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At least 811 records · Page 45Linked to original sources
PubMed1999

A single hydrophobic residue confers barbiturate sensitivity to gamma-aminobutyric acid type C receptor.

Barbiturate sensitivity was imparted to the human rho1 homooligomeric gamma-aminobutyric acid (GABA) receptor channel by mutation of a tryptophan residue at position 328 (Trp328), which is located within the third transmembrane domain. Substitutions of Trp328 with a spectrum of amino acids revealed that nearly all hydrophobic residues produced receptor channels that were both directly activated and modulated by pentobarbital with similar sensitivities. Previous studies with ligand-gated ion channels (including GABA) have demonstrated that even conservative amino acid substitution within the agonist-dependent activation domain (N-terminal extracellular domain) can markedly impair agonist sensitivity. Thus, the lack of significant variation in pentobarbital sensitivity among the Trp328 mutants attests to an intrinsic difference between pentobarbital- and the GABA-dependent activation domain. Compared with the heterooligomeric alphabetagamma receptor channel, the mode of modulation for homooligomeric Trp328 mutants by pentobarbital was more dependent on the GABA concentration, yielding potentiation only at low concentrations of GABA (fractions of their respective EC50 values), yet causing inhibition at higher concentrations. Agonist-related studies have also demonstrated that residue 328 plays an important role in agonist-dependent activation, suggesting a functional interconnection between the GABA and pentobarbital activation domains.

Amino Acid Sequence↗
PubMed1994

Enhancement of hepatocarcinogenesis and induction of specific cytochrome P450-dependent monooxygenase activities by the barbiturates allobarbital, aprobarbital, pentobarbital, secobarbital and 5-phenyl- and 5-ethylbarbituric acids.

To test predictions that barbiturates which are long-acting sedatives and/or strong inducers of CYP2B-mediated monooxygenase activities would be effective promoters of hepatocarcinogenesis, a series of clinically-useful barbiturates and structural analogs were tested for ability to promote hepatocellular carcinogenesis in male F344/NCr rats initiated with N-nitrosodiethylamine and for efficacy as inducers of CYP2B activity in non-initiated rats of the same sex and strain. The barbiturates were administered in the diet at concentrations equimolar to 500 p.p.m. of the known liver tumor promoter phenobarbital, which served as the positive control for this study. Phenobarbital, which has the longest duration of sedative action of this series of compounds, caused the greatest induction of CYP2B activity, and displayed strong liver tumor promoting effects. Allobarbital and aprobarbital, two intermediate-duration sedatives, were found to promote hepatocarcinogenesis, with allobarbital proving to be as effective as phenobarbital in this respect and aprobarbital being somewhat weaker as a promoter. These intermediate-duration sedatives were each relatively weak CYP2B-type inducers, causing approximately 25% of the induction displayed by phenobarbital. The nonsedatives, 5-phenyl- and 5-ethyl-barbituric acids, were essentially inactive as CYP2B-type inducers and were also found to be relatively inactive as promoters of hepatocarcinogenesis. Of the shorter-duration sedatives, pentobarbital was found to promote, and was relatively effective as a CYP2B-type inducer, while secobarbital showed little or no promoting activity and was less effective as an inducer of CYP2B activities. Pentobarbital thus proved an important exception to our hypothesis that only long-acting sedative barbiturates would promote hepatocarcinogenesis. Although both the durations of sedative action and the degrees of CYP2B-type induction exhibited by these compounds correlate with a quantitative parameter for liver tumor-promoting activity (relative promotion index), neither parameter appears to be sufficient, by itself, as a predictor of promoting activity for rat liver.

Animals↗
PubMed1979

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).

Amobarbital↗
PubMed2001

Separation of barbiturates and phenylthiohydantoin amino acids using the thermally tuned tandem column concept.

There are many more choices of column type than of eluent type for method development in reversed-phase liquid chromatography. It is common to switch between different column types or between the same type from different suppliers to achieve the desired separations. The key difficulty in modulating band spacing by adjusting the column type is that it is a discontinuous, "hit or miss" proposition. The thermally tuned tandem column (T3C) concept effectively solves this problem by connecting two columns in series and independently controlling the two column temperatures. The columns are chosen to have distinctively different chromatographic selectivities (band spacing), so that the unresolved peaks on one column are separated by the other. The optimized separation in the T3C is achieved by simultaneously tuning the two column temperatures. In this study, we used the T3C combination of a carbon and a conventional bonded phase for the separation of barbiturates and phenylthiohydantoin amino acids (PTH-amino acids). Good peak shapes and comparable retention times were observed on the two phases at room temperature. The selectivities on the two phases are quite different. Baseline separations were easily achieved with the T3C set although neither column could individually resolve all the peaks. We further compared the separation of barbiturates optimized by the T3C approach with that optimized by adjusting the mobile phase. We found that T3C gave a better separation. We believe that the T3C combination of a carbon phase and a bonded conventional reversed-phase material provides a powerful and general method to optimize the separation of various mixtures.

Algorithms↗
PubMed1986

Brain-stem areas tonically inhibiting dorsal horn neurones: studies with microinjection of the GABA analogue piperidine-4-sulphonic acid.

In barbiturate anaesthetized cats, tonic inhibition of the excitation of lumbar dorsal horn neurones by impulses in unmyelinated primary afferents was measured by reversibly cooling the spinal cord at the thoraco-lumbar junction. Tonic inhibition was reduced by microinjection of the GABA analogue, piperidine-4-sulphonic acid (2.5 nM in 0.5 microliter) mainly at AP -7, L 2-5 and V -8 to -10. This area in the ventrolateral medulla is just ventral to the facial nucleus and has been shown to be important in cardiovascular control, particularly in relation to fear-defence reactions. It is proposed that tonic inhibition of the nociceptive responses of spinal neurones is part of such a reaction in response to the trauma of surgery. Since previous experiments had shown that the ventrolateral medulla was important in spinal inhibition produced by PAG stimulation, these experiments support the proposal that analgesia does not occur in isolation but is part of a complex behavioural response of an animal in a potentially injurious environment.

Action Potentials↗
PubMed1981

[Cerebral amino acid metabolism in acute barbiturate poisoning].

An experimental study on the protein and aminoacid cerebral metabolism in Barbiturate poisoning coma has been carried out. Some significant alterations in central aminoacid pattern have been found. These changes suggested Hypothesis on particular biochemical pathways of brain tissue related to the pathological status. An attempt of correlation between the aminoacid alterations and cerebral energetic need is also reported.

Amino Acids↗