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      Effects of Protein Meals on the Urinary Excretion of Various Plasma Proteins in Healthy Subjects

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          To examine whether hemodynamic changes in response to acute protein loadings with different protein sources cause increases in urinary excretion of plasma proteins in healthy subjects, urinary excretions of various plasma proteins with various molecular radii and isoelectric points, namely albumin (Alb), IgG, IgG4, ceruloplasmin (CRL), and α<sub>2</sub>-macroglobulin (A2), were measured in healthy subjects after ingestion of a beef meal or of a tuna fish meal. Significant increases in urinary excretions of the negatively charged IgG4 and CRL and of the neutrally charged IgG were found in parallel with enhanced creatinine clearances after each protein ingestion. These renal responses returned to basal levels 9 h after the test. This finding suggests that in healthy subjects, the increase in glomerular filtration rate after acute protein loading caused selective enhancement of urinary excretions of plasma proteins with a molecular radius of approximately 55 Å (the radius of IgG, IgG4, and CRL), irrespective of the charge barrier of the glomerulus. The increases in these three plasma proteins may be induced by leakage via the shunt pathway in the glomerulus, as proposed earlier (see text). In contrast, increases in urinary excretions of A2 and Alb were not found. The former finding may be explained by the possibility that A2 would not pass through this pathway, since the molecular radius of A2 (88 Å) is larger than that of IgG, although the latter finding may be partially explained by preferential renal tubular reabsorption of Alb.

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          The case for intrarenal hypertension in the initiation and progression of diabetic and other glomerulopathies.

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            Renal functional reserve in humans

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              Short-term protein loading in assessment of patients with renal disease.

              The effect of short-term protein loading on the glomerular filtration rate in normal persons and patients with renal disease was evaluated. Previous studies have demonstrated that in healthy subjects, protein loading results in an increased glomerular filtration rate. By determining the glomerular filtration rate preceding (baseline glomerular filtration rate) and following (test glomerular filtration rate) oral protein loading, it was possible to define (1) the filtration capacity (test glomerular filtration rate) and (2) the renal reserve (test glomerular filtration rate - baseline glomerular filtration rate) of the kidney. In normal persons, filtration capacity averaged 157 +/- 13 ml per minute and renal reserve 34 ml per minute. The test glomerular filtration rate was reproducible and independent of protein intake, whereas baseline glomerular filtration rate was significantly influenced by diet. Patients with renal disease were found to have a reduced renal reserve and/or a diminished filtration capacity. The reduction in filtration capacity appears to correlate with the damage sustained by the organ. It is suggested that an abnormal response to protein loading in renal disease may herald the fall in the baseline glomerular filtration rate and the rise in plasma creatinine level.

                Author and article information

                S. Karger AG
                April 1999
                31 March 1999
                : 81
                : 4
                : 398-405
                Division of Geriatric Medicine, Akita University Hospital, Akita, Japan
                45323 Nephron 1999;81:398–405
                © 1999 S. Karger AG, Basel

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                Figures: 1, Tables: 4, References: 33, Pages: 8
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