Lack of initiating and promoting activity of thiourea in rat liver foci bioassay.

Thiourea (TU) fails to enhance the incidence of foci deficient in adenosine-5'-triphosphatase (ATPase) either by initiation or by promotion in a rat liver foci bioassay. To weanling female Sprague-Dawley rats, 3 x 200 or 3 x 500 mg/kg body wt of TU, respectively, were applied for initiation. One week later Clophen A 50, a technical mixture of polychlorinated biphenyls (PCBs) 2 x 10 mg/kg body wt were given twice weekly as promoting agent for 11 weeks. For promotion 0.2% of TU was administered with the drinking water for 51 days to rats of both sexes, and 0.1% and 0.05% of TU, respectively, for 70 days to females after initiation with 1 x 8 mg/kg body wt of diethylnitrosamine (DEN).