THE EXTENT TO WHICH RADIOACTIVE CHLORIDE PENETRATES TISSUES, AND ITS SIGNIFICANCE

Abstract

The radioactive chloride isotope (17 Cl38 of half-life 37 min.) was injected into rats and rabbits in an isotonic soln. of LiCl. After suitable intervals of time the animals were killed, and the tissues and body fluids analysed for radioactivity with a Geiger-Muller counter and for chloride (Cl) by a chemical method. The extent to which Cl38 penetrated tissues from the plasma was detd. by comparing the ratio of the tissue to plasma conc. of Cl38 to a corresponding ratio for CL When Cl38 had penetrated the entire Cl-containing phase of a tissue the ratios were equal. The data showed that Cl38 entered the entire Cl phase of liver, muscles and connective tissues within a few mins. after inj., suggesting that all of the chloride in these tissues is extracellular in position. In pyloric mucosa and testes a volume equal to the Na phase but equal to only one-half of the Cl phase was penetrated by Cl38 in 52 mins. Penetration proceeded slowly into brain, demonstrating the presence of a barrier to plasma chloride in the region of the cerebral capillaries. The possible character of the barrier is discussed. Cl38 was used to measure the extracellular fluid which was 29% of the body wt. in rats and 21% in rabbits.