Measurement of Total Body Water in Sheep Using I131 Labeled 4-Iodo-Antipyrine

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Abstract
A simple and rapid procedure is presented for the in vivo measurement of total body water in sheep using 1-131 4-iodo-antipyrine as the test substance. The body water values for 62 young and mature sheep averaged 61.3 [plus or minus] 6.5 and 55.3 [plus or minus] 6.3, respectively, by the antipyrine method, and 62.3 [plus or minus] 6.8 and 56.2 [plus or minus] 6.6%, respectively by the labeled antipyrine procedure. Thyroid uptake of I-131 from the labeled test substance amounted to 3-5% and urinary excretion was less than 20% of the administered dose during the critical 5-hour test period. Protein binding was evidenced, indi- eating 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.