Measurement of Total Body Water in Sheep Using I 131 Labeled 4-Iodo-Antipyrine

Summary

A simple and rapid procedure is presented for the in vivo measurement of total body water in sheep using I¹³¹ 4-iodo-antipyrine as the test substance. Body water values for 62 young and mature sheep averaged 61.3 ± 6.5 and 55.3 ± 6.3, respectively, by the antipyrine method, and 62.3 ± 6.8 and 56.2 ± 6.6%, respectively by the labeled antipyrine procedure. Thyroid uptake of I¹³¹ from labeled test substance amounted to 3 to 5% and urinary excretion was less than 20% of administered dose during the critical 5-hour test period. Protein binding was evidenced, indicating that in sheep both test substances were reversibly bound to plasma protein. Consideration is given to the use of these body water volume values in establishing a predictable relationship to body constituents and to provide additional criteria for estimating animal response to experimental treatments.