Renal glomerular and tubular function in relation to the hyperuricemia of pre-eclampsia and eclampsia

Abstract

Perhaps the most outstanding change in the blood chemistry in eclampsia and pre-eclampsia is in the uric acid, which usually increases. Stander and Cadden,1 from a study of 148 cases, concluded that the blood uric acid “… gives us an accurate index of the severity of pre-eclampsia and the extent of liver damage, if present … and thus is our best criterion for any given type of treatment.” As is implied in the quotation, these workers considered that hyperuricemia points to impairment of liver function.The factors which, if uncompensated, would make for hyperuricemia are: 1.1. Increased production of uric acid in the body.2.2. Decreased renal excretion.3.3. Decreased destruction of uric acid in the body.The question as to increased production of uric acid in pre-eclampsia remains unanswered, and almost unasked. As for the second factor, Cadden and Stander2 reported normal excretion in five cases of eclampsia. By “normal excretion” they meant that the eclamptics, on a purine-free diet, excreted from 130 to 740 mg. of uric acid per twenty-four hours. This they compared with the 300 to 500 mg. excretion which Burian and Schur3 found in normal individuals. As we shall show in the discussion below, these data of Cadden and Stander may be reinterpreted.Schaffer, Dill, and Cadden4 have measured simultaneously the clearances of diodrast, inulin, urea, and uric acid in normally pregnant and in pre-eclamptic women. They found that in pre-eclampsia the uric acid clearance averaged 31 per cent less than in their normals. They attributed the diminished uric acid clearance to a decrease in glomerular filtration (which showed a reduction of 20 per cent). Their data are open to the objection that they measured their clearances in the presence of plasma diodrast concentrations of the order of 1 to 2 mg. per 100 ml. Such plasma levels of diodrast will increase the uric acid clearance two- to threefold.5, 6 It is uncertain whether diodrast would have quantitatively the same effect upon the pre-eclamptic kidney as upon the normal. Furthermore, detailed study of their data for individual cases leaves one unconvinced that a reduction in the filtration rate is chiefly responsible for the decreased uric acid clearances. Recalculation of their data shows a more general factor—in pre-eclampsia there seems to be an increased tubular reabsorption of filtered uric acid. (Uric acid is filterable from human plasma.7)In the present paper we are reporting the measurements of simultaneous clearances of inulin, urea, and of uric acid as determined by two methods. Inulin does not affect the uric acid clearance.5