Short-term in vivo initiation/promotion bioassay for hepatocarcinogens

We have investigated a short-term initiation/promotion assay in rat liver for chemical carcinogens. Diethylnitrosamine was used as the initiator and phenobarbital and partial hepatectomy as promoters. Initiation was determined as the focal induction of gamma-glutamyl transpeptidase activity. The protocol of the assay consisted of the following: (1) the initiator was administered, (2) one week later the rats were given 500 ppm phenobarbital in their drinking water (3) one week later 2/3 partial hepatectomy was performed and (4) the rats were maintained on 100 ppm phenobarbital for an additional four weeks. The assay was sensitive to 0.003 mmole/kg diethylnitrosamine and the number of gamma-glutamyl transpeptidase positive islands increased as a function of diethylnitrosamine dose up to at least 2 mmole/kg. Multiple doses containing a low level of diethylnitrosamine were additive. It is proposed that the assay can be used to detect initiators and promoters.