Antagonism definition

Allosteric antagonism definition of, 99 detection of, 140-142 with efficacy changes, 221-222 insurmoun table, 136-137 nature of, 127-129... 

Negative efficacy, by definition, efficacy is that property of a molecule that causes the receptor to change its behavior toward the biological host. Negative efficacy refers to the property of selective affinity of the molecule for the inactive state of the receptor this results in inverse agonism. Negative efficacy causes the active antagonism of constitutive receptor activity but is only observed in systems that have a measurably elevated basal response due to constitutive activity. It is a property of the molecule and not the system. 

The definition of desired therapeutic and side effects in the case of the benzodiazepines very much depends on the clinical problem in question. The sedative and hypnotic actions are desired effects in the treatment of insomnia, but undesired effects in the treatment of anxiety disorders. Effects that are usually undesired include daytime drowsiness, potentiation of the sedative effects of ethanol, and anterograde amnesia. They are mediated via the benzodiazepine site of GABAa receptors, since they can be antagonized with flumazenil. 

Black, JW, Duncan, WAM, Durant, CJ, Ganellin, CR and Parsons, ME (1972) Definition and antagonism of histamine H2 receptors. Nature 236 358-390. 

The answer is b. (Katzung, p 4822) Haloperidol, a butyrophenone, is by far the most likely antipsychotic to produce extrapyramidal toxicides Other agents, such as piperazine (an aromatic phenothiazine), thiothixene (a thioxanthene), and pimozide (a diphenylbutyropiperidine) are comparitively less likely to produce extrapyramidal toxicity than haloperi-dol. The antagonism of dopamine in the nigrostriatal system might explain the Parkinson-like effects Both haloperidol and pimozide act mainly on D2 receptors, whereas thioridazine and piperazine act on ooadrenergie receptors, and have a less potent but definite effect on D2 receptors. 

In the following, several terms used to describe interactions between chemicals are mentioned as well as basic concepts used in the hazard and risk assessment of chemical mixmres. The description of these basic concepts, first outlined by Bliss (1939) and Placket and Hewlett (1952), are based on the publications by Konemann and Pieters (1996), Cassee et al. (1998), and Groten et al. (2001). The definitions of additivity, synergism, antagonism, and potentiation are those of Klaassen (1995) and Seed et al. (1995). 

Atropine, a tertiary amine, competitively antagonizes acetylcholine activity. Full therapeutic doses of atropine produce definite and prolonged inhibitory effects on the motor activity of the stomach, duodenum, jejunum, ileum, and colon, characterized by a decrease in tone and in amplitude and frequency of peristaltic contractions. 

Black JW, Duncan WA, Durant CJ, Ganellin CR, Parsons EM. Definition and antagonism ofhistamine H2-recep-tors. Nature, 1972 236, 385-390. 

Interaction Chemicals influence each other by physical, chemical, or biological means before or after reaching the molecular site of toxic action. Toxicological interactions are responses that deviate from those expected under some definition of additivity (e.g., following the concepts of IA or CA). The most commonly used terms for interaction are synergism and antagonism. ... 

In the early days of the work on explosives the Service representatives had attitudes ranging from tolerance to definite antagonism. . . for the creation of an explosives program within NDRC. It is probable that in the large majority of cases lack of co-operation came from the sincere but smug conviction that the Services knew all that was to be known about explosives and that amateurs could not make significant contributions. [Noyes, page 20]. 

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