Enhancement of the ambulation-increasing effect of opioid analgesics by ethanol in mice

The interaction between opioid analgesics (morphine and buprenorphine) and central depressants (ethanol, pentobarbital and diazepam) was investigated by means of ambulatory activity in mice. The ambulation-increasing effect of both morphine (10 mg/kg, s.c.) and buprenorphine (1 mg/kg, s.c.) was enhanced by the combined administration of ethanol (0.8-3.2 g/kg, p.o.) in a dose-dependent manner. Naloxone (0.1 mg/kg, s.c.) was effective for reducing the enhanced ambulatory activity. The pretreatment with Ca-cyanamide (5 mg/kg, p.o., 30 min before) reduced the enhancement of the ambulation-increasing effect induced by the combined administration of opioid analgesics with ethanol, although it scarcely modified that of morphine and buprenorphine alone. On the other hand, neither pentobarbital (1-30 mg/kg, s.c.) nor diazepam (0.25-2 mg/kg, s.c.) modified markedly the ambulation-increasing effect of morphine and buprenorphine. The present results suggest that ethanol specifically interacted with opioid analgesics when the mouse's ambulatory activity was used as the indicator.

Establishment of chronic intravenous drug self-administration in the C57BL/6J mouse

A wide variety of drugs that have significant human abuse potential have been demonstrated to function as positive reinforcers in animals. The present study was designed to characterize a new mouse model of chronic intravenous drug self-administration. Adult male C57BL/6J mice, implanted with external jugular infusion catheters, were given access to response-contingent injections. They did not initiate responding for saline delivery, whereas the C57BL/6J mice initiated morphine, cocaine, methamphetamine and pentobarbital self-administration. Drug-maintained responding was consistently and significantly higher for each compound than for saline responding. In contrast to C57BL/6J mice, DBA/2J mice failed to initiate cocaine self-administration. Thus, chronic intravenous drug self-administration procedures can be adapted to the inbred mouse.

Effects of inhalation and intravenous anesthetic agents on pressor response to NG-nitro-L-arginine

The effects of anaesthetic agents on pressor effect of NG-nitro-L-arginine (L-NNA), a potent inhibitor of nitric oxide (NO) synthesis, were examined in rats. I.v. bolus of L-NNA (1-32 mg/kg) in conscious rats dose dependently increased mean arterial pressure (MAP) to a maximum value of 53 +/- 2 mmHg at 16 mg/kg with ED50 value of 4.7 +/- 0.9 mg/kg. The effects of a single i.v. bolus dose (32 mg/kg) of L-NNA were examined in conscious rats and rats anaesthetised with pentobarbital, chloralose, ketamine, althesin (mixture of alphaxalone and alphadolone), urethane, enflurane or halothane. In conscious rats, peak MAP (51 +/- 3 mmHg) was reached 10 min after i.v. injection and the effect lasted more than two hours. The magnitudes of peak MAP differed under the influence of anaesthetic agents with the following rank order: althesin greater than conscious = pentobarbital = chloralose = ketamine = urethane greater than enflurane much greater than halothane (in which there was negligible change in MAP). The onsets were delayed in rats anaesthetised with pentobarbital, althesin, chloralose and enflurane but not altered with ketamine and urethane compared to that in conscious rats. Therefore, L-NNA caused intense and prolonged pressor response in conscious rats and rats anaesthetised with the i.v. anaesthetic agents pentobarbital, chloralose, ketamine, althesin and urethane. MAP effect of L-NNA was markedly attenuated by the inhalation anaesthetics halothane and enflurane.

Discriminative stimulus effects of diazepam in humans

Humans were trained to discriminate between 10 mg of diazepam (DZ) and placebo. Subjects reported to the laboratory in the morning several times a week for a total of 23 sessions. They filled out subjective effects questionnaires, ingested a capsule and then were free to leave. They also filled out questionnaires 1, 3 and 6 hr after leaving. During the first four sessions the drugs were identified to the subject before ingestion by letter code. During the next seven sessions the procedure was the same except the capsules were not identified to the subject. Six hours after receiving the capsule, subjects telephoned the experimenter to report their identification. When correct, they received a monetary bonus. If the identification was correct on five of the seven sessions, subjects entered the third phase. This phase had six additional training sessions as described previously. During the other six sessions that were intermixed, subjects received capsules that contained test drugs. Sixteen of 18 subjects learned the discrimination and 14 entered the third phase. They identified 2 mg of DZ, 1 mg of lorazepam and 10 mg of d-amphetamine as placebo and 2 mg of lorazepam as 10 mg of DZ. Over half of the subjects identified 5 mg of DZ and 50 mg of pentobarbital as 10 mg of DZ. DZ (10 mg) produced significant time-related changes on several subjective effect measures and these effects were typical of those produced by sedative-like drugs. The subjective effects of the test compounds were largely correlated with the drug identification. These results indicate that 10 mg of DZ can function as a discriminative stimulus in humans and this discrimination is dose-related and pharmacologically specific.

Comparison of several combinations for anesthesia in rabbits

Few safe and effective anesthesia regimens have been described for use in rabbits, partially because of the susceptibility of this species to sometimes fatal respiratory depression. Although inhalant anesthetics are generally safer than injectable anesthetics, their use may be limited by lack of equipment or facilities. This study was conducted to compare effects of several injectable anesthetics in rabbits on response to noxious stimuli, heart rate, respiratory rate, and rectal temperature. Six injectable anesthetic combinations were administered to rabbits: xylazine-ethyl-(1-methyl-propyl) malonyl-thio-urea salt (EMTU), ketamine-EMTU, xylazine-pentobarbital, xylazine-acepromazine-ketamine (XAK), ketamine-chloral hydrate, and ketamine-xylazine. All combinations induced a depression of respiratory rate. Although rectal temperature values were reduced to some degree in each group, the most profound hypothermia was induced by XAK. The combination that induced the longest duration of anesthesia was XAK. It was concluded that XAK was preferable for longer periods of anesthesia (60 to 120 minutes), although it induces severe hypothermia. For short periods of anesthesia, xylazine-pentobarbital, xylazine-EMTU, or ketamine-xylazine were deemed adequate; however, xylazine-EMTU induced the best survivability and consistency.

Evaluation of intraperitoneal and intrahepatic administration of a euthanasia agent in animal shelter cats

One hundred eighty-one adult cats, with body weight greater than 1.8 kg, were obtained from animal shelters, then were administered a sodium pentobarbital-lidocaine euthanasia agent by either the intraperitoneal (IP; n = 77) or intrahepatic (IH; n = 85) route. A preliminary study (n = 19 cats) indicated that most cats gave no indication of perception of injection (responding) if restraint was minimal and injection was rapid. During IP injection, 3 of the 77 cats (4%) responded (turned the head backward or vocalized). Of the 85 cats given IH injection, 8 (9%) responded; however, no response approached the magnitude of that observed after IM injection of ketamine hydrochloride. After either injection route, cats were observed for excitement (any exaggerated activities of stage-I and -II anesthesia (eg, vocalizing, flopping, sneezing, licking, running, paddling), and after cardiac standstill, cats were necropsied to identify exact location (final site) of the injection. Of 53 initial IP injections, final site for 22 (42%) was in the peritoneal cavity (PC). Use of a sideport needle (n = 24) did not significantly increase accuracy of IP injection. The small and large intestines were penetrated by 27% (15/55) of the IP injections from the right side, and the spleen was penetrated by 32% (7/22) of the left-side injections. Intrahepatic injection was significantly (P less than 0.05) more accurate, with 70 of 85 (82%) of the final sites being the liver only, the liver/PC, or the PC only. Twenty-five percent (13/53) of IP injections resulted in excitement (all stage-I and -II anesthesia-exaggerated activities cumulative to 30 seconds).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of diltiazem, verapamil, nifedipine, and nicardipine on sympathetic tachycardia in decentralized hearts of anesthetized dogs

Intravenous diltiazem (10-300 micrograms/kg), verapamil (10-300 micrograms/kg), nifedipine (1-100 micrograms/kg) and nicardipine (1-100 micrograms/kg) inhibited the tachycardia caused by cardiac sympathetic nerve stimulation (SNS, 0.5-4 Hz) in decentralized hearts of anesthetized dogs. The dose range of each drug required to inhibit the SNS-induced tachycardia was almost equivalent to that required to produce the increase in coronary blood flow and the decrease in blood pressure. Nifedipine and nicardipine were equi-active and about 10 times more potent than diltiazem and verapamil in inhibiting the SNS-induced tachycardia. They produced a slight but dose-dependent slowing of the resting heart rate. The negative chronotropic potency was approximately nicardipine, verapamil greater than nifedipine, diltiazem. Bay K 8644 (30 micrograms/kg) antagonized the inhibitory effects of diltiazem (100 micrograms/kg) and nifedipine (30 micrograms/kg) on the SNS-induced tachycardia. Tachycardia induced by intracoronary norepinephrine (0.03-0.3 micrograms) was suppressed by diltiazem (30-300 micrograms/kg) and nifedipine (10-100 micrograms/kg). The inhibitory effects of calcium entry blocking drugs on the sympathetic tachycardia appear to be explained by the interference of the beta-adrenoceptor-mediated increase in slow inward current in the sinoatrial (SA) node. It is also suggested that other mechanisms different from calcium entry blocking action contribute to the negative chronotropic response to these calcium entry blocking drugs.

A double isotope technique to determine regional albumin permeability: effects of anesthesia

The transvascular leakage of albumin in various organs and tissues was studied with a double isotope technique in rats anesthetized with sodium pentobarbital, given intraperitoneally or intravenously, and in unanesthetized (conscious) rats. 125I-labeled albumin and 131I-labeled albumin were injected into the tail vein 1 hr apart. The albumin permeability index in tissues and organs is indicated by the local ratio (Xa/Ya)/(Xb/Yb), where (Xa/Ya) is the ratio of 125I/131I-albumin activities per g of tissue and (Xb/Yb) is the ratio of 125I/131I-albumin activities per g of blood. If there is no passage of albumin across the capillary membrane over the 1-hr period of study, the permeability index will be equal to one. In unanesthetized rats, the liver, lung, kidney, femoral muscle, and femoral skin were regions with a high albumin permeability index (above 2). In these organs, intraperitoneal and intravenous anesthesia caused a decrease or no significant change of the albumin permeability index. There was no significant albumin leakage over 1-hr period (index not significantly different from 1) in the mesentery, abdominal muscle, abdominal skin, cremaster, heart, and brain of unanesthetized rats. Intraperitoneal anesthesia caused the albumin permeability index to increase to approximately 4 in the mesentery, abdominal muscle, and the abdominal skin, but not in the cremaster, heart, or brain. These results demonstrate that pentobarbital anesthesia when given into the peritoneal cavity causes a significant increase in albumin leakage in the abdominal region.

Initiation and execution of locomotion elicited by diencephalic stimulation: regional differences in response to nembutal

At moderate levels of Nembutal, within the anesthetic range, locomotor stepping can be elicited by brain stimulation. We determined if Nembutal (7, 14 and 28 mg/kg) had different effects on locomotion elicited by stimulation at different brain regions. Two regions were compared: the medial forebrain bundle (MFB, 13 sites) and the areas medial and dorsal to it (MED/DORSAL, 20 sites). Locomotion was produced by electrical stimulation (50 microA, 0.5 msec pulses, 10 to 160 Hz) of unrestrained rats in a rotary runway. The latency to initiate locomotion and the time to complete 1 revolution of the rotary were measured. With no drug, MFB locomotion was initiated sooner but took longer to complete than MED/DORSAL locomotion. Nembutal at 7 mg/kg did not affect initiation of MFB or MED/DORSAL locomotion. Nembutal at 14 mg/kg shortened MFB initiations, but this dose prolonged MED/DORSAL initiations. Initiations with both types of sites were blocked with 28 mg/kg. The 7 and 14 mg/kg doses prolonged the locomotor completion times of the MFB sites but not of the MED/DORSAL sites. The results indicate that the response to Nembutal differs qualitatively for locomotion elicited by stimulation of the MFB and locomotion elicited by stimulation of the medial and dorsal hypothalamus. The mechanisms underlying the difference remain to be elucidated; they may relate to nonlocomotor behaviors also elicited by stimulation or to the motivational states reflected in those behaviors.

The effect of euthanasia technique on vascular arachidonic acid metabolism and vascular and intestinal smooth muscle contractility

This study was designed to determine the effects that specific euthanasia methods have on vascular arachidonic acid metabolism and vascular and intestinal smooth muscle contractility. Rats were euthanatized by decapitation (DC), pentobarbital overdose (PB), or anesthesia with CO2, methoxyflurane or ether followed by DC (CO2-DC, Met-DC, Ether-DC, respectively). Rabbits were killed by a similar protocol, but CO2 overexposure replaced Ether-DC. The rat and rabbit aortas produced mainly 6-keto PGF1 alpha, the prostacyclin metabolite, and lesser amounts of PGE2. No qualitative differences were seen in arachidonate metabolites. However, aortic tissue from rabbits and rats killed by Met-DC produced more prostacyclin. In contrast, aorta from rabbits euthanatized by CO2-DC produced less prostacyclin than controls, whereas aorta from rats killed in the same way yielded greater amounts of prostacyclin. Aortic tissue from rabbits killed by Met-DC and CO2-OD was less responsive to acetylcholine (ACH). Intestinal contractility to ACH was increased in rabbits when Met-DC was used as the method of euthanasia, while colon from rats sacrificed by Met-DC showed decreased responsiveness to ACH. Colon from rats killed by intraperitoneal PB exhibited altered contractility to ACH and norepinephrine. The results of this study show that methoxyflurane, carbon dioxide (rabbit) and pentobarbital (rat) alter the vascular synthesis of prostacyclin and smooth muscle contractility. We conclude that the method of euthanasia affects certain physiologic parameters and careful consideration should be given to the selection of a particular euthanasia technique.

Cerebral radioprotection by pentobarbital: dose-response characteristics and association with GABA agonist activity

Pentobarbital reduces cerebral radiation toxicity; however, the mechanism of this phenomenon remains unknown. As an anesthetic and depressant of cerebral metabolism, pentobarbital induces its effects on the central nervous system by stimulating the binding of gamma-aminobutyric acid (GABA) to its receptor and by inhibiting postsynaptic excitatory amino acid activity. The purpose of this study is to investigate the role of these actions as well as other aspects of the radioprotective activity of pentobarbital. Fischer 344 rats were separated into multiple groups and underwent two dose-response evaluations. In one set of experiments to examine the relationship of radioprotection to pentobarbital dose, a range of pentobarbital doses (0 to 75 mg/kg) were given intraperitoneally prior to a constant-level radiation dose (70 Gy). In a second series of experiments to determine the dose-response relationship of radiation protection to radiation dose, a range of radiation doses (10 to 90 Gy) were given with a single pentobarbital dose (60 mg/kg intraperitoneally). Further groups of animals were used to evaluate the importance of the timing of pentobarbital administration, the function of the (+) and (-) isomers of pentobarbital, and the role of an alternative GABA agonist (diazepam). In addition, the potential protective effects of alternative methods of anesthesia (ketamine) and induction of cerebral hypometabolism (hypothermia) were examined. Enhancement of survival time from acute radiation injury due to high-dose single-fraction whole-brain irradiation was maximal with 60 mg/kg of pentobarbital, and occurred over the range of all doses examined between 30 to 90 Gy. Protection was seen only in animals that received the pentobarbital before irradiation. Administration of other compounds that enhance GABA binding (Saffan and diazepam) also significantly enhanced survival time. Ketamine and hypothermia were without protective effect. Protection from acute radiation-induced mortality by pentobarbital in the rat model is a reproducible phenomenon and is associated with the GABA agonistic activity of the compound. This property of GABA agonists offers the potential for a novel approach to enhancement of the efficacy of radiation therapy in the treatment of brain tumors.

Sedation of children for CT and MRI scanning

This paper reports on 350 pediatric patients who were studied over a 17-month period to determine the efficacy and safety of oral and intramuscular sedation techniques. The protocol using oral chloral hydrate, 50 mgm/kg, for infants under 1 year of age or intramuscular pentobarbital, 5 mgm/kg, for children over 1 year was found to be an effective, safe and fairly simple approach to pediatric sedation. Of the 350 sedated patients, 343 (98 percent) had satisfactory scans on the same day the examination was scheduled after a single dose or an initial dose and supplementary sedation.

Reinforcing effects of a pentobarbital-ethanol combination relative to each drug alone

The reinforcing effects of an orally delivered combination of 1 mg/ml pentobarbital plus 1% ethanol were evaluated in four rhesus monkeys. The drug combination and another liquid (either water, 1 mg/ml pentobarbital, or 1% ethanol) were concurrently available under identical fixed-ratio (FR) schedules. Substantially higher response rates were maintained by the drug combination than by any of the three other liquids. Thus, the reinforcing effects of the pentobarbital-ethanol combination were greater than those of either component drug. In a second experiment, water (the vehicle) was concurrently available with one other liquid (1 mg/ml pentobarbital, 1% ethanol, or the pentobarbital-ethanol combination). All three drug solutions functioned as reinforcers since they maintained much higher response rates than water. These results demonstrate that the greater relative reinforcing effects of the drug combination in the first experiment were not due to a lack of reinforcing effects of the 1 mg/ml pentobarbital or 1% ethanol solutions. In a final experiment, the drug combination was scheduled concurrently with 1 mg/ml pentobarbital, and FR size was systematically varied. The drug combination was then scheduled concurrently with 1% ethanol, and FR size was again varied. As FR size increased, the relative amount of responding maintained by the drug combination increased. Thus, differences in relative reinforcing effects that were evident in the first experiment were again evident in the final experiment when appropriate schedule-parameter values were used.

The perioperative effects of oral premedication in children

The pre- and postoperative effects of oral diazepam (0.5 mg/kg), trimeprazine (4 mg/kg), pentobarbitone (3 mg/kg) and a placebo were compared in a randomized double-blind clinical trial in 149 children, aged one to ten years, undergoing adenotonsillectomy. The anaesthetic was standardised and each patient received intraoperative intramuscular papaveretum (0.3 mg/kg). Preoperative sedation was assessed in the ward before transfer onto the theatre trolley, on leaving the ward, on arrival on the theatre floor, on arrival in the induction room and on induction of anaesthesia. There was no significant difference in sedation between the four drug groups except for the placebo group which had a significantly greater unsatisfactory rating at the stage of induction of anaesthesia (P = 0.001). There were no differences in waking times between the diazepam, pentobarbitone and placebo groups, but the trimeprazine group's waking times were significantly prolonged (P less than 0.001). However, the trimeprazine group exhibited significantly less distress in the recovery unit (P = 0.02) and had half the incidence of vomiting (P less than 0.001) than did the other premedication groups.

Pressor effect of NG-nitro-L-arginine in pentobarbital-anesthetized rats

The pressor effect of NG-nitro-L-arginine (L-NNA), a potent inhibitor of nitric oxide (NO) synthesis, was studied in pentobarbital anesthetized rats. Iv injections of L-NNA from 0.25 to 8 mg/kg caused bradycardia and a dose-dependent increase in mean arterial pressure (MAP) with a maximal response of 43 +/- 5 mmHg and ED50 value of 1.3 +/- 0.2 mg/kg. The time course of the response to the injection of a single dose of L-NNA was also determined. Peak response was reached 60 min after the injection of a single dose (4 mg/kg, iv) and the effect lasted greater than 5 h. The rising phase of the pressor response was accompanied by slight bradycardia while the recovery phase was associated with significant tachycardia. Iv injections of L-arginine (12.5-200 mg/kg) caused transient dose-dependent reductions in MAP. The pressor effect of L-NNA (4 mg/kg, iv bolus) was dose-dependently attenuated by L-arginine. The results show that L-NNA is an efficacious and long-acting pressor agent and are consistent with the hypothesis that endogenous NO plays an important role in the regulation of blood pressure.

Self-administration of the isomers of pentobarbital and secobarbital by rhesus monkeys

Previous studies have shown that the isomers of pentobarbital and secobarbital have behavioral effects that are qualitatively similar to those of the racemic mixture, but that the S-(-) isomers are more potent than the R-(+) isomers. The present study was designed to compare the reinforcing effects of the isomers of these compounds to those of the racemic mixtures in monkeys experienced in the intravenous self-administration of barbiturates. Rhesus monkeys (N = 3) were prepared with indwelling intravenous catheters and allowed to self-administer racemic pentobarbital in 1-hour sessions under a fixed ratio 5 schedule. When responding was stable, various doses of (+,-) pentobarbital, (+,-) secobarbital and single doses of both isomers of these compounds were substituted for the baseline drug in a mixed order. All of the compounds functioned as positive reinforcers in all monkeys. R-(+) isomer were self-administered at higher rates than the racemic mixtures which were self-administered at higher rates than the S-(-) isomers. The results demonstrate that both isomers of these barbiturates can function as positive reinforcers.

[Premedication in ENT operations under local anesthesia]

Midazolam 15 mg orally, was compared with the combination of pentobarbital, promethazine, opial and scopolamine as premedication for ear surgery under local anaesthesia in the first of a series of three double blind clinical trials. Sedation, pain sensation and appreciation by patient and surgeon alike were in favour of the pentobarbital regime. Anxiolysis was the same for both regimes. The number of actions needed to administer the medication was basically lower for midazolam. Comparing in a similar, second study midazolam 15 mg with higher doses of 20 mg and 25 mg, the results were satisfactory with the highest dose. Pain during the administration of the local anaesthesia was felt in 16% of the patients. Adding 10 mg morphine intramuscularly in a third study did not prove to diminish the percentage of patients with pain complaints. It is concluded that 25 mg midazolam taken orally 45 minutes pre-operatively is a satisfactory premedication for ear surgery and less troublesome than the pentobarbital, promethazine, opial, scopolamine we used before. In day-care surgery this short acting premedication in our opinion is quite useful.

Oral self-administration of pentobarbital by rhesus monkeys: maintenance of behavior by different concurrently available volumes of drug solution

For 4 rhesus monkeys, mouth-contact responses with either of two brass spouts were reinforced according to fixed-ratio schedules by 0.65-mL liquid deliveries during daily 3-hr sessions. Three experiments were conducted. In each experiment, independent fixed-ratio schedules were concurrently in effect at the two spouts. Following completion of each fixed ratio on a spout, a specified number of liquid deliveries were available from that spout under a continuous-reinforcement schedule. The number of such deliveries available at each spout was manipulated independently. In Experiment 1, a 1-mg/mL pentobarbital solution was simultaneously available with water (the drug vehicle) under concurrent fixed-ratio schedules of 32 responses for 3 subjects and 64 responses for the remaining subject. The number (N) of liquid deliveries that were available after completion of each fixed ratio was varied in the following order: 8, 4, 2, 1, and 8 (retest). For each subject at each condition, drug maintained more responding than water. The number of drug deliveries obtained per session was directly related to the amount of drug available per fixed ratio (i.e., to N), whereas the number of fixed ratios completed per session generally was inversely related to the value of N. In Experiment 2, fixed-ratio size was the same for each subject as in Experiment 1, but deliveries of a 1-mg/mL pentobarbital solution were available at both spouts. The number of drug deliveries available under one fixed-ratio schedule (Ns, the "standard" reinforcer amount) was held at eight, and the number of drug deliveries available under the second schedule (Nc, the "comparison" reinforcer amount) was changed across blocks of six sessions of stable responding in the following order: 1, 2, 4, 8, 4, 2, and 1. The identical series of comparison reinforcer amounts (Nc) was then tested twice more, but with the standard reinforcer (Ns) held first at four and then at two deliveries. Across the three choice series, reinforcing effects were directly related to reinforcer magnitude. In Experiment 3, deliveries of a 1-mg/mL pentobarbital solution again were available at both spouts. However, the two reinforcer amounts were held constant at N = 8 deliveries under one schedule and N = 4 deliveries under the second schedule, and fixed-ratio size was systematically varied. Across the range of fixed-ratio sizes from low to high, the degree to which behavior was better maintained by the larger of the two drug quantities was an inverted U-shaped function of fixed-ratio size.(ABSTRACT TRUNCATED AT 400 WORDS)

A flavor paired with lithium chloride blocks the formation of a pentobarbital-lithium chloride association

Thirsty rats were used in order to determine whether a vinegar solution, which had been paired with an injection of lithium chloride, could block the formation of an association between a pentobarbital- and a lithium chloride-induced state. During phase 1 the rats in the blocking group had a 2.0% vinegar solution paired with an injection of 240 mg/kg of lithium chloride, during phase 2 these rats were reexposed to the vinegar prior to each injection of 20 mg/kg of pentobarbital and 240 mg/kg of lithium chloride, and during phase 3 these rats were given access to a novel 0.75% saccharin solution and were injected with pentobarbital after saccharin removal. Animals with this history did not form an association between the pentobarbital- and lithium chloride-induced states during phase 2 as evidenced by their refusal to consume the saccharin solution over repeated pairings of saccharin with pentobarbital during phase 3. Control groups that received forward pairings of pentobarbital and lithium chloride, in the absence of a previously conditioned vinegar solution during phase 2, formed an association between pentobarbital and lithium chloride. These findings indicate that drug states and flavors can interfere with each others' capacity to predict the occurrence of lithium chloride.

Influence of nutritional status on the pharmacokinetics and pharmacodynamics of pentobarbital

The influence of dietary protein deficiency on the pharmacokinetics and pharmacodynamics of pentobarbital was investigated in male Sprague-Dawley rats fed for 4 weeks on a 23% (control) or 5% (low) protein diet ad libitum. Following a single iv dose of 40 mg/kg sodium pentobarbital, the average mean residence time (MRT) was prolonged by 144% (2.3 +/- 0.2 to 5.6 +/- 1.5 hr, mean +/- SD) in the protein-deficient rats, whereas the mean total body clearance (CL) per kilogram of body weight decreased from 0.56 +/- 0.09 to 0.22 +/- 0.06 liter/hr/kg. As a result, the terminal disposition rate constant was decreased by approximately 60% (0.398 +/- 0.037 to 0.178 +/- 0.050 hr-1 when compared to rats on a normal protein diet. No significant differences were found in the two groups of rats with respect to the apparent steady state volume of distribution (Vss). In order to investigate the effect of nutritional status on the concentration-pharmacologic activity relationship, pentobarbital was infused iv at a constant rate of 0.55 mg/min until the animals lost their righting reflex (16 +/- 3 min and 8 +/- 1 min in control and protein-deficient animals, respectively). The total dose and concentration of pentobarbital in plasma were not significantly different between the two groups of animals. However, the concentrations of pentobarbital in plasma water (unbound) and brain were appreciably higher in the rats on a low protein diet. Thus, a diet low in protein appears to be associated with a decreased sensitivity of the central nervous system to the depressant effect of pentobarbital.

Discriminative stimulus properties of local anesthetics in d-amphetamine- and pentobarbital-trained pigeons

Pigeons were trained to discriminate either d-amphetamine (1.7 mg/kg, IM) or pentobarbital (10 mg/kg, IM) from saline in a two-key, food-reinforced drug discrimination paradigm. Cocaine, procaine, and lidocaine were administered before test sessions to determine if these local anesthetics shared discriminative stimulus (DS) properties with either training drug. Cocaine (0.1-3.0 mg/kg) substituted for d-amphetamine in all 4 birds from the d-amphetamine-trained group. Procaine (3.0-56 mg/kg) substituted in 3 of the 4 birds from this group, and lidocaine (3.0-30 mg/kg) did not substitute in any bird. In contrast, cocaine, procaine, and lidocaine did not substitute for pentobarbital in any bird in the pentobarbital-trained group. These results suggest that the DS properties of some local anesthetics may be similar to those of psychomotor stimulants. Further, although some local anesthetics may have sedative-like actions, apparently these are not the basis of their DS effects.

Treatment of refractory generalized tonic-clonic status epilepticus with pentobarbital anesthesia after high-dose phenytoin

We report the results of treatment of refractory generalized tonic-clonic status epilepticus in 17 adults. Of 13 patients who received high-dose phenytoin (PHT, mean dose 23.8 mg/kg), seizure control was sustained in five patients. In 12 cases, anesthetic doses of pentobarbital rapidly suppressed convulsions, but sustained control required prolonged treatment. Break-through seizures were, in most cases, explained by inadequate serum pentobarbital concentrations, although we could not establish a therapeutic range of serum concentrations. EEG monitoring is necessary to assess the therapeutic response but is not a reliable index of depth of anesthesia. Some cases developed pharmacodynamic tolerance to pentobarbital. The most serious treatment complications were cardiorespiratory, but the most common and disabling side effects, although reversible, were neurologic. Fifteen patients were discharged from the hospital in stable condition; two patients died, but not as a direct consequence of treatment. Our results suggest a very good outcome of pentobarbital anesthesia for patients in refractory status epilepticus who are a reasonable medical risk and who receive optimal medical management.

Evaluation of pentobarbital as a drug for standing sedation in cattle

Pentobarbital (1.0, 1.5, and 2.0 mg/kg intravenously [IV]) was administered to four adult cows to determine a dose suitable for producing standing sedation in adult cattle, and to evaluate its effects on cardiopulmonary function and rumen motility. The response was assessed after 15, 30, 60, and 90 minutes. The 1.0 and 1.5 mg/kg doses induced mild sedation at 15 and 30 minutes, and no sedation at 60 and 90 minutes. The 2.0 mg/kg dose produced moderate sedation at 15 and 30 minutes, and mild sedation at 60 minutes. The 2.0 mg/kg dose was judged to be the most suitable. The effects of pentobarbital (2.0 mg/kg IV) on heart rate, blood pressure, respiratory rate, blood gases, and rumen motility were measured in five cows during a 90 minute period. Respiratory rate was significantly depressed at 15, 30, and 60 minutes, but there were no significant changes in the other variables. Pentobarbital (2.0 mg/kg IV) is reliable in adult cattle for standing sedation of short duration.