A field study of the effect of lameness on mechanical nociceptive thresholds in sheep

Threshold responses to a mechanical pressure test were measured in two groups of adult female sheep taken from 27 flocks in north Devon. The first group consisted of 470 healthy sheep and the second of 139 sheep suffering from obvious lameness, clinically diagnosed as foot rot. The lame sheep were assessed for the severity of the lesion and the level of lameness and assigned a score. In flocks with sheep with a severe degree of lameness, the sheep had a significantly lower threshold to a mechanical nociceptive stimulus than their matched sound controls and their thresholds remained low when tested three months later, after the apparent resolution of the foot rot lesion. In flocks where the lame sheep were less severely affected there was no difference in the threshold responses to a mechanical stimulus between the sound and lame sheep.

The effects of opioid and alpha 2 adrenergic blockade on non-steroidal anti-inflammatory drug analgesia in sheep

The analgesic effects of the non-steroidal anti-inflammatory drugs (NSAIDs) flunixin and dipyrone were assessed in healthy sheep with no pre-existing inflammation, and in sheep with a chronic inflammatory lesion, using a mechanical noxious stimulus. Saline and dexamethasone were given as controls. Blood taken from healthy sheep after NSAID administration was assayed for thromboxane B2 (TxB2) to compare the ability of these drugs to inhibit cyclo-oxygenase. Both flunixin and dipyrone produced a small but statistically significant rise in pain thresholds (18% and 21% of maximum possible effect respectively) in the healthy sheep which peaked at 30 min and had returned to pre-drug values by 2-3 h. In the lame sheep a similar effect occurred but the response was smaller, much more variable and tended to be prolonged. Saline and dexamethasone had no effect on thresholds over 6 h in either group of sheep. The rise in thresholds was prevented by pre-treatment with naloxone (an opioid antagonist) or atipamezole (an alpha 2-adrenergic antagonist) in the healthy sheep. Naloxone and atipamezole had no effect on thresholds when given alone to healthy sheep. Both NSAIDs inhibited the production of TxB2 to a similar extent. These results indicate that central mechanisms may be involved in NSAID analgesia.

Radioreceptor assay for determination of xylazine and medetomidine in sheep plasma

A radioreceptor assay technique is described for the measurement of xylazine and medetomidine in sheep plasma. The assay was based on the displacement of tritiated clonidine from a2-adrenoceptors in a rat brain homogenate by xylazine or medetomidine extracted from plasma. Plasma samples from sheep which had been given xylazine and medetomidine were treated with alumina to remove endogenous catecholamines which would otherwise have bound to alpha 2-adrenoceptors and interfered with the assay. The drugs were then extracted using chloroform, reconstituted in buffer and used to displace [3H]clonidine. The concentration of alpha 2-agonist was calculated by reference to standard curves. The method had a detection limit of 2.5 ng/mL for xylazine and 0.24 ng/mL for medetomidine. The assay could also be used to detect metabolites capable of binding to alpha 2-receptors.

Antinociceptive activity of midazolam in sheep

The purpose of this study was to examine the effects of midazolam on the nociceptive threshold responses in sheep. The intravenous administration of midazolam (0.1-0.3 mg/kg) produced a significant dose-dependent elevation of the mechanical and thermal nociceptive thresholds. The intravenous administration of flumazenil (20 micrograms/kg) markedly attenuated the antinociceptive activity of midazolam in the mechanical nociceptive test, whereas intravenous naloxone (0.2 mg/kg) had no significant effect on midazolam-mediated analgesia. The intrathecal administration of midazolam (1 mg), via chronically implanted cervical subarachnoid catheters, produced a significant elevation in the mechanical threshold responses. These results indicate that midazolam has antinociceptive actions in the sheep and suggest that this effect is, at least partially, mediated at the spinal level.

Effect of chronic pain associated with lameness on plasma cortisol concentrations in sheep: a field study

Plasma cortisol concentrations were measured in two groups of sheep taken from 29 flocks in north Devon. The first group were healthy adult females and the second group were adult females suffering from footrot in one forefoot. These sheep were assessed for the severity of the lesion and the level of lameness and assigned a score. The plasma cortisol concentration was significantly higher in the lame sheep than in the healthy sheep and remained so for up to three months after the apparent resolution of the clinical lesion. There was no correlation between the severity of the footrot and the concentration of plasma cortisol.

Antinociceptive effects of combining low doses of neuroleptic drugs and fentanyl in sheep

Effects of low doses of the neuroleptic drugs droperidol and zuclopenthixol, combined with a subanalgesic dose of the opioid mu-agonist, fentanyl, on mechanical nociceptive thresholds were evaluated in sheep. Intravenously administered droperidol (5 micrograms/kg of body weight) did not induce any change in the nociceptive thresholds when administered alone, but caused marked increase in threshold responses when combined with a subanalgesic dose of fentanyl (5 micrograms/kg). Similarly, a combination of i.v. administered zuclopenthixol (100 micrograms/kg) and fentanyl induced significant (P < 0.05) antinociceptive effects, whereas zuclopenthixol administered i.v. alone had no effect on the threshold responses. Intrathecal administration of a low dose of droperidol (5-micrograms total dose) combined with i.v. administered fentanyl also increased mechanical thresholds significantly (P < 0.05). These results indicate that interactions exist between dopaminergic and opioid systems in the processing of nociceptive information and that these effects may, at least partially, be mediated spinally.

Endocardial pacing, cardioversion and defibrillation using a braided endocardial lead system

The clinical efficacy and safety of a second-generation braided endocardial pacing, cardioversion and defibrillation lead system was evaluated in 25 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF). The lead system consisted of two 8Fr active fixation endocardial leads each with pacing and defibrillation electrodes and a thoracic patch electrode. Monophasic and biphasic shocks were delivered using a triple-electrode configuration with a right ventricular common cathode and right atrial and thoracic patch anodes. VT and VF were electrically induced. Rapid VT (rate > or = 180 beats/min) and VF were initially terminated by 20 J (550 V) shocks and slow VT (rate < 180 beats/min) by 10 J (400 V) shocks. One hundred fourteen episodes (rapid VT/VF 73, slow VT 41) were treated with 128 shocks (monophasic 80, biphasic 48). Mean ventricular pacing threshold was 0.7 +/- 0.5 ms before and 0.9 +/- 0.5 ms after endocardial shock delivery (p > 0.2). Mean ventricular electrogram amplitude in sinus rhythm was 11.9 +/- 5.7 mV before and 11.4 +/- 5.1 mV after shock delivery (p > 0.2). Simultaneous monophasic endocardial shocks terminated 53% of VF episodes at < or = 20 J. Simultaneous biphasic shocks terminated 94% of all VF episodes at < or = 20 J (p < 0.03). Efficacy of > or = 10 J shocks for rapid VT/VF was greater for biphasic (92%) versus monophasic (74%) shocks (p < 0.05) at lower average shock energy (15 +/- 7 J vs 19 +/- 7 J, respectively, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The spinal antinociceptive activity of the alpha 2-adrenoceptor agonist, xylazine in sheep

1. The intrathecal administration of xylazine (100 micrograms), via a chronic indwelling, cervical intrathecal catheter, produced a marked elevation of the mechanical nociceptive thresholds in the sheep. This antinociceptive effect was abolished by the prior intrathecal administration of the alpha 2-adrenoceptor antagonist, idazoxan. 2. The intrathecal administration of the selective alpha 2-antagonists, idazoxan (100 micrograms) and RX811059 (33 micrograms), significantly attenuated the antinociceptive activity of intravenous xylazine, with a 60-65% reduction in the area under the antinociceptive curve. The intrathecal administration of the antagonists alone had no significant effect on nociceptive thresholds. 3. Examination of the distribution of tritiated idazoxan (25 microCi in 100 microliters) indicated that the site of action of the drug was limited to the cervical spinal cord after intrathecal administration. 4. These studies demonstrate that a significant proportion of the antinociceptive effect of systemically administered xylazine is mediated by spinal alpha 2-adrenoceptors.

A technique for recording from spinal neurones in awake sheep

A technique is described for implanting a chamber on 1 or 2 vertebrae of the spinal column of the sheep. This chamber protrudes permanently through the dorsal skin of the back and is covered by a light bandage. Between recording sessions the chamber houses an inner cap sealing the hole that gives access to the cord. During recording sessions this cap is removed and a miniature manipulator inserted instead. This manipulator can accept a motor drive that holds a glass-coated tungsten microelectrode. The drive has a hole through which an arthroscope tube can be passed so that insertion of the electrode can be performed under visual control. Extracellular recordings have been made of single spinal neurones for up to 4 h in animals that are drug-free, untrained and only lightly restrained. Recording sessions can be repeated on a daily basis for several weeks until the dura and/or arachnoid becomes too thickened to permit electrode penetrations. Animals remain healthy and their behaviour remains normal throughout this time.

Analgesic effects of detomidine in thoroughbred horses with chronic tendon injury

This study was undertaken to assess the analgesia provided by detomidine (20 micrograms kg-1 intravenously) in thoroughbred horses. Pain thresholds to a mechanical noxious stimulus were measured before and after a period of mild chronic pain in one foreleg. Detomidine was a good analgesic in control animals; their pain thresholds were significantly elevated for about 60 minutes. After injury, the injured leg had a significantly lower pain threshold and the intensity and duration of analgesia provided by detomidine were significantly reduced. The analgesia in the opposite (sound) leg was also reduced, indicating that there were both central and peripheral aspects to this increased sensitivity to painful stimuli. Detomidine deserves to be considered as a potent analgesic in the horse rather than a sedative with analgesic side effects.

Effects of clinically occurring chronic lameness in sheep on the concentrations of plasma noradrenaline and adrenaline

Plasma adrenaline (AD) and noradrenaline (NA) concentrations were measured by high performance liquid chromatography with electrochemical detection in blood samples from control and lame sheep. The lame sheep suffered from naturally occurring foot rot and showed behavioural characteristics normally associated with chronic pain. The lame sheep were scored both for impairment of gait and pathology of the foot and divided into mild and severely affected groups. Both the mildly and severely lame group showed a significant increase in plasma AD and plasma NA which tended to persist even after clinical resolution of the condition. The measurement of plasma AD and NA may provide information which can be used to assess animals experiencing chronic pain, when taken in conjunction with other parameters, such as nociceptive thresholds and plasma hormone levels.

Dietary impact on biliary lipids and gallstones

Although dietary factors influence bile lithogenicity and gallstone formation, the main dietary effect appears to be indirect, depending on an interaction between caloric consumption and gender-specific aspects of lipoprotein metabolism. Excessive energy intake elicits its detrimental effect by altering lipoprotein and hepatic cholesterol metabolism in association with hyperinsulinemia. Factors, dietary and genetic, that favor elevated hepatic cholesterol synthesis and production of a bile acid profile in which chenodeoxycholic acid predominates appear to be associated with lithogenic bile. An inconsistent effect of dietary fat saturation on gallstones is that polyunsaturates possibly increase risk in men and decrease risk in women. Vegetable protein may reduce the risk of cholelithiasis. Whereas both the amount and type of dietary fiber influence cholesterol and bile lipid metabolism, specific associations between fiber and gallstones in humans remain elusive.

Venom immunotherapy: 10 years of experience with administration of single venoms and 50 micrograms maintenance doses

For the past 10 years, we have administered venom immunotherapy with single venoms, whenever it is possible, and maintenance doses of 50 micrograms. The choice of venoms was based on clinical history, skin test reactions, and a knowledge of venom cross-reactivity. There have been 258 re-stings in 108 patients with only three systemic reactions (2.7% per patient; 1.2% per sting). Two of these re-stings reactions were very mild, hives and facial edema, in patients who had had initial severe anaphylaxis. Five other patients had transient ill-defined symptoms, not considered allergic after re-stings. The patients covered a wide age range. Twenty-seven patients, nine under age 16 years, had initial dermal reactions only, and 44 patients had severe anaphylaxis. Most patients had multiple positive skin tests. Seventy-five patients received single venoms (yellow jacket, 58; honeybee, 15; hornet, 2), and 30 patients received two venoms. Re-stings occurred from 1 month to 8 years, (mean, 2 years) after starting treatment. Results indicate that this approach with 50 micrograms top doses and single venom immunotherapy may be sufficient in most patients with an associated decrease in the cost as well as possible increased morbidity associated with the use of multiple venom antigens.

Chronic intrathecal catheterization in the sheep

This paper describes a relatively simple and noninvasive method for the chronic implantation of intrathecal catheters in the sheep. The technique has been carried out on 17 occasions in nine sheep, with 60% of attempted catheterizations producing a correctly positioned, functional catheter. The placement and integrity of the catheters were confirmed by radiography using a contrast medium. Correctly placed catheters have been maintained for up to 16 months without problems.

The autoradiographic binding of [3H] quinuclidinyl benzilate to muscarinic receptors in the spinal cord of the sheep

Autoradiography of [3H] quinuclidinyl benzilate was used to demonstrate the distribution of muscarinic acetylcholine binding in the spinal cord of sheep. Binding was confined to the grey matter of the cord, and was most densely distributed in the substantia gelatinosa region of the dorsal horn, the lamina X region around the central canal, the intermediolateral columns and in various regions of the ventral horn. The use of specific M1 and M2 receptor subtype ligands, pirenzipine and 4-DAMP indicated that both receptor subtypes were present in most regions of dense binding.

Further studies on the antinociceptive activity and respiratory effects of buprenorphine in sheep

The thermal and mechanical analgesic profile of buprenorphine at a dose rate of 1.5 micrograms/kg i.v. was investigated in five sheep. This dose produced significant analgesia for 40 min against the thermal stimulus, but no mechanical antinociception. A higher dose rate of 12 micrograms/kg also failed to produce antinociception to a mechanical stimulus. In addition, the effect of the drug (6 micrograms/kg) on respiratory gas tensions was determined and no significant changes were observed.

Effects of chronic lameness on the concentrations of cortisol, prolactin and vasopressin in the plasma of sheep

Plasma cortisol, prolactin and vasopressin concentrations were measured by radioimmunoassay in blood samples from control and lame sheep. The lame sheep were all suffering from naturally occurring clinical cases of footrot and showed all the behavioural characteristics of chronic pain; they were scored for impairment of gait and pathology of the foot and divided into mild and severely lame groups. The severely lame sheep had increased plasma prolactin and decreased plasma cortisol concentrations. Plasma vasopressin was variable and showed no consistent changes with lameness. The relationships between plasma cortisol, prolactin and vasopressin may be a useful index in the assessment of animals experiencing chronic pain, when taken in conjunction with other measurements.

Analgesic activity and respiratory effects of butorphanol in sheep

The analgesic drug butorphanol tartrate has proved useful clinically in horses and dogs but its analgesic profile had not yet been investigated in sheep. This study was initiated to determine the thermal and mechanical antinociceptive activity of butorphanol (at the dose rates 0.05, 0.1 and 0.2 mg kg-1) in sheep. The drug produced significant analgesia in the thermal test system, the duration of which was dose related but no significant elevation in mechanical pressure thresholds could be detected. In a further set of experiments the dose rate was increased to 0.4 mg kg-1 and mechanical testing was repeated. There was still no clinically significant elevation in pressure thresholds. At a dose rate of 0.2 mg kg-1 the drug had no detectable effect on respiratory blood gas tensions. Behavioural changes were severe if a dose rate of 0.2 mg kg-1 was exceeded.

The influence of chronic pain on the analgesic effects of the alpha 2-adrenoceptor agonist, xylazine, in sheep

A comparison of the analgesic potency of the alpha 2-adrenoceptor agonist, xylazine, in control healthy sheep and sheep suffering chronic pain from footrot, indicated that the analgesic effectiveness of xylazine was significantly reduced in the animals experiencing chronic pain. This was measured by recording the threshold to a mechanically applied pressure stimulus. Furthermore, when the condition was apparently resolved, by conventional treatment over a period of 2 to 3 weeks, the decreased analgesic effectiveness of the alpha 2-agonist was still apparent although the animals were clinically cured of the footrot.