Mechanism of N,N'-diallylpentobarbital potentiation of pentobarbital-induced sleep in mice

Potentiation mechanism of pentobarbital (PB)-induced sleep by N,N'-diallylpentobarbital (DAPB) was studied in mice. DAPB significantly prolonged the PB [40 mg/kg, intraperitoneal (i.p.)]-induced sleeping time by two routes of administration [intravenous (i.v.) and intracerebroventricular (i.c.v.)], nevertheless DAPB alone was devoid of hypnotic activity even by both routes of administration (i.v. and i.c.v.). In addition, DAPB (160 and 320 mg/kg, i.p.) significantly prolonged the sleeping time induced by i.c.v. injection of PB (200 micrograms/mouse). The brain PB half-life (T1/2) of DAPB (80 mg/kg, i.p.) treated group (9.0 h) was 13-fold longer than that of the control (0.7 h). The plasma PB half-life (T1/2) of DAPB treated group (15.2 h) was longer than that of the control (0.6 h). Moreover, DAPB significantly decreased the activities of ethylmorphine (EM) N-demethylase and aniline hydroxylase, and the content of cytochrome P-450 in mouse liver microsomes. The inhibitory effect of DAPB (40 mg/kg, i.p.) on the mouse hepatic drug-metabolizing enzymes was shown til 6 h after administration. DAPB exhibited non-competitive inhibition on the EM N-demethylase activity in vitro. These results indicate that DAPB prolongs the PB-induced sleeping time by both its depressant action to the central nervous system (CNS) and inhibitory effect on the hepatic drug-metabolizing enzymes.

Intrathecal diazepam suppresses nociceptive reflexes and potentiates electroacupuncture effects in pentobarbital-anesthetized rats

Using noxious heat-evoked tail flick in rats anesthetized with pentobarbital infusion, we studied the effects of diazepam applied intrathecally. This drug caused a marked suppression of nociceptive reflexes in a dose-dependent manner. In addition, a small non-suppressive dose of diazepam potentiated electroacupuncture effects. These results are discussed in terms of gamma-aminobutyric acid (GABA) since it is known that diazepam enhances binding of GABA to its receptor and hence potentiates inhibitory effects of GABA in the spinal cord. The possible synergism of diazepam and pentobarbital is also discussed.

The effects of local intraparenchymal pentobarbital on intracranial hypertension following experimental subarachnoid hemorrhage

Barbiturates are often utilized clinically in circumstances in which elevated intracranial pressure is expected. In this study, the mechanism of action of barbiturates was examined in dogs with intracranial hypertension induced by injecting autogenous incubated blood into the chiasmatic cistern. Intracranial pressure and systemic blood pressure were continuously monitored. A single bilateral administration of powdered pentobarbital (2 mg and 0.4 mg) in experimental animals and solid d-glucose (2 mg) in control animals was given into the posterior hypothalamus, pontine reticular formation, or medullary reticular formation when intracranial pressure reached 20-30 mmHg after the blood injection--usually in 3-6 h. The increased intracranial pressure following the experimental subarachnoid hemorrhage was always associated with either intracranial pressure irregularities or concomitant blood pressure variations, suggesting the presence of vasomotor instability. Administration of both 2 mg and 0.4 mg of pentobarbital into the medulla caused a significant (P less than 0.01) decrease of the intracranial pressure to 44 and 65% of control and stabilization of the intracranial pressure irregularities, whereas pentobarbital given at the other sites did not. The blood pressure was also decreased significantly (P less than 0.01) to 80 and 88% of control and the blood pressure variations were stabilized in animals after administration of pentobarbital into the medulla, whereas in those given pentobarbital at the other sites, it was not. The results suggest that, in the presence of elevated intracranial pressure following experimental subarachnoid hemorrhage, the mechanisms of action of barbiturates in reducing the intracranial pressure may result from alleviation of cerebral vasomotor instability by depression of the vasomotor center of the medulla.

Pentobarbital pharmacokinetics in patients with severe head injury

Intravenous administration of high-dose pentobarbital has been proposed as a treatment for elevated intracranial pressure refractory to other measures in brain-injured patients. The purpose of this clinical study was to examine the pharmacokinetics of high-dose continuous intravenous infusion of pentobarbital in this critical care setting. Six patients received a 25-34 mg/kg intravenous loading dose followed by a 1-3 mg/kg/h continuous infusion for 61-190 hours. Dosing rates were adjusted based on the patient's clinical status. The mean clearance was 0.72 ml/min/kg, with a volume of distribution (Vd) of 1.03 L/kg and a terminal half-life of 19.1 h. Considerable variation in individual patient parameters was observed. In addition, a change in clearance was suggested in patients requiring a longer infusion duration.

Effects of therapeutic agents in a rabbit model of Reye syndrome

Six potential therapeutic agents were evaluated in an experimental model simulating Reye syndrome produced by infusion of the short-chain fatty acid, sodium octanoate, into rabbits. Administration of carnitine, dexamethasone, or fatty acid-free albumin resulted in prolongation of survival, less rise in intracranial pressure, and amelioration of some of the metabolic abnormalities found typically during octanoate infusion. Treatment with pentobarbital or dimethyl sulfoxide prevented intracranial pressure elevations but had no protective effect on survival. Hypertonic glucose administration produced no improvement in any of the parameters studied.

Hemodynamic effects of high dose pentobarbital: studies in elective neurosurgical patients

High dose barbiturate therapy has been used clinically for about 10 years. However, the hemodynamic consequences of such therapy have not been well defined in humans. We therefore examined the effects of a brief (30-minute), high dose (0.6 mg/kg/minute or 18 mg/kg total) infusion of pentobarbital in nine otherwise healthy patients (aged 20 to 30) scheduled to undergo operation for the removal of large or deeply seated arteriovenous malformations. Monitored variables included intravascular pressures, cardiac output, arterial and mixed venous blood gases and hematocrit, and the electroencephalogram (EEG). After a brief rest period and the collection of control data, pentobarbital infusion was begun, muscle relaxants were given, and normocarbia was maintained by mask ventilation. Because our primary intent was to examine the effects of the drug on the heart and arterial circulation, lactated Ringer's solution was infused continuously to keep pulmonary capillary wedge pressure (PCWP) at control values in an attempt to keep constant the ventricular "preload" (although PCWP is only an approximation of the true preload). Drug infusion resulted in progressive EEG suppression ending in a pattern of deep burst suppression (1 to 3 bursts/minute) at t = 30 minutes, with measured plasma pentobarbital concentrations (in four patients) of 34 +/- 4 micrograms/ml (mean +/- SD). There were no changes in PaO2, PaCO2, or pH, nor were there any changes in PCWP. The cardiac index did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetic effect and distribution of infused pentobarbital in the rat at 71 ATA

The anesthetic dose requirement and distribution of 14C-labeled pentobarbital were studied in rats at 1 ATA air and at 71 ATA He-O2. Pentobarbital was infused intravenously at a rate of 5 mg X kg-1 X min-1. The depth of anesthesia was assessed by EEG using the burst suppression of 1-s duration (silent second) as the biological end point. The mean anesthetic dose was 45.6 and 68.0 mg X kg-1 at 1 and 71 ATA, respectively, representing a 49% increase at pressure (P less than 0.001). The corresponding concentrations in the brain were 81.6 and 92.3 micrograms X g-1 (not significant). The hepatic and renal pentobarbital concentrations increased by 44 and 41%, respectively, at pressure (P less than 0.001). Interindividual variations in required doses and infusion lengths made comparison between tissue pentobarbital values difficult to interpret. A second series of experiments was therefore undertaken using a subanesthetic dose of pentobarbital infused at the same constant rate for 7 min. No significant changes were found in the organ distribution of the drug at pressure. The results show that high pressure antagonizes the narcotic effect of pentobarbital and that the distribution of pentobarbital is not significantly altered in the rat at 71 ATA.

Benzodiazepine self-administration in rhesus monkeys: estazolam, flurazepam and lorazepam

The ability of three benzodiazepines to maintain self-administration behavior was studied in rhesus monkeys using a substitution procedure. Lever-press responding was maintained in six monkeys under a fixed-ratio schedule of IV pentobarbital delivery in daily sessions of 3 hr duration. Each of several doses of flurazepam, lorazepam and estazolam as well as saline and vehicle was periodically substituted for 4-13 consecutive sessions. Between dose or vehicle substitutions, responding was maintained by pentobarbital. All six monkeys self-administered flurazepam above vehicle or saline levels. In addition four of five monkeys tested with lorazepam and four of six tested with estazolam self-administered at least one dose of drug above control levels. These results indicate that self-administration performance can be reliably maintained in rhesus monkeys by certain benzodiazepines under appropriate experimental conditions.

Gross and microscopic characteristics of liver lesions induced by direct injection of pentobarbital sodium into rats

The hepatotoxic effects of anesthetics brought about by their faulty intraperitoneal application was investigated. Using a syringe with a 26G needle, we injected 0.05 ml/rat of a 50 mg/ml solution of pentobarbital sodium directly into the livers of Sprague-Dawley rats. The animals were killed at 15, 30, or 45 minutes after injection. Massive hemorrhagic necrosis of the liver was seen in all animals injected, while focal necrosis accompanied by inflammatory cell infiltration was observed in the rats killed at 30 and 45 minutes after injection. The histological characteristics of these liver lesions were composed of three types, namely, massive hemorrhagic necrosis, focal cell infiltration separate from the necrosis, and focal necrosis with inflammatory cell infiltration. The infiltrates were composed of both neutrophils and lymphocytes. The characteristic liver lesions closely resembled the hepatic lesions produced by captopril (Helliwel et al., 1985), cyclopiazonic acid (Morrissey et al., 1985), as well as spontaneous liver lesions. The study of serum transaminase levels showed that the elevation of both SGPT and SGOT activities was correlated with the time after injection. Also, a significant increase in the total bilirubin level was noted in all animals treated.

Interaction of pentobarbital and morphine in the tail-flick test performed on rats: synergism at the spinal and antagonism at the supraspinal level

The dose-dependence of the effects and interaction of pentobarbital and morphine administered by intrathecal (i.t.) and intraperitoneal (i.p.) injection was determined in experiments performed on the tail-flick response to radiant heat applied to the tail of rats. I.t. injection of pentobarbital and morphine, and i.p. injection of morphine depressed the tail-flick response, while i.p. injection of pentobarbital facilitated it. The effects caused by i.t. injection of the two drugs depended on the intensity of noxious stimulation. When pentobarbital and morphine were administered in combination by i.t. injection, they potentiated each other's effect. After i.p. injection of pentobarbital and morphine the facilitatory effect of pentobarbital was abolished and the antinociceptive effect of morphine was enhanced. The results reveal a synergism of the actions of pentobarbital and morphine at the spinal level and an antagonism at the supraspinal level which is probably of the functional type.

Intravenously administered pentobarbital sodium for sedation in pediatric CT

A retrospective study of 5,134 consecutive pediatric patients undergoing computed tomographic (CT) evaluation from January 1983 through December 1985 was conducted to analyze the need for sedation in a pediatric population; the safety, efficacy, and efficiency of various sedation regimens; and the pediatric radiologists' changing preference for certain sedatives. A marked preference for intravenous administration of pentobarbital sodium (Nembutal) evolved over the 3-year period analyzed. Intravenous Nembutal facilitated the most efficient use of available CT scanning time. Recovery times were reduced, and patient convenience was augmented. There were only two sedation failures in the 419 patients sedated with intravenous Nembutal, and there were no sedation-related complications.

Effect of dosing frequency on the development of physical dependence and tolerance to pentobarbital

Many studies have suggested the importance of the rate of drug elimination in the development of pharmacodynamic tolerance and physical dependence to sedative-hypnotic drugs. Our previous study demonstrated that the role of individual variation in elimination kinetics played an important part in producing pharmacodynamic tolerance and physical dependence when the drug was given at a fixed dose-frequency schedule. The present study investigated the effect of various dose-frequency schedules on the production of tolerance and physical dependence. Controlling the frequency of administration was thought to be the most rational clinical approach in avoiding the production of tolerance and physical dependence with repeated sedative-hypnotic medication. Groups of animals were treated with Na pentobarbital according to the "maximally tolerable" dosing schedule described previously, except that with different dose-frequency schedules, i.e., twice a day, once every day, once every 1.5 days and once every other day for 70 consecutive doses and then withdrawn abruptly. The relationship between the number of Na pentobarbital doses under each dose-frequency schedule and the pharmacokinetic and pharmacodynamic tolerance production, plus the intensity of withdrawal, were studied. The withdrawal intensity was further correlated to the time lag between each drug administration by estimating the maximal time allowed between doses that does not produce any spontaneous withdrawal convulsions and overt withdrawal signs. It was concluded that the time required for repeated Na pentobarbital administration that does not produce withdrawal convulsion and overt withdrawal signs was 4.9 and 5.7 times the average pentobarbital half-life, respectively.

Diazepam action on gamma-aminobutyric acid-activated chloride currents in internally perfused frog sensory neurons

The Cl- current (ICl) in gamma-aminobutyric acid (GABA)-sensitive frog sensory neuron was separated from other Na+, Ca2+, and K+ currents using a suction pipette technique which allows internal perfusion under a single-electrode voltage clamp. Diazepam (DZP) itself evoked no response but facilitated the dose- and time-dependently GABA-induced ICl without changing the GABA equilibrium potential (EGABA) at concentrations ranging widely, from 3 X 10(-9) to 10(-4) M. In the presence of DZP, the GABA dose-response curve shifted to the left without changing the maximum current, indicating that DZP modifies the interaction between GABA and its receptor rather than affecting directly the channel activation step. The enhancement of the GABA-induced ICl by DZP depended neither on the membrane voltage nor on the inward or outward direction of the ICl. DZP also potentiated the ICl elicited by GABA agonists such as beta-alanine, taurine, homotaurine, 5-aminovaleric acid, l-GABOB, d-GABOB, glycine, and muscimol. The GABA response enhanced by pentobarbital (PB) was further enhanced by adding DZP, indicating that DZP and PB do not act in the same way. Ro5-3663, a diazepam analogue, enhanced the GABA-induced ICl only in a narrow range of the concentrations but inhibited the current at concentrations higher than 2 X 10(-6) M.

Sedative-hypnotic anomalies related to dose of pentobarbital in long-sleep and short-sleep selectively-bred mice

Hypnotic effects following administration of three doses of pentobarbital were evaluated in mice selectively-bred for differential hypnotic sensitivity to ethanol. Although the ethanol-sensitive Long-Sleep (LS) line displays greater sedation to a wide variety of CNS depressants (alcohols, barbiturates, benzodiazepines, general anesthetics), when compared to the ethanol-insensitive Short-Sleep (SS) line, the response pattern to pentobarbital remains equivocal. Thus, to clarify the effect of pentobarbital, certain variables (dose, sex, circadian rhythmicity) believed to be important in the expression of sleep time were evaluated. For all doses examined "sex" and "time of day tested" impacted on sleep time. With these provisos, 40 mg/kg consistently induced shorter sleep time in SS mice. The 60 mg/kg dose either failed to distinguish these two lines, or induced greater sleep times in the SS mice. The 80 mg/kg dose tended to have the same effect as the 60 mg/kg dose, but to a greater degree. Overall, it appears that for each line the dose response curve for pentobarbital is sigmoidal, but that the slope of the curve for the middle range of doses is greater for the SS line. Since pentobarbital has a unique effect on these lines of mice that is dissimilar to those reported for other barbiturates, the implication is that an additional factor, that is unimportant for other barbiturates, is essential for pentobarbital-induced hypnosis. Factors that could be responsible for this effect include differential metabolism of Gabaergic receptor dynamics.

Chronic treatment with haloperidol affect the response of the brain to pentobarbital

Treatment of mice with haloperidol increased the number of dopamine D2 receptors (Bmax). The animals were given 40 or 50 mg of pentobarbital. Animals treated with haloperidol had a shorter duration of narcosis induced by pentobarbital than the controls, suggesting a decreased sensitivity to pentobarbital which was functional (CNS), since the animals treated with haloperidol had higher levels of pentobarbital in the brain upon awakening than the controls. The results suggest that increased Bmax reduces the sensitivity of the brain to pentobarbital.

Brain metabolic correlates of hypoxic-ischemic cerebral necrosis in mid-gestational sheep fetuses: significance of hypotension

Mid-gestational sheep fetuses exposed to marked hypoxia for 2 h remain brain intact if MABP is maintained above 30 mm Hg. On the other hand, similarly hypoxic fetuses, if they experience reductions in MABP below 30 mm Hg, develop foci of necrosis that predominantly affect hemispheric white matter and neostriatum. Cortex damage is more restricted and is usually associated with more massive underlying white matter damage. The present study examines the brain metabolic basis for the important role of hypotension in brain injury development in marked hypoxia. Sheep fetuses rendered hypoxic by respiring their ewes with 11% oxygen (fetal PaO2 = 8-12 mm Hg) in which MABP was maintained above 30 mm Hg showed increases in brain lactic acid concentrations to 7-13 mumol/g but unaltered energy charge. In contrast, fetuses that sustained MABP reductions below 30 mm Hg showed increases in lactic acid concentrations in vulnerable structures to 16-24 mumol/g accompanied by marked decreases in energy charge. The vulnerable structures also showed reductions in fructose concentrations but a variable behavior of other brain metabolites including phosphocreatine, glycogen, and glucose. Thus, the present findings suggest a relation between hypotension during marked hypoxia, low energy charge, lactic acid accumulation in brain at high concentrations, and fetal brain injury. The ewes of hypoxic hypotensive fetuses received pentobarbital at lower doses than did those of fetuses that maintained blood pressure. This suggests that pentobarbital plays an important role in protecting the fetal brain from asphyxia by extending the hypoxic fetus's ability to maintain blood pressure in addition to reducing its brain metabolism.

Spinal and supraspinal mechanisms for morphine-pentobarbital antinociceptive interaction in relation to cardiac acceleration response in rats

In rat experiments, morphine-pentobarbital antinociceptive interaction affecting cardiac acceleration in response to somatic noxious stimulation was analyzed with the use of intrathecal and intracerebroventricular injections of morphine. Cardiac acceleration response was induced by tail compression, and heart rate was monitored by electrocardiogram. Pentobarbital, in a subanesthetic intravenous dose, antagonized the antinociceptive effect of morphine in relation to cardiac acceleration response when morphine was administered intracerebroventricularly. Without pentobarbital, morphine, 8 micrograms, almost completely blocked the cardiac acceleration response, which was only 1 +/- 1 beats/min. When pentobarbital (10 mg/kg intravenously) was administered in a combination with the same dose of morphine, the cardiac acceleration response was 29 +/- 3 beats/min (P less than 0.0001). In contrast, when morphine was administered intrathecally, the antagonism by pentobarbital of the cardiac acceleration response was absent. The results suggest that supraspinal mechanisms play a decisive role in morphine-pentobarbital antagonism in relation to cardiac acceleration response to somatic noxious stimulation.

Monitoring of pentobarbital plasma levels in critical care patients suffering from increased intracranial pressure

Pentobarbital plasma levels were determined in 16 critical care patients receiving a dose of approximately 30 mg/kg/day and suffering from severe head injury. In 10 patients monitored more than six times, a continuous decrease in plasma concentrations, caused by a mean increase in pentobarbital total plasma clearance from 0.81 to 1.06 ml/min/kg, was found. This effect might be due to autoinduction of hepatic drug-metabolizing enzymes. As clearance values showed marked inter- and intraindividual variability, it is necessary to monitor pentobarbital plasma levels frequently to adapt the dosage to the changes in clearance. Infrequent determinations are of little clinical value, as the necessary changes in pentobarbital dosage will not be predicted precisely enough.

Effect of xylocaine and carbachol applied to the caudate nucleus of rats on barbiturate sleeping time

Since lesion of subcortical structures may affect the barbiturate sleeping time (bST), we decided with the present study to elucidate the role of the caudate nucleus in the determination of central sensitivity to barbiturates. Rats implanted with a cannula in the caudate nucleus of one or both sides, as well as with a jugular cannula, were utilized. Intravenous injections of sodium pentobarbital (40 mg/kg), intracerebral injections of Xylocaine (0.04 microgram), carbachol (0.2 micrograms) or artificial cerebrospinal fluid (ACF) into the caudate nucleus were performed. Both Xylocaine and carbachol, but not ACF, increased the bST regardless of the preparation used, the only exception being Xylocaine which did not alter the bST, if injected into the left caudate nucleus. The results suggest that the caudate nucleus may act as a modulator of the central sensitivity to barbiturates.

The effects of Ro 15-1788 on anxiolytic self-administration in the rhesus monkey

The ability of a benzodiazepine antagonist, Ro 15-1788, to modify the self-administration of anxiolytics was determined in rhesus monkeys. Lever-press responding was maintained in four monkeys under a fixed-ratio 10 schedule of drug delivery in daily sessions of 2 hr duration. Responding was maintained either by flurazepam, lorazepam or pentobarbital. When responding was stable for each of these drugs, a range of doses of a benzodiazepine antagonist, Ro 15-1788 (0.0001-10 mg/kg, IM), was given 5 min prior to a session. At some doses the antagonist increased responding for lorazepam and flurazepam whereas pentobarbital self-administration was largely unaffected or reduced. These results suggest that Ro 15-1788 was able to specifically modify the effects of benzodiazepines responsible for drug-maintained performance.

Differential interactions between chlordiazepoxide, pentobarbital and benzodiazepine antagonists Ro 15-1788 and CGS 8216 in a drug discrimination procedure

Rats were trained to discriminate either chlordiazepoxide (CDP, 4 mg/kg, IP, N = 8) or pentobarbital (PB, 10 mg/kg, IP, N = 8) from saline in a two-lever food-reinforced procedure. CDP and PB dose-dependently substituted for each other (greater than or equal to 90% drug lever responses); indicating that their discriminative stimulus properties were closely similar. However, discriminative stimulus control induced by CDP and PB differentially was affected by the proposed benzodiazepine (BDZ) antagonists Ro 15-1788 (0.08-20 mg/kg, IP) and CGS 8216 (2.5-20 mg/kg, IP) in each experimental group; suggesting that the discriminative stimulus properties of CDP and PB are mediated by different mechanisms of action. When administered alone, Ro 15-1788 (5 and 20 mg/kg), but not CGS 8216, induced CDP like discriminative effects, suggesting that Ro 15-1788 may have partial (BDZ like) agonist properties, not shown by CGS 8216. Additional evidence for a behavioral difference between Ro 15-1788 and CGS 8216 is suggested by differential effects of both compounds on response rate. The results may reflect differential interactions of the compounds with the BDZ receptor-GABA receptor-Cl- ionophore complex.

Prompt arousal from fentanyl-droperidol-pentobarbital anesthesia in dogs: a preliminary study

Groups of fentanyl-droperidol-pentobarbital-anesthetized dogs (n = 6 dogs/group) were given IV saline solution (control group), graded doses of naloxone (0.01, 0.1, 1.0, 10.0 mg/kg) or fixed doses of 4-aminopyridine (0.5 mg/kg), yohimbine (0.4 mg/kg), or doxapram (5.0 mg/kg) alone or in combination with a fixed dose of naloxone (1.0 mg/kg). The purpose was to determine which drug or drug combination would produce arousal most quickly without producing obvious undesirable side effects. Control group mean arousal time, mean walk time and mean duration of postarousal sedation were 66.1 minutes, 112.4 minutes and 5.6 hours, respectively. Naloxone (1.0 mg/kg) decreased mean arousal time to 10.8 minutes without significantly decreasing mean walk time or mean duration of postarousal sedation. The combination of naloxone + doxapram decreased mean arousal time and mean walk time to 1.0 minute and 57.1 minutes, respectively, without decreasing mean duration of postarousal sedation. In all groups, emergence from anesthesia was smooth. Relapses or undesirable side effects were not observed. Naloxone + doxapram is superior to naloxone alone for arousal of fentanyl-droperidol-pentobarbital-anesthetized dogs.

Behavioral effects of CGS 8216 alone, and in combination with diazepam and pentobarbital in dogs

Beagle dogs (N = 3) responded under a multiple fixed-interval (FI) 300 sec, fixed-ratio (FR) 30 schedule of food presentation. The pyrazoloquinoline derivative CGS 8216, given either intravenously (0.01-3.0 mg/kg) or orally (0.1-30.0 mg/kg) had little effect on either the rate or temporal pattern of responding during either component. Both diazepam (0.3 to 17.5 mg/kg, PO) and pentobarbital (0.1-17.5 mg/kg, PO) produced qualitatively similar effects on behavior. Rates of responding during the FI components first increased, then decreased with increasing doses; both drugs produced only dose-related decreases in the rate of responding during the FR components. CGS 8216 antagonized some of the behavioral effects of diazepam; FI and FR response rates returned to baseline, however the effects of diazepam on quarter-life values were not appreciably altered by CGS 8216. The effects of pentobarbital on schedule-controlled responding were not antagonized by CGS 8216. These results indicate CGS 8216 is a selective benzodiazepine antagonist that does not produce benzodiazepine-like behavioral effects.

The effect of pentobarbitone anaesthesia and hypothermia on the hepatic clearance of indocyanine green and S(-)-acenocoumarol in the rat

The effect of pentobarbitone anaesthesia and the effect of hypothermia associated with the anaesthesia on the blood clearance of indocyanine green (ICG) and of S(-)-acenocoumarol (AC) was investigated in male Wistar rats using the constant rate infusion technique. During anaesthesia, body temperature was regulated by heat supply. At normothermia (rectal temperature of 37.5 degrees C), pentobarbitone anaesthesia decreased ICG clearance from 8.0 +/- 1.7 ml min-1 (mean +/- s.e.m., n = 3) in the conscious state to 4.3 +/- 0.6 ml min-1 and AC clearance from 4.9 +/- 0.4 ml min-1 to 3.4 +/- 0.3 ml min-1. Hypothermia further reduced the clearances of the compounds to 0.9 +/- 0.1 and 2.5 +/- 0.2 ml min-1 for ICG and AC, respectively. The effect of hypothermia was reversible. The results show that pharmacokinetic constants obtained in the anaesthetized animal may differ greatly from those in the conscious one. If pharmacokinetic experiments are performed in the anaesthetized animal, body temperature should be controlled and a slight hyperthermia is most favourable. Our pharmacokinetic data on ICG seriously question the use of this drug to estimate liver blood flow in the rat.