Antihistamines Compounds that counteract

These ring systems occur in nature. For example, the imidazole skeleton is present in the amino acid histidine, where it plays an important role in the reactions of many enzymes. Decarboxylation of histidine gives histamine, a toxic substance present in combination with proteins in body tissues. It is released as a consequence of allergic hypersensitivity or inflammation (for example, in hay fever sufferers). Many antihistamines, compounds that counteract the effects of histamine, have been developed. One of the better known of these is the drug benadryl (diphenylhydramine). 

Antihistamines are compounds that counteract the effects of the toxin histamine, which contains an imidazoie ring. 

Although chromone-2-carboxylic acid did not compare well with khellin in Jongebreur s work [188. 189]. Artemenko [190] found that the compound (under the name atremon) counteracted electrically- and chemically-induced tremors and spasms in mice, rats and rabbits. No antihistaminic action or other side effects were reported its LD50 value (intramuscularly) in mice was given as 585 mg kg The 6- and 7-methyl homologues of the acid have been claimed to possess spasmolytic properties [85]. 

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