflow, flow limitation upper airway resistance, and conductance. Every 10-ml lung volume increase resulted in caudal tracheal displacement of 2.1 ± 0.4 mm (mean ± SE), decreased ETPlat by 0.7 ± 0.3 cmH(2)O, increased peak inspiratory airflow of 22.8 ± 2.6% baseline (all P < 0.02), and no significant change in ETPant or EMG%max. Flow limitation was present in most rabbits at baseline, and abolished 15.7 ± 10.5 ml above baseline. Every 10-ml lung volume decrease resulted in cranial tracheal displacement of 2.6 ± 0.4 mm, increased ETPant by 0.9 ± 0.2 cmH(2)O, ETPlat was unchanged, increased EMG%max of 11.1 ± 0.3%, and a reduction in peak inspiratory airflow of 10.8 ± 1.0%baseline (all P < 0.01). Lung volume, resistance, and conductance relationships were described by exponential functions. In conclusion, increasing lung volume displaced the trachea caudally, reduced ETP, abolished flow limitation, but had little effect on resistance or conductance, whereas decreasing lung volume resulted in cranial tracheal displacement, increased ETP and increased resistance, and reduced conductance, and flow limitation persisted despite increased muscle activity. We conclude that there is a threshold for lung volume influences on upper airway airflow dynamics.

Comparison of a rat and rabbit hemorrhagic shock model in response to administration of supplemental oxygen following hemorrhage

Previous studies have shown that giving oxygen (O2) post hemorrhage results in an increased mean arterial pressure (MAP) in the anesthetized rat. This study was done to determine if in the larger anesthetized rabbit model the same effect would be observed with supplemental oxygen. Changes in MAP, cardiac output (CO), and heart rate (HR) were observed.MethodsSix rats and five rabbits were studied. Rats (443±10 gm) were anesthetized with 1.5 to 2.0% isoflurane and allowed to spontaneously breath. Initial the inspired O2 content was the same for each group, air at 21% O2. Rabbits (3.8 ± .4 kg) were similarly anesthetized and intubated. Post hemorrhage (PH), both groups were switched to100% oxygen.ResultsData are mean ± SD. In the rat baseline MAP was 76.6 ± 5.2 mmHg, HR 335 ± 30 bpm, CO 154 ± 22 ml/min and in rabbit MAP was 74.8 ± 17, HR 257 ± 42 bpm, CO 841 ± 239 ml/min. At PH in rat MAP was 54.5 ± 9 mmHg, HR was 302 ± 24 bpm, CO 114 ± 29 ml/min, and in rabbit MAP was 32 ± 5 mmHg, HR 277 ± 39 bpm, CO 361 ± 281 ml/min. With oxygen in rat MAP was 85.7 ± 10 mmHg, HR 308 ± 23, CO 110 ± 23 ml/min, and in rabbit MAP was 29 ± 7 mmHg, HR 290 ± 32, CO 303 ± 112 ml/min.ConclusionAdministering O2 following hemorrhage significantly (P = 0.002) increased MAP in the rat hemorrhage model but did not increase MAP in the rabbit model. This data suggest that oxygen may have a unique role in regulating arterial pressure in the hypovolemic rat compared to the rabbit.

Comparative in vivo uroselectivity profiles of anticholinergics, tested in a novel anesthetized rabbit model

The aim of this study was to describe a new experimental animal model for simultaneous measurement of carbachol-induced increase in intravesical pressure and salivary secretion in rabbits. Further, we also compared the in vivo potency and urinary bladder versus salivary gland selectivity profiles of Oxybutynin, Tolterodine, Solifenacin and Darifenacin. The intravesical pressure and salivary secretion were evoked by intra-arterial injection of carbachol (1.5 microg/kg). The carbachol-induced increase in intravesical pressure and salivation was simultaneously recorded before and after increasing doses of test drugs administered intravenously. The basal mean changes in intravesical pressure and salivation subsequent to carbachol administration were in the range of 6.7-7.5 mm Hg and 0.5-0.7 g respectively. Repeated administration of vehicle did not elicit any appreciable changes in intravesical pressure and salivary secretion to carbachol administration from the basal values till 3 h. All the test drugs exhibited a dose-dependent inhibition of carbachol-induced increase in intravesical pressure and salivary secretion. Darifenacin demonstrated a greater potency compared to other muscarinic receptor antagonists for inhibiting carbachol-induced increase in intravesical pressure. It also exhibited functional selectivity for the urinary bladder versus salivary gland. In contrast, Oxybutynin was functionally more selective in inhibiting carbachol-induced increase in salivary secretion. The observed urinary bladder versus salivary selectivity values were 0.6+/-0.2, 1.1+/-0.2, 1.7+/-0.5, and 2.3+/-0.5 for Oxybutynin, Tolterodine, Solifenacin and Darifenacin respectively. These results suggest that the functional selectivity of muscarinic receptor antagonists between urinary bladder and salivary glands can be readily detected in this model. Thus rabbits may represent a useful animal model for evaluating putative bladder selective muscarinic receptor antagonists for the treatment of overactive bladder.

The effect of intravesical ketoprofen on acetylcholine-evoked urinary bladder contractility and detrusor overactivity in the anesthetized rabbit model

Intraurethral procedures such as the transurethral resection of the prostate can generate detrusor overactivity and bladder irritability. The rabbit model of detrusor overactivity has proven to be an excellent model to study the effects of drugs on detrusor overactivity. Using this model, we evaluated the responses to intravesical ketoprofen. In this model, each rabbit is anesthetized and the right external carotid artery is cannulated for blood pressure monitoring. A catheter is inserted through the femoral artery and is used for administration of acetylcholine (Ach). The bladder is exposed and catheterized for bladder pressure monitoring and drug addition and the proximal urethra is ligated. Cystometry is performed, the bladder drained, and 20 ml buffer placed in the bladder. After 30 min Ach is injected proximal to the vesical artery and the response of the bladder and blood pressure is recorded. Ach administration is repeated at 10-min intervals until three consistent responses are obtained. The bladder is drained and 20 ml of ketoprofen (100 microM final concentration) is placed in the bladder. Ach injections are repeated as given above at 10 min intervals and observed for 4 h. At the end of the experiment, a second cystometry is performed. The following is a summary of the results: Ketoprofen had no effect on either micturition pressure or the intravesical volume at micturition. Ketoprofen administration resulted in a progressive 50% decrease in the response to Ach. Ketoprofen mediated a progressive decrease in detrusor overactivity amplitude and frequency, reaching a maximum at 120-180 min.

Is the sarcolemmal or mitochondrial K ATP channel activation important in the antiarrhythmic and cardioprotective effects during acute ischemia/reperfusion in the intact anesthetized rabbit model?

The relative contributions of cardiomyocyte sarcolemmal ATP-sensitive K + (K ATP) and mitochondrial K ATP channels in the cardioprotection and antiarrhythmic activity induced by K ATP channel openers remain obscure, though the mitochondrial K ATP channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we sought to investigate the effects of administration of ATP-sensitive K + channel (K ATP) openers (nicorandil and minoxidil), a specific mitochondrial K ATP channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K ATP channel blocker (HMR 1883; (1-[5-[2-(5-chloro- o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to coronary occlusion as well as prior to post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I ( n = 88), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias was achieved by tightening a previously placed loose silk ligature for 30 min. In Group II ( n = 206), arrhythmias were induced by reperfusion following a 20-min ligation of the left main coronary artery. Both in Group I and Group II, intravenous (i.v.) administration of nicorandil (0.47 mg/kg), minoxidil (0.5 mg/kg), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/minoxidil before coronary artery occlusion increased survival rate (86%, 75%, 75% and 86% vs. 55% in the control subgroup in Group I; 75%, 67%, 67% and 75% vs. 46% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias. In Group II, i.v. administration of nicorandil and minoxidil before coronary artery occlusion significantly decreased myocardial infarct size. However, i.v. administration of nicorandil or minoxidil before reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and minoxidil were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K ATP channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and minoxidil. We conclude that intervention by intravenous administration of nicorandil and minoxidil (through the selective activation of mitochondrial K ATP channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to coronary occlusion. The cardiomyocyte mitochondrial K ATP channel may be a pharmacologically modulable target of cardioprotection and antiarrhythmic activity.

Post-ischemic cardioprotection by A2A adenosine receptors: dependent of phosphatidylinositol 3-kinase pathway.

Activation of myocardial A2A adenosine receptors during reperfusion has been shown to be cardioprotective. The intracellular mechanisms underlying this protection remain unknown. To understand the beneficial effects of activated A2A adenosine receptors in such a state, we investigated whether the enzymes phosphatidylinositol 3-kinase (PI3K) and caspase-3 can account for this post-ischemic cardioprotective effect in an anesthetized rabbit model of myocardial infarction (30 minutes ischemia; 5 hours reperfusion). Administration of the A2A agonist CGS21680 (0.2 microg/kg/min) 5 minutes before reperfusion began (Early) reduced infarct size expressed as a percentage of the area at risk (25.7 +/- 5.3% versus 46.5 +/- 5.3% for the control group; * P < 0.05). Treatment with the A2A agonist 5 minutes after the onset of reperfusion (Late) had no effect on infarct size (38.2 +/- 6.2%). In the presence of a selective inhibitor of PI3K (LY294002), the beneficial effects of CGS21680 on infarct size was no longer observed (43.9 +/- 7.9%). After 5 hours of reperfusion, higher PI3K activity in the ischemic region was observed in the Early group compared with the other experimental groups. Caspase-3 activity was not observed in these different groups. In another set of experiments, PI3K activity was significantly higher during the first 15 minutes of reperfusion in the Early group as compared with the Control group. Caspase-3 activity increased rapidly during the first 15 minutes of reperfusion in the Control group and remained stable in the Early group. These results indicated that post-ischemic cardioprotection afforded by A2A adenosine receptor activation is PI3K-dependent and modulate rapidly other signaling pathways such as caspase-3.

Mitochondrial K ATP channel activation is important in the antiarrhythmic and cardioprotective effects of non-hypotensive doses of nicorandil and cromakalim during ischemia/reperfusion: a study in an intact anesthetized rabbit model

The roles of cardiomyocyte sarcolemmal ATP-sensitive K + (K ATP) and mitochondrial K ATP channels in the cardioprotection and antiarrhythmic activity induced by K ATP channel openers remain obscure, though the mitochondrial K ATP channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we investigated the effects of administration of non-hypotensive doses of ATP-sensitive K + channel (K ATP) openers (nicorandil and cromakalim), a specific mitochondrial K ATP channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K ATP channel blocker (HMR 1883; (1-[5-[2-(5-chloro- o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to and during coronary occlusion as well as prior to and during post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I ( n=80), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias were achieved by tightening a previously placed loose silk ligature for 30 min. In Group II ( n=184), arrhythmias were induced by reperfusion following a 20 min ligation of the left main coronary artery. Both in Groups I and II, early intravenous infusion of nicorandil (100 μg/kg bolus+10 μg/kg/min), cromakalim (0.2 μg/kg/min), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/cromakalim just prior to and during ischemia increased survival rate (75%, 67%, 86% and 75% versus 60% in the control subgroup in Group I; 75%, 75%, 75% and 67% versus 50% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias and significantly decreased myocardial infarct size. However, late intravenous administration of nicorandil or cromakalim at the onset and during reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and cromakalim were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K ATP channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and cromakalim. We, therefore, conclude that intervention by intravenous administration of nicorandil and cromakalim (through the selective activation of mitochondrial K ATP channels), increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to and during coronary occlusion. The mitochondrial K ATP channel may be a potential site of cardioprotection and antiarrhythmic activity.

Laser oximetry: A novel noninvasive method to determine changes in penile hemodynamics in an anesthetized rabbit model.

This study was designed to determine the utility and validity of laser oximetry in measuring changes in penile hemodynamics. Anesthetized male New Zealand White Rabbits were divided into 2 groups, and penile hemodynamics were assessed by either laser oximetry (oxyhemoglobin, deoxyhemoglobin concentration, and oxygen saturation) or intracavernosal pressure (ICP) monitoring during penile erection induced by pelvic nerve stimulation (PNS) or intracavernosal administration of phentolamine, nitroprusside, papaverine, or sildenafil. PNS caused significant frequency-dependent increases in penile ICP. PNS also caused significant increases in penile tissue oxyhemoglobin concentrations and tissue oxygen saturation in a frequency-dependent manner. The changes in oxyhemoglobin concentrations and oxygen saturation correlated with frequency-dependent increases in ICP. Intracavernosal vasoactive drug administration produced significant increases in ICP, tissue oxyhemoglobin concentration, oxygen saturation, and duration of response as a function of increasing drug concentration. Laser oximetry permits reproducible and valid assessment of changes in penile hemodynamics comparable to conventional ICP measurements. Thus, we consider laser oximetry a reliable technique in evaluating penile hemodynamics. Its sensitivity in detecting small changes in oxyhemoglobin concentration and its noninvasive nature make it advantageous over invasive methods such as ICP monitoring and laser Doppler flowmetry.

Proarrhythmic effects of intravenous quinidine, amiodarone, D-sotalol, and almokalant in the anesthetized rabbit model of torsade de pointes.

The proarrhythmic effects of four antiarrhythmic agents were examined during alpha1-adrenoceptor stimulation in chloralose-anesthetized rabbits. Each dose of almokalant (26, 88, and 260 microg/kg), D-sotalol, quinidine, or amiodarone (each 3, 10, and 30 mg/kg) was infused i.v. over 5 min and there was a 20-min interval between each infusion. D-sotalol and almokalant evoked torsade de pointes (TdP) and other arrhythmics, frequently. The incidences of TdP were 0, 50, and 40% after administering the first, second, and third doses of the nonselective I(Kr) inhibitor D-sotalol, respectively. Similarly, these values were 20, 40, and 33% after administering the first, second, and third doses, respectively, of the selective I(Kr) inhibitor almokalant. Quinidine elicited only a few arrhythmics, but not TdP. Quinidine, D-sotalol, and almokalant evoked conduction blocks in a dose-related manner (p < 0.05) and prolonged QT and QT(c) intervals (p < 0.05). Amiodarone neither prolonged QT and QT(c) nor evoked ventricular tachyarrhythmias, blocks, or other proarrhythmias. In conclusion, these results show no direct correlation between the occurrence of TdP and the infusion rate or dose of anti-arrhythmics. Furthermore, the lack of TdP with quinidine warns of false-negative results in the applied model.

Sentinel node biopsy and lymphoscintigraphy with a technetium 99m labeled blue dye in a rabbit model

Background. Lymphatic mapping for sentinel node biopsy in breast cancer and melanoma usually involves initial peritumoral injection of a radioisotope, gamma camera detection of the sentinel lymph node several hours prior to the operation, and separate perioperative injection of a blue dye. We have developed a combined approach using technetium 99m labeled blue dye (Evans Blue) for use in lymphoscintigraphy that may be injected as a single dose just prior to the operation. Methods. In an anesthetized rabbit model we dissected a hind limb to display the popliteal node and afferent lymphatic. Technetium 99m Evans Blue (99mTc-EB) (22 MBq; 0.5 mL) was injected subdermally in the dorsum of the paw. Simultaneous digital and gamma camera images were obtained at 14 time intervals to 30 minutes post injection. For each of these time intervals the percentage of radioactivity and percentage blueness of the popliteal node were determined. Urine and afferent lymphatic fluid were analyzed by chromatography. The popliteal node was excised post mortem, placed into solvent solutions and analyzed for blueness and radioactivity. Results. Time-activity curves for radioactivity and time-blueness curves for Evans Blue uptake showed strong correlation (r = 0.958). Lymph analysis suggested 99mTc-EB is mainly bound to endogenous proteins. Urine was radioactive but not colored, 99mTc-EB being metabolized and excreted in the urine as 1,7-diamino-8-naphthol-2,4-disulfonic acid. Prolonged exposure of node to solvents did not dissociate any blue coloration or radioactivity. Conclusions.99mTc-EB and Evans Blue are simultaneously retained and concentrated in the sentinel lymph node. This process is rapid and reproducible. 99mTc-EB migrates at the same rate as Evans Blue in lymph, where it is transported as bound to endogenous proteins. These dye molecules are metabolized by reductive cleavage in the liver and then excreted renally as colorless, radioactive metabolites. This novel agent has the potential to facilitate lymphatic mapping and subsequent sentinel node biopsy for a range of solid malignancies including breast cancer and melanoma. (Surgery 2002;131:44-9.)

Rabbits as models for impotence research.

The anesthetized rabbit model is useful and has many advantages: ability to perform neurophysiological studies; more administration routes, including intracavernous injection; haemodynamic measurements in parallel to measurements of intracavernous pressure or penile volume; and direct measurement of intracavernosal pressure and blood flow. This model has been evaluated with many different types of drugs. The conscious rabbit model is a simple and valid model for the assessment of compounds with potential for treatment of ED. It offers several methodological advantages as a screening model for compounds with erection stimulating properties. It was clearly successful in demonstrating the efficacy and the mechanism of the new potent and selective PDE5 inhibitor vardenafil. The model was also effective in demonstrating erection-generating properties through other mechanisms, eg PDE3 inhibitors and alpha-receptor blockers. In conclusion, both anaesthetized rabbit model and the newly developed conscious-rabbit models are well-suited for studies in impotence research.

Ischemia-reperfusion lung injury in rabbits: mechanisms of injury and protection.

To study the mechanisms responsible for ischemia-reperfusion lung injury, we developed an anesthetized rabbit model in which the effects of lung deflation, lung inflation, alveolar gas composition, hypothermia, and neutrophils on reperfusion pulmonary edema could be studied. Rabbits were anesthetized and ventilated, and the left pulmonary hilum was clamped for either 2 or 4 h. Next, the left lung was reperfused and ventilated with 100% oxygen. As indexes of lung injury, we measured arterial oxygenation, extravascular lung water, and the influx of a vascular protein (131I-labeled albumin) into the extravascular space of the lungs. The principal results were that 1) all rabbits with the deflation of the lung during ischemia for 4 h died of fulminant pulmonary edema within 1 h of reperfusion; 2) inflation of the ischemic lung with either 100% oxygen, air, or 100% nitrogen prevented the reperfusion lung injury; 3) hypothermia at 6-8 degreesC also prevented the reperfusion lung injury; 4) although circulating neutrophils declined during reperfusion lung injury, there was no increase in interleukin-8 levels in the plasma or the pulmonary edema fluid, and, furthermore, neutrophil depletion did not prevent the reperfusion injury; and 5) ultrastructural studies demonstrated injury to both the lung endothelium and the alveolar epithelium after reperfusion in deflated lungs, whereas the inflated lungs had no detectable injury. In summary, ischemia-reperfusion injury to the rabbit lung can be prevented by either hypothermia or lung inflation with either air, oxygen, or nitrogen.

Treatment With 1-cis Diltiazem Before Reperfusion Reduces Infarct Size in the Ischemic Rabbit Heart In Vivo

1-cis Diltiazem, an optical isomer of diltiazem, protects against myocardial dysfunction in vitro, whereas its Ca2+ channel blocking activity is about 100 times less potent than that of diltiazem. However, there is no evidence that 1-cis diltiazem actually protects against ischemia/reperfusion injury in vivo. To assess this, we employed an anesthetized rabbit model, where the left circumflex artery was occluded for 15 min and reperfused for 360 min. Treatment with diltiazem before and during ischemia (bolus 200 μg/kg and 15 μg/kg per minute for 25 min, i.v.; 575 total) showed slightly depressed hemodynamic parameters, while 1-cis diltiazem (1150 μg/kg) had no effect. Treatment with 1-cis diltiazem produced a high recovery of the thickening fraction and limited the infarct size in a dose-dependent manner. Furthermore, the treatment with 1-cis diltiazem (1150 μg/kg) or diltiazem (575 μg/kg) 5 min before reperfusion also limited the infarct size, but not after reperfusion. These results suggest that 1-cis diltiazem affects some events in the onset of reperfusion, independently of Ca2+-channel-blocking action. Our observations are the first to show that 1-cis diltiazem demonstrated its cardioprotective action in the ischemic rabbit heart in vivo.