An animal model for nonimmunologic contact urticaria.

The suitability of the guinea pig for studies on nonimmunologic contact urticaria (NICU) was investigated. Groups of five, female Hartley guinea pigs were challenged by applying 50 microliters of various concentrations of human NICU agents, benzoic acid (BA), sorbic acid (SA), cinnamic acid (CA), cinnamaldehyde (CAL), methyl nicotinate (MN) and dimethyl sulfoxide (DMSO), in absolute ethyl alcohol to both sides of the earlobe. The thickness of the ear (0.85 +/- 0.11 mm, means +/- SD, 100 animals) was measured with a string micrometer before application and at 5- to 30-min intervals thereafter. Maximal increase in ear thickness was produced within 30 to 40 min by 20% BA (0.70 +/- 0.09 mm), 10% SA (0.30 +/- 0.05 mm), 15% CA (0.58 +/- 0.12 mm), 5.0% CAL (0.37 +/- 0.09 mm), 0.2% MN (0.80 +/- 0.03 mm), and 100% DMSO (0.74 +/- 0.11 mm). All responses were dose dependent. The histology of the maximal reactions showed dermal edema, and intra- and perivascular infiltrate of heterophils (neutrophils in man), eosinophils, and some lymphocytes. DMSO also caused vacuolization of the epidermal cells. CAL, MN, and DMSO, applied to different parts of the guinea pig body, produced only erythema most frequently on the upper back, but BA, SA, and CA did not cause any reactions. The guinea pig ear-swelling test provides a quantitative animal model to screen human NICU agents.