Blood clearance of 3H-thymidine and 3H-uridine ingrowing rats

The clearance of 3H-thymidine and 3H-uridine from the blood was studied in rats of ages 5, 15 and 30 days. The clearance curves were integrated to get measure of the total availability of the precursors. Age-dependent differences were found, especially for uridine, which showed a lower availability when the animals became older. In the case of thymidine lesser differences were found. The catabolic rate, as measured by the appearance of 3H-water, was much increased, both in case of 3H-thymidine and 3H -uridine as the rats became older. It was observed that the amount of catabolic products (except 3H-water) in the blood was much larger for uridine than for thymidine. Rats were given 160 rad on the first day after birth. Only in the case of 3H-thymidine, in 5-days-old rats, an effect of irradiation could be seen, i.e. a somewhat lowered efficiency to catabolize thymidine. (author)