Distribution of phosphorus in the blood

Abstract

It is well known that when blood is allowed to stand after it has been drawn, its content of inorganic phosphate will gradually increase to 1 mgm. or more above the figure which is obtained when the determination is carried out immediately. This indicates that the organic substances containing phosphoric acid which occur in the blood, particularly in the red cells, in connection with which Greenwald has introduced the name “acid soluble phosphorus” are slowly hydrolyzed to yield inorganic phosphate. This hydrolysis, however, is incomplete even when aided by boiling with dilute acid. This finding would seem to indicate that there must be two types of organic phosphoric acid combination in the blood,—one of which is easily hydrolyzed and the other one not. To investigate this further, we have carried out phosphorus determinations by Tisdall's micromethod on the protein-free filtrate of blood, obtained by means of trichloracetic acid. We determined the inorganic phosphate immediately and again after boiling the filtrate for two hours. The total phosphorus in the filtrate (acid soluble phosphorus) was also determined. The results are shown in the accompanying chart. This shows that a constant amount of phosphoric acid is split off by boiling, approximately 10 mgm. of phosphorus being thus obtained in human blood and 13 mgm. in rat's blood. This then leaves for the organic hydrolysable phosphoric acid in the human 6-7 mg. and in the rat 5-7 mg. If we subtract the figure obtained after boiling from the total acid soluble, we obtain the figure representing the amount of phosphoric acid contained in organic combination which is not hydrolysed under the conditions stated. We have, therefore, evidence of three forms of phosphoric acid which will pass into aqueous filtrates on coagulation of the protein.