Liposome-encapsulated oxymorphone hydrochloride provides prolonged relief of postsurgical visceral pain in rats

Adequate pain control is necessary for optimal postsurgical recovery and humane treatment of laboratory and companion animals. Opioid drugs are currently the most potent analgesic agents available in human and veterinary medicine. Long-acting formulations of opioid drugs confer several important advantages over standard pharmaceutical preparations, especially for use in animals. A long-acting formulation of oxymorphone hydrochloride was produced by encapsulation into liposomes. Liposome-encapsulated (LE) oxymorphone was tested in a rat model of visceral postoperative pain. Rats were given one subcutaneous injection of LE oxymorphone (1.2 or 1.6 mg/kg of body weight) or standard oxymorphone (0.3 mg/kg) at the time of intestinal transection or resection. A single administration of LE oxymorphone hydrochloride was as effective for relief of postoperative pain in rats (P = 0.18), as were multiple (q4 h or q8 h) injections of 0.3 mg/kg of the standard pharmaceutical preparation. The rats given LE oxymorphone prior to intestinal resection also had significantly higher body weight at three and seven days after surgery than did rats that were given standard oxymorphone. In conclusion, LE oxymorphone was effective in treating visceral pain associated with intestinal surgery in rats. On the basis of body weight gain, rats treated with LE oxymorphone had improved recovery outcome, compared with rats treated with repeated injections of standard oxymorphone.     

Evaluating postoperative analgesics in mice using telemetry

The study examined the efficacy of preemptive or postoperative analgesia on surgical pain in the mouse. Radiotelemetry transmitters were surgically implanted in 28 female ICR mice. A mock ova implantation surgery was then performed. Mice were treated with a single dose of buprenorphine or flunixin meglumine prior to or after surgery, three doses of buprenorphine, or were untreated. Heart rate, blood pressure, home cage activity, food and water consumption, and body weight were measured. The no-analgesia group showed no significant differences between any parameters collected prior to surgery and those collected at similar times during the day of surgery. Significant increases in mouse activity on the day of surgery occurred with all analgesic treatments, compared with pre-surgical activity. There were no consistent significant changes in any other telemetry parameter after treatment with analgesics compared with no analgesia. Food consumption and body weight the day after surgery were reduced significantly in the animals treated with three doses of buprenorphine compared with untreated mice and mice given a single dose of buprenorphine. We conclude that the mock ova implant procedure does not induce sufficient pain to cause alterations in heart rate and blood pressure in the mouse. Activity was significantly reduced in the first 6 h after surgery in mice without analgesia, compared with activity prior to surgery. There were no significant differences between pre-emptive and postoperative analgesia. Body weight and food and water consumption were poor measures of pain because analgesia alone affected these parameters.     

Adverse effects on growth rates in rats caused by buprenorphine administration

As a routine postoperative treatment, a single dose of buprenorphine was given to rats at a dose of 0.05 mg/kg subcutaneously. However, some rats developed abnormal secretions around the nose and mouth and some animals died 3-5 days after surgery and analgesic treatment. At autopsy a yellow fibrous mass was found in the stomach and intestines. Observations of animals given buprenorphine revealed an abnormal ingestion of bedding material. This caused a disturbance to normal digestion, with gastric distension, weight loss or decreased growth rate, constipation and occasionally death. In this study rats were monitored for 6 days following surgery and analgesic treatment. A comparison of growth rates was made between rats given saline and buprenorphine or nalbuphine and between animals kept on bedding or grid floors for the first 24h after treatment. Of the animals held on bedding, the buprenorphine-treated animals did not lose weight as the other animals did, but had on the other hand a decreased growth rate during the measuring period of 6 days after surgery. When denied access to bedding for the first 24 h after surgery, rats given saline or nalbuphine had a reduced weight gain over the first 24 h, similar to the groups held on bedding. Rats held on grid floors and given buprenorphine continued to gain weight for the first 24 h. From day 3, there was no significant difference between the groups, which all gained weight.     

Are repeated doses of buprenorphine detrimental to postoperative recovery after laparotomy in rats?

Buprenorphine is a widely used analgesic for relief of postoperative pain in rats. The effect of repeated doses of buprenorphine throughout the postoperative pain and stress response is unknown. This investigation tested the hypotheses that (a) daily analgesic doses of buprenorphine for 7 d ameliorate the stress response after laparotomy in rats and (b) preoperative buprenorphine better ameliorates the response than do peri- and postoperative administration. Postoperative effects on body weight, daily food and water consumption, and daily fecal and urinary outputs were monitored in groups of rats treated for 7 d with analgesic doses of buprenorphine initiated at different time points relative to the time of laparotomy. Analgesic doses of buprenorphine had no effect on the study parameters in healthy unoperated rats. Daily injection of buprenorphine delayed the time at which the preoperative body weight was restored without decreasing the postoperative changes in daily food consumption, water intake, and fecal and urinary outputs in the operated rats. The effects of daily analgesic doses of buprenorphine for 7 d on body weight, daily food, and water consumption, and fecal and urinary outputs were minimal and less statistically significant than the changes caused by surgery itself. However, this dosing regimen seems to delay the restoration of body weight after abdominal surgery in rats.     

A comparison of pre- and post-surgical administration of bupivacaine or buprenorphine following laparotomy in the rat

The effects of bupivacaine, a long-acting local anaesthetic, and buprenorphine, an opioid analgesic, administered either pre- or post-operatively, were investigated in a rat laparotomy model. Surgical anaesthesia was induced and maintained with halothane. The type of analgesic treatment was a significant factor in the reduction in body weight and food and water intake which occurred following surgery. The largest reductions were seen in the bupivacaine-treated groups and those animals which received no analgesics. The timing of administration of analgesics had no influence on the effect of bupivacaine administration. The group receiving buprenorphine before surgery showed less depression in food intake than the group receiving buprenorphine at the end of surgery. Animals which received buprenorphine showed less depression of activity than those receiving saline or bupivacaine.     

Duration of effects on clinical parameters and referred hyperalgesia in rats after abdominal surgery and multiple doses of analgesic

This study evaluated the duration of clinical effects and referred hyperalgesia in rats (n = 10 per group) undergo ing abdominal surgery with analgesics (ketoprofen at 3 mg/kg and buprenorphine at 0.01 or 0.1 mg/kg) administered intramuscularly twice daily for 72 h beginning prior to surgery; no-surgery and no-analgesia control groups were included. Food and water consumption and body weight were monitored daily. As a measure of referred hyperalgesia, tail-flick latency was measured daily, before and 4 h after analgesia administration. Compared with those of the no-surgery controls, significant decreases in food consumption and body weight occurred 24 h after surgery without analgesics. There were nonsignificant reductions in these effects by analgesics, but the benefits were not significantly different than those of saline. These parameters continued to be decreased with variable significance in the buprenorphine groups at 48 and 72 h after surgery. In both buprenorphine-treated groups, water consumption was significantly increased at 24 h after surgery but not at 48 or 72 h. Tail-flick latency was not significantly different between the no-surgery and no-analgesia groups but was significantly increased 4 h after high-dose buprenorphine administration and declined nonsignificantly over time in the other groups. We conclude that painful effects from surgery are present primarily during the first 24 h after surgery. The analgesic regimens tested did not completely reduce these effects. Buprenorphine was associated with adverse effects for as long as 72 h after surgery. Referred hyperalgesia from this abdominal surgery could not be measured using the tail-flick assay.     

Effects of buprenorphine on immunogenicity and protective efficacy in the guinea pig keratoconjunctivitis model (Sereny test)

Shigellosis is a disease of global proportions, with an estimated 164.7 million episodes annually throughout the world as well as an estimated 1.1 million associated mortalities in developing countries. Due to increasing incidence, and continued emergence of multi-drug resistant strains, Shigella vaccine development is considered a top public health priority. The guinea pig keratoconjunctivitis model, the basis for the Sereny test, remains the most reliable in vivo indicator of virulence of Shigella strains and immunogenicity and protective efficacy of Shigella vaccine candidates. The model is effective in evaluating the ability of Shigella strains to invade the corneal epithelia of guinea pigs and spread to contiguous cells, with the more virulent strains causing ulcerative keratoconjunctivitis. However, analgesia is not routinely used to relieve this painful condition because of potential immunomodulation and confounding of experimental results. The objective of the study reported here was to evaluate use of buprenorphine hydrochloride as an analgesic during the Sereny test. Local and systemic immune responses were measured in guinea pigs given buprenorphine versus those responses in controls. Results of this study suggest that buprenorphine, administered at an analgesic dose of 0.05 mg/kg of body weight twice daily, can be successfully used with the model without significantly affecting immunologic evaluation of Shigella vaccine candidates. However, in buprenorphine-treated animals, there was a significant increase in the amount of mucopurulent ocular discharge, requiring frequent cleaning of the affected eyes. Additionally, animals treated with buprenorphine had significant reduction in body weight, in comparison with saline controls.     

Influence of buprenorphine analgesia on post-operative recovery in two strains of rats.

The objective of this study was to establish an effective post-operative analgesic regimen for Sprague-Dawley (SD) and Dark Agouti (DA) rats. Buprenorphine (0.01 or 0.05 mg/kg), a partial mu opioid agonist, was administered subcutaneously immediately on completion of a standardized surgical procedure, involving anaesthesia, laparotomy and visceral manipulation. Two of the four treatment groups and the saline control group received a second injection 9 h later. Behavioural observations by three independent observers provided no information in assessing pain in this model. All rats lost weight, consumed less food and water after surgery. On the first day, both SD and DA rats receiving buprenorphine lost less weight than untreated control groups. Using weight loss as an efficacy criterion, low-dose buprenorphine, given once or twice, provided effective analgesia in SD rats. A higher single dose provided no additional benefit and a second dose was detrimental, reducing body weight and food intake. In DA rats, the high dose, given twice, appeared to be more effective than the lower dose. All DA cage cohorts consumed < 10% pre-operative food despite buprenorphine treatment, suggesting a higher dosage may be necessary. However, all SD and 80% DA rats who received no buprenorphine gained body weight on the second day, whereas most of the buprenorphine-treated rats continued to lose weight for another 2 days, despite increased food consumption by both strains. Buprenorphine may adversely affect intestinal function over a number of days due to its enterohepatic circulation; this effect may be more severe in DA rats. Adverse metabolic effects of buprenorphine and other opioids may preclude their use in the future if it can be shown that non-steroidal anti-inflammatory drugs (NSAIDs) provide equally effective analgesia.     

Voluntary Exercise and Its Effects on Body Composition Depend on Genetic Selection History

Little is known about how genetic variation affects the capacity for exercise to change body composition. We examined the extent to which voluntary exercise alters body composition in several lines of selectively bred mice compared to controls. Lines studied included high runner (HR) (selected for high wheel running), M16 (selected for rapid weight gain), Institute of Cancer Research (ICR) (randomly bred as control for M16), M16i (an inbred line derived from M16), HE (selected for high percentage of body fat while holding body weight constant), LF (selected for low percentage of body fat), C57BL/6J (common inbred line), and the F1 between HR and C57BL/6J. Body weight and body fat were recorded before and after 6 days of free access to running wheels in males and females that were individually caged. Total food intake was measured during this 6‐day period. All pre‐ and postexercise measures showed significant strain effects. While HR mice predictably exercised at higher levels, all other selection lines had decreased levels of wheel running relative to ICR. The HR × B6 F1 ran at similar levels to HR demonstrating complete dominance for voluntary exercise. Also, all strains lost body fat after exercise, but the relationships between exercise and changes in percent body were not uniform across genotypes. These results indicate that there is significant genetic variation for voluntary exercise and its effects on body composition. It is important to carefully consider genetic background and/or selection history when using mice to model effects of exercise on body composition, and perhaps, other complex traits as well.     

Effects of vasopressin replacement during food-restriction stress

The effects of subcutaneous injections of vasopressin in vasopressin-deficient (Brattleboro or DI) rats were observed during nonstress (habituation) and stress (food-restriction) conditions as compared to other rats. Four groups of animals were employed: 1) Long-Evans (LE) rats that were food restricted with no injections (normal control animals), 2) DI rats that were food restricted with no injections, 3) DI rats injected with vasopressin, and 4) DI rats injected with peanut oil (vehicle). The parameters studied were: body weight, food intake, water intake, and gastric ulcer formation. With respect to body weight, water intake, and ulcer formation, two sets of animals emerged. The vasopressin-injected DI rats resembled the LE control rats, whereas the peanut oil-injected DI rats were similar to the DI rats with no injections. The former set of animals showed a higher body weight, reduced water intake, and fewer gastric ulcers than the latter set of animals. Thus the vasopressin-injected DI rats and the LE control rats could cope with the stress of food restriction, but the peanut oil-injected DI rats and the DI rats with no injections could not.     

Analgesic efficacy of orally administered buprenorphine in rats: methodologic considerations

Buprenorphine has been widely recommended for treatment of pain in rodents. We have previously documented that the recommended postoperative oral dose of buprenorphine in male Long-Evans rats, 0.5 mg/kg, is not as effective as the recommended parenteral dose of buprenorphine (0.05 mg/kg, s.c.) as an analgesic. In the series of experiments reported here, we compared: the analgesic effect of buprenorphine when prepared in two ways in the laboratory with that of a commercially available injectable solution of buprenorphine; the analgesic effect of buprenorphine in Long-Evans rats with that in Sprague-Dawley rats; and Long-Evans and Sprague-Dawley rats for development of pica, a commonly reported side effect of buprenorphine. We followed the pica experiment with assessment of the effectiveness of buprenorphine in establishing a conditioned flavor aversion. The results indicated that method of preparation did not result in any significant differences in the efficacy of injected buprenorphine. Strain of rat was not associated with a significant difference in the efficacy of buprenorphine. However, a significant strain difference was found in development of pica. Buprenorphine treatment was effective in inducing a conditioned flavor aversion. We concluded that the recommended oral dose of buprenorphine (0.5 mg/kg) is ineffective as an analgesic, and that this was not the result of method of preparation of the buprenorphine or strain of rat used. Furthermore, we concluded that buprenorphine treatment may induce gastrointestinal distress in both strains tested. The results reaffirm our previous conclusion that oral administration of buprenorphine at 0.5 mg/kg, despite the general recommendation, is not a reasonable treatment for postsurgical pain in rats.     

Does preoperative administration of metamizol (Novalgin) affect postoperative body weight and duration of recovery from ketamine-xylazine anaesthesia in mice undergoing embryo transfer: a preliminary report

Thirty-two female mice used for embryo transfer or as controls received either metamizol or equal volumes of normal saline administered subcutaneously following induction of anaesthesia with ketamine-xylazine. Body weight was measured immediately before surgery, after 24 and after 48 h. The duration of the surgical anaesthesia was recorded and postoperative behavioural responses were measured. Comparison of the treatment groups revealed no significant differences in body weight and recovery times, nor were other signs of discomfort detected in either treatment group. It was concluded that administration of metamizol did not provide additional analgesia following embryo transfer in mice anaesthetized with ketamine-xylazine.     

Ciliary neurotrophic factor upregulates ubiquitin-proteasome components in a rat model of neuronal injury

Neuronal injury triggers the release of ciliary neurotrophic factor (CNTF), promoting local neuronal repair but producing systemic effects of anorexia and lean body weight loss. Due to the rapid rate of systemic protein loss stimulated by CNTF, we hypothesized involvement of the hepatic ubiquitin-proteasome proteolytic (UPP) pathway in CNTF-induced proteolysis. To assess the role of central CNTF in systemic UPP regulation, we measured hepatic UPP mRNA and proteasome activity in a rat model of neuronal injury and determined alterations induced by intracerebroventricular (ICV) administration of CNTF-neutralizing antibody or additional exogenous CNTF. We also assessed proteolytic parameters and nutritional status by measuring caloric intake, body weight, and protein levels. We produced neuronal injury by implanting a lateral ventricle cannula and giving daily ICV saline bolus injections, which increased hepatic 20S proteasome mRNA and enzymatic activity while reducing caloric intake, body weight, and protein levels compared to controls. Administration of ICV anti-CNTF antibodies (but not control antibodies) prevented these effects. Addition of exogenous CNTF augmented the weight loss along with the increases in 20S proteasome mRNA and proteolytic activity induced by neuronal injury. We conclude that CNTF decreases lean body weight through a combination of appetite inhibition and UPP pathway activation.     

Oral buprenorphine and aspirin analgesia in rats undergoing liver transplantation

The objective of this study was to establish effective postoperative analgesia for Dark Agouti rats undergoing liver transplantation with minimal additional stress due to handling and no adverse effect on transplant outcome. Oral administration of buprenorphine (0.5 mg/kg/dose) or aspirin (100 mg/kg/dose) in raspberry-flavoured gelatine were compared to controls receiving no treatment or plain gelatine. The drugs were presented five times: immediately on recovery from anaesthesia and at 12 h intervals thereafter. All rats underwent right nephrectomy and replacement of their liver by an arterialized liver isograft preserved optimally for 24 h. All groups had reversible hepatic damage, lost weight and demonstrated severely reduced dark cycle activity after surgery. Neither treatment appeared to ameliorate the loss of body weight that probably reflected hepatic insufficiency during the first week as well as pain and surgical stress. In the second week, when liver function was 'normal', rats began to regain weight at the pre-transplant rate. Aspirin treatment significantly increased activity during the first and second dark cycles after surgery, whereas buprenorphine significantly increased activity during the second dark cycle only. Neither drug had any apparent adverse effects on the rats or on graft function. Postoperative oral administration of aspirin should be incorporated into future programmes of liver transplantation in rodents. More effective treatment in the immediate postoperative period may require oral administration of analgesia prior to surgery or a single subcutaneous injection of an analgesic agent on completion of surgery in addition to postoperative oral administration of aspirin.     

Analgesic effects of tramadol, carprofen or multimodal analgesia in rats undergoing ventral laparotomy

In this study, the authors evaluated the analgesic efficacy of tramadol (an opioid-like analgesic), carprofen (a nonsteroidal anti-inflammatory drug) and a combination of both drugs (multimodal therapy) in a rat laparotomy model. The authors randomly assigned rats to undergo either surgery (abdominal laparotomy with visceral manipulation and anesthesia) or anesthesia only. Rats in each group were treated with tramadol (12.5 mg per kg body weight), carprofen (5 mg per kg body weight), a combination of tramadol and carprofen (12.5 mg per kg body weight and 5 mg per kg body weight, respectively) or saline (anesthesia control group only; 5 mg per kg body weight). The authors administered analgesia 10 min before anesthesia, 4 h after surgery or (for the rats that received anesthesia only) anesthesia and 24 h after surgery or anesthesia. They measured locomotor activity, running wheel activity, feed and water consumption, body weight and fecal corticosterone concentration of each animal before and after surgery. Clinical observations were made after surgery or anesthesia to evaluate signs of pain and distress. The authors found that carprofen, tramadol and a combination of carprofen and tramadol were all acceptable analgesia regimens for a rat laparotomy model.     

Buprenorphine does not affect acute murine toxoplasmosis and is recommended as an analgesic in Toxoplasma gondii studies in mice

Groups of mice were infected with tachyzoites of the RH strain of Toxoplasma gondii, treated with the opioid analgesic buprenorphine, sodium sulfadiazine, a combination of buprenorphine and sodium sulfadiazine, or nothing in the drinking water, on days -1 to 12 postinfection. Mice in the T. gondii-infected buprenorphine-treated group did not live significantly longer (P > 0.05) than mice given T. gondii and not treated with buprenorphine. Clinical observations of mice indicated that buprenorphine treatment reduced distress and pain in mice with acute toxoplasmosis. Mice treated with sodium sulfadiazine alone or sodium sulfadiazine combined with buprenorphine survived the 28-day study. Mice treated with buprenorphine and not infected with T. gondii also survived the 28 days. This study demonstrates that buprenorphine does not adversely interfere with acute T. gondii infection and indicates that buprenorphine can be given to mice to alleviate pain and distress associated with a T. gondii infection, and not adversely influence the results of toxoplasmosis studies. Analgesic (buprenorphine) treatment should now be the standard of care for mice in acute toxoplasmosis studies.     

Post-Surgical Analgesia in Rainbow Trout: Is Reduced Cardioventilatory Activity a Sign of Improved Animal Welfare or the Adverse Effects of an Opioid Drug?

The use of fish models in biomedical research is increasing. Since behavioural and physiological consequences of surgical procedures may affect experimental results, these effects should be defined and, if possible, ameliorated. Thus, the use of post-surgical analgesia should be considered after invasive procedures also in fish, but presently, little information exists on the effects of analgesics in fish. This study assessed the effects of an opioid drug, buprenorphine (0.05 mg/kg IM), on resting ventilation and heart rates during 7 days of postsurgical recovery in rainbow trout (Oncorhynchus mykiss) at 10°C by non-invasively recording bioelectric potentials from the fish via electrodes in the water. Baseline ventilation and heart rates were considerably lower compared to previously reported values for rainbow trout at 10°C, possibly due to the non-invasive recording technique. Buprenorphine significantly decreased both ventilation and heart rates further, and the effects were most pronounced at 4–7 days after anaesthesia, surgical procedures and administration of the drug. Somewhat surprisingly, the same effects of buprenorphine were seen in the two control groups that had not been subject to surgery. These results indicate that the reductions in ventilation and heart rates are not caused by an analgesic effect of the drug, but may instead reflect a general sedative effect acting on both behaviour as well as e.g. central control of ventilation in fishes. This resembles what has previously been demonstrated in mammals, although the duration of the drug effect is considerably longer in this ectothermic animal. Thus, before using buprenorphine for postoperative analgesic treatment in fish, these potentially adverse effects need further characterisation.     

The use of buprenorphine as an analgesic after rodent embryo transfer

Many researchers are reluctant to administer analgesia after rodent embryo transfer, primarily out of concern that analgesia will affect embryo implantation. According to the Animal Welfare Act and the Guide, however, embryo transfer constitutes major survival surgery and is likely to cause pain and distress despite its minimally invasive nature. The authors examined the effects of a single dose of the analgesic buprenorphine on mice that underwent embryo transfer. In mice treated with buprenorphine, the number of viable implanted embryos was typically equal to or greater than that in untreated mice. All mice seemed quiet, alert and active after surgery.     

G2 restriction point within populations of hepatocytes and tongue keratinocytes in young, growing mice

The authors studied the effect of either extracts from liver (LE) or the malignant tumour ES2 (TE) or plasma from intact mice (PI) or tumour-bearing animals (PT) on the mitotic activity of the hepatocytes and tongue keratinocytes in young, growing C3H/s male mice (28+/-1 days old). Animals standardized for periodicity analysis were injected intraperitoneally with either TE, LE, PI, PT, or saline (S) at 16:00 h with 0.01 ml of sample/g of body weight and were then killed at (time of day/h post-injection) 20:00/04, 00:00/08, and 04:00/12. Colchicine (2 microg/g) was injected 4 h before death. Samples of the liver and tongue from each animal were processed for histology and assessment of mitotic index. The results were expressed as colchicine-arrested metaphases/1000 nuclei. The TE and LE stimulated the mitotic activity of hepatocytes and tongue keratinocytes. Taking into account the time elapsed between the injections and the measurements made in these light-dark synchronized animals, we conclude that the increase in mitotic index observed in those tissues stemmed from a reinitiation of cell-cycle traverse in a subpopulation of G2-arrested, noncycling cells.     

Effects of buprenorphine on body temperature, locomotor activity and cardiovascular function when assessed by telemetric monitoring in rats

Buprenorphine is a potent analgesic commonly used clinically in humans and rodents experiencing severe pain. However, effects of therapeutic doses on locomotor activity and the cardiovascular system have not been studied in conscious animals. The effects of buprenorphine were therefore evaluated in this study using telemetric monitoring in conscious animals. Telemetry transmitters were implanted in the peritoneal cavity of Wistar rats with a pressure catheter in the aorta and electrodes for electrocardiogram (ECG) recording subcutaneously. After a single subcutaneous administration of saline, each rat was administered single subcutaneous doses of 0.006, 0.03 or 0.15 mg/kg body weight (bw) of buprenorphine. During a 10 h period after administration, buprenorphine induced a varying dose-dependent increase in body temperature, heart rate, dP/dt and systolic-diastolic blood pressure, as well as a corresponding decrease in QT time. At high dose, however, QT time was still decreased 24 h post-administration, but no arrhythmias or visual changes were observed in the ECG complex. Body temperature and heart rate increased at the high dose of buprenorphine, even at 20-24 h after administration. Moreover, the high dose of buprenorphine induced a biphasic response in diastolic blood pressure, with an early and pronounced increase that, at 14 h after administration, reversed to a decrease, failing to normalize within 24 h post-dosage. The results indicate that buprenorphine induces long-lasting effects (such as body temperature and cardiovascular effects) in the rat after a single subcutaneous dose at 0.15 mg/kg bw.