Effects of tramadol on behavioural indicators of colic pain in a rat model of ureteral calculosis

Pain Recognition in Rodents

Available methods for recognizing and assessing pain in rodents have increased over the last 10 years, including the development of validated pain assessment scales. Much of this work has been driven by the needs of biomedical research, and there are specific challenges to applying these scales in the clinical environment. This article provides an introduction to pain assessment scale validation, reviews current methods of pain assessment, highlighting their strengths and weaknesses, and makes recommendations for assessing pain in a clinical environment.

Construction of a novel rabbit model of ureteral calculi implanted with flowable resin

BACKGROUND

The purpose of this study was to characterize the pathophysiological changes of hydronephrosis caused by ureteral calculi obstruction in a new rabbit ureteral calculi model by implanting flowable resin.

METHODS

Forty New Zealand rabbits were randomly divided into two groups: the calculi group and the sham control group. In the calculi group (n = 20), rabbits were operated at left lower abdomen and the left ureter was exposed. Then flowable resin (flowable restorative dental materials) was injected into the left ureter using a 0.45 mm diameter intravenous infusion needle. Then light-cured for 40 s by means of a dental curing light to form calculi. In the sham control group, normal saline was injected into the ureter. Rabbits underwent X-ray and routine blood and urine tests preoperatively, as well as X-ray, CT, dissection, HE staining and routine blood and urine tests on 1, 3, 5 and 7 days postoperatively. Stone formation was assessed by X-ray and unenhanced CT scan after surgery. The pathophysiological changes were evaluated through dissection, HE staining and routine blood and urine tests.

RESULTS

Ureteral calculi models were successfully constructed in 17 rabbits. In calculi group, high-density shadows were observed in the left lower abdomen on postoperative day 1st, 3rd, 5th and 7th by X-ray and CT scan. Dissection found obstruction formation of the left ureters, dilatation of the renal pelvis and upper ureter during 7 days after surgery. The renal long-diameters of the left ureters increased only on the 1st postoperative day. HE staining found ureteral and kidney damage after surgery. In calculi group and sham group,the serum creatinine, urea nitrogen, white blood cells and urine red blood cells were raised at day 1 after surgery. However, the indicators returned to normal at day 3, 5, and 7.

CONCLUSIONS

This is a stable, less complicated operation and cost-effective ureteral calculi model by implanting flowable resin. And this novel model may allow us to further understand the pathophysiology changes caused by ureteral calculi obstruction.

Analgesia and mouse strain influence neuromuscular plasticity in inflamed intestine

BACKGROUND

Mouse models of inflammatory bowel disease (IBD) identify an impact on the enteric nervous system (ENS) but do not distinguish between Crohn's disease and ulcerative colitis phenotypes. In these models, analgesia is required, but its influence on different strains and disease outcomes is unknown. Therefore, changes to the ENS and intestinal smooth muscle were studied in trinitrobenzene sulfonic acid (TNBS) and dextran sodium sulfate (DSS) induced colitis to identify the effects of analgesia, and compared between two mouse strains.

METHODS

Colitis was induced in CD1 or BALB/c mice receiving analgesia with either buprenorphine or tramadol. Euthanasia was on Day 8 (DSS) or Day 4 (TNBS). Outcomes were Disease Activity Index and cytokine assay, and quantitative histology and immunocytochemistry were used to evaluate effects of inflammation on neurons and smooth muscle.

KEY RESULTS

In BALB/c mice, both models of colitis caused >2-fold increase in smooth muscle cell number. DSS caused axon proliferation without neuron loss while TNBS caused significant neuron loss and axonal damage. Buprenorphine (but not tramadol) was generally anti-inflammatory in both strains, but correlated with lethal outcomes to TNBS in BALB/c mice.

CONCLUSIONS AND INFERENCES

Smooth muscle growth is common to both models of colitis. In contrast, ENS damage in TNBS is correlated with the severe response of a Crohn's disease-like phenotype, while DSS correlates with a milder, ulcerative colitis-like outcome in the deeper tissues. Analgesia with tramadol over buprenorphine is supported for mouse studies of IBD.

Effects of PDE5 Inhibitors and sGC Stimulators in a Rat Model of Artificial Ureteral Calculosis

Urinary colics from calculosis are frequent and intense forms of pain whose current pharmacological treatment remains unsatisfactory. New and more effective drugs are needed to control symptoms and improve stone expulsion. Recent evidence suggested that the Nitric Oxide (NO) / cyclic guanosine monophosphate (cGMP) / phosphodiesterase type 5 (PDE5) system may contribute to ureteral motility influencing stone expulsion. We investigated if PDE5 inhibitors and sGC stimulators influence ureteral contractility, pain behaviour and stone expulsion in a rat model of ureteral calculosis. We investigated: a)the sex-specific PDE5 distribution in the rat ureter; b)the functional in vitro effects of vardenafil and sildenafil (PDE5 inhibitors) and BAY41-2272 (sGC stimulator) on induced ureteral contractility in rats and c)the in vivo effectiveness of vardenafil and BAY41-2272, alone and combined with ketoprofen, vs hyoscine-N-butylbromide alone or combined with ketoprofen, on behavioural pain indicators and stone expulsion in rats with artificial calculosis in one ureter. PDE5 was abundantly expressed in male and female rats’ ureter. In vitro, both vardenafil and BAY41-2272 significantly relaxed pre-contracted ureteral strips. In vivo, all compounds significantly reduced number and global duration of “ureteral crises” and post-stone lumbar muscle hyperalgesia in calculosis rats. The highest level of reduction of the pain behaviour was observed with BAY41-2272 among all spasmolytics administered alone, and with the combination of ketoprofen with BAY41-2272. The percentage of stone expulsion was maximal in the ketoprofen+BAY41-2272 group. The NO/cGMP/PDE5 pathway is involved in the regulation of ureteral contractility and pain behaviour in urinary calculosis. PDE5 inhibitors and sGC stimulators could become a potent new option for treatment of urinary colic pain.

Pharmacokinetics of tramadol following intravenous and oral administration in male rhesus macaques (Macaca mulatta)

Recently, tramadol and its active metabolite, O-desmethyltramadol (M1), have been studied as analgesic agents in various traditional veterinary species (e.g., dogs, cats, etc.). This study explores the pharmacokinetics of tramadol and M1 after intravenous (IV) and oral (PO) administration in rhesus macaques (Macaca mulatta), a nontraditional veterinary species. Rhesus macaques are Old World monkeys that are commonly used in biomedical research. Effects of tramadol administration to monkeys are unknown, and research veterinarians may avoid inclusion of this drug into pain management programs due to this limited knowledge. Four healthy, socially housed, adult male rhesus macaques (Macaca mulatta) were used in this study. Blood samples were collected prior to, and up to 10 h post-tramadol administration. Serum tramadol and M1 were analyzed using liquid chromatography-mass spectrometry. Noncompartmental pharmacokinetic analysis was performed. Tramadol clearance was 24.5 (23.4-32.7) mL/min/kg. Terminal half-life of tramadol was 111 (106-127) min IV and 133 (84.9-198) min PO. Bioavailability of tramadol was poor [3.47% (2.14-5.96%)]. Maximum serum concentration of M1 was 2.28 (1.88-2.73) ng/mL IV and 11.2 (9.37-14.9) ng/mL PO. Sedation and pruritus were observed after IV administration.

The assessment of post-vasectomy pain in mice using behaviour and the Mouse Grimace Scale

BACKGROUND

Current behaviour-based pain assessments for laboratory rodents have significant limitations. Assessment of facial expression changes, as a novel means of pain scoring, may overcome some of these limitations. The Mouse Grimace Scale appears to offer a means of assessing post-operative pain in mice that is as effective as manual behavioural-based scoring, without the limitations of such schemes. Effective assessment of post-operative pain is not only critical for animal welfare, but also the validity of science using animal models.

METHODOLOGY/PRINCIPAL FINDINGS

This study compared changes in behaviour assessed using both an automated system ("HomeCageScan") and using manual analysis with changes in facial expressions assessed using the Mouse Grimace Scale (MGS). Mice (n = 6/group) were assessed before and after surgery (scrotal approach vasectomy) and either received saline, meloxicam or bupivacaine. Both the MGS and manual scoring of pain behaviours identified clear differences between the pre and post surgery periods and between those animals receiving analgesia (20 mg/kg meloxicam or 5 mg/kg bupivacaine) or saline post-operatively. Both of these assessments were highly correlated with those showing high MGS scores also exhibiting high frequencies of pain behaviours. Automated behavioural analysis in contrast was only able to detect differences between the pre and post surgery periods.

CONCLUSIONS

In conclusion, both the Mouse Grimace Scale and manual scoring of pain behaviours are assessing the presence of post-surgical pain, whereas automated behavioural analysis could be detecting surgical stress and/or post-surgical pain. This study suggests that the Mouse Grimace Scale could prove to be a quick and easy means of assessing post-surgical pain, and the efficacy of analgesic treatment in mice that overcomes some of the limitations of behaviour-based assessment schemes.

Visceral pain originating from the upper urinary tract

Pain originating from the upper urinary tract is a common problem and stone colic is one of the most intense pain conditions that can be experienced in the clinic. The pain is difficult to alleviate and often leads to medical attention. In humans, pain mechanisms of the upper urinary tract pain are still poorly understood, which often leads to a trial and error approach in clinical pain management. Pain from the upper urinary tract seems to have all the characteristics of pure visceral pain, including referred pain with or without hyperalgesia/trophic changes in somatic tissues and viscero-visceral hyperalgesia. However, further studies are needed to better understand these visceral pain mechanisms with regard to optimising pain management. This review gives an introduction to visceral pain in general and upper urinary tract pain in particular, with special reference to pain pathways and pharmacological and non-pharmacological pain modulation.

Effects of vasectomy surgery and meloxicam treatment on faecal corticosterone levels and behaviour in two strains of laboratory mouse

Behaviour was assessed in 32 C57BL/6JCrl and 32 C3H/HeN male mice 1 h following vasectomy; saline or meloxicam was administered 30 min prior to surgery at 5, 10, or 20 mg kg(-1). Faeces were collected 24 h prior to, and 3, 6, 9, 12, 24 h following, vasectomy for measurement of faecal corticosterone. Peak corticosterone levels were significantly higher in mice that underwent vasectomy and received saline (p<0.001) or meloxicam at 5 or 10 mg kg(-1) (p=0.021, and p<0.001, respectively) compared with normal un-operated controls. Mice that underwent vasectomy and received 20 mg kg(-1) meloxicam had peak corticosterone levels that were not different from normal un-operated mice (p=0.254). Discriminant analysis was used to identify behaviours responsible for group separation; these were summed to create two behaviour scores. Score 2 (the frequency of flinching, writhing, rear leg lift and press 2) was thought to be pain related; mice that underwent vasectomy and received saline exhibited significantly more of these behaviours than the normal controls (p=0.032), and the mice that received meloxicam (at any dose). Strain differences were observed in both the stress response to vasectomy and the behavioural changes; the C3H/HeN mice had higher pain scores (behaviour Score 2) and peak corticosterone responses than the C57BL/6JCrl mice. We have demonstrated that significant changes occur in the behaviour of mice following vasectomy, and these changes are reduced by use of meloxicam. Vasectomy elicits a rise in corticosterone levels that was only reduced by the highest dose of meloxicam.

Use of Tramadol Drip in Controlling Renal Colic Pain

BACKGROUND AND PURPOSE

Although the continuous perfusion of antispasmodic drugs has been the traditional mainstay in the treatment of renal colic, the results more often than not are unsatisfactory. Our hypothesis was that a continuous intravenous (IV) drip of tramadol would be an effective and safe alternative.

PATIENTS AND METHODS

In this prospective study, 300 patients with renal colic were randomized into four treatment groups, single blind for the patients. At the start, all received an anti-inflammatory drug intramuscularly and an antiemetic and antispasmodic IV. Group A was given the classical IV antispasmodic perfusion combined with a sham drip. Group B received the classical antispasmodic perfusion in combination with a tramadol drip. Group C had a sham perfusion and drip. Group D received a sham perfusion and tramadol drip. There was no significant difference in the degree of pain between the groups on a visual analog scale (VAS) at the start. The pain was scored again on the VAS at 30 minutes, 1 hour, and 4 hours after the start of the treatment and at IV urography. Side effects, as well as the need for rescue medication, were registered.

RESULTS

Both tramadol groups scored significantly better after 60 and 240 minutes and during IV urography (P < 0.005). There was a significant decrease in VAS in group B after 30 minutes. The tramadol groups needed significantly less rescue medication (P = 0.001). There was no significant difference in the reported side effects. The combination spasmolytic-tramadol drip scored the best, although the difference was not statistically significant.

CONCLUSION

We consider our hypothesis proved that a continuous tramadol drip is a safe and valuable analgesic regimen in renal colic.

Behaviour-based assessment of the duration of laparotomy-induced abdominal pain and the analgesic effects of carprofen and buprenorphine in rats

Prevention of unnecessary pain in laboratory animals requires reliable and practically useful tools for assessing pain severity and analgesic efficacy. We have used a behaviour-based pain scoring system to determine the duration of pain resulting from laparotomy, and the duration of analgesia afforded by orally administered (p.o.) buprenorphine and subcutaneously administered (s.c.) carprofen or buprenorphine in rats. One hour before laparotomy Fisher 344 rats received either saline as a control (0.2 ml/100 g s.c.), carprofen (5 mg/kg s.c.) or buprenorphine (0.05 mg/kg s.c. or 0.4 mg/kg p.o.). The rats were housed singly for 10-min periods of behaviour recording, beginning 30 min after completing surgery. Recording was repeated at three time points every 2 h. The behaviour of controls was distinct from that of the analgesic-treated animals throughout recording; however, the major signs of pain (back-arching, staggering and writhing) were prominent during only the first 270 min in the saline group. This was followed by a period of more subtle differences between the saline- and drug-treated groups. It was concluded that the most acutely painful effects of surgery in this model lasted for between 270 and 390 min, and that this was alleviated throughout its duration by subcutaneously administered carprofen or buprenorphine, and also buprenorphine administered orally. The study demonstrates a clinically relevant and practically useful approach to assessing the duration of post-surgical abdominal pain and analgesic effects in rats.