[A study of urinary immunoglobulins and electrolyte excretion after lordosis]

We described a transient low or non-selective proteinuria after forced lordosis as a characteristic of orthostatic proteinuria and the heteroporous theory and sieving function theory which might explain the mechanism of orthostatic proteinuria. The angiogenic action of the renin-angiotensin system played an important part in these theories. Angiotensin II was recognized as the key regulator of renal sodium excretion, because it reduced the urinary Na/K ratio. Since the purpose of this study is to investigate the influence of the renin-angiotensin system on the mechanism of orthostatic proteinuria, proteins and electrolytes in the urine were examined before and after lordosis in 9 healthy children (Group A) and in 6 children with orthostatic proteinuria (Group B). The urinary ratio of protein/creatinine (P/cre) in Group B was already significantly higher than that in Group A before lordosis and significantly increased after lordosis, while P/cre in group A did not increase after lordosis. The urinary Na/K ratio (Na/K) in Group B was already significantly lower than that in Group A before lordosis, and after forced lordosis, Na/K in Group A decrease with no difference between both groups observed. It is suggested that a significant increase on P/cre after lordosis was obtained only in Group A, whereas in both groups the renal vein may be compressed by forced lordosis and as a result angiotensin II may be stimulated. There might be a difference of the responsibility to angiotensin II in glomerular mesangium contraction between both groups.

[A study of urinary immunoglobulin excretion after forced lordosis]

Changes in the urinary excretion of immunoglobulins (IgG and IgA) before and after forced lordosis were studied in 26 children with orthostatic proteinuria (group OA, where proteinuria disappeared within 120 min after lordosis was referred to as group OAA and where if disappeared after more than 120 min was group OAB) and 9 children with chronic glomerulonephritis in the clinically stable state (group GN). Urinary immunoglobulins were measured by ELISA (enzyme linked immunosorbent assay). In resting urine, the urinary excretion rates (total protein, IgG, and IgA) and the urinary protein ratio (IgG/protein, IgA/protein, and IgA/IgG) did not significantly differ between groups OA and GN. When forced lordosis was carried out, at maximum protein excretion, the urinary IgA/IgG ratio in groups OAA and OAB were significantly decreased (from 198 + 44% to 17.3 + 12.9% and from 147 + 88% to 18.7 + 16.9%, respectively). The ratio of IgA/IgG in groups OAA and OAB was significantly lower than that in group GN (88.9 + 53.9%, p less than 0.01). The urinary IgA/IgG ratio after lordosis in group OA was similar to the serum IgA/IgG ratio. These findings suggest that transient low or non-selective proteinuria after lordosis is a characteristic of orthostatic proteinuria. Analysis of the urine after forced lordosis, especially using the urinary IgA/IgG ratio at maximum protein excretion, may be an useful examination for differentiating OA from other glomerulonephritides.

[A study of serum and urinary immunoglobulins after forced lordosis]

We described transient low or non selective proteinuria after forced lordosis was as a characteristic of orthostatic proteinuria and the decrease in the urinary IgA/IgG ratio after lordosis was useful in confirming the diagnosis of the disease. In this study we examined the urinary excretion of IgG, IgA and IgG4, an anionic immunoglobulin, after forced lordosis in 44 orthostatic proteinuria children (group OA) and 24 chronic glomerulonephritis patient in stable stage (group GN). Urinary IgG4/IgG after lordosis was not significantly different between groups OA and GN. It showed that urinary IgG4/IgG ratio was not so useful in the differential diagnosis of this disease. In group OA, urinary IgA/IgG correlated significantly with serum IgA/IgG (y = 0.35X + 7.0, r = 0.354, p less than 0.05), and urinary IgG4/IgG also correlated significantly with serum IgG4/IgG (y = 1.22x + 0.14, r = 0.813, p less than 0.001). From these results it is suggested that proteinuria after forced lordosis in children with orthostatic proteinuria is composed of a transient low or non selective proteinuria in terms of both size and charge of protein. It seems more likely that the so-called heteroporous theory and sieving function theory explain the mechanism of orthostatic proteinuria.