Effects of exposure to diethyl phthalate, 4-(tert)-octylphenol, and 2,4,5-trichlorobiphenyl on activity of chitobiase in the epidermis and hepatopancreas of the fiddler crab, Uca pugilator

Seven-day exposure of fiddler crabs, Uca pugilator, to diethyl phthalate at 50.0 mg l(-1) significantly inhibited the activity of chitobiase (also kno wn as N-acetyl-beta-glucosaminidase) in the epidermis and hepatopancreas. E pidermal chitobiase activity of crabs exposed to 10.0 mg l(-1) 4-(tert)-oct ylphenol for 7 days significantly decreased. PCB29 at 0.5 and 2.0 mg l(-1) significantly inhibited chitobiase activity in the epidermis and hepatopanc reas of crabs exposed for 3 days. The inhibitory effects rendered by diethy l phthalate and PCB29 can at least partly account for the delayed molting t hey cause because chitobiase is needed to break down the old exoskeleton of crustaceans prior to ecdysis. Since chitinolytic enzymes are apparently th e products of ecdysteroid regulated genes in arthropods, the decline in chi tobiase activity after exposure to diethyl phthalate, 4-(tert)-octylphenol, and PCB29 along with the delayed molting they cause strongly suggests that these xenobiotics disturb the Y-organ-ecdysteroid receptor axis. Such dist urbance may involve an interaction between ecdysteroid receptors and steroi d mimics where the steroid mimics act as antagonists of endogenous steroid molting hormones, and/or arise from the interference with synthesis and exc retion of ecdysteroids by these compounds. (C) 1999 Elsevier Science Inc. A ll rights reserved.