Determination of rate of cross circulation in parabiotic rats with P³²-labeled erythrocytes

¹ Department of Physiology, University of Kansas, Lawrence, Kansas

Litter-mate female rats parabiosed at 21 days by the Bunster-Meyer method were allowed to mature for several months. Volumes of blood obtained from donor animals were incubated at 37°C with P³², in the form of buffered isotonic sodium phosphate. A plasma-free suspension of labeled erythrocytes was prepared and a sample of known activity was injected into the femoral vein of one member of each parabiotic pair. Four pairs of 100 lambda blood samples, obtained by venipuncture, were taken at varying intervals, for the succeeding 150 minutes. Using the dye dilution principle, it was possible to determine the blood volume of the injected rat after the first sample, and that of the pair at the time of equilibrium. The average blood volume was 6.53% of body weight. The concentration of tagged cells reached equal values in both members of the pairs at an average time of 90 minutes. There was less than a 20% loss of total activity in all the pairs used for determinations. An equation was derived for the calculation of the rate of exchange. The average for 15 pairs was 2.09 blood volumes per hour. The range was from 3.95 bl. vol/hr. in the fastest pair to 0.74 bl. vol/hr. in the slowest.