Abstract
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.
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