Moreover, another factor, according to Folin and Denis, that operates in the same direction is the binding capacity of the tissues for uric acid. Pratt of Boston’s observations, too, appear to indicate “That the uric acid derived from exogenous purin does not accumulate in the blood unless there is a disturbance in the uric acid metabolism.”
On the other hand, given damage to the kidney (even when this has not progressed to the point when nitrogen retention is apparent, as shown by the non-protein nitrogen values), an accumulation of uric acid takes place in the blood after a short period of purin feeding.[22]
Now, as to the second regulating factor, the retention capacity of the tissues for uric acid, it may be said that the amount, in normal subjects, would appear to be small. But Fine, it may be noted, found that the uric acid content in divers tissues was relatively proportionate to that of the blood, whether normal or increased in amount.
But, to resume, Denis also demonstrated that the uric acid content of the blood in patients suffering from various chronic diseases other than gout was also not increased on a purin-rich diet. To sum up, the researches of Denis would appear to indicate that:—
(1) In normal subjects no increase in the uric acid content of the blood follows exogenous purin intake.
(2) The uric acid content of the blood in patients suffering from chronic diseases, other than gout or renal disease, is similarly not augmented on a purin-rich diet.
(3) The uric acid content of the blood is increased more or less markedly, after a short period of purin feeding, in the presence of defective renal elimination.
In amplification of the second of the foregoing postulates some observations by Pratt may be quoted. This authority is of opinion that the low amount of uric acid present in the blood of unselected psychiatric patients on a mixed diet (Folin and Denis, Adler and Ragle) shows that a retention of uric acid in the blood in any considerable amount for twenty-four to twenty-eight hours rarely occurs. For, as he informs us, these patients at the Boston Psychopathic Hospital, when on ordinary diet, are eating purin-containing food daily, and they might take as much or more purin during the forty-eight hours preceding the blood analysis as is contained in a single sweetbread meal. Now, as Pratt argues, if the uric acid thus derived accumulated in the blood, the amount found would be considerably greater than that of individuals on a purin-free diet. But, on the contrary, it transpires that the average amount of uric acid found by Adler and Ragle in the blood of patients on an ordinary diet was only 0·3 mg. more than that found by McLester in normal individuals on a purine-free diet. The diagnostic significance of these observations will be better appreciated when we come to discuss the sequential increase of the uric acid content of the blood in gouty subjects after the ingestion of purin-rich substances.