22-OXA-1,25(OH)(2)VITAMIN D-3, A SYNTHETIC ANALOG OF VITAMIN-D-3, HASNO 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 sy nthesis. F344 rats were given a single intraperitoneal injection of di ethylnitrosamine (200 mg/kg body wt.) and subjected to two-thirds part ial 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 w eeks, at the same time as OCT and/or propylene glycol as the vehicle i njected intraperitoneally 5 times a week. OCT demonstrated no promotin g activity for rat hepatocarcinogenesis, and, in fact, showed a tenden cy 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, intergrou p differences in areas and numbers per unit area as well as in BrdU la beling indices were not statistically significant.