Demonstration of Early Renal Uptake of Potassium-42 by an Autoradiographic Method for Water-soluble Isotopes of Short Half-life

Abstract

STUDIES of the distribution of intravenously injected potassium-42 in rats have shown that the kidney takes up this cation from the plasma at considerably higher rates than does any other organ^1,2. In the first few minutes after the injection, the specific activity in the renal tissues exceeds that of the plasma^2,3. At 2 min., approximately 15 per cent¹ and 10 per cent⁴ of the injected dose were found in rabbit kidneys and about 12 per cent (unpublished observations) in rat kidneys. These fractions are far greater than the expected equilibrium value. Analysis of these findings indicated that all the potassium arriving in the plasma in the kidney is exchanged with potassium from cells. Morel and Guinnebault have recently presented evidence that the renal cortex is the main site of this very rapid exchange³. From their experiments it appears that in the rabbit as much as 15 per cent of the total potassium present in the cortex is exchanged per minute. This was corroborated macroscopically by autoradiography in which X-ray films were exposed to 2-mm. thick frozen kidney slices. The resulting autoradiograms indicated that in the 5 min. following an intravenous injection, the intense activity emanated from a region roughly corresponding to the cortex.