Studies on mode of action of vitamin A.

Effect of feeding 5000,10 000, 20 000, 30 000 and 40 000 I.U. of vitamin A for two days to 25 days old rats has been studied on liver protein, RNA and DNA, liver and plasma lipids and adrenal cholesterol. The incorporation of palmitate- I-14-C into liver and plasma lipids has been studied in vitamin A fed rats. Two patterns of effects of vitamin A were observed in rats on their liver protein, RNA and DNA and liver and plasma lipids. At lower amounts of vitamin A feeding either the above did not change or were increased, but at higher amounts of vitamin A feeding the above were decreased as compared to the controls. Plasma nonesterified fatty acids were increased and adrenal cholesterol decreased in rats fed 5000 I.U. of vitamin A, but were not affected in rats fed higher amounts of vitamin A. The utilization of palmitate-I-14-C for the synthesis of liver triglycerides and phosphoglycerides was reduced in rats fed higher amounts of vitamin A, but was not significantly different from the controls in rats fed liver amounts of vitamin A. The effects of vitamin A are influenced by the age of the animal as well as the amounts of vitamin A fed. The results show that the effects of vitamin A are exerted by the stimulation of adrenal activity (increased corticoid synthesis).