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Results for “BARBITURIC ACID”

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At least 1,171 records · Page 65Linked to original sources
PubMed1985

Mechanism of nasal absorption of drugs I: Physicochemical parameters influencing the rate of in situ nasal absorption of drugs in rats.

The effect of rate of perfusion, volume, pH of the perfusate, and partition coefficient of the drug on the rate of in situ nasal absorption in rats was examined. The studies showed that the rate constant for the nasal absorption of phenobarbital was independent of the rate of perfusion above a value of 2 mL/min. The nasal absorption of benzoic acid was found to depend on the pH of the perfusate with the benzoate anion being absorbed at a rate one-fourth of that of benzoic acid. The effect of lipid solubility on the extent of nasal absorption was studied using a series of barbiturates. The rate and extent of absorption was found to be dependent on the chloroform-water partition coefficient of the barbiturate. The effect of the volume of the perfusate on the absorption rate constant of phenobarbital, phenol red, tyrosine, and propranolol was studied. The data obtained showed that a linear relationship existed between the rate constants of absorption and the reciprocal of the volume of the perfusate. Using this in situ relationship it was possible to predict in vivo absorption rate constants for propranolol and L-tyrosine when volumes of 0.1 mL were administered. The calculated values for these compounds were found to be close to those determined in in vivo experiments. This indicates that the in situ technique can be used to predict in vivo absorption rate constants.

Absorption↗
PubMed1979

Erythrocyte ghost--buffer partition coefficients of phenobarbital, pentobarbital, and thiopental support the pH-partition hypothesis.

The partition coefficient (lambda) between red cell ghosts and buffer has been determined for three barbiturates over a range of pH. Experimental partition coefficients were linearly proportional to the calculated degree of association of the barbiturates. Lambda was 9.5 +/- 0.52 for phenobarbital, 12.7 +/- 0.91 for pentobarbital, and 27 +/- 4.9 for thiopental in their acid forms. Lambda for all three barbiturates in their anionic forms was zero. Our data support the assumption of the pH-partition hypothesis that the dependence of lambda on pH in biological membranes behaves essentially like that in organic solvents. However, the relative magnitudes of the erythrocyte partition coefficients correlate much more closely with the physiological permeability constants than do those of organic solvents, which tend to overestimate the differences between these compounds.

Buffers↗
PubMed1991

PIVKA-II (protein induced by vitamin K absence-II) status in newborns exposed to anticonvulsant drugs in utero.

Using PIVKA-II and Hepaplastin test, 5 neonates exposed to anticonvulsant drugs in utero were assessed 5 days after birth. None showed any sign of clinical bleeding, but all had PIVKA-II values over 1 microgram/ml. In controls, only 96 of 1,166 (8.2%) neonates had PIVKA-II values over 1 microgram/ml. The difference in the incidence rate was significant (p less than 0.005). Three of 5 epileptic mothers received valproatic acid and/or diazepam but no barbiturates and/or hydantoin.

Adult↗
PubMed1981

Analysis of barbiturates by gas chromatography.

This review surveys the evolution of gas chromatographic procedures for the quantification of barbiturates as either the free acids or their derivatives obtained by direct and on-column reactions. Among the aspects discussed, some emphasis is placed on recognized and other sources of interference encountered during analyses.

Barbiturates↗
PubMed1993

Effects of contraction and lactic acid on the discharge of group III muscle afferents in cats.

1. In barbiturate-anesthetized cats we examined the interaction of lactic acid and static contraction on the discharge of group III muscle afferents. Only afferents whose receptive fields were located in the triceps surae muscles were studied. 2. Twelve of 20 afferents were stimulated by a 60-s static contraction. The majority of firing occurred within the first few seconds of contraction. Thirteen of 20 afferents were stimulated by femoral arterial injections of 24 mM lactic acid (1-4 ml) with the muscle at rest. Repeated injections of lactic acid with the muscle at rest led to tachyphylaxis. Lactic acid was then injected (24 mM; 4 ml) during the last 15 s of static contraction. In eight of nine afferents that were tachyphylactic to lactic acid with the muscle at rest, we noted a restored sensitivity to lactic acid during contraction. 3. In separate experiments we examined the effects of dichloroacetate (DCA) on the responses of group III muscle afferents to static contraction. DCA reduces the production of lactic acid by increasing levels of the active form of the enzyme pyruvate dehydrogenase. 4. DCA lowered arterial and venous lactate concentrations at rest and during contraction. DCA significantly decreased (31%; P < 0.05) the responses of the afferents to contraction. This effect was most prominent within the first 10 s of contraction and was not due to a reduced level of mechanical stimulation after DCA, because peak tension levels were the same during the two bouts of contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[Action mechanisms of intravenous anesthetics].

Intravenous anaesthetic agents depress the activity of the brain by acting on receptor-operated ion channels. Barbiturates enhance gamma-aminobutyric acid (GABA)-mediated inhibition, depress glutamate-mediated excitation, and hyperpolarize the membrane by increased potassium conductance. Benzodiazepines facilitate GABA-mediated inhibition by binding to a benzodiazepine recognition site on the GABA receptor complex, and affect potassium channels. Opioids bind to opioid receptors and hyperpolarize the membrane by enhanced potassium and calcium conductances. Ketamine depresses excitatory synaptic transmission by acting on glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype. Propofol acts at a recognition site on the GABA receptor, which differs from the binding sites of both barbiturates and benzodiazepines.

Analgesics, Opioid↗
PubMed1993

Middle cerebral artery occlusion increases cerebral capillary permeability.

One hour after middle cerebral artery occlusion, the regional blood to brain transfer coefficient of alpha-aminoisobutyric acid was determined in eight barbiturate anaesthetized rats. The transfer coefficient (microliter/min-1/g-1) was significantly higher in the ischaemic cortex (10.6 +/- 2.3) than in the contralateral cortex (6.5 +/- 1.0). Cerebral regional capillary surface area was determined in another group of twelve rats using an alkaline phosphatase stain for the total capillary bed and fluorescein isothiocyanate-dextran to visualize the perfused capillaries. Perfused capillary surface area (cm2/cm3) was lower in the ischaemic cortex (141 +/- 31) than in the contralateral cortex (426 +/- 32). Using these values for the transfer coefficient, surface area and our previously published data of regional cerebral blood flow after middle cerebral artery occlusion, we calculated the extraction fraction of alpha-aminoisobutyric acid, the permeability-surface area product and the permeability of cerebral regional capillary beds. Although, there are numerous reports of permeability-surface area product of brain capillaries, to our knowledge, the permeability has never been determined before. The calculated extraction fraction ratio for alpha-aminoisobutyric acid for ischaemic cortex/contralateral cortex was 3.1. Similar ratios for permeability-surface area product and capillary permeability were 1.6 and 4.4, respectively. Thus, there was a more than four fold increase in capillary permeability to small molecules in the ischaemic cortex one hour after middle cerebral artery occlusion.

Aminoisobutyric Acids↗
PubMed2002

Medicinal chemistry and molecular pharmacology of GABA(C) receptors.

GABA(C) receptors belong to the nicotinicoid superfamily of ionotropic receptors that include nicotinic acetylcholine receptors, bicuculline-sensitive GABA(A) receptors, strychnine-sensitive glycine receptors and 5HT3 serotonin receptors. The GABA(C) receptor concept arose from medicinal chemical studies of a conformationally restricted analog of GABA. Receptors matching the predicted properties of GABA(C) receptors were cloned from the retina. Post cloning studies revealed the unique physiology and pharmacology of these relatively simple homomeric receptors. Three subtypes of GABA(C) receptors have been cloned from mammalian sources and pharmacological differences between the rho1, rho2 and rho3 GABA(C) receptors have been described. There is evidence for functional GABA(C) receptors in the retina, spinal cord, superior colliculus, pituitary and the gut and their involvement in vision, aspects of memory and sleep-waking behaviour. This review concentrates on the medicinal chemistry and molecular pharmacology of GABA(C) receptor subtypes emphasising possible new investigational tools with which to investigate further GABA(C) receptor function. The most useful currently available ligands that show some GABA(C) receptor subtype selectivity are TPMPA, P4PMA, imidazole-4-acetic acid, 2-methyl-TACA and (+/-)-TAMP.

Amino Acids, Cyclic↗