ZOU, E.; BONVILLAIN, R.; Nicholls State Univ., Thibodaux, LA; Nicholls State Univ., Thibodaux, LA: Chitinase activity in the epidermis of the fiddler crab, Uca pugilator, as an in vivo screen for molt-interfering xenobiotics

An in vivo screening assay is described that uses epidermal chitinase activity as the endpoint following a seven-day exposure of Uca pugilator to test chemicals. Chitinase, a chitinolytic enzyme, is the end product of endocrine cascades of a multi-hormonal system for control of crustacean molting. Wherever a molt-interfering agent attacks on the Y-organ-ecdysteroid receptor axis, the effect should be reflected by chitinase activity in the epidermis. Therefore, epidermal chitinase activity is an ideal endpoint for molt-interfering effect of xenobiotics. The validity of epidermal chitinase activity being used for such a purpose is supported by our finding that two injections of 20-hydroxyecdysone at 25 mg/g live weight induced a two-fold increase in chitinase activity in the epidermis of Uca pugilator. We screened a total of nine chemicals for molting hormone and anti-molting activities. o,p�-DDT was found to significantly inhibit epidermal chitinase activity while kepone and methoxychlor showed a tendency of inhibition of enzymatic activity. None of the remaining six chemicals, including p,p�-DDT, atrazine, tributyltin (TBT), methoprene, dieldrin and permethrin, had an effect on epidermal chitinase activity.