Observations on the metabolism of potassium from a study of the renal clearance.

The object of the investigations recorded here was to obtain further information about the metabolism of potassium with particular reference to its rate of excretion in relation to the plasma level and to its retention, if any, by the tissues. The r6le played by potassium in the regulation of the water balance has been attracting an increasing amount of attention in recent years. It has been shown, for example, that in dehydrated infants with diarrhoea there is an excessive loss of potassium by the bowel (Butler et al., 1933). Recently, Darrow (1946) has recommended the use of a transfusion fluid for intravenous use which contains a relatively high concentration of potassium in order to replace this loss. By this means he aims at the restoration of intracellular water and salts as well as extracellular fluid. The potassium is held in the body mainly within the cells, while sodium is under normal conditions mostly without the cell-that is, in the plasma and other extracellular fluids. Certain metabolites such as chloride are classified as threshold substances. When the concentration of such a metabolite in the blood reaches a certain level it is excreted in increasing degrees as the level rises. Such a correlation for potassium has not been found. McCance and Young (1941) estimated potassium clearances in infants and adults and noted that 'individual idiosyncrasies of which we have no certain knowledge far outweigh the influence of absolute serum levels on the clearance.' These workers showed that in adults the clearance tended to increase with the minute volume of urine secreted, while in the infants, where the urine flow was much less, this did not occur. They were unable to show any relation between the plasma level of potassium and its excretion in the urine.