Pharmacological evidence for the involvement of alpha-2 adrenoceptors in the sedative effect of detomidine, a novel sedative-analgesic

Lidocaine, dexmedetomidine and their combination reduce isoflurane minimum alveolar concentration in dogs

The effects of intravenous (IV) lidocaine, dexmedetomidine and their combination delivered as a bolus followed by a constant rate infusion (CRI) on the minimum alveolar concentration of isoflurane (MAC_ISO) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MAC_ISO/BASAL) was determined after a 90-minute equilibration period. Thereafter, each dog received one of the following treatments (loading dose, CRI): lidocaine 2 mg kg⁻¹, 100 µg kg⁻¹ minute⁻¹; dexmedetomidine 2 µg kg⁻¹, 2 µg kg⁻¹ hour⁻¹; or their combination. MAC was then determined again after 45- minutes of treatment by CRI. At the doses administered, lidocaine, dexmedetomidine and their combination significantly reduced MAC_ISO by 27.3% (range: 12.5–39.2%), 43.4% (33.3–53.3%) and 60.9% (46.1–78.1%), respectively, when compared to MAC_ISO/_BASAL. The combination resulted in a greater MAC_ISO reduction than the two drugs alone. Their use, at the doses studied, provides a clinically important reduction in the concentration of ISO during anaesthesia in dogs.

Pharmacological modulation of functional connectivity: α2-adrenergic receptor agonist alters synchrony but not neural activation

Correlative low frequency fluctuations in functional MRI (fMRI) signals across brain regions at rest have been taken as a measure of functional connectivity to map large-scale neural networks; however, the neural origin is still not clear. Receptor-targeted pharmacological manipulation could elucidate the role of neuroreceptor systems in resting-state functional connectivity to provide another perspective on the mechanism. In this study, the dose-dependent effects of an α(2)-adrenergic receptor agonist, medetomidine, on brain activation and functional connectivity were investigated. Forepaw stimulation-induced activation and resting-state fluctuation in the rat somatosensory cortices and caudate putamen were measured using the blood oxygenation level dependent (BOLD) fMRI. The results showed significant dose-dependent suppression of inter-hemispheric correlation but not the amplitude in the somatosensory areas, while the stimulation-induced activation in the same areas remained unchanged. To clarify the potential change in the hemodynamic response caused by the vasoconstrictive effect of medetomidine, the resting perfusion fluctuation was studied by arterial spin labeling and showed similar results as the BOLD. This suggests that the oxygen metabolic rate and hence the neural activity may not be affected by medetomidine but only the synchrony between brain regions was suppressed. Furthermore, no change in functional connectivity with medetomidine dosages was seen in the caudate putamen, a region with much lower α(2)-receptor density. These results indicate that resting-state signal correlation may reflect underlying neuroreceptor activity and a potential role of the adrenergic system in the functional connectivity.

Interactions of xylazine and detomidine with alpha2-adrenoceptors in brain tissue from cattle, swine and rats

Xylazine is an alpha2-adrenoceptor agonist sedative with a much higher interspecies variability in effect than detomidine, another alpha2-agonist used in veterinary practice. In the present study, we have used radioligand binding in brain tissue to investigate if the high species variation in sensitivity to xylazine could be explained in terms of receptor interactions. Species known to be more (cattle) or less (swine and rats) sensitive to xylazine were used. There was no variation in the density or the subtype pattern of the alpha2-adrenoceptors that could explain the species variation recorded in vivo, as a homogenous population of the alpha2A/D-subtype (200-300 fmol/mg protein) was found in all species. The species differences in the affinities of xylazine and detomidine were minor and similar for the two drugs. The only parameter investigated where a significant species difference was found for xylazine but not for detomidine was the slope of the inhibition binding curve when the G-protein coupling was diminished. For xylazine this slope was considerably lower than unity (i.e. 0.77 +/- 0.075) using cattle preparations compared with 0.92 +/- 0.037 (mean +/- SE) and 0.90 +/- 0.028, respectively for swine and rats, while for detomidine this parameter was close to unity in all species (cattle, swine, rat). This finding indicates that the species variation in effect for xylazine could be due to differences at the G-protein level or further down-stream in the effect cascade.

Alpha-2 adrenergic agonists as analgesics in horses

Administration of alpha-2 agonists to horses produces a variety of behavioral effects (sedation, somnolence, analgesia), and physiological effects. One of the most significant beneficial effects of administering alpha-2 agonists is the degree of analgesia they provide. Alpha-2 agonists have been the mainstay of analgesia for colic pain in horses since their introduction to clinical veterinary medicine. The increased potency of the more recently introduced alpha-2 agonists allows the provision of analgesia for conditions not previously relieved by other drugs. Unfortunately, there are significant side effects associated with alpha-2 agonist administration. Studies are underway to identify the physiologic effects associated with the stimulation of each alpha-2 receptor subtype, in hopes of developing subtype-specific alpha-2 agonists and antagonists.

Detomidine-diazepam-ketamine anaesthesia in buffalo (Bubalus bubalis) calves

Eight buffalo calves (8-12 months, 70-100 kg) were randomly assigned to two groups of four animals each. Animals of group I were given detomidine (100 micrograms/kg), whereas animals of group II received a mixture of detomidine (100 micrograms/kg), diazepam (100 micrograms/kg) and ketamine (3 mg/kg) (DDK) intravenously. Various clinical parameters, such as weak time, down time, pedal and pinprick reflexes, muscle relaxation and extent of sedation, as well as heart and respiratory rates and electrocardiograms were measured before (time 0) and 15, 30, 45, 60, 75 and 90 min after treatment. In all the animals of group II (DDK), the pedal reflex was completely abolished (score: 3.00 +/- 0.00) within 5 min, the pinprick response was either very weak or it was completely abolished at this interval. Muscle relaxation and sedation were excellent within 5 min of DDK administration. The depth of sedation and analgesia was maximum from 5 to 15 min postinjection. Detomidine alone, however, failed to produce appropriate depression of the pedal and pinprick reflexes, sedation was mild and muscle relaxation was inadequate. Heart rate showed a significant (P < 0.05) decrease in group I, but the decrease was non-significant in group II. A more pronounced increase in respiratory rate was observed in group I as compared to group II. Animals of both groups recovered within 90 min without any complication. Minimal changes in the cardiovascular system in the group given the DDK combination were an advantage over the group given detomidine. The results indicated that DDK combination is safe and suitable for 15 min of anaesthesia with excellent muscle relaxation and has only limited cardiorespiratory effects in buffaloes.

Characterisation of the cardiovascular pharmacology of medetomidine in the horse and sheep

Medetomidine was administered to sheep and horses at a dose rate of 5 microg kg(-1) (i.v.). Heart rate and blood pressure were recorded. Medetomidine induced bradycardia and a biphasic blood pressure response consisting of a transient hypertension followed by hypotension. Administration of prazosin (an alpha1 adrenoceptor antagonist; 100 microg kg(-1), i.v.) had no effect on the cardiovascular response to medetomidine (5 microg kg(-1), i.v.), but inhibited the cardiovascular response of methoxamine (an alpha1 adrenoceptor agonist; 75 microg kg(-1), i.v.). L-659,066 (an alpha2 adrenoceptor antagonist which does not cross the blood brain barrier; 264 microg kg(-1), i.v.) attenuated the medetomidine induced bradycardia, but had no effect on the cardiovascular response to methoxamine. L659,066 also reduced the medetomidine induced hypertension in sheep, but had less effect on the horse. It is concluded that both alpha1 and alpha2 adrenoceptors are important in the control of cardiovascular function in horses and sheep. Medetomidine appears to act on alpha2 adrenoceptors alone in the sheep. The cardiovascular effects of medetomidine in the horse are complex and may be influenced by central alpha2 adrenoceptor regulation or effects on other receptor subtypes as well as direct stimulation of peripheral alpha2 adrenoceptors.

Ketamine modulation of the temporal pattern of discharges and spike train interactions in the rat substantia nigra pars reticulata

This study compares the temporal pattern of discharges of extracellularly recorded substantia nigra pars reticulata (SNr) single units in two experimental conditions: Equithesin- and ketamine-induced anesthesia. The analysis of the statistical properties of the spike trains recorded in the Equithesin group of animals showed that this experimental condition could be considered as a control condition with respect to previous data reported in the literature. We investigated the glutamatergic modulation of SNr activity at spike train level in a steady-state condition by using the anesthetic agent ketamine, which is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) glutamatergic receptors. The most relevant effect of ketamine at single unit level was to induce burst discharges, with an intraburst frequency rate near 50 Hz, specifically in units characterized by an initial long refractoriness in the Equithesin condition. The other classes of single units tended to discharge at a higher rate without any significant change in their temporal pattern of firing. Simultaneous recording of the spike trains of 108 SNr pairs (46 and 62 during Equithesin and ketamine condition, respectively) were equally distributed between pairs of units simultaneously recorded from the same electrode and from distinct electrodes at a distance up to 400 microm in the same hemisphere. Ketamine induced a significant increase in the number of pairs with synchronous firing (from 4 to 49%), which was strongly, but not exclusively, associated with an increased tendency to fire in bursts. Neighboring cells tended to fire with a similar pattern in either condition of recording, whereas synchronous firing between distant cells was observed only during ketamine condition.

Central alpha 2-adrenoceptors are highly stereoselective for dexmedetomidine, the dextro enantiomer of medetomidine

To determine whether different alpha 2-adrenoceptor-mediated functions have different stereochemical requirements in the central nervous system, we studied the pharmacological activities of the purified optical enantiomers of medetomidine (dl-4-[1(2,3-dimethylphenyl)ethyl]-1H-imidazole), a specific and selective agonist of alpha 2-adrenoceptors. We found that dexmedetomidine (the dextro enantiomer) had the pharmacological activity of medetomidine. Dexmedetomidine had hypotensive and bradycardic actions in anaesthetized rats as well as sedative (decreased spontaneous locomotor activity and prolonged sleep induced by hexobarbital in rats), analgesic (attenuated a writhing response induced by acetic acid in mice) and midriatic actions in rats. The potency of dexmedetomidine was slightly greater than that of medetomidine. 1-Medetomidine was generally without pharmacological activity, but it showed some sedative and analgesic properties at high doses. Although the findings obtained with l-medetomidine might indicate some deviation from strict homogeneity, these experiments demonstrate that the different alpha 2-adrenoceptor-mediated functions have similar stereochemical requirements in the central nervous system.

Cardiovascular effects of detomidine, a new alpha 2-adrenoceptor agonist, in the conscious pony

The cardiovascular effects of detomidine and xylazine were compared in six chronically instrumented, conscious ponies. Ponies were instrumented with a micromanometer in the left ventricular chamber, a Doppler flow probe on a coronary artery and sonomicrometer crystals in the left ventricular free wall. Heart rate, ventricular systolic pressure, stroke work, dP/dtmax, minute work and coronary blood flow were measured for 4 h following intravenous injection of detomidine at several doses or xylazine at 1.1 mg/kg. Both drugs caused a profound hypertensive response at 15 s post-injection. The magnitude of the pressure change did not increase with detomidine doses greater than 20 micrograms/kg. There was a dose-dependent effect on the duration of the hypertension. Bradycardia and A-V blockade of similar magnitude followed the hypertension at all drug doses. Both drugs caused a negative inotropic effect on the heart at all doses. Minute work, a mechanical index of myocardial O2 demand, and coronary flow decreased to a similar extent following all drug treatments. With the exception of a greater hypertensive response, detomidine at the dosages studied, produced cardiovascular effects that were very similar to those of the recommended dosage of xylazine.

Can UK-14, 304-18 lower IOP in rabbits by a peripheral mechanism?

Unilateral topical administration of alpha 2 adrenoceptor agonists lowers intraocular pressure (IOP) bilaterally in laboratory animals and man. Investigators have suggested that this decrease in IOP is mediated, in part, by alpha 2 adrenoceptors in the central nervous system (CNS). In the present study, the hypotensive activity of the alpha 2 agonist, UK-14,304-18 (UK), was evaluated following topical and intracameral administration. The unilateral administration of a relatively selective alpha 2 adrenoceptor agonist, UK (50 micrograms), lowered IOP bilaterally when applied topically to the eyes of rabbits. Intracamerally administered UK (0.05-50 ug) lowered IOP unilaterally in a dose-related manner with minimal pupillary and cardiovascular changes. The ocular hypotensive action of UK administered intracamerally was absent in rabbits that had been surgically sympathectomized. While these data demonstrate that UK can lower IOP in the rabbit independent of alpha 2 adrenoceptor stimulation in the CNS and other systemic sites, the expression of this response is dependent upon the presence of intact sympathetic innervation.

Objective assessment of detomidine-induced analgesia and sedation in the horse

The effects of detomidine, a veterinary sedative analgesic, were studied in the horse. Novel objective techniques were employed to assess the analgesic and sedative potency of this compound. Intravenous doses of 0.010, 0.020 and 0.040 mg/kg were administered to eight adult Thoroughbred racehorses according to a double-blind crossover design. Analgesia was measured by determining the latency to onset of the skin twitch and hoof withdrawal reflexes following noxious thermal stimulation of the withers and fetlock, respectively. Sedation was assessed by quantifying spontaneous locomotor activity in horses confined to an activity chamber, and by electronic measurement of head ptosis. Linear, dose-related increases in the intensity and duration of analgesia were observed. However, dose-related increases in duration, rather than intensity of sedation were observed. In conclusion, detomidine is an effective analgesic in the horse, but it is more potent in producing sedation than analgesia.

Anesthetic considerations for emergency equine abdominal surgery

The physiologic changes that take place in horses presented for emergency abdominal surgery and the effects of these changes on the horse's anesthetic management are discussed.

Metabolism of detomidine in the rat. I. Comparison of 3H-labelled metabolites formed in vitro and in vivo

The biotransformation of detomidine, a new alpha 2-adrenoceptor agonist, was studied using rat as the model animal. In vivo metabolism of the tritiated drug was compared to in vitro incubations with liver homogenates and intact, isolated hepatocytes. Metabolites were analysed by HPLC with radioactivity detection. The metabolic patterns in all systems were closely related. HPLC of urine gave twelve radioactive peaks. Tritiated water and unchanged 3H-detomidine were minor components. The two major peaks were tentatively identified as hydroxylated detomidine (14%) and its O-glucuronide (43%). Sulphate conjugates were not found. Isolated hepatocytes converted detomidine to the same two major products; the relative amount of the glucuronide increased with incubation time. In liver post-mitochondrial supernatant, hydroxylation was the dominant reaction, and the hydroxylated product comprised 74% of the total metabolites with non-induced and 50% with phenobarbital-induced liver. The major biotransformation in rat was thus concluded to be hydroxylation by the liver monooxygenases followed by glucuronic acid conjugation. The maximal rate of oxidation or the enzymatic capacity of a whole liver was estimated to be at least 100 nmol/min allowing for a high hepatic extraction ratio for detomidine. Together with the effective excretion of the glucuronide, this reaction sequence alone could account for the rapid elimination of the drug.

Colonic alpha 2-adrenoceptor-mediated responses in the pony

The motor responses of the caecum and colon to stimulation of alpha 2-adrenoceptors by xylazine and detomidine at the recommended dose levels of 0.6 and 0.1 mg/kg were investigated in three ponies. The motor changes of the left ventral colon induced by continuous intra-arterial infusion of a prostaglandin (PGF2 alpha) were used to assess the relative inhibitory effects of xylazine and detomidine in a colic model. The administration of alpha 2-agonists inhibited the spiking activity on the whole of the large intestine for 20-30 min (xylazine) or 2-3 h (detomidine). However, the detomidine-induced inhibition was preceded by a short period of increased smooth muscle basal tone as indicated by strain-gauge force transducer measurements. This pattern of activity was neither reversed nor prevented by the administration of tolazoline (10 micrograms/kg/min) intra-arterially. In contrast, inhibition of the colonic phasic and tonic motor activity by alpha 2-adrenoceptor stimulation was reversed competitively by tolazoline. The intra-arterial infusion of prostaglandin F2 alpha (10 micrograms/kg/min) induced prolonged and sustained spiking activity that might be related to signs of mild colic. Detomidine, and to a lesser extent xylazine, relaxed the whole of the large intestine and this was accompanied by alleviation of the signs of visceral pain.

Depression of reticulo-ruminal motor functions through the stimulation of alpha 2-adrenoceptors

Inhibition of the cyclical contractions of the reticulum and the rumen by detomidine (10-40 micrograms/kg, i.v.), xylazine (20-80 micrograms/kg, i.v.) and clonidine (2.5-10 micrograms/kg, i.v.) were compared in sheep and cattle housed individually in box stalls. Two alpha 2-adrenergic receptor blocking agents, tolazoline and yohimbine, were administered intravenously for prevention (0.1-0.4 mg/kg) or reversal (0.4-1.2 mg/kg) of these effects. Continuous recording of the reticuloruminal contractions and measurement of the volume of ruminal gas eliminated through the upper respiratory tract indicated that the three alpha 2-agonists inhibited the primary ruminal contractions associated with the reticular contractions. The occurrence of secondary ruminal contractions was also blocked in sheep, but only suppressed in cattle. The inhibition of reticulo-ruminal contractions was prevented or reversed competitively by the two alpha 2-blocking agents, suggesting an alpha 2-adrenoceptor mediation of the inhibition of cyclical motor activity of the reticulo-rumen. In contrast with tolazoline, yohimbine was unable to alleviate the accumulation of gas resulting from inhibition of the secondary ruminal contractions.

Alpha-adrenoceptor activity of arylalkylimidazoles is improved by alpha-methylation and impaired by alpha-hydroxylation

To investigate the effects of hydroxyl and methyl substitution of the alkyl bridge bond on the alpha-adrenoceptor activity of arylalkylimidazole derivatives, the cardiovascular effects of the molecules were studied in anaesthetized and pithed rats. The compounds studied were 4(5)-substituted imidazole derivatives with a methano, ethano or etheno bridge between the imidazole and the 2-, 2,3- or 2,6-methyl substituted phenyl rings. The hypotensive and bradycardic activities of the molecules in the anaesthetized rat were always reduced by alpha-hydroxylation and usually augmented by alpha-methylation of the bridge between the imidazole and phenyl rings. Hydroxylation was associated with a consistent, marked decrease in vasopressor and sympatho-inhibitory activity in the cardiovascular system of the pithed rat, but a methyl moiety as a "bulky substituent" in the alpha-position of the alkyl bridge did not decrease but even caused an increase in alpha-adrenoceptor activity in this test system. The detrimental effect of alpha-hydroxylation of the compounds at alpha 1- and alpha 2-adrenoceptors supports the notion that the interaction of the imidazoles at alpha-adrenoceptor is different from that of the classical, noradrenaline-like phenethylamines. The results also suggest that the alkyl bridge between the phenyl and imidazole rings of the imidazoles may contribute directly to the binding process.

Antinociceptive activity and mechanism of action of detomidine

The antinociceptive activity and mechanism of action of detomidine, a novel sedative-analgesic, were studied in mice and rats. Xylazine and morphine were included in the studies for comparison. In both acetic acid-induced writhing test in mice, and in tail flick test in rats, detomidine had potent, dose-dependent antinociceptive effects with ED50 values of 0.06 and 0.2 mg/kg i.p., respectively. Both xylazine and morphine were clearly less potent than detomidine in these tests. The antinociceptive effect of detomidine was only inhibited by alpha-2 antagonists (idazoxan, rauwolscine), which suggests that this action is mediated through stimulation of alpha-2 adrenoceptors. The significance of these findings for the use of detomidine in veterinary medicine is discussed.

Effect of detomidine on the release and turnover of noradrenaline in rat brain

The effect of detomidine, a novel veterinary sedative/analgesic, on the release and turnover of noradrenaline in rat brain was studied using both in vitro and in vivo techniques. Xylazine was included in the studies for comparison. Rat occipital cortex slices were preloaded with 3H-noradrenaline and the potassium-evoked release of tritium was measured using a superfusion system. Both detomidine and xylazine produced concentration dependent inhibition of stimulation evoked tritium release. A maximal inhibition of 66 and 50% was achieved at detomidine and xylazine concentrations of 1 X 10(-7) and 1 X 10(-6) M, respectively. The dose-response curve of detomidine was shifted to the right in a parallel manner by the selective alpha 2-antagonist idazoxan. Detomidine, while not altering the endogenous levels of noradrenaline, dopamine and 5-hydroxytryptamine, induced a dose-dependent inhibition of noradrenaline turnover as measured by the alpha-methyl-p-tyrosine method. Moreover, detomidine decreased the concentration of MHPG-SO4, the principal metabolite of central noradrenaline, in rat brain. Xylazine was in these tests at least two orders of magnitude less potent than detomidine.

alpha 2-Adrenoceptor agonists decrease free 3-methoxy-4-hydroxyphenylglycol in rat cerebrospinal fluid

The effects of alpha 2-adrenoceptor agonists on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were determined. Clonidine and two new imidazole derivatives, detomidine and medetomidine, and diazepam (as a control substance) were administered in sedative doses and the concentrations of unconjugated 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in CSF were monitored for 48 h. The alpha 2-agonists caused a dose-dependent, statistically significant decrease in the concentration of MHPG in CSF compared to the concentration in animals treated with saline or diazepam. Detomidine caused a statistically significant increase in the concentration of 5-HIAA compared to control treatments. The present results demonstrate the usefulness of monitoring drug-induced alterations in central nervous system (CNS) noradrenergic activity by measuring free MHPG in repeatedly collected cisternal CSF samples from freely moving rats. The alpha 2-agonists reduced the concentration of MHPG in CSF, indicating a decreased release, metabolism and turnover of noradrenaline in the CNS.

Cardiovascular action of detomidine, a sedative and analgesic imidazole derivative with alpha-agonistic properties

The cardiovascular effects of detomidine, a new veterinary sedative and analgesic imidazole derivative were studied in rats and cats using as reference compound xylazine, a widely employed veterinary antinociceptive and sedative drug with alpha-agonistic potency. Detomidine (1-30 micrograms/kg i.v.) and xylazine (10-1000 micrograms/kg i.v.) had both dose-dependent hypotensive and bradycardiac effects in anaesthetized rats. After i.v. administration of 3-100 micrograms/kg detomidine and 0.1-3 mg/kg xylazine to conscious rats, detomidine was more active in reducing the heart rate than in lowering the blood pressure. In anaesthetized cats, detomidine (1-30 micrograms/kg i.v.) was hypotensive and bradycardiac in a dose-dependent manner. A low dose of detomidine into the vertebral artery was more effective than i.v. application in reducing blood pressure. Idazoxan (0.3 mg/kg i.v. and 0.03 mg/kg into the vertebral artery) antagonized the hypotensive and bradycardiac effects of detomidine injected into the femoral vein or vertebral artery, respectively. In pithed rats, detomidine and xylazine stimulated presynaptic and postsynaptic alpha 2-adrenoceptors, and to a lesser extent postsynaptic alpha 1-adrenoceptors. The results indicate that detomidine is an agonist of central and peripheral alpha 2-adrenoceptors which exerts its hypotensive and bradycardiac effects via activation of the central alpha 2-adrenoceptors.

Comparison of the effects of detomidine and xylazine on some alpha 2-adrenoceptor-mediated responses in the central and peripheral nervous systems

The effects of detomidine, a novel veterinary sedative analgesic, on some alpha 2-adrenoceptor-mediated responses in the central and peripheral nervous systems were studied. In pithed rats, detomidine was a very potent agonist at both pre- and postsynaptic alpha 2-adrenoceptors. Doses of 1.9 micrograms/kg and 6.5 micrograms/kg inhibited electrically induced tachycardia by 50% and increased mean blood pressure by 50 mmHg, respectively. In comparison, xylazine, though similar in specificity, was 40 times less potent than detomidine in this preparation. In unanaesthetized rats, detomidine both caused sedation and induced complex changes in body temperature. Low doses caused decreases in rectal temperature but these were reversed as the dose was increased. The decrease in rectal temperature could be blocked by yohimbine. Prazosin somewhat inhibited but did not eliminate the hyperthermia seen with the very high doses of detomidine. Xylazine caused much more severe falls in rectal temperature which could not be completely antagonized by alpha 2-adrenoceptor blockade. Both detomidine and xylazine caused dose-dependent mydriasis in anaesthetized rats, detomidine being about 10 times more potent than xylazine. The mydriatic effects of detomidine could be prevented by alpha 2- but not by alpha 1-adrenoceptor blockade. It is concluded that detomidine is a potent and rather specific alpha 2-adrenoceptor agonist in the central and peripheral nervous systems. In comparison with xylazine, detomidine has higher potency and greater specificity, especially at central alpha 2-adrenoceptors.