Distribution Kinetics of Urea Between Plasma and Red Blood Cells of Normal Human Blood 1

Summary

The distribution kinetics of urea between plasma and the red blood cells of normal human blood have been investigated in vivo using [¹⁵N] urea and in vitro using [¹⁵N] urea and [¹⁴C] urea. The partition ratio of free exchangeable urea between the cell and plasma is found to be the same as that of water distribution, showing the identical concentration (urea/ml water) of free urea in these two compartments of blood. However a significant difference (18%) is observed in the sp act ([¹⁵N] atom % excess) between the urea present in the cell and plasma compartments of blood. This indicates that about one-fifth of the cell urea may not be in a freely exchangeable form. The fractional turnover rate of urea from the red blood cells is different from that of the plasma compartment suggesting the relatively bound state of intra-cellular urea and its slow mobilization.