(n.) A white, bitter, crystallizable substance, obtained from coffee. It is identical with the alkaloid theine from tea leaves, and with guaranine from guarana.
Example Sentences:
(1) Blood was collected from pups and dams to determine its caffeine concentration.
(2) When caffeine evokes a contraction, and only then, crayfish muscle fibers become refractory to a second challenge with caffeine for up to 20 min in the standard saline (5 mM K(o)).
(3) As expected, chronic administration led to complete tolerance to caffeine's locomotor stimulant effect, while subchronic administration produced sensitization.
(4) Caffeine and 6-methylaminopurine riboside (6-N-methyladenosine differentially inhibit uptake of radioactivity from adenosine and inosine, and thus the vesicles apparently possess seperate transport systems for uptake of radioactivity from purine nucleosides and from uridine.
(5) The inositol 1,4,5-trisphosphate (IP3) binding inhibitor, heparin, has no effect on ryanodine binding, and ryanodine and caffeine do not influence the binding of [3H]IP3, which is enriched in the cerebellar fractions.
(6) Post-labeling addition of 1 mM caffeine increased perpetuated blocks to a frequency of about 10% of the initial number of dimers in 4 h in XP16KO-II cells, but not in XP16KO-I and normal cells.
(7) Thus, in human lymphocytes the frequencies of chromatid aberrations induced by most clastogenic agents were strongly enhanced when caffeine was given during the G2 phase, but little affected by post-treatments with caffeine during the S phase.
(8) The Na(+)-induced Ca++ release from the sarcolemmal vesicles was stimulated with caffeine in a concentration-dependent manner; about 80% increase in the activity was observed at 0.1 mM caffeine.
(9) All other dietary constituents, such as protein, fiber, fluid, minerals (including Ca, Mg, Na, K, and P), and caffeine intake, were kept constant.
(10) All calcium, magnesium, and zinc contents per bone decreased in the 1- and 2-mg caffeine groups as compared to either controls or 0.5-mg caffeine group, whereas phosphorus stayed relatively constant regardless of the different levels of caffeine intake.
(11) In the presence of agents that inhibit sarcoplasmic reticulum (SR) function (10 mM caffeine, 100-500 nM ryanodine), reduction of the [Na] gradient produced increases in contractile force similar to that observed in the absence of caffeine or ryanodine.
(12) On the basis of these findings, it is suggested that screening for malignant hyperpyrexia by in vitro pharmacological testing of skeletal muscle should be carried out at 37 degrees C, and should include exposure of the sample to halothane, caffeine, suxamethonium and potassium rather than to halothane alone.
(13) The mechanism responsible for the potentiated anti-inflammatory and mild analgesic activity of aspirin remains unknown since caffeine did not alter the plasma salicylate levels or prostaglandin synthetase inhibition produced by aspirin.
(14) Their pups continued to consume the caffeine diet until 50 days.
(15) The pups were divided into caffeine and noncaffeine groups.
(16) In this study, eight patients participated in a standardized protocol to assess the effects of caffeine on seizures in ECT.
(17) These patients may have an increased risk of cardiovascular and cerebral excitation associated with higher concentrations of caffeine, which could complicate withdrawal from alcohol.
(18) were elevated significantly (P less than 0.05 at 0.3, 0.6 and 1 h after injection) when caffeine 5 or 10 mg kg-1 i.v.
(19) This study supports the findings of others in that caffeine restriction is an effective means of management of breast pain associated with fibrocystic disease.
(20) Aminophylline and caffeine can mimic this effect; however, papaverine and 1-methyl-3-isobutylxanthine, at concentrations inhibitory to phosphodiesterase, are without effect on glucocorticoid receptor binding to DNA.
Theobromine
Definition:
(n.) An alkaloidal ureide, C7H8N4O2, homologous with and resembling caffeine, produced artificially, and also extracted from cacao and chocolate (from Theobroma Cacao) as a bitter white crystalline substance; -- called also dimethyl xanthine.
Example Sentences:
(1) A HPLC-method for rapid, simultaneous and specific determination of proxyphylline, theophylline, glyphylline, theobromine, caffeine and 3-methylxanthine using 8-chlorotheophylline as internal standard is presented.
(2) Kinetic experiments indicated that the formation of each of the N-demethylated metabolites paraxanthine, theobromine and theophyline was mediated by both a high- and a low-affinity catalytic site over a substrate concentration range from 0.05 mM to 80.0 mM, although only the high-affinity component is likely to be of any importance at normally encountered in vivo caffeine concentrations.
(3) A study of the fluorescence quenching of human serum albumin (HSA) by caffeine, theophylline and theobromine, based on temperature dependence, has shown that it is predominantly static.
(4) Current concepts about the mechanisms underlying the therapeutic effects of dietary methylxanthines (caffeine, theophylline, and theobromine) favor their actions as antagonists of adenosine receptors, and attribute their other possible modes of action, namely those associated with translocation of intracellular calcium, inhibition of phosphodiesterase enzyme (PDE) activity, or the release of catecholamines, to high (near-toxic) doses.
(5) Similar potentiation was induced when theobromine and the protein synthesis inhibitors were tested.
(6) Theophylline, caffeine and theobromine were less effective.
(7) Although caffeine, theophylline, and theobromine supposedly inhibit maturation of oocytes, studies using the starfish oocyte showed that theobromine does not inhibit maturation and the inhibition caused by caffeine and theophylline is reversible.
(8) Although these results might appear to differ from other reports of inhibition of theobromine elimination after five consecutive daily doses of theobromine in aqueous suspensions, both the rate and extent of absorption of theobromine in chocolate were less than that of theobromine in solution.
(9) Using reversed-phase high pressure liquid chromatography caffeine, paraxanthine, theophylline, and theobromine were analysed in blood plasma collected before and after an oral dose of caffeine.
(10) Paraxanthine accounted for 67.3% of the total dimethylxanthines in plasma, while theobromine and theophylline accounted for 24.4% and 8.3%, respectively.
(11) Potentiometric method for determination of papaverine hydrochloride (PAP) and theobromine (Tb) in a mixture, without separation of the components was designed.
(12) Overall, there was relatively little variation in risk of BPED with total methylxanthine intake, or with intake of caffeine or theophylline, while there was a positive association between theobromine intake and risk of BPED, but only when cases were compared with biopsy controls.
(13) After reconstitution in 200 microliter of mobile phase, the extracted xanthines, including theophylline, caffeine, theobromine and 1.7-dimethylxanthine, were baseline-resolved in less than 15 min.
(14) Like enzymes from higher eukaryotes, the activity from Helix pomatia is inhibited by thymidine, theophylline, theobromine nicotinamide, 3-methoxybenzamide and 3-aminobenzamide, and is dependent on histone and DNA.
(15) Theobromine and theophylline have a limited therapeutic use and in addition they occur in plants used in the preparation of a number of widely consumed drinks.
(16) Sertoli cell toxicity could account for these early and subtle effects as well as for the late and severe effects of subchronic exposure of rats to theobromine as reported in the literature.
(17) The metabolic profile of caffeine biotransformation by CYP1A2 averaged 81.5% for paraxanthine, 10.8% for theobromine and 5.4% for theophylline formation.
(18) However, only the primary metabolites were formed through oxidative N-demethylation giving theophylline, paraxanthine and theobromine and, through C-8 hydroxylation, giving 1,3,7-trimethyluric acid and a ring-opened compound the 6-amino-5[N-formylmethylamino]1,3-dimethyl uracil.
(19) It was anticipated that the results would form a basis for discussions relating to the establishment of a threshold value for theobromine in horse urine.
(20) A sensitive and specific high-performance liquid chromatographic (HPLC) procedure is developed for simultaneously quantitating the levels of caffeine, theophylline, theobromine and paraxanthine in breast milk.