Inhibition by aspirin of ribose conjugation in the metabolism of histamine

Evidence for rapid histamine turnover and loss of histamine from immature rat mast cells

Histamine synthetic activity which is high in young mast cells decreases as the cells mature [Beaven et al., J. Pharmac. exp. Ther. 224, 620 (1983)]. In this study we show that a substantial proportion of newly formed histamine in young mast cells leaked to the extracellular environment. The cells acquired the full ability to sequester newly formed histamine once the numbers of intracellular granules and the supply of sulfated mucopolysaccharide material within them had increased. Rat peritoneal mast cells were separated into successive fractions of increasing size and maturity by counter current elutriation. Loss of histamine from fractions of immature cells was demonstrated by a progressive accumulation of histamine in the medium without any decrease in intracellular histamine content. The estimated turnover time of histamine was less than 10 hr. In fractions of more mature cells, the proportion of cellular histamine released into the medium was substantially lower, giving estimated turnover times of 20 hr or longer. Studies with radiolabeled histidine also indicated that little, if any, newly formed histamine was lost from fractions of mature cells. Both release of endogenous histamine and formation of radiolabeled histamine from labeled histidine were inhibited by the histidine decarboxylase inhibitor alpha-fluoromethylhistidine (10 microM). Histamine turnover times were similar in the presence or absence of external histidine, a possible indication that the supply of intracellular histidine was sufficient to maintain normal histamine synthetic activity.

Treatment of urticaria

Urticaria represents a wide variety of conditions characterized by urticarial papules, wheals, and angioedema. The number of potential causes of urticaria is legion, but a diligent search by careful history and examination is indicated. Laboratory testing depends upon the specific situation, but routine screening examinations are not cost effective. Histamine from mast cells plays an important role in urticaria. Multiple factors, such as aspirin and other nonsteroidal anti-inflammatory agents, direct histamine-releasing agents (including benzoates), tartrazine and other azo dyes, and perhaps blockers of beta 2-adrenergic activity and H2 receptors, adversely influence histamine release either directly or indirectly. Vasodilation is also detrimental. Treatment of both acute and chronic urticaria necessitates removal of the patient from aggravating factors as well as the cause of the outbreak (if one can be found), along with effective antihistaminic agents and perhaps beta 2-adrenergic agonists. Treatment of specific entities within the urticarial group is briefly outlined in this article.

Inhibition of histamine methylation in vivo by the dimaprit analog, SKF Compound 91488

The Dimaprit analog, S-[4-(N,N-dimethylamino)-butyl]isothiurea (SKF Compound 91488), which is a noncompetitive inhibitor (Ki, 0.9 microM) of histamine-N-methyltransferase in vitro, inhibited the methylation of labeled histamine in mice. When administered in combination with the diamine oxidase inhibitor, aminoguanidine, an almost complete block of histamine metabolism was observed. The inhibition was dependent on dose of drug and was apparent with doses of 50 mg/kg and greater. Since Compound 91488 is reported to have no agonist activity of its own, the drug may help to identify the actions of histamine released from endogenous stores in response to physiological and pathological stimuli.

Interference with histamine and imidazole acetic acid metabolism by salicylates: a possible contribution to salicylate analgesic activity?

In man, rats and mice, the urinary excretion of the histamine and L-histidine metabolite, imidazole acetic acid, is increased and that of the conjugated metabolite, ribosylimidazole acetic acid, decreased by small doses of salicylates. In contrast to salicylates, other non-salicylate anti-inflammatory drugs, indomethacin, phenylbutazone, phenacetin and acetaminophen do not influence the excretion of the urinary metabolites of histamine and L-histidine. Since imidazole acetic acid is reported to have analgesic and narcotic activity, there is the inference that the analgesic properties of salicylate might be due in part to interference in imidazole acetic acid metabolism.