U. Lennart Hulthén

Mutations and Variants of the Epithelial Sodium Channel Gene in Liddle’s Syndrome and Primary Hypertension

Liddles syndrome is a rare monogenic form of hypertension caused by truncating or missense mutations in the C termini of the epithelial sodium channel beta- or gamma-subunits. These mutations delete or alter a conserved proline-rich amino acid sequence referred to as the PY-motif. We report here a Liddles syndrome family with a betaArg564X mutation with a premature stop codon deleting the PY-motif of the beta-subunit. This family shows marked phenotypic variation in blood pressure, serum potassium levels, and age of onset of hypertension. Given the similarity with primary hypertension, changes in the C termini of the beta- or gamma-subunits may contribute to the development of primary hypertension or to hypertension associated with diabetic nephropathy. Accordingly, the coding sequences for the cytoplasmic C termini of the beta- and gamma-subunits were screened for mutations with the use of polymerase chain reaction, single-strand conformation polymorphism, and direct DNA sequencing in 105 subjects with primary hypertension and 70 subjects with diabetic nephropathy. One frequent polymorphism was identified, but its frequency did not differ among subjects with primary hypertension, subjects with diabetic nephropathy, or control subjects. Two of the 175 subjects with primary hypertension or diabetic nephropathy showed variants that were not present in 186 control subjects. None of the variants changed the PY-motif sequence. In conclusion, a betaArg564X mutation is the likely cause of Liddles syndrome in this Swedish family, but it is unlikely that mutations in the beta- and gamma-subunit genes of the epithelial sodium channel play a significant role in the pathogenesis of primary hypertension or diabetic nephropathy.

Heritability of ambulatory and office blood pressure phenotypes in Swedish families.

Objective The aim of this study was to estimate the heritability of 24-h ambulatory blood pressure and office blood pressure phenotypes in Swedish families. Methods We measured ambulatory and office blood pressure in 260 siblings without antihypertensive treatment from 118 families. Blood pressure heritability was estimated using standard quantitative genetic variance component analysis implemented in the ‘SOLAR’ software package after adjustment for significant covariates. Results Heritability values were significant for night-time systolic (37%), diastolic (32%) and mean (32%) ambulatory blood pressure (P < 0.05 for all). During daytime, systolic ambulatory blood pressure was significantly heritable (33%, P < 0.05). Twenty-four-hour systolic (30%) and diastolic (29%) ambulatory blood pressure also had significant values of heritability (P < 0.05). Pulse pressure ambulatory blood pressure was significantly heritable over 24 h (63%, P < 0.01), during daytime (53%, P < 0.01) and at night (34%, P < 0.05). None of the office blood pressure phenotypes had a significant heritability. Conclusions We conclude that ambulatory blood pressure, in particular at night, seems better than office blood pressure to capture the heritable part of blood pressure, suggesting that ambulatory blood pressure may be a more exact estimate of an individuals true blood pressure. Genetic studies using ambulatory blood pressure as the phenotype are likely to be more powerful than those using office blood pressure. The high heritability of pulse pressure ambulatory blood pressure indicates that variation in arterial stiffness in subjects free from antihypertensive medication is strongly affected by genetic factors.

Genetic Variants of Thiazide-Sensitive NaCl-Cotransporter in Gitelman’s Syndrome and Primary Hypertension

Gitelman’s syndrome is an autosomal recessive disorder characterized by electrolyte disturbances and low blood pressure. The disease is caused by homozygous or compound heterozygous inactivating mutations in the thiazide-sensitive NaCl-cotransporter gene leading to reduced renal sodium reabsorption. We report 4 patients with Gitelman’s syndrome from southern Sweden, all in whom we identified compound heterozygous mutations in the thiazide-sensitive NaCl-cotransporter gene (Gly439Ser, Gly731Arg, Gly741Arg, Thr304Pro, and 2745insAGCA), of which the latter 2 have not been described before. We hypothesized that such mutations in their heterozygous form protect against primary hypertension in the general population and that the gene may also harbor activating mutations that increase the risk for primary hypertension. Accordingly, the gene was screened for mutations in 20 patients with primary hypertension and in 20 normotensive subjects by single-strand conformation polymorphism and direct DNA sequencing. The Arg904Gln, Gly264Ala, and C1420T variants, found in the mutation screening of subjects without Gitelman’s syndrome, were studied further. Population genotype frequencies were determined in 292 unrelated patients with primary hypertension and 264 unrelated normotensive subjects from southern Sweden. Gln904 homozygotes were overrepresented in hypertensive patients compared with normotensive subjects (5 of 292 versus 0 of 264;P =0.03). In conclusion, we confirm that Gitelman’s syndrome is caused by mutations in the thiazide-sensitive NaCl-cotransporter gene. Our results further suggest that subjects homozygous for the Gln904 variant have an increased risk for development of primary hypertension.

Moderate salt restriction effectively lowers blood pressure and degree of salt sensitivity is related to baseline concentration of renin and N-terminal atrial natriuretic peptide in plasma.

Objective The effect of salt restriction on blood pressure is under intense debate. We tested the effect of 100 mmol salt reduction on ambulatory blood pressure (ABP) in 46 Swedish individuals, 39 of whom completed the study, using a double-blind, placebo-controlled, cross-over design. Furthermore, we tested whether the basal plasma concentration of renin or N-terminal atrial natriuretic peptide (Nt-proANP) predict the degree of salt sensitivity. Methods Participants received all meals and drinks with a total daily NaCl content of 50 mmol during 8 weeks. In addition, NaCl capsules (100 mmol/day) and corresponding placebo capsules were administered for 4 weeks each in random order. ABP after high-salt intake (150 mmol/day) was compared with ABP after low-salt intake (50 mmol/day). Salt sensitivity was defined as the difference between 24-h systolic ABP at the high-salt versus the low-salt periods. Baseline renin and Nt-proANP were related to salt sensitivity. Results Lowering of salt intake from 150 to 50 mmol/day induced significant blood pressure reductions (mean reduction, 95% confidence interval) in systolic and diastolic 24-h ABP (5.8, 3.4–8.2 and 2.6, 0.91–4.4 mmHg), daytime ABP (5.5, 2.9–8.1 and 2.3, 0.42–4.1 mmHg) and night-time ABP (6.4, 3.5–9.3 and 3.4, 1.4–5.5 mmHg). Baseline ln(renin) correlated inversely with salt sensitivity (r = −0.50, P = 0.001) whereas baseline ln(Nt-proANP) correlated directly (r = 0.33, P = 0.04). Conclusion Lowering of salt intake with 100 mmol/day induces clinically relevant ABP reductions. Renin and Nt-proANP, measured with individuals on their habitual diet, could be useful biomarkers to identify individuals with the greatest blood pressure-lowering benefit from reduced salt intake.

Carotid Artery Surgery. Local versus General Anaesthesia as Related to Sympathetic Activity and Cardiovascular Effects

Arterial plasma catecholamines, blood pressure and heart rate were determined in 75 patients before, during and after carotid endarterectomy. Local anaesthesia given as a cervical block with skin infiltration containing 200 micrograms adrenaline was used in 28 patients (LA-group), general anaesthesia (nitrous oxide, fentanyl, isoflurane) with skin infiltration containing 200 micrograms adrenaline in 32 patients (GAs-group) and general anaesthesia without skin infiltration in 15 patients (GAo-group). In the LA-Group plasma noradrenaline (P-NA) levels were significantly higher during anaesthesia and surgery, with an increase from preanaesthesia levels (P less than 0.05). P-NA decreased from a preanaesthesia level in the GAo-group (P less than 0.01) but remained unaltered in the GAs-group. P-NA values in the GAo-group were lower than those of the GAs-group (P less than 0.001) following anaesthesia and surgery. Plasma adrenaline (P-A) increased in the LA- and the GAs-group and decreased in the GAo-group (P less than 0.001) following anaesthesia and surgery. In the LA-group P-A was similar before the skin incision and clamping but higher after declamping as compared to the GAs-group. Before the skin incision and thereafter P-A was lower in the GAo-group as compared to the other groups. There was a positive correlation between plasma catecholamines, on the one hand, and mean blood pressure and heart rate on the other. Two patients in the LA-, eight in the GAs- and seven in the GAo-group showed a hypotensive blood pressure reaction (SBP less than 100 mmHg; LA vs. GAo, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma ProANP(1-30) reflects salt sensitivity in subjects with heredity for hypertension

The aim of the present study was to investigate whether plasma concentration of proANP1–30, the N-terminal fragment of the atrial natriuretic peptide prohormone, or 24-hour urinary excretion of urodilatin reflects the degree of salt sensitivity in hypertension-prone individuals. Plasma concentration of proANP1–30 and urinary urodilatin excretion were determined at baseline, after 1 week on a low-salt diet (10 mmol/d) and after another week on a high-salt diet (240 mmol/d) in 30 healthy subjects with heredity for hypertension. Salt sensitivity was defined as the difference between mean arterial blood pressure after the high-salt diet and the mean arterial blood pressure after the low-salt diet. High- versus low-salt intake increased proANP1–30 (668±330 versus 358±150 pmol/L;P <0.00001) and urodilatin (18.7±5.2 versus 16.0±8.3 pmol/24 h;P <0.05). ProANP1–30 correlated with salt sensitivity at baseline (r =0.76, P <0.000001), after the low- (r =0.80, P <0.0000001) and high-salt diets (r =0.85, P <0.00000001). The increase in proANP1–30 induced by changing from the low- to the high-salt diet was also directly related to salt sensitivity (r =0.78, P <0.000001). ProANP1–30 was not related to urinary sodium excretion. Neither urodilatin nor the sodium-induced change in urodilatin correlated with salt sensitivity. However, urodilatin was related to the urinary sodium excretion at baseline (r =0.58, P <0.01) and after the high-salt diet (r =0.62, P <0.001). In conclusion, the close correlations between proANP1–30 and salt sensitivity suggest that proANP1–30 may serve as a marker for salt sensitivity and could be useful in identifying subjects who would benefit from dietary salt restriction to prevent development of hypertension.

No evidence of a relation between 11beta-hydroxysteroid dehydrogenasetype 2 activity and salt sensitivity.

BACKGROUND The ratio of urinary concentrations of tetrahydrocortisol plus allotetrahydrocortisol to tetrahydrocortisone [(THF + ATHF)/THE] reflects the activity of the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11BHSD2), which converts cortisol to cortisone in the kidney and thereby protects the mineralocorticoid receptor from the mineralocorticoid action of cortisol. The aim of the present study was to investigate whether 11BHSD2 activity is affected by salt intake and if it is related to salt sensitivity. METHODS Concentrations of THF, ATHF, and THE in 24-h urine collections was determined by gas chromatography at baseline, after 1 week on a low salt diet (10 mmol/d), and after another week on a high salt diet (240 mmol/d) in 29 healthy subjects with heredity for hypertension. Salt sensitivity was defined as the difference between mean arterial blood pressure (BP) after the high salt diet and mean arterial BP after the low salt diet. RESULTS The high salt diet increased (THF + ATHF)/THE by 5.1% +/- 9.4% (P =.009) when compared to the low salt diet. The salt-induced change of (THF + ATHF)/THE was not related to salt sensitivity. There was no correlation between salt sensitivity and (THF + ATHF)/THE at baseline (r = -0.18, P =.34), whereas salt sensitivity was inversely related to (THF + ATHF)/THE after the low (r = -0.38, P =.05) and after the high (r = -0.39, P =.04) salt diets. CONCLUSIONS We found no support for an association between enhanced salt sensitivity and reduced 11BHSD2 activity.

Determinants of kidney function in Swedish families: role of heritable factors

The aim of this study was to evaluate the determinants of kidney function and the role of heritable factors in a sample of 249 siblings free from known cardiovascular disease and without antihypertensive drugs belonging to 110 families. Four different measures and estimates of kidney function were considered. Blood pressure was recorded during 24 h by ambulatory blood pressure monitoring. Heritability was estimated with and without adjustment for significant covariates. In multivariate analysis, in addition to age, sex, BMI, HDL-cholesterol, 24-h systolic and mean blood pressure, systolic nocturnal blood pressure dipping resulted independently related to serum creatinine, estimated Cockcroft–Gault-creatinine clearance and estimated by the modification of diet in renal disease–glomerular filtration rate. After full adjustment, the heritability values were 51% for the measured creatinine clearance (P < 0.01), 58% for the estimated Cockcroft–Gault-creatinine clearance (P < 0.001), 40% for the estimated by the modification of diet in renal disease–glomerular filtration rate (P < 0.001), but 8% (P = 0.34) for serum creatinine. Our data confirm that kidney function is partially under genetic control and that genetic variants of importance for this trait could be mapped. The association of the circadian rhythm of blood pressure with kidney function in this sample deserves further investigation.

Glucose Tolerance and Secretion and Clearance of Insulin during Long Term Felodipine Treatment

ConclusionsGlucose tolerance was unaltered during long term felodipine treatment. Furthermore, felodipine did not affect glucose-stimulated insulin release as the incremental area under the curve for peripheral venous C-peptide, which reflects insulin secretion (Binder & Faber 1985), was unchanged. The decreased incremental area under the curve for insulin during felodipine treatment suggests increased insulin clearance.

Effect of Long Term Felodipine Treatment on Renal Vascular Tone, Glomerular Filtration Rate and Renal Tubular Function in Essential Hypertension

The effect of long term felodipine i treatment on renal vascular tone, glomerular flltration rate and renal tubular function was explored in 10 male patients with essential hypertension on a standardised daily intake of Na+ (150 nmol), K+ (75 nmol) and water (2500ml). The results of felodipine given IOmg bid for 8 weeks were compared with placebo intake (table I). Renal plasma flow and glomerular flltration rate (GFR) were measured as l3lhippurateand slCr-EDTAclearance using single injection technique. 24-hour renal clearance of creatinine (C-Q), electrolytes and urate were measured by routine methods. Fractional excretion was taken as the ratio of clearance electrolytes and urate! creatinine clearance. Mean blood pressure (MBP), renal blood flow (RBF), renal vascular resistance (RVR) and flltration fraction (FF) were calculated and the results are presented as median (M) and upper (UQ) and lower (LQ) quartiles. There was a positive correlation between glomerular flltration rate and creatinine clearance after placebo as well as after felodipine (0.83; p < 0.01 and 0.69; p < 0.05, respectively).