Studies on Carotenoid Metabolism

Abstract

The administration of large amounts of vitamin A to hens receiving a basal diet high in carotenoids resulted in a marked and progressively greater suppression in the pigment content of the egg yolk as the vitamin A intake was increased. On the diet in which 15,000 I. U. of vitamin A was incorporated per pound, the lowering was significant, while it was decreased to only 25% of the basal level in chickens receiving the basal diet containing 200,000 I. U. of vitamin A per pound of food. A similar effect was noted in the blood and liver; it was also strikingly evident in the body fat of group 7 which had received a supplement of 100,000 I. U. of vitamin A for over 6 months but not in the case of group 8 which received twice the level of vitamin A for 3 months. This is considered to be the resultant of the sluggish turnover of the carotenoids in body fat. The vitamin A in the yolk was unchanged from the average control level of 46.8 I. U. per gram when 1,000, 2,000 or 15,000 I. U. of this vitamin were added per pound of food. With higher doses of vitamin A in the diet, significantly increased levels were found in the yolks, the values respectively being the following: 30,000 I. U. group, 54.6; 60,000 I. U. group, 62.3; 100,000 I. U. group, 99.3 I. U.; and with the 200,000 I. U. group, 120.7 IU. The maximum level found was 226 I. U. There was no evidence of the development of a tolerance for vitamin A with a resultant decrease in the vitamin A excreted during a 6-month period. The vitamin A is progressively increased in the body fat with the higher intake in the diet. This was augmented from a value of 32.3 I. U. per gram in the control group to a mean value of 222.6 I. U. per gram in the group receiving 200,000 I. U. per pound of food. Maximum levels of vitamin A in the liver were found in the 60,000 I. U. group and no greater increases were noted when the intake was further augmented. The vitamin A in the serum was unaltered except that a slight increase probably occurred when the supplement was fed at the highest level.