A comparison of the selenate and sulfate ions in man and dog.

During the past year we have been interested in measuring the body's extra cellular fluid space (ECF) in various metabolic and renal disorders. The radio active indicators 82Br and 35S sulfate do provide reasonable approximations of the ECF, yet they have certain practical disadvantages. The short 35 hour half life of 82Br requires that the isotope be continually supplied to the laboratory. The use of beta emitting 35S sulfate requires care and time in the preparation of plasma samples for counting to accurately quantitate their activity. It would be desireable to have an equally safe yet longer lived gamma emitting indicator ofECF. In 1962 Ganther and Bauman (1) reported nutritional studies in rats which suggested that sulfate and selenate may be metabolized similarly. Other investi gators (2) (3) have also pointed out the biochemical similarity of many S con taining compounds and their selenium containing analogues. Because of the pos sibility that 120 day half life, gamma-emitting 75Se-selenate ion (SeOfl may be distributed primarily in the ECF as is sulfate ion (SOy ), the selenate ion was studied in the dog and man. The purpose of this report is to present the results of studies of the apparent volume of distribution, excretionand tissuelocalization of T5Se-selenateand to indicate the differences between the selenate and sulfate ions.