A Study of Water and Electrolyte Metabolism in Sheep: II.—The Volumes of Distribution of Antipyrine, Thiosulphate and T1824 (Evans Blue) and Values for Certain Extracellular Fluid Constituents

SUMMARY Measurements were made of antipyrine space, thiosulphate space, plasma volume (7-1824) space, proportions of water and total solids in plasma, plasma protein concentrations and venous blood haemoglobin and haematocrit values of cross-bred Suffolk sheep. Mean values for antipyrine spaces, expressed as a percentage of fleece-free body-weights, from 7 determinations in ewes, and 26 determinations in wethers, were found to be 53·7 ± 8·4 and 43·0 ±5·1, respectively. The mean rates at which antipyrine disappeared from the blood of these 2 groups was 27·3 ± 7·5 and 42·6±6.5%/hour, respectively. Throughout the course of any one determination of antipyrine space, the rate at which antipyrine disappeared from the blood, remained constant, but changed in the individual animal with deprivation of water, and resultant fall in feed intake. When measurements of change in total body water (TBW) volume were obtained, concurrently, from antipyrine space and from external water balance data, the changes in antipyrine space invariably were smaller than changes estimated from balance data. The mean values for thiosulphate space from 44 measurements in wethers, ewes, and lambs, were found to be 14·9 ± 1·5, 15·5 ± 1·6 and 19·7 ± 2·6% of fleece-free body-weight, respectively. From 36 measurements of plasma volume, mean values in wethers and lambs were found to be 40·0 ± 4·8 and 56·1 ± 5·6 ml./kg. body-weight, respectively. In 2 adult wethers, the observed volumes of the body fluid compartments remained relatively constant over a period of 14 months despite body weight increases of 36 and 56% respectively.