The influence of vitamin a on the susceptibility of the rat lung to 3‐methylcholanthrene

Abstract

The susceptibility of rats to pulmonary carcinogens is increased in the absence of vitamin A intake even when considerable amounts (0.4 nmole/mg) of vitamin A are stored in the liver and deficiency symptoms are absent. This was demonstrated in studies on the induction of metaplastic lung nodules by intratracheally administered 3‐methylcholanthrene. Only moderate amounts of all‐trans‐retinyl acetate in the diet (7.6 nmole/g of diet) were required to prevent the development of this state of enhanced susceptibility. A further increase in intake of retinoids (by intragastric administration of either all‐trans‐retinyl acetate or 13‐cis‐retinoic acid) provided no additional protection against the effects of carcinogen.