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Thiopental sodium (TPTS) is a barbiturate general anesthetic, while its effects on hypoxia/reoxygenation (H/R)-induced injury are still unclear. This study aimed to investigate whether TPTS exerts protective effects against the H/R-induced osteoblast cell injury and explore the underlying mechanisms. Osteoblast cell injury model was induced by the H/R condition, which was treated with or without TPTS. Cell viability and lactate dehydrogenase (LDH) release were determined by the corresponding commercial kits. The levels of oxidative stress were determined in the experimental groups. Cell apoptosis and Caspase-3 activities were determined by propidium iodide staining and substrate-based assay, respectively. Western blotting and qRT-PCR were performed to measure the mRNA and protein levels, respectively. Treatment with TPTS was able to increase cell viability and reduce LDH release in H/R-induced osteoblasts. Additionally, TPTS regulated oxidative stress in H/R-induced osteoblasts by suppressing malondialdehyde (MDA) and reactive oxygen species (ROS) as well as boosting superoxide dismutase (SOD). TPTS was able to suppress cell apoptosis by suppressing Caspase-3 activity and cleavage. TPTS exerted protective effects against cell injury and apoptosis induced by the H/R conditions, which were associated with its regulation of Akt signaling. Moreover, TPTS induced osteoblast differentiation under the H/R condition. In summary, TPTS attenuates H/R-induced injury in osteoblasts by regulating AKT signaling., (© 2023. The Society for In Vitro Biology.)

Objective: The aim: To determine the peculiarities of the antioxidant-prooxidant balance in the kidney of rats of different ages under conditions of experimental cranioskeletal trauma (CST)., Patients and Methods: Materials and methods: The experiments involved 147 male white Wistar rats of different age groups. The first experimental group included immature animals aged 100-120 days. The second group included sexually mature animals aged 6-8 months. The third group included old animals aged 19-23 months. In all experimental groups, CST was modelled under thiopental-sodium anaesthesia. The control groups of rats was only injected with thiopental-sodium anaesthesia. The animals were withdrawn from the experiments under anaesthesia after 1, 3, 7, 14, 21 and 28 days by total bleeding from the heart. The content of reagents to thiobarbituric acid and catalase activity was determined in a 10 % kidney homogenate extract, and the antioxidant-prooxidant index (API) was calculated from the ratio of these two parameters., Results: Results: As a result of the application of CST in rats of different age groups, a decrease in the value of renal API was observed with a maximum in immature rats - after 7 days, in mature and old rats - after 14 days. By day 28, the index increased in all experimental groups, but did not reach the control level. The degree of decrease in renal API in old rats under the influence of CCT was significantly higher than in other experimental groups. In immature rats, the impairment of renal API after the application of CST was less, indicating higher reserve capacity of the renal antioxidant defence system in this age group of rats., Conclusion: Conclusions: Simulation of CST in rats of different age groups is accompanied by a decrease in the value of API, which by day 28 does not reach the control level in any of the experimental groups. The degree of decrease in renal API value statistically significantly increases with increasing age of rats at all times of the post-traumatic period.

Background: In the literature, it has been suggested that ketamine-related oxidative organ damage results from increased blood adrenaline level, and thiopental-related oxidative damage is caused by decreased adrenaline level, suggesting that ketamine-thiopental combination (KT) may be beneficial in reducing the hepatotoxic effect of ketamine., Objectives: To biochemically investigate the effects of ketamine, thiopental and KT on the liver in rats., Material and Methods: Male albino Wistar type rats received intraperitoneally (ip.) 30 mg/kg ketamine in the ketamine alone (KG) group (n = 6), 15 mg/kg thiopental in the thiopental alone (TG) group (n = 6), and 30 mg/kg ketamine + 15 mg/kg thiopental in the ketamine+thiopental (KTG) group (n = 6). The same volume of distilled water as solvent was given to the healthy (HG) animal group. This procedure was repeated once daily for 30 days. At the end of this period, the animals were killed by decapitation and their livers were removed. In liver tissue, malondialdehyde (MDA), total glutathione (tGSH), total oxidant status (TOS), total antioxidant status (TAS), tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin-6 (IL-6) levels were measured. The IL-1β, IL-6, TNF-α, adrenalin (ADR), noradrenalin (NDR), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels were determined in blood samples taken from the tail veins., Results: In the group treated with ketamine and thiopental alone, MDA, TOS, IL-1β, IL-6, TNF-α, ADR, NDR, ALT, and AST levels were found to be high, and those of tGSH and TAS to be low. However, there was no significant change in the levels of these parameters in the KTG., Conclusions: These results indicate that oxidative stress and inflammation developed in the liver tissue of the group that used ketamine and thiopental alone, suggesting that the KT form may be safer in terms of toxicity in the clinical usage.

Inhibitors of acetylcholinesterase (AChE), which have an important role in the prevention of excessive AChE activity and β-amyloid (Aβ) formation are widely used in the symptomatic treatment of Alzheimer's disease (AD). The inhibitory effect of anesthetic agents on AChE was determined by several approaches, including binding mechanisms, molecular docking and kinetic analysis. Inhibitory effect of intravenous anesthetics on AChE as in vitro and in vivo have been discovered. The midazolam, propofol and thiopental have shown competitive inhibition type (midazolam > propofol > thiopental) and Ki values were found to be 3.96.0 ± 0.1, 5.75 ± 0.12 and 29.65 ± 2.04 µM, respectively. The thiopental and midazolam showed inhibition effect on AChE in vitro, whereas they showed activation effect in vivo when they are combined together. The order of binding of the drugs to the active site of the 4M0E receptor was found to be midazolam > propofol > thiopental. This study on anesthetic agents that are now widely used in surgical applications, have provided a molecular basis for investigating the drug-enzyme interactions mechanism. In addition, the study is important in understanding the molecular mechanism of inhibitors that are effective in the treatment of AD.

Cys-loop receptors are molecular targets of general anesthetics, but the knowledge of anesthetic binding to these proteins remains limited. Here we investigate anesthetic binding to the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel (GLIC), a structural homolog of cys-loop receptors, using an experimental and computational hybrid approach. Tryptophan fluorescence quenching experiments showed halothane and thiopental binding at three tryptophan-associated sites in the extracellular (EC) domain, transmembrane (TM) domain, and EC-TM interface of GLIC. An additional binding site at the EC-TM interface was predicted by docking analysis and validated by quenching experiments on the N200W GLIC mutant. The binding affinities (K(D)) of 2.3 ± 0.1 mM and 0.10 ± 0.01 mM were derived from the fluorescence quenching data of halothane and thiopental, respectively. Docking these anesthetics to the original GLIC crystal structure and the structures relaxed by molecular dynamics simulations revealed intrasubunit sites for most halothane binding and intersubunit sites for thiopental binding. Tryptophans were within reach of both intra- and intersubunit binding sites. Multiple molecular dynamics simulations on GLIC in the presence of halothane at different sites suggested that anesthetic binding at the EC-TM interface disrupted the critical interactions for channel gating, altered motion of the TM23 linker, and destabilized the open-channel conformation that can lead to inhibition of GLIC channel current. The study has not only provided insights into anesthetic binding in GLIC, but also demonstrated a successful fusion of experiments and computations for understanding anesthetic actions in complex proteins., (Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Abeta peptide is the major component of senile plaques (SP) which accumulates in AD (Alzheimer's disease) brain. Reports from different laboratories indicate that anesthetics interact with Abeta peptide and induce Abeta oligomerization. The molecular mechanism of Abeta peptide interactions with these anesthetics was not determined. We report molecular details for the interactions of uniformly (15)N labeled Abeta40 with different anesthetics using 2D nuclear magnetic resonance (NMR) experiments. At high concentrations both isoflurane and propofol perturb critical amino acid residues (G29, A30 and I31) of Abeta peptide located in the hinge region leading to Abeta oligomerization. In contrast, these three specific residues do not interact with thiopental and subsequently no Abeta oligomerization was observed. However, studies with combined anesthetics (thiopental and halothane), showed perturbation of these residues (G29, A30 and I31) and subsequently Abeta oligomerization was found. Perturbation of these specific Abeta residues (G29, A30 and I31) by different anesthetics could play an important role to induce Abeta oligomerization.

Low-frequency (0.5-2.5 Hz) and individually defined high-frequency (7-11 or 8-12 Hz; 11-15 or 14-18 Hz) oscillatory components of the electroencephalogram (EEG) burst activity derived from thiopental-induced burst-suppression patterns (BSP) were investigated in seven sedated patients (17-26 years old) with severe head injury. The predominant high-frequency burst oscillations (>7 Hz) were detected for each patient by means of time-variant amplitude spectrum analysis. Thereafter, the instantaneous envelope (IE) and the instantaneous frequency (IF) were computed for these low- and high-frequency bands to quantify amplitude-frequency dependencies (envelope-envelope, envelope-frequency, and frequency-frequency correlations). Time-variant phase-locking, phase synchronization, and quadratic phase couplings are associated with the observed amplitude-frequency characteristics. Additionally, these time-variant analyses were carried out for modeled burst patterns. Coupled Duffing oscillators were adapted to each EEG burst and by means of these models data-based burst simulations were generated. Results are: (1) strong envelope-envelope correlations (IE courses) can be demonstrated; (2) it can be shown that a rise of the IE is associated with an increase of the IF (only for the frequency bands 0.5-2.5 and 7-11 or 8-12 Hz); (3) the rise characteristics of all individually averaged envelope-frequency courses (IE-IF) are strongly correlated; (4) for the 7-11 or 8-12 Hz oscillation these associations are weaker and the variation between the time courses of the patients is higher; (5) for both frequency ranges a quantitative amplitude-frequency dependency can be shown because higher IE peak maxima are accompanied by stronger IF changes; (6) the time range of significant phase-locking within the 7-11 or 8-12 Hz frequency bands and of the strongest quadratic phase couplings (between 0.5-2.5 and 7-11 or 8-12 Hz) is between 0 and 1,000 ms; (7) all phase coupling characteristics of the modeled bursts accord well with the corresponding characteristics of the measured EEG burst data. All amplitude-frequency dependencies and phase locking/coupling properties described here are known from and can be discussed using coupled Duffing oscillators which are characterized by autoresonance properties.

Thiopental (TPL) is a commonly used barbiturate anesthetic. Its binding with human serum albumin (HSA) was studied to explore the anesthetic-induced protein dysfunction. The basic binding interaction was studied by UV-absorption and fluorescence spectroscopy. An increase in the binding affinity (K) and in the number of binding sites (n) with the increasing albumin concentration was observed. The interaction was conformation-dependent and the highest for the F isomer of HSA, which implicates its slow elimination. The mode of binding was characterized using various thermodynamic parameters. Domain II of HSA was found to possess a high affinity binding site for TPL. The effect of micro-metal ions on the binding affinity was also investigated. The molecular distance, r, between donor (HSA) and acceptor (TPL) was estimated by fluorescence resonance energy transfer (FRET). Correlation between the stability of the TPL-N and TPL-F complexes and drug distribution is discussed. The structural changes in the protein investigated by circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy reflect perturbation of the albumin molecule and provide an explanation for the heterogeneity of action of this anesthetic.

1. Florida red tides produce profound neurotoxicity that is evidenced by massive fish kills, neurotoxic shellfish poisoning, and respiratory distress. Red tides vary in potency, potency that is not totally governed by toxin concentration. The purpose of the study was to understand the variable potency of red tides by evaluating the potential for other natural pharmacological agents which could modulate or otherwise reduce the potency of these lethal environmental events. 2. A synaptosome binding preparation with 3-fold higher specific brevetoxin binding was developed to detect small changes in toxin binding in the presence of potential antagonists. Rodent brain labeled in vitro with tritiated brevetoxin shows high specific binding in the cerebellum as evidenced by autoradiography. Synaptosome binding assays employing cerebellum-derived synaptosomes illustrate 3-fold increased specific binding. 3. A new polyether natural product from Florida's red tide dinoflagellate Karenia brevis, has been isolated and characterized. Brevenal, as the nontoxic natural product is known, competes with tritiated brevetoxin for site 5 associated with the voltage-sensitive sodium channel (VSSC). Brevenal displacement of specific brevetoxin binding is purely competitive in nature. 4. Brevenal, obtained from either laboratory cultures or field collections during a red tide, protects fish from the neurotoxic effects of brevetoxin exposure. 5. Brevenal may serve as a model compound for the development of therapeutics to prevent or reverse intoxication in red tide exposures.

1. As pharmacokinetic differences between the thiopentone enantiomers seem insufficient to explain the approximately 2 fold greater potency for CNS effects of (-)-S- over (+)-R-thiopentone, this study was performed to determine any enantioselectivity of thiopentone at the GABA(A) receptor, the primary receptor for barbiturate hypnotic effects. 2. Two electrode voltage clamp recording was performed on Xenopus laevis oocytes expressing human GABA(A) receptor subtype alpha1beta2gamma2 to determine relative differences in potentiation of the GABA response by rac-, (+)-R- and (-)-S-thiopentone, and rac-pentobarbitone. Changes in the cellular environment pH and in GABA concentrations were also evaluated. 3. With 3 microM GABA, the EC50 values were (-)-S-thiopentone (mean 26.0+/-s.e.mean 3.2 microM, n=9 cells) >rac-thiopentone (35.9+/-4.2 microM, n=6, P=0.1) >(+)-R-thiopentone (52.5+/-5.0 microM, n=8, P<0.02) >rac-pentobarbitone (97.0+/-11.2 microM, n=11, P<0.01). Adjustment of environment pH to 7.0 or 8.0 did not alter the EC50 values for (+)-R- or (-)-S-thiopentone. 4 Uninjected oocytes responded to >100 microM (-)-S- and R-thiopentone. This direct response was abolished by intracellular oocyte injection of 1,2-bis(2-aminophenoxy)ethane-N, N,N1,N1-tetraacetic acid (BAPTA), a Ca2+ chelating agent. With BAPTA, the EC50 values were (-)-S-thiopentone (20.6+/-3.2 microM, n=8) <(+)-R-thiopentone (36.2+/-3.2 microM, n=9, P<0.005). 5 (-)-S-thiopentone was found to be approximately 2 fold more potent than (+)-R-thiopentone in the potentiation of GABA at GABA(A) receptors expressed on Xenopus oocytes. This is consistent with the differences in potency for CNS depressant effects found in vivo.

Using N1E-115 neuroblastoma cells as an experimental model, we have examined if four commonly used i.v. anaesthetic induction agents interact with 5-HT3 receptors. Specifically, we tested the hypothesis that the antiemetic effects of propofol may result from 5-HT3 receptor antagonism. Binding of tropisetron (a 5-HT3 selective reference compound), etomidate, ketamine, thiopentone and propofol to 5-HT3 receptors was assessed by measuring the displacement of [3H]BRL 43694 from whole N1E-115 cells. The rank order potency (Ki) was tropisetron (1.7 (SEM 0.2) nmol litre-1) >> etomidate (83.(4) mumol litre-1) > or = ketamine (97 (4) mumol litre-1) > thiopentone (177 (9) mumol litre-1) > propofol (819 (171) mumol litre-1). With the exception of thiopentone these effects were outside the clinical range and suggest that anaesthetic agents are unlikely to interact directly with 5-HT3 receptors, and that other mechanism(s) must underlie the antiemetic effects of propofol.

It is generally believed that barbiturates can protect neural tissues from the damage induced by cerebral hypoxia. One of the mechanisms for protecting neurons is through the inhibition of lipid peroxidation (LPO). We therefore examined LPO in rat brain, liver and kidney by measuring the accumulation of thiobarbituric acid-reactive substances (TBAR) after thiopental administration under 21% O2. We also designed an in vitro study to gain insight into free radical generation leading to the formation of LPO from thiopental by electron spin resonance (ESR). An accumulation of TBAR in the rat liver was observed after the administration of a large dose of thiopental (70 mg/kg intraperitoneally). However, no change in LPO in the brain and kidney was observed. In the in vitro study, thiopental could scavenge superoxide (O2-.) radicals, while it spontaneously generated hydroxyl radicals (.OH) in solution. We conclude that thiopental can scavenge O2-., while producing .OH, subsequently resulting in membrane lipid peroxidation under physiologic O2 conditions. This formation of .OH may damage cell membrane lipids.

Background: Although low doses of barbiturates are widely believed to increase sensitivity to pain, studies of the electrophysiologic effects of these drugs on the neurons involved in nociception in the spinal cord have detected only depressant effects. The goal of the studies reported here was to quantify the hyperalgesia resulting from low-dose thiopental infusions and to measure the associated concentrations of thiopental in the plasma, brain, and spinal cord., Methods: Nociception was measured using the threshold for motor response to pressure stimulation of the tail (nociceptive threshold) and tail flick latency in the rat. Thiopental was administered by intravenous infusions designed to produce plasma concentrations that either slowly increased or remained at a steady state. Plasma and tissue thiopental concentrations were measured by high-performance liquid chromatography., Results: We observed a reduction in nociceptive threshold that was correlated with the plasma thiopental concentration over the range 2-20 micrograms.ml-1 (7.6-76 microM). The relationship was nonlinear. Nociceptive threshold reached a nadir (36% less than control values) at a mean plasma thiopental concentration of 13.7 micrograms.ml-1 (51.9 microM). The steady-state study showed a similar reduction in nociceptive threshold, with an equilibrium plasma thiopental concentration of 7.6 +/- 1.3 micrograms.ml-1 (28.8 +/- 4.9 microM). Concentrations of thiopental in brain and spinal cord samples were 1.7 +/- 0.03 and 3.5 +/- 1.7 micrograms.g-1, respectively., Conclusions: These studies confirm previous reports of hyperalgesia in association with small doses of thiopental. Reductions in nociceptive threshold and tail flick latency were observed in association with spinal cord concentrations of thiopental in a range reported by others to depress the electrophysiologic activity of neurons involved in nociception.

At pH 7.4 the binding of thiopental to human serum albumin (HSA) was increased in the presence of halothane. In order to obtain information about the mechanism of this interaction, in vitro binding experiments by means of equilibrium dialysis were carried out at different pH values. At pH 4.97 the binding of thiopental to HSA 1% was low (23% bound) and not influenced by halothane. An increase of thiopental binding caused by halothane could be seen at pH 7.4 (55% bound vs. 41% in the control = without halothane) and at pH 8.23 (62% vs. 54%). At pH 10.15 an opposite interaction was found: in the presence of halothane thiopental binding was considerably decreased (36.2% vs. 47.0% in the control). Evaluation of the binding parameters of experiments using increasing substrate concentrations (Scatchard plot) revealed quite different changes of the two classes of binding sites of HSA for thiopental. It is assumed that halothane causes reversible conformational changes of the albumin molecule resulting in altered binding characteristics for thiopental.

The equilibration between drug serum concentration and drug effect under non-steady state concentrations has been classically modeled using an effect compartment where the transfer from the serum to the effect compartment is considered to be a first-order process. The purpose of the present study was to examine whether an effect compartment with first-order transfer was adequate for describing thiopental serum concentration-EEG pharmacodynamics. The study has two facets: (i) Successive pseudo steady state serum concentrations of thiopental having a square wave shape were produced and maintained in six human subjects by means of a computer-driven infusion pump. An aperiodic wave form transformation of the electroencephalogram (EEG) was used as a continuous measure of thiopental EEG drug effect. The time course of the EEG effect following each thiopental serum concentration square wave showed an exponential pattern. The first-order rate constant for equilibration of the effect site concentration with the drug serum concentration (keo) was estimated by fitting a monoexponential model to the effect vs. time data resulting from the pseudo steady state thiopental serum concentration profile. (ii) In a second experiment, data were obtained from a classical design, i.e., a zero-order intravenous infusion of thiopental. The same subjects were studied. The keo was estimated by means of a semiparametric iterative method using convolution (effect compartment, transfer of drug from serum to site of action is assumed to be a first-order process). The mean pseudo steady state value for keo of 0.51 min-1 was not different from the mean value of 0.46 min-1 from the semi parametric approach when data from a linear portion of the drug concentration vs. effect curve were examined. The pseudo steady state technique gave inaccurate estimates of keo in the nonlinear portion of the thiopental concentration vs. response curve, i.e., at the peak of the biphasic concentration-effect relationship.

In vitro thiopental binding (substrate concentration 0.04.10(-3) M = 10 micrograms/ml) to 1% human serum albumin (HSA) increased significantly from 40.2% (= control) to 47.3% in the presence of 1.18.10(-3) M = 2.84 vol% halothane. A 4-fold higher halothane concentration (4.71.10(-3) M) had an even greater effect with an increase in the thiopental fraction bound to 55.5%. With a constant HSA concentration (1% or 5%) and thiopental concentrations in the range 0.01-1.5.10(-3) M or 0.01-0.38.10(-3) M, respectively, the halothane effect (increase in thiopental binding) was always evident, as well as in other experiments with constant thiopental concentration (0.04.10(-3) M) and variation in the HSA concentration (0.5-10%). Two classes of binding sites for thiopental were apparent at the HSA molecule. In the control experiments the following binding parameters were found: n1 = 0.01, k1 = 181.10(3) M-1; n2 = 45.73, k2 = 0.08.10(3) M-1, K = 5.47.10(3) M-1. In the presence of halothane the binding parameters changed as follows: n1 = 0.14, k1 = 29.4.10(3) M-1; n2 = 11.68, k2 = 0.42.10(3) M-1, K = 9.02.10(3) M-1.

Anaesthesia for planned caesarian section in nine women was induced with an i.v. thiopental injection. The injection was stopped when the ciliary reflex disappeared. 250-300 mg was given over 60-85 seconds. The concentration of thiopental in peripheral venous blood 20 s after the disappearance of the ciliary reflex varied from 4.3 to 33.7 micrograms/ml. The simultaneously obtained concentrations at delivery (11-25 min after the start of the induction) were 1.7-6.0 micrograms/ml in venous blood from the mothers and 1.3-5.5 micrograms/ml in cord vein blood. In two of the newborns, the Apgar scores were 8 and 9, in the other seven it was 10. The baby with Apgar score 8 was delivered after 25 min and had a concentration in cord vein blood of 3.5 micrograms/ml. The decline in the concentration of thiopental in the venous blood of the mothers was described by a three-compartment open model. The terminal half-life was relatively short, between 91 and 595 min. The blood levels of thiopental in the newborns were followed for 22-33 h. The terminal half-lives in the babies ranged from 616 to 2560 min.

Pharmacokinetics and duration of anesthesia of methohexital, pentobarbital, thiamylal, and thiopental in Greyhound and non-Greyhound, mixed-breed dogs were compared. In all dogs evaluated, pentobarbital induced the longest duration of anesthesia and methohexital induced the shortest duration. Pharmacokinetics of pentobarbital and methohexital were similar in both groups of dogs. Thiobarbiturates induced longer anesthetic effects in Greyhound dogs than in mixed-breed dogs. Plasma thiobarbiturate concentrations remained above normal longer in Greyhound dogs than in mixed-breed dogs. Disposition of thiobarbiturates in Greyhound dogs was characterized by nonlinearity from 45 minutes to 8 hours after dosing.

Trazodone and its metabolite, m-chlorophenylpiperazine (CPP) prolonged significantly thiopentone-induced sleep in mice. Neither trazodone, nor CPP changed the cerebral concentrations of thiopentone. As cyproheptadine by itself did not affect thiopentone sleep and did not antagonize the effect of CPP, the effect of trazodone and CPP seems to be independent of their respective 5-HT-antagonistic and 5-HT-agonistic properties.

The plasma concentrations and elimination half-life of pentobarbitone were determined in 14 surgical patients receiving a continuous, exponentially decreasing, infusion of thiopentone (mean total dose, 1.05 g; SD 0.34; mean duration of infusion 2.4 hours, SD 0.7) as the primary anaesthetic agent. The plasma pentobarbitone concentration increased gradually, to reach a maximum of 1.49 micrograms/ml (SD 0.61) at the end of the thiopentone infusion, which was 15.5 per cent (SD 6.04) of the plasma thiopentone concentration. The elimination half-life of pentobarbitone measured over the following 70 hours in nine of the patients was 34.3 hours (SD 8.2), which is within the range of values reported previously in several studies in which pentobarbitone was administered directly to volunteers. It was concluded that the formation of this active metabolite during 2-3 hour thiopentone infusions was unlikely to be of clinical relevance, but that significant concentrations may occur with longer thiopentone infusions.

Physiological studies by Setchell and others have described the existence of a blood-testis barrier (BTB) surrounding the seminiferous tubules of the mammalian testis. These studies were initiated to better define the role of the BTB with regard to the penetration of exogenous chemicals to male germ cells. The rete testis was cannulated in rats and fluid was collected. Test chemicals or drugs were usually administered by continuous i.v. infusion. Permeability of nonelectrolytes of various molecular sizes, acidic compounds with varying partition coefficients and pKalpha values, such as salicylic acid, barbiturates, and sulfonamides, across the BTB were studied. Permeability of nonelectrolytes was demonstrated to be dependent upon their molecular size, suggesting bulk flow through water-filled pores. On the other hand, permeability of acidic drugs with varying pKalpha values depended upon their partition coefficients. Transport of these chemicals from blood to seminferous tubules closely resembled their transport from blood to cerebrospinal fluid. It appears that the BTB is a complex multicellular system composed of membranes surrounding the semiferous tubules and the several layers of spermatogenic cells organized within the tubules, which restrict the permeability to the male germ cells of many foreign compounds. This must be borne in mind when extra-polating data from in vitro mutagenic test systems to man.

The anaesthetic interaction between hexobarbital and thiopental in different combinations were investigated in male rats by using the isobolografic method. Data on dose, serum or brain concentrations at an EEG-criterion induced with a threshold method were utilized. The criterion was defined by a burst suppression in the EEG of 1 sec. or more (the "silent second"). With rats more than 115 days of age a synergistic interaction (potentiation) was obtained when a low dose of hexobarbital and a high dose of thiopental were used. The relationship between serum and brain concentrations of hexobarbital and thiopental in the different tested combinations gave no evidence for a pharmacokinetic interaction. Thus the synergistic interaction was located in the brain and probably related to the mechanisms of action. The same tests performed on rats at an age of approximately 90 days gave not only a potentiation when a low dose of hexobarbital and a high dose of thiopental were used, but also a potentiation when a high dose of hexobarbital and a low dose of thiopental were used. These results indicate an age-related change in sensitivity in the CNS between 90 and 115 days of age. Further investigations of this age-related change showed that this change from a potentiation to an additive interaction occurred between the age of 85 and 96 days.

The pharmacokinetics and plasma protein binding of thiopental were investigated in 5 female patients who received a bolus intravenous dose of the drug for induction of anesthesia for gynecologic surgery. Blood samples were collected for 3 to 4 days after the dose. Plasma protein binding determinations were also carried out by ultrafiltration and equilibrium dialysis on samples from a panel of healthy volunteers. Plasma concentrations of thiopental were determined by reverse-phase, high-performance liquid chromatography. The coefficient of variation of the method was 2.8 per cent (n equals 10). In healthy volunteers, the plasma protein binding of thiopental was concentration dependent. Percentage bound ranged from 96.7 (n equals 4, SD equals 0.8) at 150 micrograms/ml. Therefore, saturation of binding sites on rapid administration of the drug may occur, exposing vital organs to unexpectedly high concentrations of free drug. Values of the fraction of thiopental bound in plasma obtained from the surgical patients during the hour following drug administration were similar to values obtained in healthy volunteers at comparable concentrations. Mean pharmacokinetic parameters obtained for thiopental in the surgical patients were as follows: initial distribution volume 13.81 (SD equals 9.4), apparent volume of distribution 233 1 (SD equals 98), volume of distribution at steady state 97.51 (SD equals 40), elimination half-life 11.5 h (SD equals 1.0) and systemic plasma clearance 0.150 l/min (SD equals 0.063). None of these parameters correlated with body weight. Values reported by other workers vary from ours and this variation may be explained by the much shorter duration of blood collection used in those studies.

The effects and pharmacokinetics of thiopental were studied in eight patients undergoing renal transplantation. The results were compared with findings in a group of patients with normal renal function. No differences were observed in induction doses or between arterial or venous sleep concentrations. The average V3 in the renal failure group was 1441 or 2.5 times the value of the control group (P less than 0.01). The apparent differences indicating longer elimination half-lives and higher serum clearances in the renal patients were not significant. The average binding of thiopental to serum protein shortly after the induction was 83.9% (78.2-88.1) in the renal patients and 89.0% (85.2-91.6) in the control patients (P less than 0.05). The difference in V3 could be explained by the differences in protein binding and when the serum clearance was calculated by using the unbound fraction, this "intrinsic clearance" was significantly lower in the renal failure group (P less than 0.05). Haemodynamic parameters were determined during the initial 5 min. No significant difference was observed between the thiopental-induced changes in stroke volume. Cardiac output was unchanged in both patient groups.

The average dose of thiopental necessary for induction was 3.4 mg/kg body weight in seven patients on long-term therapy with digoxin and a diuretic and 4.7 mg/kg body weight in seven matched control patients (P less than 0.05). The initial volumes of distribution (V1) did not differ significantly. The amounts of thiopental redistributed (removed from V1) during the induction were calculated as V1 X k12 X ct and V1 X k13 X ct, where k12 and k13 are the rate constants describing the drug transfer from V1 to V2 and V3 and ct the computer-calculated average thiopental concentration in V1 during the initial 40 s of the induction period. There was no evidence of a lower amount being removed during the induction in the cardiac patients. The intravascular drug concentration at the time of sleep was expressed as the average of the arterial and the venous sleep concentrations. In the cardiac patients the average of that value was 20.1 micrograms/ml and in the control patients 30.2 micrograms/ml (P less than 0.05). It is concluded that the lower dose requirement in the cardiac patients was caused at least in part by a higher cerebral sensitivity to the drug.

Injection of thiopental sodium, 25 or 40 mg/kg, i.p., into normal rats produced a prompt sleep which lasted 8.3 plus or minus 2.9 and 16.8 plus or minus 2.7 min, respectively. Injection of morphine sulphage, 20 mg/kg, i.p., itself produced only mild sedation but prolonged the thiopental induced sleep to 50 and 67.3 min, respectively. At 1 min after onset of sleep the brain thiopental concentration in morphine pretreated animals was significantly lower than in control animals. Furthermore the latter also awoke with higher brain thiopental concentrations; the morphine pretreated animals slept for a longer time despite lower brain thiopental concentration. The t1/2 of brain thiopental was longer in the morphine pretreated animals, 25 min, than in the control animals, 9 min. Distribution of thiopental in several tissues at various time periods following injection of thiopental revealed some time-related quantitative differences between the two groups but a similar qualitative pattern. It is suggested that morphine lowers the brain threshold for thiopental induced sleep.

Thiopental pharmacokinetics and protein binding were determined in 24 pediatric surgical patients with normal hepatic and renal function, ranging in age from 5 months to 13 yr. These pharmacokinetic data were compared with those from 11 adult patients previously studied at our institution. All pediatric patients received a single intravenous bolus of thiopental, 4.0 +/- 0.08 mg . kg-1 (mean +/- SD), while the adult patients received 6.0 +/- 0.74 mg . kg-1. Distribution phase kinetics and volume of distribution at steady state (Vdss) did not differ statistically between the two groups. The degree of serum protein binding of thiopental also was similar in pediatric and adult patients with free fractions of 13.2% +/- 1.5% and 13.6% +/- 1.3%, respectively. The two patient groups showed a marked difference in elimination half-time and clearance of thiopental. Total drug clearance was 6.6 +/- 2.2 ml . kg-1 . min-1 for pediatric patients and 3.1 +/- 0.5 ml . kg-1 . min-1 for adults (P less than 0.001). The elimination half-time of 6.1 +/- 3.3 hours found in pediatric patients was significantly shorter (P less than 0.005) than that for adults, 12 +/- 6 hours. Linear regression of the pediatric data failed to achieve significance (P = 0.06) for elimination half-time to increase with age, while clearance decreased (P less than 0.001) with increasing age. The shorter elimination half-time seen in infants and children was due solely to greater hepatic clearance. Thus, recovery time after large or repeated doses may be more rapid for infants and children than for adults because of the higher clearance.

A physiologically based pharmacokinetic model, which is an extension of the Bischoff-Dedrick multiorgan model, was developed to described the kinetics of barbiturates (hexobarbital, phenobarbital, and thiopental) in the rat. The model is composed of 11 organ or tissue compartments. The brain compartment was featured as a nonflow-limited organ for some low lipid soluble barbiturates. Michaelis-Menten constants for drug metabolism (Km, Vmax) were determined from in vitro experiments using liver microsomes. Binding of drugs to plasma and tissue proteins was measured in vitro using an equilibrium dialysis method. Distribution of drugs to red blood cells was measured in vitro with thiopental exhibiting a concentration dependent distribution. Penetration rates of the barbiturates into the brain were predicted on the basis of their lipid solubilities. A set of mass balance equations included terms for the inflow and outflow of drug carried by the perfusing blood, drug metabolism, protein binding, and penetration rate into the brain as well as blood flow rate and tissue mass. Solution of the system of equations yielded the time courses of drugs in each organ. However, predicted time course of drugs in plasma and brain were not in good agreement with those observed. Therefore, the tissue to plasma distribution ratios evaluated from in vivo experiments were substituted for the in vitro values, resulting in fairly good agreement between predicted and observed values.

A comparative study on the fate of thiopental, DDE, and 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB) with emphasis on adipose tissue kinetics was carried out after single i.v. doses to adult male rats. The time course of the concn. in blood, adipose and other tissues were determined for the three compounds for periods up to 40 h, 14 and 28 d, respectively, allowing for mass balances and for calculation of pharmacokinetic parameters. Appreciable amounts of thiopental, DDE and 6-CB appeared in adipose tissues, but the kinetics were profoundly different, the adipose tissue concn. peaking after one hour, 17 h, and five to six weeks, respectively. Thus, although DDE and 6-CB are much more lipophilic than thiopental, they were very much slower in entering adipose tissue. The results indicate that adipose tissue storage of drugs and other xenobiotics cannot be explained as a simple partition phenomenon. Rather, disposition in adipose tissue may be determined by initial binding in other tissues.

Thiopental-14C (30 mg and 10 muCi/kg) was injected intravenously into rats 36-48 hours following bilateral nephrectomy and one minute after pretreatment with sulfadimethoxine (30 mg/kg, iv). Control groups of normal and sham-operated animals were used. The distributions of radioactivity in plasma, brain, and heart 1, 5, and 30 minutes after injection were examined. Uremic and sulfonamide-pretreated rats showed significantly higher levels of 14C in brain and heart and more free thiopental in plasma at each time than did control animals. There was a significant correlation between the free thiopental in plasma and total drug concentrations in the brain and heart. Uremic rats bound less thiopental in plasma compared with controls in spite of normal total plasma protein and albumin concentrations. It is concluded that reduced protein binding of thiopental leads to accelerated distribution and increased drug concentrations in the brain and and heart.

Thiopental is an anaesthetic drug which is currently used for cerebral resuscitation. In this last indication the drug is administrated at high doses over a period of several days. Under clinical trials thiopental and two metabolites namely 5 ethyl-5 (1' methyl-3' hydroxy-butyl) 2 thiobarbituric acid and 5 ethyl-5 (1' methyl-3' carboxy-propyl) 2 thiobarbituric acid have been determined by high performance liquid chromatography and mass spectrometry. In human plasma high concentrations of thiopental and 5 ethyl-5 (1' methyl-3' hydroxy-butyl) 2 thiobarbituric acid and a lower concentration of 5 ethyl-5 (1' methyl-3' carboxy-propyl) 2 thiobarbituric acid have been found. In urine samples these metabolites are excreted in large and approximately equal quantities, whereas small amounts of thiopental were recovered.

The uptake and distribution of two i.v. anaesthetics agents, thiopentone and Althesin, were studied in mice with normal and subnormal nutritional states. The results show that, following the administration of thiopentone, the induction time was signficantly shorter, and that the sleeping time was significantly longer following the administration of Althesin and thiopentone in mice that have low net protein utilization, and decreased total and dry body mass. The increase in the sleeping time in these undernourished mice was 2.2 times greater for Althesin and 4.0 times greater for thiopentone when compared with well-nourished mice.

The effect of obesity on the disposition kinetics of thiopental was studied in seven morbidly obese (age 25 to 46 years) and eight age-matched lean patients (age 25 to 43 years), undergoing primarily abdominal surgery. Based upon total (bound + free) thiopental concentrations, the average (+/-SD) volumes of distribution in the terminal disposition phase and at steady-state (V beta and V ss) were significantly larger in the obese (7.94 +/- 4.55 1/kg and 4.72 +/- 2.73 1/kg, respectively) than in the age-matched lean patients (1.95 +/- 0.63 1/kg and 1.40 +/- 0.46 1/kg, respectively). Clearance of total thiopental, normalized for total body weight was not significantly different between the obese (0.18 +/- 0.081 . h-1 . kg-1) and lean patients (0.21 +/- 0.06 1 . h-1 . kg-1). However, total body clearance not normalized for total body weight was significantly larger in the obese (24.98+/- 14.87 1/h) than in the lean patients (11.86 +/- 3.66 1/h). The elimination half-life of thiopental was significantly longer in the obese (27.85 h) than in the lean patients (6.33 h) and this difference was primarily a function of a larger apparent volume of distribution for thiopental. The unbound fraction of thiopental in serum (range, 17.8 per cent to 27.6 per cent) was not correlated with the degree of obesity. The most appropriate means of comparing intrinsic metabolizing capacity (i.e., normalized vs. non-normalized for weight) between lean and obese subjects remains unresolved.

The pharmacokinetics of thiopentone was studied in six mongrel dogs using a high-performance liquid chromatographic method for measurement of the drug in the plasma. An intravenous bolus dose (20 mg/kg) of 2.5% thiopentone sodium solution was injected into the cephalic vein. While the two- and three-compartment models were used in the analysis of the experimental data, the disposition curve was adequately described by a biexponential equation. Plasma protein binding of thiopentone was determined in vitro using the equilibrium dialysis technique. The drug was bound to a moderately high extent (73.8 +/- 4.1%). The half-time of the initial phase, which comprises distribution/redistribution, was 14.9 +/- 3.3 mins. The apparent volume of distribution was quite high for an organic acid (843 +/- 194 ml/kg). This may be attributed to the high lipid solubility of the thiobarbiturate. The half-life was 6.99 +/- 2.18 h and a body clearance value of 1.51 +/- 0.60 ml/kg-min was obtained. It can be concluded from this study that the half-time of the distribution/redistribution phase approximates the duration of anaesthetic effect. Consequently, physiological conditions and disease states which influence distribution/redistribution rather than those affecting hepatic biotransformation of the drug are likely to affect anaesthesia.

Pretreatment with HgCl2 (2 mg/kg sc) 24 h before administration of thiopental (35 mg/kg ip) significantly potentiated the duration of thiopental sleeping time in adult male rats but did not influence the onset time for anesthesia. The plasma concentration of free thiopental was significantly higher in the Hg-treated animals 15 and 45 min after thiopental injection (i.e., during the period of thiopental anesthesia), with a concomitant increase of the free thiopental concentration in the brain at 15 min. However, total and free brain thiopental concentrations in Hg-treated rats at the time of awakening were not different from those in saline-treated animals. Urinary thiopental remained unchanged from 0 to 2 h, but was increased in the treated urine from 0 to 27 h. In vitro studies showed a strong inhibition of thiopental binding in 24-h Hg-treated plasma. The results suggest that the prolongation of thiopental anesthesia induced by Hg pretreatment is probably related to changes in the disposition of thiopental in the plasma and brain rather than to an alteration in the sensitivity of the central nervous system.

The role of metabolism, relative to redistribution, in the termination of anesthesia was examined in patients receiving a single bolus iv injection of thiopental. Additionally, it was determined if nonlinear protein binding occurs immediately after the bolus iv injection of thiopental, possibly enhancing thiopental effect. Thiopental pharmacokinetics and protein binding were determined in 12 surgical patients with normal hepatic function. Using the pharmacokinetic equations listed in the appendix, plasma concentration over time data were used to quantitate the contribution of metabolism to the early decline of thiopental plasma concentrations after a single iv bolus administration. The fraction of thiopental loss from the central compartment due to metabolism was calculated to be 0.14 +/- 0.06 (mean +/- SD) at 1 min and 0.18 +/) 0.04 at 15 min. These data confirm that metabolism is far less important than distribution in the initial decline of blood and brain concentrations of thiopental, and, therefore, termination of thiopental anesthetic effect. The protein binding of thiopental from 0.5 to 15 min was found to be linear over a concentration range of 93 +/- 60 micrograms/ml to 6.9 +/- 0.62 micrograms/ml. Thus, concentration-dependent or nonlinear protein binding of thiopental after a single iv bolus administration could not be demonstrated and does not enhance thiopental anesthetic effect.