Histamine selective microelectrode based on a synthetic organic liquid ion exchanger

A two-barrel organic ion-sensitive microelectrode has been developed to electrochemically detect histamine activity. The synthesis of the histaminesensitive liquid ion exchanger, composed of tetrafluorophenylboron histamine plus 3-nitro-o-xylol, and the construction of the two-barrel microelectrode (0.1–0.5 μm tip diameter) sensitive to histamine based on such an exchanger is reported. The calibration curves, their slope, selectivity, stability and detection limits for different solutions are described. High selectivity for Na⁺, K⁺, Ca²⁺ was observed.     

Analgesic effects of antihistaminics

The literature provides considerable evidence indicating that several, but not all antihistaminics, are indeed analgesic agents and some are analgesic adjuvants as well. Those for which effectiveness is reported includes diphenhydramine, hydroxyzine, orphenadrine, pyrilamine, phenyltoloxamine, promethazine, methdilazine, and tripelennamine. The proposed mechanisms of analgesic action of antihistaminics are reviewed and discussed. The literature suggests that more than one mechanism of action exists for them. There is considerable evidence suggesting that histaminergic and serotoninergic central pathways are involved in nociception and that antihistaminic drugs can modulate their responses (1). The evidence for a role for norepinephrine and dopamine and the effects of antihistaminics on them are less well established. Still other pathways have been proposed. A greater understanding of pain mechanisms will aid in elucidating the role of antihistaminics in analgesia.     

Histamine and microcirculation

Recent research of histamine metabolism suggests that microvascular smooth muscle and endothelial cells are under the continuous dilator influence of minute quantities of intrinsically formed histamine, produced by action of an inducible form of histidine decarboxylase. Various autonomous dilator activities of the microcirculation, e.g., vasomotion, reactive and post- exercise hyperemia and autoregulation, may all involve interplay of this intrinsic dilator with an intrinsic constictor mechanism. Drastic stimuli which cause a marked increase in histamine output locally or systemically, may lead to the early, slowly-developing microvascular changes in inflammation and shock, respectively.