Histamine effect

The term antihistamines describes drags which bind to the Hi-histamine receptor and antagonize (block) the histamine effect in Type I allergic responses. 

Binds to DNA and prevents separation of the helical strands Affects neuronal transmissions Binds to opiate receptors and blocks pain pathway Acts as central nervous system depressant Inhibits Na/K/ATPase, increases intracellular calcium, and increases ventricular contractibility Blocks the actions of histamine on Hi receptor Blocks ai-adrenergic receptor, resulting in decreased blood pressure Inhibits reuptake of 5-hydroxytryptamine (serotonin) into central nervous system neurons Inhibits cyclooxygenase, inhibition of inflammatory mediators Inhibits replication of viruses or tumor cells Inhibits HIV reverse transcriptase and DNA polymerase Antagonizes histamine effects... 

Easton, R. E., and S. D. Murphy. Experimental ozone preexposure and histamine. Effect on the acute toxicity and respiratory function effects of histamine in guinea pigs. Arch. Environ. Health 15 160-166, 1%7. 

Antihistaminic action The antihistaminics blocks histamine effects at a variety of sites. They inhibit most responses of smooth muscles to hista-... 

Diphenhydramine Competitive antagonism at Hi receptors Reduces or prevents histamine effects on smooth muscle, immune cells also blocks muscarinic and adrenoceptors highly sedative IgE immediate allergies, especially hay fever, urticaria some use as a sedative, antiemetic, and antimotion sickness drug Oral and parenteral t duration 4-6 h Toxicity Sedation when used in hay fever, muscarinic blockade symptoms, orthostatic hypotension Interactions Additive sedation with other sedatives, including alcohol some inhibition of CYP2D6, may prolong action of some 13 blockers... 

The Hi Receptor and its ligands. The 11, receptor mediates most uf the important histamine effects in allergic diseases. These include smooth muscle contraclion. increased vascular permeability, pruritus, prostaglandin generation, decreased atrioventricular node conduction time with resultant tachycardia, activation of vagal reflexes, and increased cyclic guant sine monophosphate tcGMP) production. 

O Donnell, S.R, and Persson, C.G. (1978). 02-adrenoceptor mediated inhibition by terbutaline of histamine effects on vascular permeability. Br. J. Pharmacol. 62, 321-324. 

Ingestion of histamine and saurine, when present in large amounts, results in histaminic effects. Absorption is rapid with clinical effects generally being seen within 5-90 min. The duration of untreated scombroid poisoning is generally 12-24 h. 

Loratadine Hi receptor blocker Antagonizes histamine effects... 

In addition, it is used in pruritis, minor bums, insect bites, sunburn, and skin irritations. Tripelennamine competes with histamine for the Hj receptor, thereby ameliorating histamine effects in target tissues, but does not prevent the release of histamine. 

A. Relief of symptoms caused by excessive histamine effect (eg. ingestion of scombroid-contaminated fish or niacin and rapid intravenous administration of acetylcysteine). Diphenhydramine may be combined with cimetidine or another Hj histamine receptor blocker (see p 428). 

It was soon found that excellent anti-histaminic drugs could be based on ethanolamine instead of ethylenediamine and a notable example from the United States was diphenhydramine (9.56) ( Benadryl ). Members of this class couple their anti-histaminic effect with sedative properties and are prescribed when a high degree of somnolence is advantageous. There is only one ionizing group (pA 9.0). 

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