THE DISTRIBUTION OF INJECTED RADIOACTIVE POTASSIUM IN RATS

Abstract

At different times after adm. in various ways of radioactive K to albino rats the animals were killed and samples of plasma, red cells, and various tissues were analyzed both for total K and for radioactivity. The radioactive K penetrated rapidly into most of the tissues of the body, relatively little being found in the plasma. The rate of penetration was highest in liver, heart, kidney, lung, diaphragm, and gastro-intestinal tract, intermediate in muscle and skin, and low but not absent in testes, erythro-cytes and brain. In tissues where penetration was rapid the activity per mol. of total K present in the first 1-2 hrs. was 1.5-2.5 times as high as the simultaneous plasma value. The difference was especially great after intraperit. inj., but was still present after subcut. inj. Since the increase in total K in the plasma was only a small fraction of the total K injected, elimination of K from the blood must have occurred by mass movement of K or by exchange with some other cation. The low value of the activity in the plasma indicated a nearly complete mixing of radioactive K with all the normal K in the body. Both processes indicate widespread permeability to K. After equilibrium was established the bulk of the radioactive K was found where the bulk of the total body K was, i.e., in the muscles, with skin and viscera next in importance.