ACUTE TOXICITY OF 2 PYRETHROIDS, PERMETHRIN, AND CYPERMETHRIN IN NEONATAL AND ADULT-RATS

The present study aims specifically at obtaining a comparison of the a cute toxicity of cypermethrin (CY), a type I pyrethroid, and permethri n (PERM), a type II pyrethroid, administered orally as a single dose t o neonatal and adult rats, and at assessing the importance of pyrethro id biotransformation in CY and PERM toxicity through use of drug metab olism inhibitors. Our experiments show that CY is more toxic than PERM to adult and neonatal rats. The sensitivity of neonatal rats both to CY and to PERM toxicity is higher, the younger the animals. CY is much more toxic than PERM in the neonatal rat, compared with the adult. In rats aged 8, 16, and 21 days, pretreatment with piperonil butoxide (P B), a monooxygenase inhibitor, or with tri-o-tolyl phosphate (TOTP), a n esterase inhibitor, does not produce significant variations in the l ethal effects of CY and PERM. Instead, in the adult rats, a significan t increase in CY (X2 = 5.97; p <0.05) and PERM (X2 = 4.37; p <0.05) mo rtality occurred in rats pretreated with esterase inhibitors, whereas no increase in CY and PERM toxicity was found in adult animals pretrea ted with monooxygenase inhibitor. It was concluded that the higher lev el of sensitivity of the neonate rat to pyrethroid toxicity is probabl y due to incomplete development of the enzymes which catalyze the meta bolism of pyrethroids in the liver of young animals. It is suggested t hat ester hydrolysis is an important pyrethroids detoxification reacti on in the adult rat.