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.     

Behavioural effects of luteinizing hormone-releasing hormone (LHRH) in rats.

Behavioural effects of intracerebroventricularly-injected (icv) LHRH were studied in female rats. Locomotor and exploratory activities as well as irritability were determined. A pronounced inhibitory effect of 10 micrograms doses of LHRH was found. At 100 micrograms doses of LHRH, barrel behaviour was observed. We conclude that LHRH can modify the activity of central serotonergic receptors in rats.     

The effects of morphine and various narcotic antagonist type analgesics on body temperature in rats

ED50s were determined for morphine, nalorphine, butorphanol and pentazocine induced hyperthermia in rats. Morphine produced a significant hyperthermia with the doses of 5–160 mg.kg in rats. The peak hyperthermic effect was found 1 hr after 5–20 mg/kg doses of morphine. Nalorphine, butorphanol and pentazocine produced biphasic effects on rectal temperature. Initially they produced a dose-dependent hyperthermia and later hypothermia. In a comparison of the hyperthermic ED50's of morphine, nalorphine, butorphanol and pentazocine it was found that butorphanol is more active than the others (ED50s were 4.7, 4.3, 0.54 and 11.5 mg/kg respectively). The narcotic antagonist naloxone significantly inhibited both morphine and antagonist type analgesic induced hyperthermia. These results suggests that a different mechanism(s) is involved in the hyperthermic actions of antagonist type analgesics and agonist drugs.     

The influence of clenbuterol on growth in rats.

1. The influence was studied of a beta 2-agonist, clenbuterol, on mean gain of body weight, feed efficiency and growth of muscle tissue in female Wistar rats of three different weights (70, 150 and 200 g). 2. Clenbuterol significantly increases mean gain of body weight and feed efficiency in all the studies realised, but much more effectively in animals of greater age/weight (200 g). 3. In addition, it favours protein deposition in muscle, given that it increases significantly (P less than 0.001) the muscle/body weight ratio in all of the experiments.     

Antidepressant-like effects of tramadol and other central analgesics with activity on monoamines reuptake,in helpless rats

Affective states are regulated mainly by serotonin and noradrenaline. However the opioid system has been also related to antidepressant-induced mood improvement, and the mu-opioid receptor has been involved in affective responses to a sustained painful stimulus. Similarly, antidepressant drugs induce an antinociceptive effect via both the monoaminergic and opioid systems, probably involving sensorial and affective dimensions of pain. The aim of this study was to test three opiate analgesics, which also inhibit monoamine reuptake, in the learned helplessness model of depression in rats. Helpless rats receiving (+/-)tramadol (10, 20 mg/Kg) or (-)methadone (2, 4 mg/Kg) showed a decreased number of failures to avoid or escape aversive stimulus (shock) in both the second and the third daily sessions, compared with controls. Rats receiving levorphanol (0.5, 1 mg/Kg) showed a decreased number of such failures in the third session. The number of crossings in the intertrial interval (ITI) was not significantly modified by (+/-)tramadol or (-)methadone. Levorphanol enhanced ITI crosses at 1 mg/Kg. These results, together with other clinical and experimental data, suggest that analgesics with monoaminergic properties improve mood and that this effect may account for their analgesic effect in regulating the affective dimension of pain. From this, it seems probable that the analgesic effect of opiates could be induced by adding together the attenuation produced of both the sensorial and the affective dimensions of pain.     

Facilitation of the growth of an allogeneic tumour by suppressor cells in newborn rats.

The intravenous injection of as few as 15 Walker tumour cells into newborn rats consistently resulted in the development of pulmonary metastases and the death of the recipient within 2 weeks. Neither the outcome of tumour cell injection nor the interval until death could be modified by transferring 2 x 10(7) lymphocytes from tumour-immune adult rats to the neonataal hosts. In contrast with this failure to transfer adoptive anti-tumour immune responses to intact recipients, the administration of 350 rad irradiation before transfer of 10(6) immune lymphocytes constantly afforded protection against inoculated tumour cells. The simultaneous transfer of neonatal thymus cells with immune lymphocytes interfered with the establishment of an adoptive response in the irradiated newborn. Intiation of a graft-versus-host response in F1 hybrid neonates by injecting parental strain lymphocytes conferred resistance to tumour growth of the recpient, the magnitude of this effect increasing with the strength of the graft-versus-host reaction.     

Behavioural method to detect marginal neurotoxic effects of ivermectin in DA/Orl rats.

Ivermectin (22, 23-dihydroavermectin B 1) in subtoxic doses was administered subcutaneously to young adult DA rats. Prior to treatment the rats had been trained in a visual discrimination learning programme until their response pattern was stable. The behavioural response data were recorded during continued discrimination testing following the Ivermectin injection and compared with those of a control group. The results showed that the Ivermectin injection reduced the total number of lever presses and reinforcement collections. Further the treatment caused an increase in the total number of erroneous responses.