Novel Calcium Phosphate Promotes Interbody Bony Fusion in a Porcine Anterior Cervical Discectomy and Fusion Model

STUDY DESIGN

Experimental porcine anterior cervical discectomy and fusion (ACDF) model: a proof-of-concept study.

OBJECTIVE

The effect of monetite synthetic bone graft containing calcium pyrophosphate (Ca-PP) and β-tricalcium phosphate (β-TCP) on cervical spinal fusion in a non-instrumented two-level large animal model.

SUMMARY OF BACKGROUND DATA

ACDF is the gold standard surgical technique for the treatment of degenerative cervical spinal diseases. However, pseudarthrosis associated with increased patient morbidity occurs in approximately 2,6% of the surgeries. Synthetic bone graft (SBG) may enhance bony fusion and subsequently decrease the risk of pseudarthrosis. Recent studies on monetite-based synthetic bone grafts for use in large cranial defects in humans have shown promising bone healing results, necessitating further investigation of their use in cervical spinal fusion.

METHODS

Four adult female Danish Göttingen mini-pigs received partial cervical anterior discectomy and intervertebral defects at an upper and lower level. One defect was filled with SBG and the other was left empty. Bony fusion was evaluated using computed tomography (CT) at three-month intervals for 12 months. Fifteen months post-surgery, the animals were euthanized for further ex vivo qualitative histopathological and micro-CT evaluations. Fusion rates were compared using Fisher´s exact test at each time point.

RESULTS

Increased interbody bony fusion rates were observed at synthetic bone graft levels (4/4) compared with control levels (0/4) evaluated by CT at 6- and 9-months post-surgery (P= 0.029). Fusion was observed at all synthetic bone graft levels 12 months post-surgery and at only one control level. Histopathological evaluation confirmed high-quality interbody bony fusion at all synthetic bone graft levels, and fusion by spondylosis at one control level.

CONCLUSION

This proof-of-concept study provides preliminary evidence of a novel, Ca-PP -and β-TCP-containing monetite SBG that promotes bony fusion compared to a negative control in a clinically relevant porcine model of ACDF.

LEVEL OF EVIDENCE

N/A.

A battery-less implantable glucose sensor based on electrical impedance spectroscopy

The ability to perform accurate continuous glucose monitoring without blood sampling has revolutionised the management of diabetes. Newer methods that can allow measurements during longer periods are necessary to substantially improve patients' quality of life. This paper presents an alternative method for glucose monitoring which is based on electrical impedance spectroscopy. A battery-less implantable bioimpedance spectroscope was designed, built, and used in an in vivo study on pigs. After a recovery period of 14 days post surgery, a total of 236 subcutaneous bioimpedance measurements obtained from intravenous glucose tolerance tests, with glucose concentration ranges between 77.4 and 523.8 mg/dL, were analyzed. The results show that glucose concentrations estimated by subcutaneous bioimpedance measurements correlate very well to the blood glucose reference values. The pigs were clinically healthy throughout the study, and the postmortem examinations revealed no signs of adverse effects related to the sensor. The implantation of the sensor requires minor surgery. The implant, being externally powered, could in principle last indefinitely. These encouraging results demonstrate the potential of the bioimpedance method to be used in future continuous glucose monitoring systems.

Toward Global Harmonization of Training and Certification of Specialists in Laboratory Animal Veterinary Medicine

Laboratory animal medicine (LAM) is a corner stone of animal-based research and has been a veterinary specialty for over 60 y. Today 5 Colleges of LAM (American, European, Japanese, Korean, and Indian) that certify specialists (Diplomates) in LAM are members of the International Association of Colleges of LAM (IACLAM). Goals of IACLAM are to support the development of new Colleges of LAM, to harmonize expectations for the knowledge and skills of newly certified LAM Diplomate, and to harmonize the standards (best practices) for training and examination of candidates among the member Colleges. IACLAM recently conducted an in-depth review and comparison of oversight, training, credentialing, and examination standards in the 5 Colleges as part of an initiative to create a framework for harmonization and consistency for these activities across the 5 Colleges. The process has led to an agreement on recommendations for knowledge and skill requirements for a newly certified Diplomate, as described by each College in a detailed role delineation document (RDD). The RDD is based on task analyses of the work responsibilities of laboratory animal veterinary Diplomates. This agreement is an important step toward the goal of global harmonization of LAM Diplomate training. Further efforts are planned for areas such as training, research, publication, and examination. This paper describes the role and content of the RDD and lists the differences and similarities among the RDDs of 5 Colleges of LAM.

Training Pigs for Oral Glucose Tolerance Test-Six Years' Experience of a Refined Model

Animal models of human diseases are important in biomedical research. When using animals for scientific purposes, the 3Rs (replace, reduce, refine) should be considered. Refinement of animal models is essential to ensure best use of animals, which is important for ethical reasons and to retrieve reliable research data. The present publication describes improvements to an oral glucose tolerance test (OGTT) model for pigs published in 2016. Historical data from 42 pigs were used to describe improvements in the training technique over six years. Pigs of various breeds and ages can be trained to bottle-feed glucose dissolved in water to undergo OGTT. This publication describes different tips and techniques to apply for successful training and will help researchers to minimize exclusions of pigs due to unsuccessful training. The improvements are an important contribution to the 3Rs.

Exploring the GLP-1-GLP-1R axis in porcine pancreas and gastrointestinal tract in vivo by ex vivo autoradiography

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) increases insulin secretion from pancreatic beta-cells and GLP-1 receptor (GLP-1R) agonists are widely used as treatment for type 2 diabetes mellitus. Studying occupancy of the GLP-1R in various tissues is challenging due to lack of quantitative, repeatable assessments of GLP-1R density. The present study aimed to describe the quantitative distribution of GLP-1Rs and occupancy by endogenous GLP-1 during oral glucose tolerance test (OGTT) in pigs, a species that is used in biomedical research to model humans.

RESEARCH DESIGN AND METHODS

GLP-1R distribution and occupancy were measured in pancreas and gastrointestinal tract by ex vivo autoradiography using the GLP-1R-specific radioligand ¹⁷⁷Lu-exendin-4 in two groups of pigs, control or bottle-fed an oral glucose load. Positron emission tomography (PET) data from pigs injected with ⁶⁸Ga-exendin-4 in a previous study were used to retrieve data on biodistribution of GLP-1R in the gastrointestinal tract.

RESULTS

High homogenous uptake of ¹⁷⁷Lu-exendin-4 was found in pancreas, and even higher uptake in areas of duodenum. Low uptake of ¹⁷⁷Lu-exendin-4 was found in stomach, jejunum, ileum and colon. During OGTT, there was no increase in plasma GLP-1 concentrations and occupancy of GLP-1Rs was low. The ex vivo autoradiography results were highly consistent with to the biodistribution of ⁶⁸Ga-exendin-4 in pigs scanned by PET.

CONCLUSION

We identified areas with similarities as well as important differences regarding GLP-1R distribution and occupancy in pigs compared with humans. First, there was strong ligand binding in the exocrine pancreas in islets. Second, GLP-1 secretion during OGTT is minimal and GLP-1 might not be an important incretin in pigs under physiological conditions. These findings offer new insights on the relevance of porcine diabetes models.

Guided bone tissue regeneration using a hollow calcium phosphate based implant in a critical size rabbit radius defect

Long bone fractures are common and sometimes difficult to treat. Autologous bone (AB), bovine bone and calcium phosphates are used to stimulate bone growth with varying results. In the present study, a calcium phosphate cement (CPC) that previously showed promising grafting capabilities was evaluated for the first time in a long bone defect. A radius defect of 20 mm was created in twenty rabbits. The defect was filled by either a hollow CPC implant that had been previously manufactured as a replica of a rabbit radius through indirect 3D printing, or by particulate AB as control. Defect filling and bone formation was evaluated after 12 weeks by combining micro computed tomography (μCT) and scoring of 3D images, together with histomorphometry and histology. The μCT and histomorphometric evaluations showed a similar amount of filling of the defect (combining graft and bone) between the CPC and AB group, but the scoring of 3D images showed that the filling in the CPC group was significantly larger. Histologically the AB graft could not be distinguished from the new bone. The AB treated defects were found to be composed of more bone than the CPC group, including reorganised cancellous and cortical bone. Both the CPC and AB material was associated with new bone formation, also in the middle of the defect, which could result in closing of the otherwise critically sized gap. This study shows the potential for an indirectly 3D printed implant in guided bone regeneration in critically sized long bone defects.

Bioavailability of subcutaneous and intramuscular administrated buprenorphine in New Zealand White rabbits

Background

Buprenorphine is one of the most used analgesics for postoperative pain in rabbits. The recommended dose in rabbits (0.01–0.05 mg/kg) is the same for intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration, despite lack of pharmacokinetic data. Five male and five female New Zealand White rabbits (mean ± SD body weight 3.1 ± 0.3 kg) were administered 0.05 mg/kg buprenorphine by the IV, IM and SC routes and 0.1 mg/kg by the SC route, in a cross-over design with two-week wash-out periods between treatments. Blood was collected before, and up to 8 h post buprenorphine injection, for determination of serum levels by UPHLC-MS/MS.

Results

The area under the time concentration curve (AUC_0-t) was lower after SC (398 ± 155 ng/mL/min) than IM (696 ± 168 ng/mL/min, p < 0.001) and IV (789 ± 189 ng/mL/min, p < 0.001) administration. The maximum serum concentration was lower after SC (2.2 ± 1.4 ng/mL) than after IM (11 ± 3.2 ng/mL) administration (p < 0.001). The bioavailability was lower after SC (50 ± 19%) than after IM (95 ± 21%) administration (p = 0.006). The elimination half-life was longer after SC (260 ± 120 min) than after IM (148 ± 26 min, p = 0.002) as well as IV (139 ± 33 min) injection (p < 0.001). An increase in the SC dose from 0.05 to 0.1 mg/kg resulted in an increase in the area under the time concentration curve of 50% in female (p = 0.022) and 165% in male rabbits (p < 0.001). The bioavailability did not change in the females (36 ± 14%, p = 0.6), whereas it increased in the males (71 ± 23%, p = 0.008).

Conclusions

The lower bioavailability of 0.05 mg/kg buprenorphine after SC administration could explain the lack of efficacy seen in clinical pain studies in rabbits, using this route. For immediate pain relief, IV or IM administration is therefore be recommended, whereas SC administration may be useful to sustain analgesic serum levels, once efficient pain relief has been achieved. The current data do not support an increase in dose to compensate for the lower SC bioavailability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-020-02618-7.

The effect of housing environment on bone healing in a critical radius defect in New Zealand White rabbits

In animal studies on bone healing, the effect of housing space and physical activity are seldom taken into account. Bone formation was evaluated in New Zealand White rabbits (mean ± SEM BW: 3.9 ± 0.11 kg) with a critical bone defect after 12 weeks of rehabilitation in pair-housing in 3 m² large floor pens (Floor, n = 10) or standard single housing in 0.43 m² cages (Cage, n = 10). In the randomised full-factorial study, a bone replica of calcium phosphate cement (CPC, n = 10) or autologous bone (AB, n = 10) was implanted in the unilateral 20 mm radius defect. Post-mortem, the oxidative capacity was measured by citrate synthase (CS) activity in M. quadriceps and the defect filling volume and density evaluated by microcomputer tomography (μ-CT). Histology sections were evaluated by subjective scoring and histomorphometry. Fourteen rabbits remained until the end of the study. Group Floor (n = 7; 3 CPC + 4 AB) had a higher CS activity and a larger bone defect filling volume and lower density by μ-CT measurements than group Cage (n = 7; 3 CPC + 4 AB). Three out of four rabbits in AB-Floor presented fusion of the defect with reorganisation of trabecular bone, whereas three of four in AB-Cage showed areas of incomplete healing. Floor rabbits had a higher score of bony fusion between the radius and ulna than Cage rabbits. There were no differences between groups in histomorphometry. The study found that a larger housing space increased physical activity and promoted bone formation.

Nursing and training of pigs used in renal transplantation studies

The pig is commonly used in renal transplantation studies since the porcine kidney resembles the human kidney. To meet the requirements of intense caretaking and examination without stress, a 2-week socialisation and training programme was developed. Conventional cross-breed pigs (n = 36) with high health status were trained for 15 min/day in a four-step training programme before kidney transplantation. The systematic training resulted in calm animals, which allowed for ultrasound examination, blood sampling and urine sampling without restraint. When a 2-methacryloyloxyethyl phosphorylcholine polymer-coated jugular catheter introduced via the auricular vein was used for post-operative blood sampling, clotting was avoided. To assess renal function, urinary output was observed and creatinine and cystatin C were measured; the latter was not found to be useful in recently transplanted pigs. The results presented contribute to the 3Rs (refine, reduce, replace).

A new synthetic granular calcium phosphate compound induces new bone in a sinus lift rabbit model

OBJECTIVES

The aim of this study was to investigate if a synthetic granular calcium phosphate compound (CPC) and a composite bisphosphonate-linked hyaluronic acid-calcium phosphate hydrogel (HABP·CaP) induced similar or more amount of bone as bovine mineral in a modified sinus lift rabbit model.

MATERIAL AND METHODS

Eighteen adult male New Zeeland White rabbits, received randomly one of the two test materials on a random side of the face, and bovine mineral as control on the contralateral side. In a sinus lift, the sinus mucosa was elevated and a titanium mini-implant was placed in the alveolar bone. Augmentation material (CPC, HABP·CaP or bovine bone) was applied in the space around the implant. The rabbits were euthanized three months after surgery and qualitative and histomorphometric evaluation were conducted. Histomorphometric evaluation included three different regions of interest (ROIs) and the bone to implant contact on each installed implant.

RESULTS

Qualitative assessment (p = <.05), histomorphometric evaluations (p = < .01), and implant incorporation (p = <.05) showed that CPC and bovine mineral induced similar amount of bone and more than the HABP·CaP hydrogel.

CONCLUSION

CPC induced similar amount of bone as bovine mineral and both materials induced more bone than HABP·CaP hydrogel.

CLINICAL SIGNIFICANCE

The CPC is suggested as a synthetic alternative for augmentations in the maxillofacial area.

Anaesthesia and changes in parameters that reflect glucose metabolism in pigs – a pilot study

Pigs are commonly used in diabetes research due to their many physiological similarities to humans. They are especially useful in imaging procedures because of their large size. However, to achieve imaging procedures the pig must lie completely still, and thus needs to be anaesthetized. Most anaesthetic drugs used in laboratory animals affect carbohydrate metabolism by the inhibition of insulin release. The aim of this pilot study was primarily to develop an anaesthetic protocol for pigs that did not have an effect on blood glucose levels throughout the 3 h of anaesthesia; and secondly, to evaluate the most promising protocol in combination with an oral glucose tolerance test (OGTT). Two anaesthetic protocols were used in four growing pigs. Intravenous propofol infusion caused hyperglycaemia in three out of four pigs within 5–10 min after induction and was therefore excluded. Intravenous infusion with tiletamine, zolazepam and butorphanol (TZB) for 3 h did not affect blood glucose levels. The pigs underwent OGTT twice, once without anaesthesia and once with TZB induction after glucose intake. Anaesthesia during OGTT resulted in a lower area under the curve (AUC) of glucose ( P < 0.05), higher AUC of glucagon ( P < 0.05) and an insulin response less than 10% of that during OGTT without anaesthesia. In conclusion, long-term infusion anaesthesia with TZB does not affect glucose homeostasis in pigs. However, the protocol is not effective when combined with OGTT, as glucose, insulin and glucagon levels are affected.

Assessment of ketamine/medetomidine anaesthesia in the New Zealand White rabbit

OBJECTIVE

To compare the characteristics of anaesthesia induced with four dose combinations of ketamine/medetomidine.

DESIGN

Prospective randomized study. Animals Five female New Zealand White (NZW) rabbits of approximately 2.3 kg.

METHODS

Rabbits were given one of four drug combinations (25/0.25; 15/0.5; 15/0.25 and 10/0.5 mg kg^-1 IM) on four successive occasions with a four day interval. Response to injection and then arterial blood gas and cardiovascular parameters were recorded at predetermined time points. Toe and ear pinch reflexes gave measures of total duration of surgical anaesthesia and total sleep time. Analyses used repeated measures analysis of variance.

RESULTS

Induction was smooth with little reaction to injection and intubation achieved easily. Two combinations (15/0.25, 10/0.5) produced moderate hypoxaemia (mean pO₂ < 8.0 kPa) and two (25/0.25, 15/0.5) very marked hypoxaemia (mean pO₂ < 5.3 kPa). This was reversed within 15 minutes of oxygen administration and all rabbits recovered uneventfully. Heart rates fell in all cases, with only minimal effects on arterial blood pressure and no cardiac arrhythmias. Mean duration of surgical anaesthesia was significantly longer for dose groups 25/0.25 (57 ± 12 minutes) and 15/0.5 (59 ± 17 minutes, p = 0.01) compared to dose group 15/0.25 (27 ± 8 minutes). Only three animals in the 10/0.5 mg kg^-1 group achieved surgical anaesthesia. Mean duration of loss of the ear pinch reflex was similar between doses, being, respectively, 64 ± 13, 81 ± 7, 60 ± 22 and 62 ± 24 minutes. Sleep time was significantly longer for the 15/0.5 dose (112 ± 10 minutes) compared to 15/0.25 (86 ± 22 minutes, p = 0.04). Sleep times for the 25/0.25 and 10/0.5 mg kg^-1 doses were, respectively, 103 ± 23 and 108 ± 12 minutes.

CONCLUSIONS

Ketamine/medetomidine reliably produces smooth induction and recovery in the NZW rabbit, but due to the degree of hypoxaemia produced, should only be used with simultaneous provision of oxygen.

CLINICAL RELEVANCE

Currently recommended dose rates of ketamine/medetomidine for minor procedures such as ovariohysterectomy in rabbits (25 mg/0.5 mg kg^-1) are unnecessarily high; a dose of 15/0.25 mg kg^-1 should be adequate for 15-30 minutes of surgical anaesthesia.

Anaesthesia with ketamine/medetomidine in the rabbit: influence of route of administration and the effect of combination with butorphanol

OBJECTIVE

To compare the characteristics of anaesthesia induced with ketamine/medetomidine administered by the subcutaneous and intramuscular routes and to assess the effects of the addition of butorphanol to this combination.

STUDY DESIGN

Prospective randomised study.

ANIMALS

Six female New Zealand White rabbits.

METHODS

Rabbits were given one of four combinations of ketamine and medetomidine (K/M) either subcutaneously (SC) or intramuscularly (IM) on four successive occasions with a 7-day interval between treatments. The dose combinations were; 15/0.25 mg kg^-1 SC; 15/0.25 mg kg^-1 IM; 15/0.5 mg kg^-1 SC, and 15/0.25 mg kg^-1 together with 0.4 mg kg^-1 butorphanol (K/M/B) SC. The effects of anaesthesia on arterial blood gas values and cardiovascular variables were recorded at predetermined time points. Toe and ear pinch reflexes were judged to determine the duration of surgical anaesthesia. Loss of the righting reflex was used to measure the duration of sleep time. Analyses used repeated measures analysis of variance.

RESULTS

All groups lost the righting reflex and ear pinch response. Three animals in the groups that received K/M alone lost their toe pinch reflex, whereas four lost this reflex when given K/M/B. Time of onset of loss of the righting, toe and ear pinch reflexes did not differ significantly among the groups. The higher dose combination of medetomidine with ketamine and the combination of K/M/B produced a greater duration of loss of the ear pinch response than the lower dose of K/M administered by either route. No significant differences were found among the groups in the duration of loss of the toe pinch reflex. All animals developed a moderate bradycardia (mean heart rate <166 beats minute^-1) and moderate hypoxaemia (mean P_aO₂ < 6.0 kPa). Animals given butorphanol showed the greatest reduction in respiratory rate (31 ± 13 breaths minute^-1, p < 0.05) but this was not reflected in any significant differences in arterial PCO₂, PO₂ or pH among the groups.

CONCLUSIONS

Administration of K/M by the SC route produced equivalent effects in comparison to intramuscular administration. The addition of butorphanol increased the duration of anaesthesia, but produced a slight increase in the degree of respiratory depression. All dose rates resulted in hypoxaemia so oxygen should be administered when these combinations are used in rabbits.

CLINICAL RELEVANCE

Subcutaneous administration is both technically simpler and may cause less discomfort to the animal than IM injection, and so is preferred. The combination of K/M with butorphanol has relatively minor effects on the depth and duration of anaesthesia, so offers little advantage to the use of K/M alone.

Mycotoxins in laboratory rodent feed

Twenty-one batches of fixed-formula rodent diets from three feed manufacturers were tested for the presence of five mycotoxins: deoxynivalenol (DON), nivalenol (NIV), HT-2 toxin, T-2 toxin and ochratoxin A (OTA). Five batches were also tested for the presence of zearalenone (ZEN) and six batches for aflatoxins. Detectable levels of DON (up to 298 μg/kg), NIV (up to 118 μg/kg), OTA (up to 3.1 μg/kg) or ZEN (up to 26.7 μg/kg) were found in samples from all manufacturers. Three batches contained two (DON or NIV and OTA or ZEN) and one batch contained three (DON, OTA and ZEN) different mycotoxins. Aflatoxins, T-2 and HT-2 were not detected in any of the batches. The concentrations of mycotoxins detected in the feed were low, but indicated that feed ingredients, probably the cereal ingredients, were contaminated by mycotoxins. Since mycotoxins are known to have toxic and/or immunosuppressive effects, non-contaminated ingredients should be used for production of laboratory animal feed. The results imply that an improved quality control of ingredients used for laboratory rodent feed should be implemented.

Establishment of a Refined Oral Glucose Tolerance Test in Pigs, and Assessment of Insulin, Glucagon and Glucagon-Like Peptide-1 Responses

Diabetes mellitus is increasing worldwide and reliable animal models are important for progression of the research field. The pig is a commonly used large animal model in diabetes research and the present study aimed to refine a model for oral glucose tolerance test (OGTT) in young growing pigs, as well as describing intravenous glucose tolerance test (IVGTT) in the same age group. The refined porcine OGTT will reflect that used in children and adolescents. Eighteen pigs were obtained one week after weaning and trained for two weeks to bottle-feed glucose solution, mimicking the human OGTT. The pigs subsequently underwent OGTT (1.75 g/kg BW) and IVGTT (0.5 g/kg BW). Blood samples were collected from indwelling vein catheters for measurements of glucose and the diabetes related hormones insulin, glucagon and active glucagon-like peptide-1. The study confirmed that pigs can be trained to bottle-feed glucose dissolved in water and thereby undergo an OGTT more similar to the human standard OGTT than previously described methods in pigs. With the refined method for OGTT, oral intake only consists of glucose and water, which is an advantage over previously described methods in pigs where glucose is given together with feed which will affect glucose absorption. Patterns of hormonal secretion in response to oral and intravenous glucose were similar to those in humans; however, the pigs were more glucose tolerant with lower insulin levels than humans. In translational medicine, this refined OGTT and IVGTT methods provide important tools in diabetes research when pigs are used as models for children and adolescents in diabetes research.

Intravenous sufentanil-midazolam versus sevoflurane anaesthesia in medetomidine pre-medicated Himalayan rabbits undergoing ovariohysterectomy

Objective

To compare physiological effects of sufentanil-midazolam with sevoflurane for surgical anaesthesia in medetomidine premedicated rabbits.

Study design

Prospective, randomized controlled experimental study.

Animals

Eighteen female Himalayan rabbits, weight 2.1 ± 0.1 kg.

Methods

Premedication with 0.1 mg kg⁻¹ medetomidine and 5 mg kg⁻¹ carprofen subcutaneously, was followed by intravenous anaesthetic induction with sufentanil (2.3 μg mL⁻¹) and midazolam (0.45 mg mL⁻¹). After endotracheal intubation, anaesthesia was maintained with sufentanil-midazolam (n = 9) or sevoflurane (n = 9). Ovariohysterectomy was performed. Intermittent positive pressure ventilation was performed as required. Physiological variables were studied perioperatively. Group means of physiologic data were generated for different anaesthetic periods. Data were compared for changes from sedation, and between groups by anova. Post-operatively, 0.05 mg kg⁻¹ buprenorphine was administered once and 5 mg kg⁻¹ carprofen once daily for 2–3 days. Rabbits were examined and weighed daily until one week after surgery.

Results

Smooth induction of anaesthesia was achieved within 5 minutes. Sufentanil and midazolam doses were 0.5 μg kg⁻¹ and 0.1 mg kg⁻¹, during induction and 3.9 μg kg⁻¹ hour⁻¹ and 0.8 mg kg⁻¹ hour⁻¹ during surgery, respectively. End-tidal sevoflurane concentration was 2.1% during surgery. Assisted ventilation was required in nine rabbits receiving sufentanil-midazolam and four receiving sevoflurane. There were no differences between groups in physiologic data other than arterial carbon dioxide. In rabbits receiving sevoflurane, mean arterial pressure decreased pre-surgical intervention, heart rate increased 25% during and after surgery and body weight decreased 4% post-operatively. Post-operative problems sometimes resulted from catheterization of the ear artery.

Conclusion

Sevoflurane and sufentanil-midazolam provided surgical anaesthesia of similar quality. Arterial blood pressure was sustained during sufentanil-midazolam anaesthesia and rabbits receiving sevoflurane lost body weight following ovariohysterectomy. Mechanical ventilation was required with both anaesthetic regimens.

Clinical relevance

Anaesthesia with sufentanil-midazolam in medetomidine premedicated healthy rabbits is useful in the clinical and the research setting, as an alternative to sevoflurane.

Insulin treatment of streptozotocin-induced diabetes re-establishes the patterns in carbohydrate, fat and amino acid metabolisms in growing pigs

The effects of streptozotocin (STZ) were studied in eight high-health herd-certified Yorkshire × Swedish Landrace pigs (32.5 ± 2.6 kg initial body weight [BW]), and an insulin treatment protocol was developed to re-establish their metabolisms. A single intravenous dose of 150 mg STZ/kg BW successfully induced hyperglycaemia and alterations in their fat and protein metabolisms. Within 13 h post-STZ treatment blood glucose concentration had fallen to a range of 1.3 to 4.7 mmol/L. Hypoglycaemia was promptly treated with 0.5 g glucose/kg BW intravenously. All the pigs became hyperglycaemic with blood glucose concentrations >23 mmol/L within 48 h post-STZ. Two days post-STZ serum C-peptide concentrations fell below 60 ρmol/L in all the pigs and remained below 96 ρmol/L for five weeks until the end of the study. The pigs were left untreated for one week after STZ injection. At the end of this week 13-fold and nine-fold increases in serum concentrations of triglycerides and non-esterified fatty acids, respectively, were observed. Also, at this time-point a three-fold increase in the concentration of branched-chain amino acids (BCAA) was observed, and alanine and taurine were decreased by approximately 70% and 40%, respectively. During the week when the pigs were untreated, a reduced weight gain was observed, but after the onset of insulin treatment the daily weight gain was at least as good as that of conventional high-health pigs. Then a subcutaneous treatment with short-acting insulin was initiated. The initial dose of 2/3 IU/kg BW daily, divided between two doses, was gradually increased to 1 IU/kg BW. Within three weeks, the insulin treatment restored the metabolic changes in carbohydrate, fat and protein metabolisms produced by the STZ. In conclusion, the results underscore the usefulness of this animal model in translational research as insulin treatment re-establishes the changes in carbohydrate, fat and amino acid metabolisms observed in STZ-diabetic pigs and resolves clinical signs of disease similar to those in humans.

Anaesthesia in medetomidine premedicated New Zealand White rabbits: a comparison between intravenous sufentanil-midazolam and isoflurane anaesthesia for orthopaedic surgery

Eighteen female New Zealand White rabbits (3.9 ± 0.4 kg) were anaesthetized with sufentanil-midazolam by intravenous infusion (SUF-MID, n = 9) or isoflurane (ISO, n = 9) for bilateral creation of an osteochondral defect in the medial femur condyle. Subcutaneous premedication with 0.1 mg/kg medetomidine and anaesthesia induction by intravenous infusion of 1.1 µg/kg sufentanil and 0.2 mg/kg midazolam were identical in both groups. During surgery (60 min), the effects on respiratory and circulatory variables serum lactate, total protein and blood glucose were examined. Intermittent positive pressure ventilation (IPPV) was initiated if apnoea lasted>30 s or if end-tidal CO2 ≥8 kPa. The righting reflex was lost in 3 min. IPPV was necessary during most of the anaesthesia for most of the rabbits. Maintenance doses during surgery were 2.0 µg/kg/h sufentanil and 0.4 mg/kg/h midazolam, and 1.4% isoflurane, respectively. Mean arterial blood pressure (MAP) was higher in group SUF-MID than group ISO during surgery (63 ± 12 vs 50 ± 8 mmHg). In group ISO the heart rate was higher during surgery than before anaesthesia (197 ± 26 vs 158 ± 40 bpm) as was blood glucose (9 ± 2 vs 12 ± 3 mmol/L). Serum lactate levels remained unchanged whereas total protein decreased in both groups. Time to recover from anaesthesia did not differ between groups (20 min). Intravenous sufentanil-midazolam infusion provided surgical anaesthesia with a higher MAP than isoflurane anaesthesia. The protocol can be useful in situations in which gas anaesthesia cannot be used or in animals with limited cardiovascular reserves. However, IPPV is necessary.

Continuous intravenous anaesthesia with sufentanil and midazolam in medetomidine premedicated New Zealand White rabbits

BACKGROUND

Anaesthesia in rabbits is associated with a high mortality rate, compared to that in cats and dogs. Total intravenous anaesthesia (TIVA) with drugs that provide cardiovascular stability and are rapidly metabolised could be of benefit for use in rabbits. The aim was to evaluate cardiorespiratory effects of TIVA with sufentanil-midazolam in eight New Zealand White rabbits. Subcutaneous premedication with medetomidine (0.1 mg/kg BW) was followed by IV administration of a mixture of 2.5 μg/mL sufentanil and 0.45 mg/mL midazolam at a rate of 0.3 mL/kg BW/h for anaesthetic induction. Additionally, intravenous boluses of 0.1 mL of the mixture were administered every 20 s until the righting reflex was lost. Following endotracheal intubation, anaesthesia was maintained for 60 min with an infusion rate adjusted to supress the pedal withdrawal reflex. Air and oxygen (1:2) were delivered at 3 L/min. Physiological variables were recorded before induction and at predefined time points during and after anaesthesia.

RESULTS

Righting and pedal withdrawal reflexes were lost within 3 and 5 min, respectively. Doses of sufentanil and midazolam were 0.48 μg/kg BW and 0.09 mg/kg BW for induction, and 0.72 μg/kg BW/h and 0.13 mg/kg BW/h for maintenance. Apnoea occurred in two rabbits. Induction of anaesthesia caused a significant increase in heart rate, cardiac output and arterial CO2 partial pressure and a decrease in mean arterial pressure, respiratory rate and pH. Mean time from stopping the infusion to endotracheal extubation was 5 min, and to return of the righting reflex 7 min. Anaesthesia was characterized by induction and recovery without excitation, with muscle relaxation, and absence of the pedal withdrawal reflex.

CONCLUSIONS

TIVA with sufentanil-midazolam provided smooth induction and recovery of anaesthesia in rabbits but with marked hypotension and respiratory depression, requiring mechanical ventilation. Further evaluation is needed to establish if the protocol is useful for rabbits undergoing surgery.

Cartilage repair of experimentally 11 induced osteochondral defects in New Zealand White rabbits

Articular cartilage has a limited capacity for self-repair in adult humans, and methods used to stimulate regeneration often result in re-growth of fibrous cartilage, which has lower durability. No current treatment option can provide complete repair. The possibility of growth factor delivery into the joint for cartilage regeneration after injury would be an attractive treatment option. A full thickness osteochondral defect of 4 mm in diameter and 2 mm deep was created by mechanical drilling in the medial femoral condyle in 20 female adult New Zealand White rabbits. In an attempt to improve regeneration a hyaluronic hydrogel system, with or without bone morphogenetic protein-2 (BMP-2) was delivered intraarticularly. The contralateral joint defect was treated with saline as control. Throughout the study, rabbits were clinically examined and after 12 ( n = 6) or 24 ( n = 9) weeks, the rabbits were euthanized and the joints evaluated by histology. The defects healed with fibrocartilage like tissue, and the filling of the defects ranged from less than 25% to complete. The healing of the defects varied both inter- and intra-group wise. Treatment with hyaluronan gel with or without BMP-2 had no effect on cartilage regeneration compared with controls. Instead, severe ectopic bone formation was found in seven joints treated with BMP-2. In conclusion, the present study shows that neither treatment with hyaluronic gel alone, nor in combination with BMP-2, improves the healing of an induced cartilage defect in rabbits. It further shows that BMP-2 can induce ectopic bone formation, which severely affects the functionality of the joint.

Fatal acute intestinal pseudoobstruction in mice

Here we describe the epizootiology and pathology of spontaneous, fatal acute intestinal pseudoobstruction that occurred in a mouse colony of 1000 breeding pairs, mainly of the C57Bl/6 strain and free from known pathogenic agents. Most of the mice affected were dams in the second week of lactation. At necropsy, segments of the small intestines were distended with fluid contents. Widespread apoptosis of the villus epithelium of the small intestine and superficial epithelial cells of the large intestine, associated with strong expression of active caspase 3, was a distinctive feature. Necrotic enterocytes, mucosal erosions, and acute mucosal inflammation were prominent in some mice, and morphologic signs of toxemia were generally present. No light microscopic neuronal changes were apparent in the gut, and no etiologic agents were identified. These results indicate that sudden activation of apoptosis in the trophically stimulated gut epithelium during peak lactation was instrumental for the fatal outcome of the condition, but the primary cause of the motility dysfunction of the bowel was not established.

Induction of anaesthesia with desflurane and isoflurane in the rabbit

The characteristics of two techniques of face-mask induction of desflurane anaesthesia (rapid or slow) were compared with the effects of slow isoflurane induction in five New Zealand White (NZW) rabbits. Slow induction used stepwise increments in vapour setting of 2% for desflurane and 0.5% for isoflurane at 30 s intervals. All animals were anaesthetized using each technique according to a randomized block design with one week between treatments. Observations were made of the quality of induction (any struggling or periods of apnoea) and the latency to, and the duration of loss of the righting and toe pinch reflexes recorded. Changes in respiratory rate, arterial blood gas and cardiovascular parameters were also recorded. Induction and recovery times were shorter with rapid desflurane induction in comparison to isoflurane (loss of righting reflex: 139+/-27 s cf. 205+/-48 s), but both techniques were associated with struggling and long periods of apnoea (> 1 min) during the first 4 min after administration. During this period a significant degree of bradycardia, hypercapnia and hypoxaemia occurred with both techniques, but these and the subsequent effects of rapid desflurane administration were less severe than with isoflurane. Slow induction with desflurane was tolerated best, with little or no deleterious behavioural or physiological effects, however excessively prolonged induction times (loss of righting reflex 337+/-160 s) limits the application of this method. Desflurane, administered rapidly, appears to be a more suitable agent than isoflurane. However, as with isoflurane, anaesthesia should only be induced following oxygen supplementation.

Sufentanil and medetomidine anaesthesia in the rat and its reversal with atipamezole and butorphanol

Injectable anaesthetics are widely used to anaesthetize rats, but recovery times are often prolonged. Reversible anaesthetic regimens have the advantage that animals may be recovered quickly, thus reducing the incidence of postoperative complications such as hypothermia, and also providing a means of treating inadvertent anaesthetic overdose. This study assessed and compared the characteristics of anaesthesia induced with combinations of sufentanil and medetomidine administered as a single subcutaneous or intraperitoneal dose, and reversal with butorphanol and atipamezole. Combinations of sufentanil/medetomidine at 40 microg/150 microg and 50 microg/150 microg/kg administered subcutaneously, and 80 microg/300 microg/kg by intraperitoneal injection were found to produce surgical anaesthesia for 101+/-49, 124+/-45 and 76+/-23 min (means +/- SD) respectively. All three combinations produced marked respiratory depression 30 min after injection (< 50% of resting respiratory rate). Oxygen saturation, measured by pulse oximetry, was < 50% in all groups 30 min following drug administration. Subcutaneous administration is recommended since it resulted in a more reliable and more rapid induction of anaesthesia than intraperitoneal administration. The administration of butorphanol and atipamezole (0.2/0.5 mg/kg s.c.) resulted in a rapid (< 7 min) reversal of anaesthesia and an associated respiratory depression. The induction of anaesthesia with sufentanil/medetomidine and its reversal with a combination of atipamezole and butorphanol is an effective technique for anaesthetizing rats. However, due to the marked respiratory depression and the resulting hypoxia, we recommend that this regimen should only be used in animals which are free from respiratory disease and that oxygen should be provided during anaesthesia.

Effects of repeated anaesthesia with ketamine/medetomidine and of pre-anaesthetic administration of buprenorphine in rats

Two groups of rats were anaesthetized at weekly intervals for 6 weeks with either ketamine/medetomidine alone (60 mg/0.4 mg/kg i.p.) or ketamine/medetomidine (45 mg/0.3 mg/kg i.p.) one hour following buprenorphine (0.05 mg/kg s.c.). Animals that received buprenorphine had longer periods of surgical anaesthesia (P = 0.04) and a greater depression of both mean pedal withdrawal score (P < 0.01) and mean respiratory rate (P = 0.014). Mean total duration of anaesthesia was also greater in the buprenorphine group on day 1. Sleep times reduced with successive doses of anaesthetic in the buprenorphine group (P = 0.024). Two animals in the buprenorphine group died. Repeated anaesthesia with ketamine/medetomidine alone was not associated with anaesthetic mortality. These results indicate that although buprenorphine has a clear anaesthetic-sparing effect, its use with ketamine/medetomidine may be associated with an increased risk of anaesthetic-related mortality.

Induction of anaesthesia with sevoflurane and isoflurane in the rabbit

The effects of induction of anaesthesia with sevoflurane and isoflurane were studied in rabbits. All rabbits had periods of apnoea (ranging from 30-180 s) during induction which resulted in moderate hypercapnia and acidosis. Arterial pCO2 rose from 4.1 +/- 0.3 kPa to a peak of 7.6 +/- 0.4 kPa (mean +/- SD) (both agents). All animals showed a significant reduction in heart rate (P < 0.05). Heart rate (HR) fell from 226 +/- 33 to a minimum during induction of 57 +/- 32 (sevoflurane) and 199 +/- 41 to 45 +/- 11 (isoflurane). Most animals struggled violently during induction. Use of sevoflurane did not prevent the breath-holding response seen during induction of anaesthesia with other volatile anaesthetics in this species, and the severe apnoea which occurs may represent a significant hazard. The behaviour of the animals indicated that both sevoflurane and isoflurane are aversive, suggesting that this technique should be avoided whenever possible.