The turnover of ribosomes and soluble RNA in a variety of tissues of young adult and aged rats

The turnover of ribosomes and soluble RNA from a variety of tissues of young adult (12-months old) and aged (24-months old) rats was measured by following the loss of radioactivity, injected intraperitoneally as14C-labelled orotic acid, from purified ribosomal and soluble RNA fractions. The decay pattern was single exponential in the case of ribosomes from liver, kidney, lung, spleen and intestinal mucosa. No age-associated differences were observed. The half-lives for ribosomes in the above tissues from young adult animals were 5.89, 6.53, 8.98, 8.61 and 8.13 days, respectively. The turnover pattern for soluble RNA was single exponential for lung but double exponential for intestinal mucosa, no age-associated difference in either tissue being observed. The half-lives for young adults were 8.75 days for lung, and 1.0 day and 11.4 days for the first and second components, respectively, of intestinal mucosa. A significant age difference was observed in the turnover rate of soluble RNA from spleen; the half-lives were 8.29 and 6.46 days for spleens of aged and young adults, respectively, the turnover pattern being single exponential. The soluble RNA's from liver and kidney of young adults decayed in a single exponential pattern, whereas those from liver and kidney of the aged animals decayed in a double exponential pattern. The half-life of the second or slow component (5.34 days) of old liver soluble RNA did not differ significantly from the half-life of young liver soluble RNA (4.59 days). The first components of soluble RNA from both old liver and old kidney had about the same half-lives (1.1–1.2 days). The second component of old kidney soluble RNA (9.51 days) differed significantly from that of young kidney soluble RNA (4.99 days).