Determination of red cell survival in rabbits by fluorescent excitation analysis of stable rubidium

Nonradioactive rubidium was used to label red cell in rabbits and its concentration was determined by employing a simple version of radioisotope-induced x-ray fluorescence analysis. About 10 ml of red cells were labeled in vitro with 0.5-1 mg of RbCl and subsequently reinjected, resulting in a Rb concentration of about 50 ppm by the red cells. Four milliliters of blood were collected about every week, the concentrated erythrocytes deposited on filter paper disks, and the Rb content analyzed. Except for the first four to seven days, a function of the type N = Noe-kt fitted very well the experimental Rb disappearance curve data. The mean half-time value deduced from the experimental data was 310 +/- 15 days, which should be compared with the values of T1/2 = 260 +/- 20 h and T1/2 = 206 +/- 30 h obtained, respectively, by these authors and by Price et al., employing radioactive 51Cr-labeled red cells. The possibility of labeling human red cells with stable Rb is discussed.