RADIOACTIVE INDICATORS IN BIOCHEMISTRY 98 <j 



DETERMINATION OF THE AMOUNT OF CIRCULATING RED 



CORPUSCLES 



Although the determination of 1he life-cycle of the red corpuscles 

 necessitates a type of labelling which remains in the corpuscles throughout 

 their life, the measurement of the amount of red corpuscles circulating 

 in the body can be carried out in a few minutes. Hence it suffices to fix 

 the radioactive label to the corpuscles for a comparatively short time. 

 This procedure can be carried out in vitro^^^). We secure a blood sample 

 of a human subject, add a few microcuries of labelled sodium phosphate 

 of negligible weight, and shake the material lor 1 hour at body temper- 

 ature. Let us denote the number of red corpuscles injected into the 

 circulation by A, and the ratio of red corpuscles in 1 gm of the injected 

 blood to those in 1 gm of blood secured from the circulation after the 

 injection by B; then the total amount of red corpuscles present in the 

 circulation {x) is given by x = AB. 



If to 100 ml. of a blood sample kept at body temperature we add 

 labelled sodium phosphate of negligible weight, about one-third of the 

 32P atoms added are found in the red corpuscles after 1 hour. It follows 

 that in 1 hour— it being assumed that the inorganic P content of the 

 plasma is 4 mgm % and the weight of the plasma constitutes 55% of that 

 ol the blood— about 0.7 mgm of inorganic P moves from the plasma into 

 the corpuscles, and vice versa. In the course of this interchange some of 

 the 32p added to the plasma penetrates into the red corpuscles and is 

 replaced by ^ip atoms moving in the opposite direction. 



The red corpuscles contain appreciable amounts of labile organic 

 phosphorus compounds. In glycolytic and other enzymic processes 

 taking place in the erythrocytes these compounds are degraded and 

 resynthesized at a remarkable rate. Shortly after their intrusion as 

 inorganic phosphate most of the 32p atoms participate in the resynthesis 

 of labile organic phosphorus compounds and are incorporated with 

 them (52). The presence of a comparatively large amount of labile organic 

 phosphorus molecules makes it possible to fix 32p j^ red corpuscles 

 during an interval which amply suffices to carry out a determination of 

 the circulating erythrocyte volume. 



If we suspend the labelled corpuscles obtained in inactive plasma, or 

 inject them into an inactive circulation, the interchange of inorganic 

 P between the labelled red corpuscles and the inactive plasma continues, 

 involving respectively 0.7 mgm of inorganic plasma and corpuscle P in 

 100 ml. of blood per hour. While, however, during the activation process, 



(si>Hevesy and Zerahn, Acta Physiol. Scand. 4, 370(1942); Bohr, Kgl. 

 Danske Vidensk. Selskab. Biol. Medd. 18, Nr. 1 (1950). 

 (52)Aten and Hevesy, Nature, Lond. 142, 871 (1938). 



