The transport of radioactive carbon dioxide in the blood stream of the dog after administration of radioactive bicarbonate

Movements of radioactive carbon dioxide within the animal body during oxidation of 14C‐labelled substances

“…This negative difference was considerably greater than could be accounted for by simple dilution of arterial 14CO2 by 12CO2 derived from oxidation of non-radioactive material in the limb, since the change in specific activity was several times greater than the arteriovenous differences in total C02. It could therefore only be due, like the similar negative difference found in experiments where 14C-bicarbonate was injected (Coxon & Robinson, 1959), to dilution in the pool of C02 in the limb. Since about 40% of the cardiac output passes through tissues of the same general type as those making up the hind limb and since 499 R. V. COXON AND R. J. ROBINSON in the early stages of an experiment the lowering of specific activity of C02 as between samples from the femoral artery and femoral vein is about 50 %, it is apparent that under these conditions about 20% (i.e.…”

“…Now it may be inferred both from what is known of the intracorporeal distribution of glucose and from the results of Steele, Wall, de Bodo & Altszuler (1956), that a two-way movement of isotopic glucose into and out of tissues must occur as well as a two-way movement of C02, such as was found, for example, in our own earlier experiments with "4C-bicarbonate (Coxon & Robinson, 1959). Thus the rate at which the glucose pool in the tissues mixes with blood glucose will be an important determinant of the specific activity of glucose at its site of oxidation, and the rapidity with which this mixing is effected will depend on the size of the pool.…”

“…The factors involved in the transport of 14C02 between tissues and blood after the isotope has been injected in the form of a single rather massive dose of radioactive bicarbonate have been considered in the previous paper (Coxon & Robinson, 1959). The more complicated case where 14C02 is produced within the body from glucose or other oxidizable precursor may be visualized by reference to the scheme shown in Fig.…”

“…The general arrangements for collecting and analysing samples of blood and expired air were identical with those previously described (Coxon & Robinson, 1959). In the majority of experiments the animals were under pentobarbitone anaesthesia but in one instance thiopentone (which is said to produce less change in blood sugar levels) was substituted without, however, affecting the results.…”

“…In the preceding paper (Coxon & Robinson, 1959) we have described a study of the transport in dogs of radioactive carbon dioxide into and out of different regions of the body following a single intravenous injection of radioactive bicarbonate. The present report is concerned with a similar investigation, on a regional basis, of the movements of isotopic carbon dioxide following the administration of radioactive glucose to dogs and monkeys.…”