(n.) An organic base, especially one of a class of substances occurring ready formed in the tissues of plants and the bodies of animals.
Example Sentences:
(1) Thus, alkaloid and insecticide modifications share many features but differ in how much the conducting properties of the pore are changed and whether the channel can close reversibly while the toxin remains bound.
(2) A clear structure-mutagenicity relationship was observed in a series of aporphine alkaloids (aporphine, dehydroaporphine, 7-oxoaporphine and 4,5-dioxoaporphine), and 10,11-non-substituted aporphines were suggested to exert their mutagenicity through metabolic activation of the 10,11 positions, possibly as the 10,11-epoxides.
(3) A radioactive, photoactive Vinca alkaloid, N-(p-azido-[3,5-3H]-benzoyl)-N'-beta-aminoethylvindesine [( 3H]NABV) with pharmacological and biological activities similar to vinblastine was synthesized and used to identify specific Vinca alkaloid macromolecular interactions in calf brain homogenate by photoaffinity labeling.
(4) The comparative metabolism of the pyrrolizidine alkaloid (PA) senecionine was studied in vitro in incubations of rat, guinea pig, cow, horse, and sheep hepatic microsomes.
(5) They also displayed negative correlation between activities of protein-inhibitors and the total content of protein and alkaloids.
(6) Methods have been reviewed for alkylating agents, platinum compounds, antitumour antibiotics, antimetabolites, alkaloids, suramin, 1-hydroxy-3-amino-propylidene-1,1-bisphosphonate and tamoxifen.
(7) The resistant strains exhibited cross resistance to anthracycline antibiotics, vinca alkaloids, actinomycin D, colchicine.
(8) In mice treated with cepharanthine (Cepha), a biscoclaurine alkaloid, the number of T cells was increased in the parathymic lymph nodes (PtLNs) which are considered to be the specialized lymph nodes in local differentiation of T cells.
(9) The alkaloid tubulosine inhibits the process of peptide chain elongation by eukaryotic polysomes by specifically preventing the elongation-factor-2-dependent step of translocation.
(10) Cultured roots of Stephania cepharantha, which are rich sources of bisbenzylisoquinoline alkaloids, were fed 14C-labelled tyrosine, tyramine or dopamine.
(11) As a possible mechanism underlying the alterations of DRP, the functional consequences of atrophic changes of primary central afferent terminals are being discussed in terms of the close correlation between structure and function and the possible inferences of the electrophysiological reaction to the therapeutic application of Vinca alkaloids in the iontophoretic treatment of chronic intractable pain.
(12) The poisonous principles in tansy ragwort are pyrrolizidine alkaloids, which cause gradual alteration and necrosis of liver cells with replacement by fibrous tissue.
(13) In this study, the roots of Tabernaemontana heyneana Wall were examined and the isolation and identification of additional indole alkaloids and some pharmacological properties of coronaridine are described.
(14) The area ratios of four alkaloids (tropacocaine, norcocaine, cis-cinnamoylcocaine, and trans-cinnamoylcocaine) to cocaine are calculated for each sample.
(15) The main drugs with specific action on migraine include ergot alkaloids (ergotamine, dihydroergotamine), agonists (sumatriptan) or partial agonists (methysergide) at a specific subtype of 5-HT1-like receptors, beta-adrenoceptor antagonists (propranolol, metoprolol), calcium antagonists (flunarizine) and anti-inflammatory agents (indomethacin).
(16) Effects of solution variables on the binding and self-association explain the wide variation of reported apparent binding constants for Vinca alkaloids to tubulin.
(17) The concomitance of five previously reported trans-2,5-dialkyl-pyrrolidines along with small amounts of the cis isomers and N-methyl analogues makes the venom of M. indicum the most qualitatively diverse blend of alkaloids reported from an ant to date.
(18) Strong enhancement of delayed-type hypersensitivity (DTH) was observed after treatment with the active cyclophosphamide (CY) derivative Z 7557 or the plant alkaloid VP-16 at the site of sensitization.
(19) A total alkaloid and two purified alkaloid extracts of Alangium Vitiense were revealed by our experimental screening to be oncostatic on L1210 leukemia and two other lymphoid neoplasias in Mice.
(20) Possible mechanisms underlying these effects of insecticides on alkaloid-dependent uptake are discussed in light of a qualitative model formulated from these results and previous biochemical and electrophysiological studies.
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.