Abstract
By standardization of both metallic and absorbent electrode material, an iontophoretic method has been developed which permits the detection of histamine in dilutions as high as 1:5,000,000 by the formation of wheals in the human skin. 1 The method has been serviceable in the development of a procedure for assaying histamine in human, rabbit, and guinea pig blood. Thus, histamine can be assayed directly in the blood of rabbits killed by the intravenous administration of histamine. Only 0.1 cc. of blood is required.
When histamine is administered by the galvanic current so that a wheal forms in the human skin, the positive pole is applied to force the positively charged histamine ions into the skin. It has now been found that if the negative pole be applied to the surface of the wheal formed by the scratch or by the iontophoretic method, sufficient histamine is transported out by this reversal of iontophoresis to form secondary wheals in new areas of the skin. In this way, histamine has been recovered from wheals which have been produced by iontophoresis from original dilutions as high as 1:100,000. Indeed, histamine may be recovered by diffusion alone, sufficient histamine being readily obtained for detection by means of the preceding methods within a diffusion period as short as 3 minutes. Histamine has been recovered from wheals produced by higher concentrations for as long as 40 minutes after wheal formation.
Using this method of reversed iontophoresis of histamine, attempts have been made to obtain histamine from (1) ragweed wheals, (2) timothy wheals, (3) wheals produced by ultraviolet light in a case of urticaria solare, (4) and wheals produced by stroking in a severe case of dermographism.
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