Zoletil anaesthesia in chronobiological studies

Zoletil anaesthesia does not affect vital functions; however, there is no literature evidence regarding the effect of zoletil anaesthesia on the circadian rhythm(s) of vital functions. The aims of this study, with respect to dependence on the light–dark (LD) cycle under in vivo conditions in spontaneously breathing zoletil-anaesthetized rats, were to assess ECG parameters that may to predict development of ventricular arrhythmias and to assess arterial acid–base balance, which have the direct impact on the heart electrophysiology. The experiment was performed using zoletil-anaesthetized (30 mg/kg, i.p) female Wistar rats after adaptation to LD cycle (12 h:12 h). LD differences were found in heart rate, rectal temperature, electrophysiological myocardial parameters and acid–base balance. Animals were in systemic acidosis, hypoxia and hypercapnia in the both lighted periods of the regimen day. These results suggest that zoletil can be used in chronobiological studies investigating in vivo electrophysiological myocardial properties in rat models.     

Chronobiological Study of the Pharmacological Response of Rats to Combination Ketamine–Midazolam

Ketamine is commonly administered in combination with benzodiazepines to achieve surgical anaesthesia in rats. The aim of the present study was to analyze the pharmacological response of the combination ketamine–midazolam injected intraperitoneally at different times of day to rats. The study was conducted in July 2003, during the winter in the Southern hemisphere. Female prepuberal Sprague-Dawley rats synchronized to a 12 h light:12 h dark cycle (light, 07:00–19:00 h) were used as experimental animals. A combination treatment of ketamine (40 mg/kg) and midazolam (2 mg/kg) was administered to five different clock-time groups of rats (n = 7/group). Duration of the latency period, ataxia, loss-of-righting reflex (LRR), post-LRR ataxia, and total pharmacological response were assessed by visual assessment. Significant treatment-time differences were detected in the duration of LRR, post-LRR ataxia, and total pharmacological response duration. The longest pharmacological response occurred in rats injected during the light (rest) phase, and the shortest pharmacological response occurred in rats injected during the dark (activity) phase. Cosinor analysis documented circadian rhythmicity in the duration of post-LRR ataxia. The findings of the study indicate the duration of CNS-depression of the ketamine–midazolam combination exhibits treatment-time-dependent variation in the rat.     

Pentobarbital anaesthesia in the chronobiological studies

Administration of anaesthesia may influence specific aspects of in vivo animal experiments and is an especially important consideration for experiments conducted during the daytime. Although chronobiological studies investigating interactions between general anaesthesia and circadian rhythms are sparse, all suggest that general anaesthetic agents have a significant effect on circadian rhythms. To assess the suitability of pentobarbital anaesthesia in chronobiological studies, this study was performed using pentobarbital-anaesthetized (40 mg/kg, intraperitoneal) female Wistar rats after adaptation to a light–dark (LD) cycle (12 h:12 h). Heart rate, rectal temperature (RT), electrocardiographic parameters, autonomic nervous system activity, acid–base balance and plasma concentrations of Na⁺, K⁺, Ca²⁺ and Cl^- were evaluated for their dependence on the LD cycle. LD differences were found in heart rate and RT, measured before the administration of the anaesthetic agent. Pentobarbital anaesthesia eliminated LD differences in all electrophysiological parameters, parameters of heart rate variability (except RR intervals) and parameters of acid–base balance and ion concentrations. LD differences with borderline statistical significance were found only for Na⁺ levels, with a higher level in the light period (i.e. nonactive) of the rat regimen day. During pentobarbital anaesthesia, parasympathetic tone predominates and sympathetic activity is depressed. Spontaneously breathing rats under pentobarbital anaesthesia are in an asphyxic state independent of the LD cycle in in vivo experiments. Results of this study suggest that pentobarbital anaesthesia is not suitable for chronobiological studies. However, it is suitable for cardiovascular research that is done regardless of the circadian rhythmicity, because it does not cause significant changes in heart activity.     

Guaiphenesin-ketamine-xylazine infusion to maintain anesthesia in mules undergoing field castration

Background

In order to determine whether a combination of guaiphenesin, ketamine and xylazine can induce safe and satisfactory anaesthesia in mules undergoing field castration, eight healthy adult intact male mules were employed. They were premedicated with intravenous (IV) xylazine (1.3 mg/kg); an additional dose of xylazine (0.3 mg/kg IV) was administered in case of inadequate depth of sedation. Anaesthesia was induced with IV thiopental (6 mg/kg). The quality of sedation and induction was recorded. Anaesthesia was maintained with an infusion of guaiphenesin (50 mg/mL), ketamine (2 mg/mL) and xylazine (1 mg/mL) (GKX). The spermatic cord of each testis was infiltrated with 5 mL of 2% lidocaine. During anaesthesia heart rate (HR), respiratory rate (RR), rectal temperature (RT) and haemoglobin oxygen saturation (SpO₂) were measured every 5 min. The data were analysed with simple one-way analysis of variance (ANOVA). A P value < 0.05 was considered statistically significant. Time of anesthesia, time of surgery and time of recovery were recorded.

Results

Only one mule required an additional dose of xylazine to achieve a satisfactory depth of sedation. Thiopental at the dose of 6 mg/kg IV resulted in smooth induction and lateral recumbency in all animals. GKX provided adequate anaesthesia to perform castration in all mules. Muscle relaxation was deemed adequate and physiological variables remained stable and within references values during the anaesthesia and did not change in response to surgical stimulation. Time (mean ± standard deviation) from the end of the infusion to sternal recumbency and time from sternal recumbency to standing were 27.7 ± 4.6 and 30.1 ± 7.7 min, respectively.

Conclusions

The combination of xylazine, thiopental and GKX provides satisfactory short-term anaesthesia in mules undergoing field castration.

     

Ketamine-xylazine anaesthesia in the Djungarian hamster (Phodopus sungorus)

The combination of ketamine-xylazine was assessed as a surgical anaesthetic in Djungarian hamsters acclimatized to both long (16 h light: 8 h dark) and short (8 h light: 16 h dark) photoperiods. It was concluded that 50 mg/kg of ketamine with 10 mg/kg of xylazine or 100 mg/kg of ketamine with 5-10 mg/kg of xylazine when given together by intraperitoneal injection was a satisfactory general anaesthetic. Two hundred mg/kg of ketamine with 10 mg/kg xylazine caused death in 13 of 24 animals. There were no clinically significant effects on depth of anaesthesia due to photoperiod.     

Isoflurane with morphine is a suitable anaesthetic regimen for embryo transfer in the production of transgenic rats

During our initial attempts to produce transgenic rats, we found that an anaesthetic combination typically used for embryo transfer (intramuscular injection of ketamine [90 mg/kg] with xylazine [10 mg/kg]) yielded extensive variation in both the depth and length of anaesthesia. In the present prospective study, we compared the reproductive outcomes afforded by using either isoflurane (5% for induction, 2% for maintenance, carried in 2 l/min of oxygen) with morphine (5 mg/kg s.c., given immediately after isoflurane induction) or ketamine/xylazine in adult (250-300 g), pseudopregnant Sprague-Dawley rats. Each animal was anaesthetized with either isoflurane/morphine or ketamine/xylazine, after which 30 microinjected eggs were transferred into the left uterine horn. The mean pregnancy rate for isoflurane/morphine (15%) was 50% greater than that achieved with ketamine/xylazine (10%). The mean number of live pups (just over five per litter) was comparable for both regimens. All rats given isoflurane/morphine quickly achieved a surgical depth of anaesthesia and experienced a rapid postoperative recovery (3-5 min). In contrast, 25% of rats injected with ketamine/xylazine did not reach a depth of anaesthesia within 10 min that was sufficient for laparotomy, and all that were anaesthetized successfully required an extended postoperative recovery period (60-90 min). These data show that isoflurane/morphine is well tolerated by microinjected embryos and suggest that its use during embryo transfer may provide a means for both reducing the number of pseudopregnant females used and increasing the speed with which rat transgenic projects are completed.     

Age and anesthetic effects on murine electrocardiography

Murine models offer potential insights regarding human cardiac disease, but efficient and reliable methods for phenotype evaluation are necessary. We employed non-invasive electrocardiography (ECG) in mice, investigating statistical reliability of these parameters with respect to anesthetic and animal age. Mice (C57BL/6, 8 or 48 weeks) were anesthetized by ketamine/xylazine (K/X, 80/10 mg/kg ip) or by inhalation anesthetic (halothane, HAL; sevoflurane, SEV) and 6 lead ECGs were recorded. P wave duration and QT interval was significantly prolonged with K/X compared to HAL and SEV, indicating slowed atrial and ventricular conduction. P-R interval (atrio-ventricular conduction) was significantly increased in aged mice under all anesthetics. Heart rate was inversely correlated to QT interval and P wave duration. We also detected significant age effects with respect to optimal approaches for QT interval corrections. Power analysis showed 4-fold higher number of mice/group, were required for K/X, to achieve identical statistical sensitivity. These data demonstrate the importance of anesthetic selection for relevant and reliable ECG analysis in mice and illustrate the selective influences of anesthetics and age on cardiac conductance in this species.     

Immobilization with a single dose of ketamine hydrochloride and a combination of xylazine hydrochloride-ketamine hydrochloride and antagonism by yohimbine hydrochloride in the Japanese monkey (Macaca fuscata)

Forty-nine free-ranging Japanese monkeys (Macaca fuscata) were immobilized with 4.3–15.6 mg/kg (mean±S.D.=10.0±2.5 mg/kg) of ketamine hydrochloride (HCl), and 27 Japanese monkeys kept in enclosures were immobilized with a combination of 0.8–1.4 mg/kg (1.0±0.2 mg/kg) of xylazine HCl and 4.0–7.1 mg/kg (5.0±0.6 mg/kg) of ketamine HCl. In the xylazine HCl-ketamine HCl combination, good myorelaxation was induced. The mean induction times for the single dosage of ketamine HCl and the xylazine HCl-ketamine HCl combination were 2.8±1.5 min and 6.9±4.4 min, respectively. The mean immobilization times with the single dosage of ketamine HCl and the xylazine HCl-ketamine HCl combination were 39.3±16.5 min and 58.8±34.2 min, respectively. A half dose of ketamine HCl in combination with xylazine HCl could also immobilize Japanese monkeys successfully. Administrations of 0.5 mg/kg i.v. and 1.0 mg/kg i.m. of yohimbine HCl as an antagonist to xylazine HCl at 30 min after the induction reduced the immobilization time to 31.4±0.5 min and 49.0±22.1 min, respectively. Yohimbine HCl appears to be an effective antagonist to combination anesthesia by xylazine HCl-ketamine HCl in the Japanese monkey.     

Menstrual cycles in rhesus monkeys (Macaca mulatta) are unaffected by a single dose of the anesthetics ketamine and xylazine administered during the midfollicular phase at laparoscopy

To identify an anesthetic regimen that produces more complete relaxation and analgesia than ketamine hydrochloride (Ketaset®) alone, a combination of ketamine (15 mg/kg body weight) and the hypnotic xylazine (Rompun®, 0.33 mg/kg) was evaluated. Since the desired experimental application required that the anesthetic not interfere with normal hormonal events during the menstrual cycle, this combination administered on day 6 of the cycle was tested to determine whether hormonal surges, incidence of ovulation, or cycle length would be altered relative to the use of ketamine alone. In five of six animals, ketamine plus xylazine had no effect on the occurrence of timely surges of estrogen, luteinizing hormone (LH), or follicle-stimulating hormone (FSH), or on ovulation as determined by the presence of a corpus luteum at laparoscopy and normal serum concentrations of progesterone. There were no significant differences between the cycle during treatment and previous cycles in the same animal for length of the menstrual cycle (26.0 ± 2.3 [5] days; X? ± S.D. [n] or luteal phase (13.4 ± 2.4 [5] days). Likewise, these values did not differ from those of ten control monkeys treated with ketumine only on day 5 or 6 of the cycle (incidence of ovulation, 10/10; cycle length, 27.9 ± 1.8 [10]; luteal phase length, 15.1 ± 1.4 [10], P > 0.05). Patterns of circulating progesterone were not altered by the addition of xylazine anesthesia. These findings indicate that xylazine, given in the midfollicular phase, did not alter ovulatory events or menstrual cycle characteristics in rhesus monkeys. Ketamine plus xylazine apparently provides anesthesia appropriate for laparoscopy.     

Chemical immobilization of red foxes (Vulpes vulpes)

Red foxes (Vulpes vulpes) were immobilized with one of the following drug combinations: ketamine/xylazine (n = 22), ketamine/promazine (n = 35), ketamine/midazolam (n = 13), or tiletamine/zolazepam (n = 22). Foxes given ketamine/xylazine had the shortest induction and longest recovery times relative to other drug combinations, whereas foxes given ketamine/midazolam had the longest induction times. Recommended doses for the various combinations are given. Foxes given ketamine/xylazine were given either 0.1, 0.2, 0.4 mg/kg yohimbine, or saline 40 min after anesthetic induction. Administration of yohimbine significantly shortened arousal and recovery times relative to control values (P less than 0.001).     

Ketamine/xylazine/butorphanol: a new anesthetic combination for rabbits.

Ketamine is often used in combination with tranquilizers to produce surgical anesthesia in rabbits. While generally effective, there is considerable variation in the depth and duration of anesthesia achieved with ketamine combinations. Butorphanol is a mixed agonist-antagonist opioid that is widely used in a variety of other species. In this study, the commonly used ketamine (35 mg/kg)/xylazine (5 mg/kg) combination is compared with ketamine (35 mg/kg)/xylazine (5 mg/kg)/butorphanol (0.1 mg/kg). Rabbits were anesthetized on consecutive weeks with one of the two regimens. Physiologic parameters including heart rate, respiratory rate, blood pressure and arterial blood gases (pH, PO2, PCO2) were measured throughout anesthesia. Loss of palpebral, pedal and righting reflexes were recorded and reflexes were subsequently evaluated. The addition of butorphanol prolonged reflex loss to 140% (X = 68 min +/- 20 SEM) of control for palpebral reflex; 506% (X = 52 min +/- 18 SEM) of control for pedal reflex; and 159% (X = 128 min +/- 21 SEM) of control for righting reflex. Addition of butorphanol to ketamine/xylazine resulted in mild alterations in the physiologic changes traditionally associated with this combination. Butorphanol can be safely added to the ketamine/xylazine combination in rabbits and results in moderate increases in the duration of reflex loss.     

The effects of different anaesthetic treatments on the adreno-cortical functions and glucose levels in NZW rabbits

The effects of five anaesthetics on the corticosterone, cortisol and glucose concentrations were investigated in the NZW rabbit. Sixty animals were assigned to 6 treatment groups (n= 10 per group): control ( iv saline solution injection), ketamine (10 mg/kg iv) with either xylazine (3 mg/kg iv) or diazepam (2 mg/kg iv), pentobarbitone (30 mg/kg iv), thiopentone (20 mg/kg iv) and fentanyl/droperidol (1 mg/kg sc). Plasma glucocorticoids were measured by competitive enzymeimmunoassay EIA and glucose by an autoanalyzer, previously validated for this species in both cases. Blood samples were obtained at 6 time-points: before injection, at 10, 30, 60, 120 min and 24 h after injection of the anaesthetics/saline. A significant decrease of plasma glucocorticoids at 10-60 min was observed in the pentobarbitone and fentanyl/ droperidol groups, whereas the administration of ketamine/diazepam or thiopentone stimulated plasma glucocorticoid release, principally in the recovery period. However, in the ketamine/xylazine group no changes were observed in the glucocorticoid levels, except for a significative increase of cortisol at 60-120 min. Glucose levels significantly increased after ketamine/diazepam administration and principally, after ketamine/xylazine treatment. The present data suggest that ketamine/xylazine has little effect on glucocorticoid levels and provides an adequate level of surgical anaesthesia, hence it would be the anaesthetic of choice, although the hyperglycaemic effect after injection has to be considered for any experimental procedures in rabbits.     

Immobilization of swift foxes with ketamine hydrochloride-xylazine hydrochloride

There is an increasing need to develop field immobilization techniques that allow researchers to handle safely swift foxes (Vulpes velox) with minimal risk of stress or injury. We immobilized captive swift foxes to determine the safety and effectiveness of ketamine hydrochloride and xylazine hydrochloride at different dosages. We attempted to determine appropriate dosages to immobilize swift foxes for an adequate field-handling period based on three anesthesia intervals (induction period, immobilization period, and recovery period) and physiologic responses (rectal temperature, respiration rate, and heart rate). Between October 1998-July 1999, we conducted four trials, evaluating three different dosage ratios of ketamine and xylazine (2.27:1.2, 5.68:1.2, and 11.4:1.2 mg/kg ketamine:mg/kg xylazine, respectively), followed by a fourth trial with a higher dosage at the median ratio (11.4 mg/kg ketamine: 2.4 mg/kg xylazine). We found little difference in induction and recovery periods among trials 1-3, but immobilization time increased with increasing dosage (P < 0.08). Both the immobilization period and recovery period increased in trial 4 compared with trials 1-3 (P < or = 0.03). There was a high variation in responses of individual foxes across trials, making it difficult to identify an appropriate dosage for field handling. Heart rate and respiration rates were depressed but all physiologic measures remained within normal parameters established for domestic canids. We recommend a dosage ratio of 10 mg/kg ketamine to 1 mg/kg xylazine to immobilize swift foxes for field handling.     

Effects of repeated anaesthesia with ketamine/medetomidine and of pre-anaesthetic administration of buprenorphine in rats

Two groups of rats were anaesthetized at weekly intervals for 6 weeks with either ketamine/medetomidine alone (60 mg/0.4 mg/kg i.p.) or ketamine/medetomidine (45 mg/0.3 mg/kg i.p.) one hour following buprenorphine (0.05 mg/kg s.c.). Animals that received buprenorphine had longer periods of surgical anaesthesia (P = 0.04) and a greater depression of both mean pedal withdrawal score (P < 0.01) and mean respiratory rate (P = 0.014). Mean total duration of anaesthesia was also greater in the buprenorphine group on day 1. Sleep times reduced with successive doses of anaesthetic in the buprenorphine group (P = 0.024). Two animals in the buprenorphine group died. Repeated anaesthesia with ketamine/medetomidine alone was not associated with anaesthetic mortality. These results indicate that although buprenorphine has a clear anaesthetic-sparing effect, its use with ketamine/medetomidine may be associated with an increased risk of anaesthetic-related mortality.     

Anaesthesia of free-ranging Northern chamois (<Emphasis Type="Italic">Rupicapra rupicapra</Emphasis>) with xylazine/ketamine and reversal with atipamezole

One-hundred and fifty-five free-ranging Northern chamois (Rupicapra rupicapra) were anaesthetised in the course of a restocking programme using xylazine plus ketamine. Mean ± SD dosages for xylazine and ketamine were 1.9 ± 0.5 and 2.2 ± 0.7 mg/kg, respectively. In 57 chamois, sedation was reversed using 0.3 ± 0.1 mg/kg atipamezole. Although all the anaesthetic dosages tested immobilised free-ranging Northern chamois, shorter induction times (4.8 ± 2.6 min), deeper sedation with no reaction to handling in >90% of the animals and quick reversal (4.0 ± 2.7 min) were obtained using 2.5 mg/kg xylazine plus 3.0 mg/kg ketamine reversed with 0.25 mg/kg atipamezole. Under the conditions of this study, suggested standard doses are 63 mg/animal xylazine plus 76 mg/animal ketamine reversed by 6.3 mg/animal atipamezole. This anaesthetic protocol improves the results from the previous study of Dematteis et al. (Vet Rec 163:184–189, 2008) using xylazine alone.     

Chronobiological Study of the Pharmacological Response of Rats to Combination Ketamine-Midazolam

Ketamine is commonly administered in combination with benzodiazepines to achieve surgical anaesthesia in rats. The aim of the present study was to analyze the pharmacological response of the combination ketamine-midazolam injected intraperitoneally at different times of day to rats. The study was conducted in July 2003, during the winter in the Southern hemisphere. Female prepuberal Sprague-Dawley rats synchronized to a 12 h light:12 h dark cycle (light, 07:00-19:00 h) were used as experimental animals. A combination treatment of ketamine (40 mg/kg) and midazolam (2 mg/kg) was administered to five different clock-time groups of rats (n = 7/group). Duration of the latency period, ataxia, loss-of-righting reflex (LRR), post-LRR ataxia, and total pharmacological response were assessed by visual assessment. Significant treatment-time differences were detected in the duration of LRR, post-LRR ataxia, and total pharmacological response duration. The longest pharmacological response occurred in rats injected during the light (rest) phase, and the shortest pharmacological response occurred in rats injected during the dark (activity) phase. Cosinor analysis documented circadian rhythmicity in the duration of post-LRR ataxia. The findings of the study indicate the duration of CNS-depression of the ketamine-midazolam combination exhibits treatment-time-dependent variation in the rat.     

Reversal of ketamine/xylazine anesthesia in the rabbit with yohimbine

Ketamine and xylazine used in combination have been shown to be effective, easily administered, cost efficient agents for surgical anesthesia in the rabbit. The effect of xylazine on the central nervous system has been shown to be mediated through alpha-2 adrenergic receptors. Yohimbine, an alpha-2 adrenergic antagonist has been shown to reverse xylazine induced depression and partially antagonize ketamine in other species. We evaluated the antagonistic effect of yohimbine on ketamine/xylazine anesthesia in the rabbit. Six New Zealand White rabbits were anesthetized with intramuscular ketamine (50 mg/kg) and xylazine (10 mg/kg) to establish baseline parameters including respiratory rate, heart rate, and palpebral, pedal and postural reflex activity. Fourteen days later each rabbit was subjected to the same anesthetic regimen followed 30 minutes later by the intravenous administration of yohimbine (0.2 mg/kg). The duration of anesthesia estimated by the time elapsed between the loss and return of the palpebral reflex was reduced in the yohimbine treated trial (means = 29.7 +/- 1.9 minutes) compared to the control trial (means = 67.0 +/- 13.5 minutes). The palpebral reflex returned within 5 minutes following yohimbine treatment. Our results indicated that yohimbine is an effective antagonist of ketamine/xylazine anesthesia in the rabbit. Yohimbine decreases anesthetic duration after intravenous administration and also may aid in the control of undesirable anesthetic effects and overdosage.     

An evaluation of three anaesthetic regimes in the gray short-tailed opossum (Monodelphis domestica)

The effect of several anaesthetic agents on the gray short-tailed opossum (Monodelphis domestica) was investigated. Pentobarbitone sodium at a dose of 50 mg/kg sedated the animals but did not produce analgesia or anaesthesia. A combination of ketamine hydrochloride and xylazine at 40 mg/kg and 5 mg/kg, respectively, sedated the animals, but anaesthetic levels were not attained. Halothane was most effective in producing anaesthesia in Monodelphis domestica. Hypothermia was a major side effect with all three anaesthetic regimes.     

A comparison of ketamine/xylazine and ketamine/xylazine/acepromazine anesthesia in the rabbit

Parenteral anesthetic combinations such as ketamine and xylazine have become the agents of choice for anesthesia in the rabbit, because they are effective, easily administered and inexpensive. A number of recent reports have recommended including acepromazine in this combination, but a critical evaluation of this combination in the rabbit has not been reported. Five adult New Zealand white rabbits were anesthetized intramuscularly with ketamine (35 mg/kg) and xylazine (5 mg/kg) with or without acepromazine (0.75 mg/kg). The study was conducted in a double blind fashion, where each rabbit was administered both combinations at a minimum of 7 day intervals. Physiologic parameters were evaluated including heart rate, respiratory rate, central arterial blood pressure, pedal, palpebral and postural reflex activity. The duration of general anesthesia, estimated by the time elapsed between the loss and return of the palpebral reflex, was greater (means = 99 +/- 20 minutes) when acepromazine was employed in the combination compared to (means = 77 +/- 5 minutes) when ketamine/xylazine were used alone. Mean central arterial blood pressure reached a lower level when acepromazine was utilized (means = 46 +/- 8 mm/Hg) than when it was not (means = 57 +/- 12 mm/Hg.). The addition of acepromazine in a ketamine/xylazine combination resulted in a 28% longer period of anesthesia, a 19% lower mean central arterial blood pressure and a 32% longer recovery of postural reflexes. The ketamine/xylazine/acepromazine combination is a useful regimen for normovolemic animals when anesthetic duration greater than that produced by ketamine/xylazine alone is required.     

Immobilization of white-tailed deer with telazol,ketamine, and xylazine,and evaluation of antagonists

Telazol–xylazine and ketamine–xylazine are versatile and safe drug combinations that are used frequently for chemical immobilization of cervids. Although neither combination consistently offers rapid induction and recovery, we hypothesized that a combination of Telazol, ketamine, and xylazine (TKX) would provide a safe and effective alternative for immobilization of white-tailed deer (Odocoileus virginianus). During a 2-stage study, we evaluated the effectiveness of yohimbine and tolazoline as alpha₂-adrenergic antagonists (2005–2006), and characterized the factors that affected chemical immobilization of male deer with a targeted dose of telazol (2.20 mg/kg), ketamine (1.76 mg/kg), and xylazine (0.44 mg/kg), using explosive-charged darts (2007–2010). During the first stage, we randomly assigned deer to antagonist treatments, including a control group that did not receive an antagonist (n = 8), a tolazoline (4 mg/kg) treatment (n = 16), and a yohimbine (0.11 mg/kg) treatment (n = 15). Recovery times were longer (P = 0.0013) for control (150.6 ± 21.7 min) and yohimbine (74.5 ± 13.1 min), compared with tolazoline (12.5 ± 12.3 min). Tolazoline resulted in faster and more complete recovery compared with the frequent incomplete antagonism and ataxia observed with yohimbine. During the second stage, 56 immobilization events (2007–2010) with TKX yielded a mean induction time of 7.8 minutes (SE = 0.44). Repeated-measures analyses indicated that induction and recovery were affected by body weight, with larger males taking longer to become recumbent (P = 0.08), but they recovered more rapidly (P = 0.003) following administration of tolazoline. Physiological parameters we measured under anesthesia were within normal ranges for white-tailed deer; however, initial temperature was higher (β = −0.86) for younger males (P = 0.014). Final physiological parameters were closely related to initial measurements, with rectal temperature being the most preserved (β = 0.90); heart and respiration rate declined (β < 0.60) during anesthesia. Our results indicate that TKX may be useful for chemically immobilizing white-tailed deer, and we recommend tolazoline as an antagonist for xylazine. © 2012 The Wildlife Society.