1. Development of a new telemetry model in rabbits using the DSI TL11M2-C50-PXT implant
Frank Cools*, Ellen Van Eynde, Annik Vanlommel, Sigrid Janssens, Jan D’Aubioul, Brigitte Loenders, David J. Gallacher
Center of Excellence for Cardiovascular Safety Research, Johnson & Johnson Pharmaceutical Research & Development, Division of Janssen Pharmaceutica N.V., B-2340, Beerse, Belgium. * Correspondence:
Introduction
Validation Results
1- Dipyridamole s.c.
Development of new experimental methods in safety pharmacology is a continuous process to provide valuable information on potential new drugs. We developed and validated a new telemetered rabbit model for the measurement of heart rate, blood pressure, ECG parameters and body temperature using the DSI small animal implant (TL11M2-C50-PXT).
*: Significantly different from solvent
Haemodynamic and body temperature changes
Material and Methods
Used animals : healthy female New Zealand white rabbits ( kg)
1- Anaesthesia, analgesia, anti-inflammation
a- Pre-medication:
Motilium Instant® (Domperidon), 2 mg/animal p.o. 30’ before surgery (to avoid regurgitation or leakage of stomach content into the oesophagus)
Temgesic® 0.3 mg/ml (Buprenorphine), mg/kg s.c. (analgesic)
b- Induction of anaesthesia
Ketalar® 50 mg/ml (Ketamine), 10 mg/kg i.m.
Domitor® 1 mg/ml (Medetomidine), 0.17 mg/kg i.m.
c- Intubation
Laryngoscope + end-piece no.1, endotracheal probe with cuff (Büsch size: )
Xylocaine® 2% (Lidocaine), one drop on the pharynx just before inserting the endotracheal tube
d- Maintenance of anaesthesia
Gas-anaesthesia-apparatus: Aestiva 5, Datex-Ohmeda, Meda
Oxygen 100%: spontaneous breathing
1-2% Isoflurane® or higher was added on effect
Evaluation of the anaesthetic state: SpO2 and heart rate monitoring (TuffSat®) and expired CO2 was monitored by means of a ETCO2 monitor, Capnogard, Novametrix, Medical systems Inc.
e- Peri-anaestetic care
Temperature: during anaesthesia, the animals were placed on a heating pad which was kept at 37ºC during surgery
Duodrops®, both eyes were moistened to avoid drying of the cornea
NaCl 0.9% (Baxter®), 25 ml s.c. to ensure a good hydratation status
f- Immediate post-operative medication
Rimadyl® 50 mg/ml (Carprofen), 2 mg/kg s.c.
Baytril® 2.5% (Enrofloxacine), 0.2 ml/kg s.c.
Antisedan® (Atipamezol-HCl), 0.12 ml/kg i.m. as antidote to Domitor®
Heparine Leo®: (Heparine 50 IU/ml), 5 ml s.c. (anticoagulant)
g- Recovery & medication
First day post-surgery: the recovery cage was equipped with an infrared-lamp to keep the implanted rabbit warm
Baytril® 2.5% (Enrofloxacine), 0.2 ml/kg s.c. for 2 days (antibiotic)
Rimadyl® 50 mg/ml (Carprofen), 2 mg/kg, 0.04 ml/kg s.c. for 4 days (anti-inflammatory)
Temgesic® 0.3 mg/ml (Buprenorphine), mg/kg, 0.05 ml/kg s.c. for 4 days (analgesia)
Heparine Leo® (Heparine 50 IU/ml), 2.5 ml for 4 days (anticoagulant)
 2- Surgical procedure: Cannulation of the Carotid Artery
Cannulation of the Carotid artery was found the most practical and less invasive method.
After inserting the cannula in the carotid artery, the arteria was ligated with Prolene 4/0® EH7581, SH-1 needle
The transmitter was secured to the subcutis of the dewlap
The neck incision was closed in two layers (Vicryl 2/0® and 3/0®)
The upper skin sutures were always intradermal sutures to prevent chewing of the sutures
 3- Electrode placement
Extensions and connecting pieces for the electrodes were delivered by DSI
The ECG leads were tunnelled s.c. to the following position:
left electrode: lateral left on the thorax and sewed on the muscles of the last intercostal space just under the skin;
right electrode: right next to the sternum and sewed on the muscles at the level of the first dug of the rabbit.
The result is a ECG lead II like pattern.
The tips of the ECG leads were stripped, hooded and secured (Mersilk 4/0® W586, SH-2 needle)
The skin was closed in one intradermal layer (Vicryl 2/0® V3170, JB needle)
 4- Measurement (see Photograph 1)
To avoid interference of the signals, metal screens were placed around the plastic tray, in which the rabbits can freely move
The plate with the build-in antenna was placed just under the plastic tray inside the metal cage (see photograph)
5- Housing (see Photograph 2)
Separate or group housing
Sawdust on the floor
Toys, hay, apples and carrots in the cage to avoid boredom and biting the sutures in the post-surgery period
Regular handlingxx
1- Measuring cages
2- Housing
Signals
2- Dofetilide p.o.
Corrected QT changes (QTcB)
ECG and blood pressure tracing of a telemetered rabbit recorded with HEM, Notocord 3.5
Validation Protocol
Study design
Two different studies were performed
To assess the possible effects of dipyridamole on blood pressure, heart rate, ECG-parameters (PQ, QRS and QT intervals) and body temperature the solvent and single doses (2.5, 10 and 40 mg/kg s.c.) were administered to awake telemetered rabbits according to an unbalanced cross-over protocol over 4 experimental runs (see scheme below).
The data and graphs of the other measured parameters are available upon request *
Conclusion
This newly designed anaesthesia and surgery protocol ensures a stable and reliable way to implant rabbits with the DSI TL11M2-C50-PXT for measurement of blood pressure, heart rate, ECG parameters and body temperature.
Validation of this model with dipyridamole and dofetilide shows that in the freely moving telemetered rabbit changes in haemodynamic and ECG parameters and body temperature can easily be detected. Moreover, our studies demonstrate that 6 months after implantation and first use the rabbits are healthy and in good condition and the implants are still suitable for measurement of heart rate, blood pressure, ECG parameters and temperature.
References
Unbalanced Cross-over
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A similar study with dofetilide was performed. The solvent and single doses: 5, 10 and 20 µg/kg of dofetilide were administered p.o. according to above-mentioned scheme.
For statistical analysis, data on parameters (except for ECG) were sampled before (0 min) and at 30, 60, 90, 120, 150, 180, 210 and 240 min after administration of the compound or its solvent. For time 0 min the median value of time –20 min to 0 min was calculated. For the other time points the median of 10 min before and after the time points was used. For the ECG, the results of the automatically calculated parameters (PQ, QRS and QT intervals) at time 30, 60, 90, 120, 150, 180, 210 and 240 min, based on the average of 10 consecutive beats just before the selected time points were controlled visually, adjusted if necessary and validated, using a semi-automatic program especially developed for this purpose. For the baseline value (time 0) of the ECG parameters the median value was calculated from 5 time points (-20, -15, ‑10, -5 and 0 min).
The statistical analysis was performed according to the ‘contrast’-statement for longitudinal data analysis in SAS.