More on the Sodium Saga

The relationship between cognitive function, depressive behaviour and sleep quality with 24-h urinary sodium excretion in patients with essential hypertension

BACKGROUND

Various studies have shown that sodium intake is related to increased blood pressure. However, the relationship between sodium intake and cognitive function and depression has not previously been studied.

AIM

The objective of this study was to investigate the relationship between 24-h sodium excretion with cognitive function, depression and sleep quality in patients newly diagnosed with essential hypertension.

METHODS

All patients underwent history taking, physical examination, blood pressure measurement, 12-lead ECG evaluation, routine urine analysis, biochemical analysis and 24-h urine collection to measure urinary sodium and protein excretion and creatinine clearance, evaluation of cognitive function, depressive behaviour and sleep quality.

RESULTS

In total, 119 patients newly diagnosed with essential hypertension (50 men and 69 women aged 54.2 ± 16.1 years) were enrolled. The 24-h urinary sodium excretion of the patients was 204.0 ± 240.4 mEq/day. The Standardized Mini Mental State Examination (SMMSE), Pittsburgh Sleep Quality Index and Beck Depression Inventory scores of the patients were 26.0 ± 2.7, 5.6 ± 3.1 and 21.6 ± 13.5, respectively. Spearman correlation analysis revealed that 24-h urinary sodium excretion was correlated with age (rho -0.258, p = 0.005), systolic blood pressure (rho 0.219, p = 0.017), diastolic blood pressure (rho 0.195, p = 0.034), creatinine clearance (rho 0.414, p < 0.0001) and SMMSE score (rho -0.257, p = 0.005). Stepwise linear regression of independent factors revealed that gender (p < 0.0001), creatinine clearance (p < 0.0001), systolic blood pressure (p = 0.031) and SMMSE score (p < 0.0001) were independently related to logarithmically converted 24-h sodium excretion.

CONCLUSION

The current study demonstrated that better cognitive function, but not depressive behaviour and sleep disturbance, is related to decreased sodium intake as evaluated by 24-h urinary sodium excretion. Studies are needed to highlight the mechanisms regarding the relationship between cognitive function and sodium intake.

The relationship between hypertension and salt intake in Turkish population: SALTURK study

This population-based epidemiological study was aimed to evaluate the daily salt intake and its relation to blood pressure in a representative group of Turkish population. The enrolled normotensive and hypertensive individuals (n = 1970) completed a questionnaire including demographics, dietary habits, hypertension awareness and drug usage. Blood pressure was measured and to estimate salt consumption, 24-h urine samples were collected. The daily urinary sodium excretion was 308.3 ± 143.1 mmol/day, equal to a salt intake of 18.01 g/day. Salt intake was higher in obese participants, rural residents, participants with lower education levels and elderly. A positive linear correlation between salt intake and systolic and diastolic blood pressures was demonstrated (r = 0.450, p = 0.020; r = 0.406, p = 0.041; respectively), and each 100 mmol/day of salt intake resulted in 5.8 and 3.8 mmHg increase in systolic and diastolic blood pressures, respectively. Salt intake and systolic blood pressure was significantly correlated in normal weight individuals (r = 0.257, p < 0.01). The Turkish population consumes a great amount of salt; salt intake and blood pressure was positively correlated. Efforts in sodium restriction are therefore crucial in the management of hypertension as part of national and global health policies.

Are all individuals equally sensitive in the blood pressure to high salt intake? (Review article)

It has been reported that only one-third of normotensive subjects and half of hypertensive patients are salt-sensitive. Many causes of salt-sensitivity have been proposed. Our suggestion is that a reduced urinary kallikrein level may be one cause, since mutant kininogen-deficient rats, which cannot generate kinin in the urine, are salt-sensitive. Renal kallikrein is secreted by the connecting tubule cells of the kidney, which are located just distal to the macula densa or the tubuloglomerular feedback system. Excess amounts of sodium taken overflow into the distal tubules and are reabsorbed in the collecting ducts. Kinins generated inhibit sodium reabsorption in the collecting ducts. Both blacks and whites with essential hypertension excrete less urinary kallikrein than do their normotensive counterparts, but the mean value in "normotensive blacks" were not different from that in "hypertensive whites". African-Americans consume less potassium than whites. Potassium and ATP-sensitive potassium channel blockers are releasers of renal kallikrein. In a small-scale study, sodium loading caused more increase in the systolic blood pressure in urinary low-kallikrein group than in urinary high-kallikrein group. Large-scale clinical studies, under strict control of potassium intake, are needed to elucidate the relationship between salt-sensitivity and urinary kallikrein levels.

Recombinant adeno-associated virus-mediated human kallikrein gene therapy prevents high-salt diet-induced hypertension without effect on basal blood pressure

AIM

To investigate the effects of the expression of human kallikrein (HK) on basal level blood pressure and high-salt diet-induced hypertension.

METHODS

We delivered the recombinant adeno-associated viral (rAAV)-mediated HK (rAAV- HK) gene and rAAV-LacZ (as the control) to normal, adult Sprague-Dawley rats. The animals were administered a normal diet in the first 4 weeks, followed by a high-salt diet. The expression of HK in the rats was assessed by ELISA and RT- PCR. Blood pressure and Na+ and K+ urinary excretion were monitored.

RESULTS

Under the normal diet, no obvious changes in blood pressure and Na+ and K+ urinary excretion were observed. When the high-salt diet was administered, systolic blood pressure in the control animals receiving rAAV-LacZ increased from 122.3+/-1.13 mmHg to a stable 142.4+/-1.77 mmHg 8 weeks after the high-salt diet. In contrast, there was no significant increase in the blood pressure in the rAAV-HKtreated group, in which the blood pressure remained at 121.9+/-1.73 mmHg. In the rAAV-HK-treated group, Na+ and K+ urinary excretion were higher compared to those of the control group. The morphological analysis showed that HK delivery remarkably protected against renal damage induced by a high-salt intake.

CONCLUSION

Our study indicates that rAAV-mediated human tissue kallikrein gene delivery is a potentially safe method for the long-term treatment of hypertension. More importantly, it could be applied in the salt-sensitive population to prevent the occurrence of hypertension.

A missing link between a high salt intake and blood pressure increase

It is widely accepted that a high sodium intake triggers blood pressure rise. However, only one-third of the normotensive subjects were reported to show salt-sensitivity in their blood pressure. Many factors have been proposed as causes of salt-sensitive hypertension, but none of them provides a satisfactory explanation. We propose, on the basis of accumulated data, that the reduced activity of the kallikrein-kinin system in the kidney may provide this link. Renal kallikrein is secreted by the distal connecting tubular cells and all kallikrein-kinin system components are distributed along the collecting ducts in the distal nephron. Bradykinin generated is immediately destroyed by carboxypeptidase Y-like exopeptidase and neutral endopeptidase, both quite independent from the kininases in plasma, such as angiotensin converting enzyme. The salt-sensitivity of the blood pressure depends largely upon ethnicity and potassium intake. Interestingly, potassium and ATP-sensitive potassium (K(ATP)) channel blockers accelerate renal kallikrein secretion and suppress blood pressure rises in animal hypertension models. Measurement of urinary kallikrein may become necessary in salt-sensitive normotensive and hypertensive subjects. Furthermore, pharmaceutical development of renal kallikrein releasers, such as K(ATP) channel blockers, and renal kininase inhibitors, such as ebelactone B, may lead to the development of novel antihypertensive drugs.

Blood pressure and hemodynamic responses to an acute sodium load in humans

The purpose of this study was to investigate the acute blood pressure (BP) and hemodynamic effects of sodium chloride (3% intravenous solution). Although many studies link a change in dietary sodium to a change in BP, few consider the effects of sodium concentration in the blood on BP. We hypothesized that an intravenous sodium load would increase BP, and we quantified alterations in cardiac output (Qc) and peripheral vascular resistance (PVR). Thirteen subjects (age 27 +/- 2 yr) underwent a 60-min 3% saline infusion (0.15 ml.kg(-1).min(-1)). BP was assessed on a beat-to-beat basis with a Finometer, Qc was assessed via the CO(2) rebreathing technique, and PVR was derived. Serum sodium and osmolality increased, and hematocrit declined during the infusion (ANOVA, P < 0.01). Mean arterial pressure (MAP) increased continuously during the infusion from 81.8 +/- 3.4 to 91.6 +/- 3.6 mmHg (ANOVA, P < 0.01). BP responsiveness to sodium was expressed as the slope of the serum sodium-MAP relationship and averaged 1.75 +/- 0.34 mmHg.mmol(-1).l(-1). BP responsiveness to the volume change was expressed as the slope of the hematocrit-MAP relationship and averaged -2.2 +/- 0.35 mmHg/%. The early change in MAP was mediated by an increase in Qc and the late change by an increase in PVR (P < 0.05), corresponding to a 30% increase in plasma norepinephrine. In conclusion, an acute infusion of hypertonic saline was effective in increasing BP, and both sodium and volume appear to be involved in this increase; acute BP responsiveness to serum sodium can be quantified using a MAP-sodium plot.