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      Urinary Excretion Rate of Tamm-Horsfall Protein Is Related to Salt Intake in Humans

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          Background/Aims: Increased salt intake and enhanced salt sensitivity are implicated in the pathogenesis of hypertension. The aim of the present study was to investigate whether the urinary excretion rate of Tamm-Horsfall protein (THP) is dependent on salt intake in healthy, genetically hypertension-prone individuals. Methods: Thirty unrelated subjects (13 men and 17 women, mean age 48.1 ± 6.7 years) with at least one first-degree relative with primary hypertension were studied. After a baseline investigation, the study subjects were put on a low-salt diet (10 mmol of sodium and 70 mmol of potassium per day) for 1 week. During the second week, sodium chloride capsules (230 mmol/day) were added to the diet to achieve a high-salt intake of 240 mmol/day. Urine samples (24-hour and overnight collections) were collected before the baseline investigation and at the end of the high- and low-salt diet weeks. The salt sensitivity was calculated as the difference between the blood pressure during high salt intake and the blood pressure during low salt intake. Results: A low salt intake induced a decrease in the urinary excretion rate of THP during the night (11.7 µg/min) compared with baseline (19.5 µg/min; p < 0.05) and high salt intake (23.1 µg/min; p < 0.01). Furthermore, a greater response in blood pressure to a high salt intake, i.e. high salt sensitivity, was associated with increased excretion of THP in urine during the change to high salt intake (r = 0.38, p < 0.05). Conclusion: We were able to confirm that urinary excretion of THP is dependent on sodium intake. Patients with a high salt sensitivity, i.e. an exaggerated blood pressure response to high salt intake, responded to the high salt intake with an even greater increase in the urinary excretion rate of THP. The mechanism underlying this response is still unknown, but it might indicate that distal nephron function in healthy, genetically hypertension-prone individuals is altered.

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          Most cited references 7

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          Bartter's syndrome, hypokalaemic alkalosis with hypercalciuria, is caused by mutations in the Na-K-2Cl cotransporter NKCC2.

          Inherited hypokalaemic alkalosis with low blood pressure can be divided into two groups-Gitelman's syndrome, featuring hypocalciuria, hypomagnesaemia and milder clinical manifestations, and Bartter's syndrome, featuring hypercalciuria and early presentation with severe volume depletion. Mutations in the renal Na-Cl cotransporter have been shown to cause Gitelman's syndrome. We demonstrate linkage of Bartter's syndrome to the renal Na-K-2Cl cotransporter gene NKCC2, and identify frameshift or non-conservative missense mutations for this gene that co-segregate with the disease. These findings demonstrate the molecular basis of Bartter's syndrome, provide the basis for molecular classification of patients with inherited hypokalaemic alkalosis, and suggest potential phenotypes in heterozygous carriers of NKCC2 mutations.
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            A study of Tamm-Horsfall protein excretion in hypertensive patients and type 1 diabetic patients.

            The study was performed in order to evaluate to what extent hypertension or diabetes mellitus may affect the urinary excretion rate of Tamm-Horsfall protein. The urinary excretion rates of albumin and Tamm-Horsfall protein, a measure of glomerular and distal tubular function, respectively were measured in patients with essential hypertension (n = 17) and in type 1 diabetes with (n = 20) or without nephropathy (n = 8) and in apparently healthy subjects (n = 10). Mean 24-h ambulatory blood pressure measurements showed higher blood pressure levels in the hypertensive (167/ 106 mmHg, p < 0.001) than in the diabetic patients with (136/84 mmHg) and without nephropathy (121/74 mmHg) and in healthy subjects (122/76 mmHg). Day and night ratios of systolic and diastolic blood pressure levels were not different among the four groups. Urinary albumin excretion rate was increased in patients with hypertension (30.8 x/ 3.4 microg/min; geometric mean x/tolerance factor; p < 0.001) and diabetes with nephropathy (462 x/ 3.5 microg/min; p < 0.001) compared with diabetic patients without nephropathy and healthy subjects (4.6 x/ 1.9 and 3.7 x/ 1.5 microg/min, respectively). The Tamm-Horsfall protein excretion rate was decreased in patients with diabetic nephropathy (11.6 x/ 3.5 microg/min) compared to patients with hypertension (36.3 x/2.1 1g/min; p < 0.01), diabetes without nephropathy (39.2 x/ 2.0 microg/min; p < 0.05) and healthy subjects (63.0 x/ 1.4 microg/min; p < 0.001), whereas no differences were found among the latter three groups. These data indicate that high blood pressure may be associated with albuminuria, while a decrease in excretion rate of Tamm-Horsfall protein may be associated with diabetic nephropathy. These associations need to be studied in a larger population.
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              Urinary Excretion of Tamm-Horsfall Protein and Epidermal Growth Factor in Chronic Nephropathy

              Tamm-Horsfall protein (THP) and epidermal growth factor (EGF) are both synthesized by tubular cells in the distal part of the nephron and excreted with the urine. The present study examines the urinary excretion rates of the two peptides in relation to functional tubular markers in patients with chronic nephropathy. Four groups of patients with moderate to severely reduced renal function were studied: glomerulonephritis (n = 10), diabetic nephropathy (n = 11), tubulointerstitial nephropathy (n = 13), and polycystic kidney disease (n = 8). The renal function was evaluated by glomerular filtration rate (GFR) as an indicator for the general renal function, lithium clearance (C Li ) as an indicator for proximal tubular function, and absolute distal reabsorption of sodium (ADR Na ) as an indicator for distal tubular function. The excretion rate of EGF was rather closely correlated with GFR, C Li and ADR Na (Spearman coefficients of variation 0.88, 0.69, and 0.74, respectively). The correlations between the excretion rate of THP and GFR, C Li and ADR Na were weaker (Spearman coefficients of variation 0.68, 0.42, and 0.44). When the effect of GFR had been accounted for by multiple variance analyses, the excretion rates of the two peptides were still associated with ADR Na but not with C Li . In conclusion, the urinary excretion rates of especially EGF but also those of THP were correlated with renal function and distal tubular reabsorption of sodium in patients with chronic nephropathy.

                Author and article information

                Nephron Physiol
                Nephron Physiology
                S. Karger AG
                May 2004
                24 May 2004
                : 97
                : 1
                : p31-p36
                aDepartment of Medicine, University Hospital of Lund, Lund, bDepartment of Endocrinology, Malmö University Hospital MAS, Malmö, Sweden
                77600 Nephron Physiol 2004;97:p31–p36
                © 2004 S. Karger AG, Basel

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                Tables: 3, References: 32, Pages: 1
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