Histamine properties

The process of reabsorption depends on the HpophiHc—hydrophiHc balance of the molecule. Charged and ioni2ed molecules are reabsorbed slowly or not at all. Reabsorption of acidic and basic metaboHtes is pH-dependent, an important property in detoxification processes in dmg poisoning. Both passive and active carrier-mediated mechanisms contribute to tubular dmg reabsorption. The process of active tubular secretion handles a number of organic anions and cations, including uric acid, histamine, and choline. Dmg metaboHtes such as glucuronides and organic acids such as penicillin are handled by this process. 

FIGURE 9.20 Design of multiple ligancl activity, (a) Dual histamine HI receptor and leukotriene receptor antagonist incorporating known antihistaminic properties of cyproheptadine and LTD4. (b) Joint ACE/NEP inhibitor formed from incorporating similarities in substrate structures for both enzymes. From [57],... 

Hill SI (1990) Distribution, properties and functional characteristics of three classes of histamine receptor. Pharmacol Rev 42 45-83... 

Opioids. Reactions to morphine, codeine phosphate, meperidine, fentanyl and its derivatives are uncommon. Because of their direct histamine-releasing properties, especially regarding morphine and codeine, distinction between anaphylaxis and non-immune-mediated histamine release is not always easy. Only 12 cases were recorded in the last 2 years epidemiologic survey in France, 9 of them being related to morphine administration [9]. 

In the preceding chapters, the synaptic pharmacology of those substances clearly established as NTs in the CNS, i.e. glutamate, GABA, ACh, NA, DA, 5-HT and certain peptides, has been discussed in some detail. There are other substances found in the CNS that could have a minor transmitter role, e.g. ATP, histamine and adrenaline, while still others that cannot claim such a property but clearly modify CNS function in some way, e.g. steroids, prostaglandins and nitric oxide. We will consider each of them in what we hope is appropriate detail. 

Treatment of ocular allergy is aimed at slowing or stopping these processes. Antihistamines block the histamine receptors and some prevent histamine production and/or inhibit mediator release from the mast cells.15 Mast cell stabilizers inhibit the degranulation of mast cells, preventing mediator release. Some topical agents have multiple mechanisms of action, combining antihistaminic, mast cell stabilization, and antiinflammatory properties (Tables 60-3 and 60-4).16... 

Marshall, P. B., Some chemical and physical properties associated with histamine antogonism, Br. J. Pharmacol. 10, 270-278 (1955). 

Schonrock, B., Busselberg, D. Haas, H. L. (1991). Properties of tuberomammillary histamine neurones and their response to galanin. Agents Actions 33, 135-7. 

Reiner, P. B. McGeer, E. G. (1987). Electrophysiological properties of cortically projecting histamine neurons of the rat hypothalamus. Neurosci. Lett. 73,... 

The chemical structure of histamine has similarities to the structures of other biogenic amines, but important differences also exist. Chemically, histamine is 2-(4-imidazolyl)ethylamine (Fig. 14-1). The ethylamine backbone is a common feature of many of the amine transmitters (e.g. dopamine, norepinephrine and serotonin). However, the imidazole nucleus, absent from other known transmitters, endows histamine with several distinct chemical properties. Among these is prototypic tautomerism, a property that permits it to exist in two different chemical forms (Fig. 14-1). The tautomeric properties of histamine are thought to be critical in the... 

Rouleau, A., Stark, H., Schunack, W. and Schwartz, J. C. Anti-inflammatory and antinociceptive properties of BP 2-94, a histamine H-3-receptor agonist prodrug./. Pharmacol. Exp. Ther. 295 219-225, 2000. 

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