Effect of Radiation on Intermediary Metabolism of the Rat

Forty-eight hours after irradiation of rats in the lethal dose range, the amount of CO/sub 2/ in expired air decreased to 75% of the control value. To investigate the reason for this decrease, some aspects of intermediary metabolism were studied by using C/sup 14/-labeled substrates. The fraction of substrate carbon recovered as C/sup 14/O/sub 2/ in expired air (ARO) was significantly reduced postirradiation when the tracers were acetate, ribose, glucose, and fructose. At earlier times, andd with lower doses of radiation, there was either no effect, or there was a decrease that was not statistically significant. The movement of CO/sub 2/ was not affected when NaHC/sup 14/O/sub 3/ was the tracer. The ARO of formate was increased. Irradiation had no influence on the C/sub 6//C/ sub 1/ ratio in C/sup 14/O/sub 2/ when the tracers were glucose-1 and glucose-6. Incorporation of glucose and pyruvate (as alanine) into glycogen was increased severalfold. The transfer of carbon from glucose into urea was impaired by radiation, but that from alanine was not affected. With bicarbonate as the tracer, fixation of CO/sub 2/ in liver glycogen was more than seventy times as great in the irradiated rats as in the controls. These findings are interpreted as follows: the reduced output of CO/sub 2/ in expired air postirradiation is not satisfactorily accounted for by impairment of oxidatton of the substrates used; liver glycogen is increased as a resuit of enhanced glycogenesis and gluconeogenesis; and the increased fixation of CO/sub 2/ in liver glycogen suggests that fat may become an important precursor for gluconeogenesis in the irradiated rat. It was concluded that irradiation in the lethal dose range has an influence on intermediary metabolism the significance of which cannot be evaluated fully with the data at hand.