The Relationship, if any, between the Amounts of Uric Acid and of Urea, and Total Non-Protein Nitrogen in Human Blood
Taking samples of human blood from (1) unselected insane subjects and (2) chronic nephritics, Folin and Denis determined the amounts therein of urea, total non-protein nitrogen, and uric acid. The figures obtained showed that “there is apparently no relationship between the amount of uric acid and the amount of urea or total non-protein in nitrogen, in human blood.”
That such a discrepancy should obtain is doubtless of profound though as yet imperfectly grasped significance. These authorities rightly assume that, since the kidney is practically the sole avenue for nitrogenous waste excretion, it follows that the urea and total non-protein nitrogen of the blood must in the main be inversely proportional to the general efficiency of the renal organs. Then, obviously, the same law, too, should, in lack of some other plausible explanation, govern the excretion of uric acid also. But, as the above generalisation portends, it is apparently not so.
Fortunately, Folin and Denis prosecuted their study still further, taking in examples of gout (with and without clinically recognisable nephritis), also instances of leukæmia and lead poisoning.
The blood, again, in these disorders betrayed the same peculiarity, viz., that while containing an excess of uric acid, it did not contain correspondingly large amounts of urea or other waste nitrogen; in other words, the findings in the blood in gout were in full accord with the above generalisation, i.e., the apparent lack of any relationship between the amount of uric acid and that of urea or total non-protein nitrogen in the blood.
Now in leukæmia the cause of the uricæmia is over-production of uric acid, but in this instance the same is correlated with an increased elimination of uric acid by the kidneys.
Turning to lead poisoning, the medicinal administration of lead acetate results in a great diminution of uric acid excretion, a response consistent with the view that lead inhibits the excretory power of the kidney for uric acid, the change, at first functional, becoming later organic; for it is held that the uricæmia, associated with plumbism, proves that the action of the lead is not due to inhibition of the formation of uric acid.
Lastly, as to gout, opinion still wavers as to whether or not the excretion of uric acid in this disorder is appreciably lowered. On the other hand, it is significant that the reverse is never claimed, viz., that in gout the uric acid output is abnormally raised. Now, as we saw in leukæmia, the high uric acid blood content is accompanied by a correspondingly high uric acid output; but, on the contrary, in gout, despite the accumulation of uric acid in the blood, there is no parallel increase in its elimination.
Reflecting on the above considerations, Folin and Denis claim that “the mere fact that the uric acid may accumulate in the blood of the gouty without being accompanied by an increased elimination constitutes definite proof that the gouty kidney is damaged with reference to its ability to eliminate uric acid.”
In all deference, we doubt the legitimacy of the inference, if only for the very excellent reason that, to quote Von Noorden’s words, even to-day “it remains uncertain whether the retention of urate arises because the outlet is blocked, or because the uric acid is held fast by chemical affinities.”
Apart from this, there are several objections to Folin and Denis’ assumption.