Modification by Polychlorinated Biphenyls（PCBs）of Cadmium Induced Lesions in the Planarian Model,Dugesia dorotocephala

The appearance of abnormal growths on the planarian,Dugesia dorotocephala,in response to cadmium with and without pre-exposure to L-buthionine-R,S-sulfoximine(BSO)and concurrent exposure to the polychlorinated biphenyls(PCBs) Aroclor 1254,PCB28,PCB110 or PCB126 is described,Pigmented rose thorn(PRT) lesions were non-invasive and appeared in response to PCBs.Post-head(PH)lesions developed in up to 100% of the animals within 6- 20 days post-dosing,progressed rather rapidly and were highly invasive.Roung tail tip(RTT) lesions appeared in lower frequencies within 10-30 days,but progressed extremely rapidly resulting in tail loss within 48h.We have referred to these types of lesions as“tumors”,bt they are not necessarily characteristic of vertebrate neoplasms.PCBs interacted with cadmium in a complex way,in some cases increasing totoal lesions and decreasing time-to-lesion and in other cases having the opposite effects.A three-factor(PCB, PCB dose,Cd dose)nested analysis of variance model was used to determine lesion rates in order to compare PCB potencies as potentiators or antagonists.The Aroclor mixture was always the least potent co-toxicant but appeared to be the most potent antagonist;the coplanar PCB 126 was the most potent co-toxicant.The complex response surfaces and the lack of stoichiometry in dose-response relstionships indicate that multiple mechanisms are responsible for PH and RTT lesions in planarians.Thes results emphasize the complexity of PCB toxictities and suggest further studies to validate the planarian model as a screen for combinations or environmental mixtures which may have altered biological potency in other species.