Changes in the levels and the rate of synthesis of transfer RNA in tissues of mice of different ages.

Levels of transfer RNA (tRNA) were determined in liver, kidney, skeletal muscle, heart, and brain of young (35-day), adult (12-month) and old (24-month) female C57BL/6J mice. Kidney and liver showed little change in tRNA levels between young and adult mice, but the levels decreased in old mice. Skeletal muscle tRNA decreased steadily from young to old mice. Heart tRNA increased during maturation to adult organisms and then decreased in old individuals. Brain levels of tRNA increased steadily. No age-related change in the rate of transport of orotic acid into cells was observed. However, all tissues exhibited a decrease in uridine pools between adult and old mice. Most importantly, all tissues of aging mice showed a decrease in the rate of tRNA synthesis.