Body compostion in vivo. VIII. Some physiological implications with respect to extracellular fluid volume arising from the distribution of thiocyanate in sheep

Abstract

The distribution of [³⁵S]-thiocyanate in sheep was studied. The specific activity in rumen fluid during the first 4 hr after injection was markedly less than in serum, and equilibration between rumen fluid and blood was not reached until 20–30 hr after injection. There were large urinary losses of the marker and approximately 50% of the dose was lost in 24 hr. Activity in rumen fluid and urine was due to [³⁵S]-thiocyanate. The thiocyanate spaces, allowing for urinary losses, during the first 4 hr after injection were 25 –30% body weight, increasing to 35–40% body weight at 20–30 hr after injection. The physiological implications of the results with respect to measuring extracellular fluid volume in sheep are discussed.