Supplemental administration of 1 alpha-hydroxyvitamin D3 inhibits promotion by intrarectal instillation of lithocholic acid in N-methyl-N-nitrosourea-induced colonic tumorigenesis in rats.

The effect of 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] on promotion by intrarectal instillation of lithocholic acid (LC) in N-methyl-N-nitrosourea (MNU)-induced colonic tumorigenesis was studied in a rodent model. Ninety-two female F344 rats received intrarectal injection of 2.5 mg of MNU twice in one week followed by 1 mg of LC or its vehicle alone three times weekly for 48 weeks. Those which received LC were given a concomitant intragastric administration of 0.04 micrograms of 1 alpha(OH)D3 or its vehicle alone three times weekly. In the group receiving MNU alone (n = 30) five rats bore colonic tumors; in the MNU + LC group (n = 32) 15 and in the MNU + LC + 1 alpha(OH)D3 group (n = 30) six rats bore colonic tumors (MNU + LC versus MNU + LC + 1 alpha(OH)D3 group, P less than 0.05). These results indicated that promotion of MNU-induced colonic tumorigenesis by LC was suppressed by supplemental administration of 1 alpha(OH)D3.