A frequent cause of contact urticaria is skin exposure to the common stinging nettle (Urtica dioica). The urticaria is accompanied by a stinging sensation lasting longer than 12 h. Little is known of the cellular and molecular mechanism of stinging-nettle urticaria. After preliminary pharmacological analysis of pro-inflammatory activity in nettle stings, the cellular response of mononuclear cells, polymorphonuclear cells and mast cells was examined in six people 5 min and 12 h after nettle contact. Only mast cell numbers were significantly increased at 12 h. Ultrastructurally, some mast cells showed evidence of degranulation at 5 min and 12 h. At 12 h mast cells were closely associated with dermal dendritic cells and lymphocytes suggesting a functional unit. The mean histamine and serotonin contents of a nettle hair were found to be 6.1 ng and 33.25 pg, respectively. Nettle-sting extracts did not demonstrate histamine release from dispersed rat mast cells in vitro. These results suggest that part of the immediate reaction to nettle stings is due to histamine introduced by the nettle. However, the persistence of the stinging sensation might suggest the presence of substances in nettle fluid directly toxic to nerves or capable of secondary release of other mediators.

Radiographic contrast media in clinical use cause unwanted allergic and pseudoallergic reactions. To investigate the mechanisms of these reactions, studies on isolated mast cells from different species and sites are necessary. In this study, the effect of six commonly used contrast media on rat (peritoneal, lung) and human (lung) mast cells was investigated. The three preparations with low osmolalities (Hexabrix, Solutrast, Ultravist) released little or no histamine from the cells examined. In contrast, the three preparations with high osmolalities (Angiographin, Telebrix, Rayvist) were potent releasing agents. However, the degree of release and the order of potency was different depending on the cells investigated. Indeed, rat peritoneal mast cells required much higher concentrations before release was observed. Since the contrast media with low osmolality also cause histamine release and reactions in vivo, other systems (e.g. complement) must be additionally involved.

Radiographic contrast media are commonly used diagnostic aids to improve imaging, e.g. in computerized tomography. However, the routine application of these agents may cause adverse allergic/pseudoallergic reactions. In order to understand more completely the underlying mechanisms involved in these reactions, experiments on histamine release both in vivo and in vitro are necessary. Using canine mast cell suspensions from lung and liver, we have investigated the histamine release caused by six commonly used preparations. The dog is an ideal model for both in vitro and in vivo studies not only by virtue of its size but also because of its similarity to man with respect to e.g. cardiovascular reactions after drug-induced histamine release. The two non-ionic preparations (Solutrast, Ultravist) released little histamine from both cell types (ca. 4-6%). The ionic contrast media (Angiographin, Hexabrix, Telebrix, Rayvist) dose-dependently released histamine from the liver cells and pulmonary cells (maximum release between 18-35%). The liver cells (the liver is the shock organ in the dog) reacted more strongly to these agents than the pulmonary cells, thus providing further evidence for mast cell heterogeneity and the importance of selecting the appropriate mast cell model for the investigation.

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Intravascular application of radiographic contrast media (RCM) can cause adverse allergic/pseudoallergic reactions in certain individuals. In view of the increased risk for the reactions associated with cardiovascular diseases, we have investigated histamine release from isolated mast cells derived from the peritoneal cavity and the lung of normotensive and spontaneously hypertensive rats. Six commonly used RCM were tested in their clinical formulations: Angiographin® (amidotrizoate), Ray vist® (ioglycate), Telebrix® (ioxithalamate), Hexabrix® (ioxaglate), Solutrast® (iopamidol), and Ultravist® (iopromide). The three RCM with low osmolality (Hexabrix®, Solutrast® and Ultravist®) released little histamine from all cell populations tested. Mast cells derived from spontaneously hypertensive rats released significantly more histamine following challenge with high osmolar RCM than those derived from normotensive rats. Higher concentrations were required to elicit release from the peritoneal cells than from the pulmonary cells. These results indicate a role for underlying cardiovascular diseases in mediator release and should be followed up by investigations on basophils or mast cells obtained from control subjects and patients with cardiovascular disease.