Observations on the use of the trypan blue and skin-twitch tests for measuring local tissue toxicity

Abstract

An objective and reasonably quantitative test method for estimating sting reaction following intradermal injection of a chemical irritant in the dog by means of the skin-twitch reponse was described. The end point, designated as the threshold twitch concentration (TTC), was defined as that concentration, expressed in per cent, which produced no more than a mild skin-twitch response. The results obtained were compared with local tissue irritancy data as measured by the trypan blue test in the rabbit (TIC). The local tissue response to hypo- and hypertonicity and to change in the pH of normal saline was essentially the same by both test methods. Of the fourteen compounds studied, sting appeared to be closely associated with irritancy in nine. Among the remaining five compounds, the TIC was found to be from 5 to 2560 times as great as the TTC. The ratio TIC: TTC, for each of these compounds was as follows: meperidine HCl, 5; tyloxapol, 7.8; polyethylene glycol 600 monooleate, 7.8; théraleptique, 500; and histamine, 2560; this indicates that it is possible to separate a sting reaction from mild reversible tissue injury. A negative sting reaction to normal saline and strongly positive sting reactions to distilled water and isotonic solutions of Théraleptique were observed following intradermal injection in man. The local tissue response to quinine HCl, as measured by the trypan blue test, was found to be the same in the rabbit and the dog.