[Changes in the concentrations and synthesis of DNA and RNA in tissues during accelerated growth and development of rats].

Daily administration of low doses of caffeine to 5-30 day old rats increases their growth, mainly due to the increase in muscle weight and results in acceleration of maturation of vegetative functions. DNA and total RNA levels in skeletal muscles and liver increase together with the increase of incorporation of labeled uridine and lysin into total RNA and proteins. These findings indicate stimulation of protein synthesis in these tissues. Significant increase in the relative weight of the thymus, its DNA and RNA contents, as well as its uridine-14C uptake may indicate anabolic effects of this gland upon growth. In control and experimental animals, the level of DNA and RNA in the thymus is 5-10 times higher as compared to that in muscles, liver and heart.