The influence of retinyl acetate on the postinitiation phase of preneoplastic lung nodules in rats.

The effects of retinyl acetate (RA) on the development of carcinogen-induced metaplastic lung nodules were investigated. Four mg of 3-methylcholanthrene were administered intratracheally to F344 rats maintained on a vitamin A-free diet and receiving 31.4 nmoles of RA per week by intragastric intubation. At 3, 5, and 10 weeks after intratracheal instillation of 3-methylcholanthrene, one group of 24 rats each was started on a weekly dose of 31,400 nmoles of RA; a control group was continued on the low-RA dose. Fifty-two weeks after 3-methylcholanthrene injection, the incidence of metaplastic lung nodules was found to be 3% in the combined high-RA-dose groups as compared with 42% in the low-RA-dose group. It is therefore concluded that RA has a significant effects on the postinitiation phase of preneoplastic lung nodules in rats.