Passive Paw Anaphylaxis in the Rat Optimum.

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Abstract
The difficulties involved in quantitating passive cutaneous anaphylaxis led to the examination of the rat paw as a site for passive anaphylaxis and to the definition of optimum conditions for passive paw anaphylaxis. Generation of homocytotropic antibodies in a number of different rat strains revealed that female Brown Norway rats were excellent producers of high titer antisera after only a single injection of antigen and Bordetella pertussis. Injection of rat paws with diluted antisera followed by short (1-2 h) or long (72 h or more) sensitization periods showed that maximum paw swelling occurred 15 min after antigen challenge. Retention of tissue sensitizing capacity in the paw for greater than 35 days but loss of this capacity following heating of antiserum at 56.degree. C indicated that the rat homocytotropic antibodies involved in passive paw anaphylaxis belong to the Ig[immunoglobulin]E class. Experiments using mepyramine [an antihistamine], methysergide [a 5-hydroxytryptamine inhibitor] and diethylcarbamazine [a slow reacting substance of anaphylaxis inhibitor] showed that 5-hydroxytryptamine [serotonin] is the most important mediator of passive paw anaphylaxis after both a short (2 h) and a long (72 h) sensitization procedure. Passive paw anaphylaxis in the rat is at least as easy to perform as passive cutaneous anaphylaxis, results can be obtained more rapidly and accurate measurement of paw thickness is not difficult. The procedure is a viable alternative to passive cutaneous anaphylaxis and may offer advantages over the latter method especially in the search for, and rapid assessment of, anti-allergic compounds.