22-OXA-1,25(OH)(2)VITAMIN D-3, A SYNTHETIC ANALOG OF VITAMIN-D-3, HAS NO PROMOTING ACTIVITY IN A RAT-LIVER MEDIUM-TERM BIOASSAY

Modifying effects of 22-oxa-1,25(OH)(2) vitamin D-3(OCT), a synthetic analogue of vitamin D,, were evaluated in a liver medium-term bioassay using glutathione S-transferase placental form (GST-P)-positive foci and 5-bromo-2'-deoxyuridine (BrdU) labeling to give an index of DNA synthesis. F344 rats were given a single intraperitoneal injection of diethylnitrosamine (200 mg/kg body wt.) and subjected to two-thirds partial hepatectomy at week 3. Commencing 2 weeks from the start, 500 p.p.m. phenobarbital sodium and/or basal diet were fed to the rats for 6 weeks, at the same time as OCT and/or propylene glycol as the vehicle injected intraperitoneally 5 times a week. OCT demonstrated no promoting activity for rat hepatocarcinogenesis, and, in fact, showed a tendency to decrease the area per unit area of (GST-P)-positive foci in the livers of rats fed 500 p.p.m. phenobarbital sodium. However, intergroup differences in areas and numbers per unit area as well as in BrdU labeling indices were not statistically significant.