Donor-Acceptor Stenhouse Adduct Displaying Reversible Photoswitching in Water and Neuronal Activity.

The interest in the photochromism and functional applications of donor-acceptor Stenhouse adducts (DASAs) soared in recent years owing to their outstanding advantages and flexible design. However, their low solubility and irreversible conversion in aqueous solutions hampered exploring DASAs for biology and medicine. It is notably unknown whether the barbiturate electron acceptor group retains the pharmacological activity of drugs such as phenobarbital, which targets γ-aminobutyric acid (GABA)-type A receptors (GABAARs) in the brain. Here, we have developed the model compound DASA-barbital based on a scaffold of red-switching second-generation DASAs, and we demonstrate that it is active in GABAARs and alters the neuronal firing rate in a physiological medium at neutral pH. DASA-barbital can also be reversibly photoswitched in acidic aqueous solutions using cyclodextrin, an approved ingredient of drug formulations. These findings clarify the path toward the biological applications of DASAs and to exploit the versatility displayed in polymers and materials science.

Seasonal Variation of Phyto-Constituents of Tea Leaves Affects Antiproliferative Potential.

Objective: Tea (Camellia sinensis Linn.; family: Theaceae) is popular as a stimulant beverage across the globe and is also utilized as a functional antioxidant in alternative medicine. This study has evaluated the impact of seasonal variation on phyto-constituents of tea. Method: The antiproliferative potential of methanolic extracts of tea leaves collected in the rainy season (MECR) was compared with the extract of tea leaves collected in the autumn season (MECA) of the same mother plant. Evaluation of in vivo antitumor activity was carried out in adult female Swiss albino mice groups inoculated with Ehrlich ascites carcinoma (EAC) cells. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to compare efficacy of MECR with that of MECA in the EAC cell line. Both qualitative and quantitative tests for phytochemical constituents present in MECA and MECR were performed. Antitumor efficacy of both the extracts was determined by evaluating different tumor markers showing dose-dependent cytotoxicity. Results: Statistically significant reduction in EAC-induced tumor was observed in MECR treated mice compared to MECA treated ones. Cell decimation was significantly higher with MECR treatment, where restoration of different parameters including tissue structures returned to normal. Moreover, gas chromatography-mass spectrometry (GC-MS) study revealed the presence of cyclobarbital and benzazulene derivative in MECR, which is thought to be a novel source of these chemicals. Conclusions: To our knowledge, there is no report that has attempted to reveal nutritional changes in terms of efficacy and variation in anticancer constituents in tea leaves, plucked in two seasons. This study revealed a novel source of barbital and benzazulene derivative. The unique presence of cyclobarbital and benzazulene, as revealed from GC-MS data, in methanolic extract of tea leaves collected during the rainy season (MECR) may have contributed to its enhanced in vitro (adopting MTT assay) and in vivo (on EAC-infected Swiss albino mice) cytotoxicity vis-à-vis antiproliferative properties compared to methanolic extract of tea leaves collected during the autumn season (MECA). The nature of plucking leaves in the two selected seasons is different.

Disulfiram enhances pharmacological activity of barbital and impairs its urinary elimination.

Disulfiram or diethyldithiocarbamate significantly enhanced the sleeping time induced by barbital in rats. At identical time intervals after rats were injected with barbital the concentration of barbital in the blood or brain of animals that had previously received disulfiram was significantly higher than the concentrations in the corresponding tissues of control animals. Urinary excretion of barbital was significantly reduced in disulfiram-treated animals.

Glutamatergic system: another target for the action of porphyrinogenic agents.

The N-methyl-diethyl-aspartate (NMDA) receptor has been reported to play an important role in several acute and chronic neuropathologic syndromes. 5-aminolevulinic acid (ALA) accumulates in acute porphyrias due to a deficiency in the heme biosynthetic pathway. Considering that glutamate uptake inhibition caused by ALA could be one of the reasons conducing to porphyric neuropathy, it was of interest to evaluate the effect of porphyrinogenic agents on NMDA glutamatergic system. To this end receptor levels and apparent affinity (Kd) were analyzed in mice brain cortex and cerebellum. NMDA levels were diminished after chronic Isoflurane anaesthesia in brain cortex. In cerebellum, a diminution was observed after acute Enflurane and Isoflurane and allylisopropylacetamide, while ethanol administration showed a significant increase. ALA administration diminished NMDA levels only in cerebellum. Affinity constant was only reduced in brain cortex after chronic Isoflurane treatment. In conclusion, glutamatergic system appears to be involved in the action of some of the porphyrinogenic drugs studied mainly in cerebellum. Receptors regulation should therefore be considered an important mechanism in the cellular response to specific drugs, with the aim of designing new therapies and elucidating the mechanisms leading to porphyric neuropathy and acute attack triggering.

Larrea divaricata Cav (Jarilla): production of superoxide anion, hydrogen peroxide and expression of zymosan receptors.

Larrea divaricata is a plant widely used in folk medicine in Argentina. This work aimed to study the mechanisms of decoction activity on the release of oxygen reactive species. Decoction increased the binding of zymosan-FITC and superoxide production. Cadmium decreased the superoxide production as well as malonate and barbital. Decoction decreased the release of hydrogen peroxide. Decoction increased the reduction of MTT but not when malonate and barbital were included. Together, decoction increased the expression of dectin-1 leading to increased superoxide production. It is possible that decoction increases the activity of peroxidase, and decreases the Cu, Zn-superoxide dismutase.

Photoactive barbiturate receptors: an ultimate lock-and-key system in which the key unlocks the lock.

Conditional photofragmentation is achieved with binary systems incorporating the isophthaloyl bis-aminopyridine barbiturate recognition motif and dithiane- or trithiane-based photolabile modules, which cleave only in the presence of an external sensitizer. The components of the host-guest molecular recognition pair were each outfitted with either the sensitizer or the photocleavable module. In these pairs, photoinduced fragmentation is contingent on a molecular recognition event, which brings the sensitizer into the immediate proximity of the photolabile latch. [structure: see text]

Effects of quinones and flavonoids on the reduction of all-trans retinal to all-trans retinol in pig heart.

We have recently purified a tetrameric carbonyl reductase from the cytosolic fraction of pig heart (pig heart carbonyl reductase). Since pig heart carbonyl reductase efficiently reduces all-trans retinal as the endogenous substrate, it probably plays an important role in retinoid metabolism in the heart. The purpose of the present study was to evaluate the inhibitory effects of quinones and flavonoids on the reduction of all-trans retinal to all-trans retinol catalyzed by pig heart carbonyl reductase, using pig heart cytosol. Of quinones tested, 9,10-phenanthrenequinone, a component of diesel exhaust particles, was the most potent inhibitor for the all-trans retinal reduction, and a significant inhibition was also observed for plumbagin and menadione. The order of the inhibitory potencies for flavonoids was kaempferol > quercetin > genistein > myricetin = apigenin = daidzein. However, the inhibitory potencies of flavonoids were much lower than that of 9,10-phenanthrenequinone. 9,10-Phenanthrenequinone competitively inhibited the all-trans retinal reduction, whereas kaempferol exhibited a mixed-type inhibition. It is likely that 9,10-phenanthrenequinone strongly inhibits the reduction of all-trans retinal to all-trans retinol by acting as the substrate inhibitor of pig heart carbonyl reductase present in pig heart cytosol.

Mechanisms of barbiturate inhibition of acetylcholine receptor channels.

We used patch clamp techniques to study the inhibitory effects of pentobarbital and barbital on nicotinic acetylcholine receptor channels from BC3H-1 cells. Single channel recording from outside-out patches reveals that both drugs cause acetylcholine-activated channel events to occur in bursts. The mean duration of gaps within bursts in 2 ms for 0.1 mM pentobarbital and 0.05 ms for 1 mM barbital. In addition, 1 mM barbital reduces the apparent single channel current by 15%. Both barbiturates decrease the duration of openings within a burst but have only a small effect on the burst duration. Macroscopic currents were activated by rapid perfusion of 300 microM acetylcholine to outside-out patches. The concentration dependence of peak current inhibition was fit with a Hill function; for pentobarbital, Ki = 32 microM, n = 1.09; for barbital, Ki = 1900 microM, n = 1.24. Inhibition is voltage independent. The kinetics of inhibition by pentobarbital are at least 30 times faster than inhibition by barbital (3 ms vs. < 0.1 ms at the Ki). Pentobarbital binds > or = 10-fold more tightly to open channels than to closed channels; we could not determine whether the binding of barbital is state dependent. Experiments performed with both barbiturates reveal that they do not compete for a single binding site on the acetylcholine receptor channel protein, but the binding of one barbiturate destabilizes the binding of the other. These results support a kinetic model in which barbiturates bind to both open and closed states of the AChR and block the flow of ions through the channel. An additional, lower-affinity binding site for pentobarbital may explain the effects seen at > 100 microM pentobarbital.

Heme oxygenase, aminolevulinate acid synthetase and the antioxidant system in the brain of mice treated with porphyrinogenic drugs.

Several drugs and stress are involved in the triggering of attacks in acute porphyrias. The central nervous system is extremely sensitive to free radical damage because of a relatively low antioxidant capacity. We have demonstrated that mice brain cholinergic system was altered by the effect of some porphyrinogenic agents. The aim of this work was to investigate how known porphyrinogenic drugs affect delta-Aminolevulinic acid synthetase (ALA-S), which is the response of heme oxygenase (HO) to this challenge and to evaluate if the xenobiotics studied develop stress oxidative in mice brain. HO activity was 50-70% induced after chronic Enflurane and Isoflurane anaesthesia, dietary Griseofulvin and starvation. An increase in mRNA HO expression was caused by chronic anaesthesia and Veronal treatments; instead allylisopropilacetamide (AIA) reduced mRNA expression. ALA-S activity was induced by acute administration of anaesthetics (89%), veronal (240%) and ethanol (80%), while ALA-S mRNA expression augmented by chronic administration of enflurane, AIA and veronal. Stress markers such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activities and malondialdehyde and reduced glutathione levels showed different responses depending on the xenobiotic assayed. In conclusion, some of the drugs studied produced oxidative stress in brain that was confirmed through HO induction and this could be one of the factors leading to porphyric neuropathy.

Effects of oxybarbiturates on the germination behaviour of Impatiens bolstii pollen.

Swelling of and cytoplasmic streaming within the grain, germination pore expansion, and pollen tube emergence, in that order, constitute the normal germination pattern of Impatiens holstii pollen grains. This normal sequence of events becomes manifest when the pollen grains are placed on water-agar, barbituric acid-agar, and on barbital-agar media whereas this sequence of events is interfered with when the pollen grains are incubated on amytal-agar or on seconal-agar media. Evidence is presented which demonstrates that the normal sequence of events which make up the normal germination pattern of Impatiens holstii pollen grains can be separated from each other by varying the concentrations of the oxybarbiturates amytal and seconal used. Evidence is also presented which indicates that the actions of barbituric acid and the oxybarbiturates barbital, amytal, and seconal on Impatiens holstii pollen germination behaviour correlate well with certain aspects of the pharmacological literature concerning the actions of these organic compounds on the central nervous system (CNS).

Drugs and taste aversion.

The literature on the effects of drugs on the acquisition and the magnitude of taste aversion is reviewed and discussed. Then, the results of a series of experiments on the effects of phenobarbital and related drugs on taste aversion are reported. A standard taste aversion model was used in all experiments; test drugs were injected prior to drinking in a one bottle situation on the first test day following the taste aversion treatment. Phenobarbital in doses ranging from 20 to 80 mg/kg significantly attenuated taste aversion induced by lithium chloride (LiCl) and x-radiation, the maximal effect occurred with the 60 mg/kg dose. The attenuating effect was found to be dependent upon the magnitude of the aversion to the sapid solution. Phenobarbital completely abolished aversion produced by 0.375 mEq LiCl while the attenuation effect decreased linearly with higher doses of LiCl. Results also indicate that phenobarbital's attenuating effect cannot be solely attributed to its dipsogenic characteristic or to its state dependent learning effect. Attenuation of LiCl aversion to a saccharin solution was also observed following single doses of amobarbital, 30 mg/kg, pentobarbital, 15 mg/kg, and chloropromazine, 0.75 mg/kg. Taste aversion was not affected by other doses of those drugs or by hexobarbital, barbital, and chlordiazepoxide. Phenobarbital's attenuating effect on taste aversion is discussed in relation to other known behavioral and neurophysiological effects of the drug.

Familial euthyroid thyroxine excess: an appropriate response to abnormal thyroxine binding associated with albumin.

Responses of the pituitary-thyroid axis and T4 binding to plasma proteins were studied in three kindreds with familial euthyroid T4 excess, an autosomal dominant condition in which affected subjects have high concentrations of plasma T4 with a high free T4 index, but normal free T4 by equilibrium dialysis. Treatment of affected subjects with exogenous T4 or T3 led to gradual suppression of TSH secretion when the free level of T4 or T3 increased above normal. When total T4 was reduced toward normal by potassium iodide treatment or previous subtotal thyroidectomy, the findings suggested mild hormone deficiency. In affected subjects from all three families, equilibrium dialysis showed increased [125I]T4 binding, with evidence of abnormal high capacity binding when an excess of unlabeled T4 was added. In contrast, T3 binding showed no major abnormality. Serum concentrations of T4-binding globulin, prealbumin, and albumin were normal, but gel electrophoresis and immunoprecipitation of binding proteins indicated that 25-30% of tracer [125I]T4 was albumin bound (normal, 10-12%). Abnormal binding, studied by an adsorption separation system in the presence of T4 excess, was inhibited by increments of barbitone. These findings suggest that T4 excess is an appropriate response to abnormal T4 binding so as to maintain normal free T4. The excess bound T4 is associated with a normal quantity of albumin. The basis for increased T4-albumin binding remains to be determined.

Three second chromosome-linked clustered Cyp6 genes show differential constitutive and barbital-induced expression in DDT-resistant and susceptible strains of Drosophila melanogaster.

The level of expression of the Cyp6a2 gene is much higher in the DDT-resistant 91-R strain than in the susceptible 91-C strain of Drosophila melanogaster (Waters et al. (1992b) Proc. Natl. Acad. Sci. USA, 89, 4855-4859). To understand the role of Cyp6a2 and related genes in insecticide resistance, we have isolated and characterized two new Cyp6 genes from the 91-R strain. The polypeptides encoded by these two genes, Cyp6a8 and Cyp6a9, show 77 and 75% amino acid sequence similarity, and 60 and 55% identity with Cyp6a2 of D. melanogaster, respectively. In the genome, Cyp6a8 and Cyp6a9 genes are closely clustered within 4 kb and map at region 51C of the second chromosome. In between them another Cyp gene is present which is more related to Cyp6a9 than to Cyp6a8. The Cyp6a8 gene which is transcriptionally highly active in 91-R, moderately active in ry506 and silent in the 91-C strain hybridizes with 2.0- and 1.8-kb RNAs. Two different-sized RNAs, 2.1 and 1.8 kb, also hybridize with the Cyp6a9 and/or Cyp6a9-related genes. While the level of 2.1-kb RNA is similar in all three strains, the level of 1.8-kb RNA is highest in the 91-R strain and barely detectable in 91-C strain. Transgenic experiments showed that a 8.3-kb BamHI fragment contains the cis-regulatory elements for the expression of both Cyp6a8 and Cyp6a9-related genes. Barbital induces all these genes in all three strains and increases the levels of the two Cyp6a8 transcripts and the 1.8-kb RNA produced by the Cyp6a9 and/or Cyp6a9-related genes. Expression of the Cyp6a8 gene is down-regulated in the hybrids of 91-R and 91-C strains despite the fact that the hybrids carry one copy of the highly active allele of the Cyp6a8 gene of the 91-R strain. Based on these results we propose that the Cyp6a8 gene in 91-C strain may be turned off by an active repressor which might be inhibited by barbital treatment. In the 91-R strain, the putative repressor may be defective, allowing high level of constitutive expression of the Cyp6a8 gene.

Constitutive and barbital-induced expression of the Cyp6a2 allele of a high producer strain of CYP6A2 in the genetic background of a low producer strain.

The levels of one or more cytochrome P450 (CYP) enzymes and the respective mRNAs are found to be higher in insecticide-resistant insects than in susceptible insects. To understand better how insects regulate the levels of CYPs, we examined the expression of the Cyp6a2 gene in various strains of Drosophila melanogaster. We also took a transgenic approach to understand the molecular mechanisms that are involved in strain variation of Cyp6a2 expression. RNA blot analysis showed that the constitutive expression of Cyp6a2 varies from strain to strain; the level of CYP6A2 mRNA is barely detectable in the underproducer ry506 strain, whereas it is very high in the overproducer 91-R and MHIII-D23 strains. The long terminal repeat (LTR) of mobile element 17.6 that is found in the 3' untranslated region (UTR) of the Cyp6a2 gene of some strains does not appear to have any role on the steady-state CYP6A2 mRNA level. We also found that the Cyp6a2 gene is inducible by barbital in 91-R, ry506 as well as 91-C, which carries an LTR insertion. To examine the genetic background of the underproducer ry506 strain with respect to Cyp6a2 expression, we transformed the ry506 strain with the Cyp6a2 allele of the overproducer 91-R strain (Cyp6a2-91 R) and measured the constitutive and barbital-induced expression of the Cyp6a2-91 R transgene in the transformed flies. The Cyp6a2-91 R transgene carrying 129 bp of DNA upstream of the ATG codon did not show any constitutive or barbital-induced expression in the ry506 host genome. However, transgenes with 1331 and 985 bp upstream DNA showed similar levels of constitutive expression that were higher than that of the endogenous Cyp6a2 gene of the ry506 host strain, but lower than the expression of the same gene in the 91-R strain. Both these transgenes, with 1331 and 985 bp upstream DNA, also showed induction with 0.1 M barbital. DNA sequence analysis revealed that in both 91-R and ry506, the upstream DNA between +1 and -985 bp contains a distal and a proximal group of three potential barbie boxes, i.e. cis-elements that are thought to be involved in barbiturate-mediated induction of CYP genes. Except for four bases located near the distal cluster of barbie boxes and two other bases, the base sequence of the upstream DNA is identical in ry506 and 91-R strains. These results suggest that the underproducer ry506 strain has the trans-regulatory factors to support constitutive and induced expression of the Cyp6a2-91 R allele carrying DNA between -129 and -1331 bp regions. Possible reasons for low constitutive expression of the endogenous Cyp6a2 gene and moderate level of expression of the Cyp6a2-91 R allele in the ry506 genetic background are discussed.

Evidence for GABA tolerance in barbiturate-dependent and withdrawn mice.

Mice were rendered tolerant and dependent to barbital by a chronic feeding schedule of barbital over 5 weeks. The behavioural effects of muscimol, imidazole-acetic acid (ImAA), and gamma-hydroxybutyric acid (GHB) were measured in control, barbital-dependent, and mice dependent on barbital 48 hr after withdrawal of the drug. The sedative effects of the GABA-mimetics imidazole-acetic acid and muscimol were increased in dependent mice, but reduced in withdrawn mice. Subanaesthetic doses of barbital, given acutely, also increased the sedative effects of imidazole-acetic acid and muscimol but not of gamma-hydroxybutyric acid. Assay of plasma barbital levels by GLC indicated that a negligible amount of barbital was present 48 hr after withdrawal compared to levels of between 60 and 120 micrograms/ml during chronic treatment with barbital. The binding of [3H]GABA to membrane preparations from brain indicated that the values of Kd and Bmax for low affinity binding were not significantly altered in mice withdrawn from chronic treatment with barbital, but that the Kd for high affinity binding was significantly increased from 4.38 to 6.06 nM in barbital-withdrawn mice. There was no difference in the enhancement of GABA binding by pentobarbital between the two groups. It is concluded that barbital-tolerant and dependent mice are cross-tolerant to GABA and that this is possibly mediated by a change in the affinity of the GABA receptor for its ligand.

The effects of chronic oral administration of barbital on cerebellar cyclic GMP.

Female Sprague-Dawley rats received increasing dosages of barbital mixed with ground LabBlox for 7 weeks. At the end of this period, the rats were given doses of barbital acutely, and the effects of this treatment on levels of cyclic guanosine monophosphate (cGMP) in the cerebellum were determined. Chronic administration of barbital resulted in a slight depression of cGMP compared to control values. The acute injections of barbital produced a dramatic, dose-related decrease in levels of cerebellar cGMP in both control (C) and barbital-dependent (BD) animals. This depression of cGMP is of particular interest because the barbital-dependent animals had considerably higher levels of serum barbital than matched controls. The overall effect of chronic administration of barbital was right shift in the dose-response curve for levels of cGMP following acute injections of barbital. No differences in motor activity were noted between the dependent and control animals. It is believed that these results indicate that a high degree of tolerance is developed in the cGMP system of the cerebellum after chronic oral administration of barbital. Further investigation of this neurochemical parameter may provide useful information in the study of mechanisms mediating the dependence and the abstinence syndrome to barbiturates.

Depression of cerebellar cGMP by barbiturates. Relationship to locomotor activity.

The intravenous administration of pentobarbital, phenobarbital or barbital produced a dose-related depression of the levels of cyclic guanosine monophosphate (cGMP) in the cerebellum of male Sprague-Dawley rats. This depression of cGMP occurred with doses of pentobarbital and barbital which did not reduce locomotor activity. Further, the time-course of the recovery of locomotor activity following the administration of an anesthetic dose of pentobarbital preceded that for the recovery of the levels cGMP in the cerebellum. In a separate study, pretreatment with picrotoxinin reversed the significant depression of cGMP in the cerebellum produced by the smallest dose of pentobarbital. Collectively, these data suggest that the effects of the barbiturates on cGMP in the cerebellum are not exclusively or predominantly the result of a drug-related depression of locomotor activity and may be, at least partially, mediated via a barbiturate-induced potentiation of a GABA receptor-mediated mechanism.

3-Halo-5,7-dimethylpyrazolo [1,5-a]pyrimidines, a nonbenzodiazepinoid class of antianxiety agents devoid of potentiation of central nervous system depressant effects of ethanol or barbiturates.

Forty derivatives (1-40) of pyrazolo[1,5-a]pyrimidine were synthesized and evaluated for antianxiety properties via gross behavioral observations in rats. Five of these compounds, including 5,7-dimethylpyrazolo[1,5-a]pyrimidine (6) and the 3-fluoro (7), 3-chloro (8), 3-bromo (9), and 3-iodo (10) derivatives, were selected for advanced evaluation. Although 6 and 7 had marginal activity, 8-10 had an anxiolytic effect in animals comparable to the clinically useful benzodiazepines, diazepam, and chlorodiazepoxide. Comparison with chlorpromazine indicated that 6-10 are probably not antipsychotic agents. These compounds also lacked activity in anticonvulsant and analgesic tests. Acute toxicity data (mouse, ip and po) indicated that 8-10 had excellent therapeutic ratios, although 10 was more poorly absorbed than 8 and 9. Further demonstration of anxiolytic efficacy was obtained by comparing the effects of 8 and 9 with the benzodiazepines in modifying provoked aggression in monkeys, rats (muricide), and fighting mice. The most remarkable observation, however, was that 8 and 9 had no effect, at the anxiolytic threshold, in potentiating the CNS depressant effects of ethanol or sodium barbital (po) in treated mice. In contrast, diazepam and chlorodiazepoxide potentiated this drug interaction effect at minimal anxiolytic doses.

The selective carotid arterial vasoconstrictor action of GR43175 in anaesthetized dogs.

1. GR43175 is a highly selective agonist at 5-HT1-like receptors in the dog saphenous vein. This study describes the haemodynamic effects of GR43175 in barbitone-anaesthetized dogs. 2. GR43175 (1-1000 micrograms kg-1, i.v.) produced dose-dependent decreases in carotid arterial blood flow with little or no change in arterial blood pressure. The decrease in blood flow was associated with an increase in carotid arterial vascular resistance. In preliminary studies, the dose of GR43175 producing 50% of the maximum carotid vasoconstrictor response was 39 +/- 8 micrograms kg-1, i.v. 3. In comparative regional haemodynamic studies, GR43175 (1-1000 micrograms kg-1, i.v.) had little effect on total peripheral resistance or resistance in the mesenteric, vertebral and coronary arterial vascular beds. Low doses of GR43175 decreased, whilst high doses (100 micrograms kg-1, i.v. and above) increased femoral arterial vascular resistance. GR43175 (1-1000 micrograms kg-1, i.v.) had no effect on respiratory inflation pressure. In doses of 100 micrograms kg-1 i.v. and above, GR43175 caused small decreases in heart rate. 4. The carotid arterial vasoconstrictor action of GR43175 was resistant to antagonism by the 5-HT2 receptor, 5-HT3 receptor and alpha-adrenoceptor blocking drugs, ketanserin, MDL72222 and phentolamine respectively, but could be antagonized by the non-selective 5-HT1-like receptor blocking drug methiothepin. Methiothepin had no effect on the carotid vasoconstrictor action of the thromboxane A2 mimetic, U46619. 5. The results demonstrate that GR43175 produces a selective vasoconstriction in the carotid arterial circulation of anaesthetized dogs via activation of 5-HT1-like receptors, which appear similar to those mediating contraction of the dog isolated saphenous vein.

Barbitone-induced tolerance to the effects of sedative-hypnotics and related compounds on operant behaviour in the rat.

1 Pretreatment doses of barbitone, pentobarbitone, ethanol, and phenytoin (diphenylhydantoin) in non-tolerant rats produced increases in operant responding at low doses and at higher doses resulted in decreases in responding.2 Daily barbitone injections (100 mg/kg, i.p.) resulted in the development of functional tolerance to both the stimulant and depressant effects of barbitone on responding.3 Barbitone tolerance development did not result in any change in the brain or plasma pharmacokinetics of barbitone.4 Barbitone-tolerant rats were cross-tolerant to the behavioural effects of pentobarbitone, ethanol, and phenytoin. The dose-effect curves for all of these drugs were shifted to the right in tolerant rats, compared to non-tolerant rats.5 Comparison of the brain and plasma levels of these drugs in non-tolerant and tolerant rats provided a means of separating functional cross-tolerance from dispositional cross-tolerance. Barbitone-tolerant rats appeared to be functionally cross-tolerant to ethanol in that there was no change in the brain and blood ethanol levels at times when the degree of behavioural impairment was substantially reduced. In contrast to ethanol, cross-tolerance to phenytoin appeared to be due to a decrease in the brain and plasma levels (dispositional tolerance). Cross-tolerance to pentobarbitone appeared to be comprised of both functional and dispositional cross-tolerance.6 The usefulness of a multidisciplinary approach in the analysis of sedative hypnotic tolerance and cross-tolerance is discussed. It is concluded that without the concurrent determination of both brain and plasma drug levels it would not be possible to distinguish between functional and dispositional tolerance.