(3) Its diagnostic valency, as a characteristic feature of gout, is correspondingly depreciated.
Lowered Endogenous Uric Acid Output
As a rule, gouty subjects, on a purin-free diet, excrete less endogenous uric acid than normal persons. Thus, according to Walker Hall, the average daily endogenous urinary uric acid output of a normal adult is about 0·5 gramme, while that of a gouty subject is about 0·45 gramme. Brugsch and Schittenhelm hold that in about 80 per cent. of cases the average endogenous excretion is lower than normal.[19]
According to these same observers, “the maximum fluctuation during attack-free periods was at first believed to be less than in the normal cases; more recent examinations, however, have shown that in the same case of gout there may be periods of high, and periods of low, endogenous uric acid excretion.” These variations, they hold, are not to be accounted for by either mild or severe attacks of gout, for they occur in the attack-free period.
Again Laird, investigating the elimination of endogenous uric acid in a case of chronic gout, noted that the output thereof was sub-normal, and, as Brugsch and Schittenhelm observed, the same presented marked variations. The leucocyte counts he found normal, but the phosphorus output and the acidity were sub-normal. Bloch again, while he agrees that endogenous purin excretion is usually below the average in gouty subjects, found that the output thereof is at its minimum before an acute attack of gout.
The foregoing observations would suggest that the retention or delayed excretion of uric acid applies both to exogenous and endogenous purins. But, when we come to analyse the foregoing findings as to the variations in uric acid output, both in acute and chronic gout, one feels inclined to agree with O. Folin, “that the clinically useful contributions obtained by urine analysis have not been very numerous.” Thus we cannot, on the basis of the variations in uric acid excretion, presume to diagnose gout; in other words, if we take urine analysis alone, it is extremely difficult to prove that the uric acid elimination in gout is really and truly abnormal. Our uncertainty, moreover, is the more pronounced when we realise that in some cases of rheumatoid arthritis, etc., there is a disturbance of purin metabolism which in some of its features is reminiscent of that obtaining in typical gout. But, before proceeding to discuss this interesting resemblance, it will, we think, be convenient here to recall that the obliquities in metabolism found in gout are not wholly restricted to uric acid.
Other Anomalies in Excretion in Gout
As Levene and Kristeller have shown, side by side with the delayed excretion of ingested purins, there occurs also a tardy elimination of the other nitrogenous products of protein food. Vogt observed that fluctuations in nitrogen retention and nitrogen loss are quite typical of gouty subjects. As to the why and wherefore, however, of this variability, it remains a mystery. Nor do we know the form in which the nitrogen is retained, though Vogt maintains that the uneliminated moiety takes the form of purin bodies. According to Brugsch, it is during the acute attacks of gout that the nitrogen loss reaches its zenith, and he suggests that the nitrogen retention in the inter-paroxysmal periods is in part compensatory. On the other hand, the gain in weight that ensues is not adequate to account for the sum total of the nitrogen retention; while, as before observed, in gout there occurs, not only retarded elimination of exogenous purins, but also of other nitrogenous products of protein food. Yet, according to Heffter, the ratio of purin bases to uric acid is unaltered in the urine of gouty subjects.
Again, all nucleins contain a phosphoric acid group, and Futcher found that the curve of the uric acid output ran in a striking parallel with that of phosphoric acid. But the attempts of subsequent investigators to show that the two end-products of nuclein disintegration—uric acid and phosphoric acid—go hand-in-hand prove contradictory. Hence Wells, in regard to phosphoric elimination, observes that, “it seems probable that it shows no characteristic alterations in gout.” Lastly, we will recall to the reader that in the chapter on protein metabolism it was pointed out that the amino-acids, especially glycocoll, are found in excess in “gouty” urines.
In conclusion, it must, we fear, be admitted that the results of urinary analyses have proved insufficient of themselves to unravel the intricacies of metabolism in gout, and, after a brief digression, we shall proceed to ascertain whether, on the other hand, chemical analysis of the blood by modern methods can in any way shed further light on this obscure problem.