Salt consumption increases blood pressure and abolishes the light/dark rhythm in angiotensin AT1a receptor deficient mice

Relationship between beliefs regarding a low salt diet in chronic renal failure patients on dialysis

OBJECTIVE

The aim of this study was to investigate the relationship between beliefs regarding a low salt diet and the nutritional behavior of sodium consumption as well their relation with sociodemographic and clinical variables among chronic renal failure (CRF) patients on dialysis.

DESIGN AND METHODS

This cross-sectional study enrolled a sample of 117 patients who answered the Brazilian version of the Beliefs about Dietary Compliance Scale (BDCS), the sodium frequency food questionnaire, and the use of discretionary salt/day.

RESULTS

The average of total salt consumption was 10.6 g/day (±6.3) and it was positively correlated with the interdialytic weight gain (r = 0.20 P = .032) and negatively correlated with the education level (r = -0.19 P = .044). The Benefits beliefs were discriminatory of the higher and lower salt consumers, and proportionally related to monthly income (r = 0.22 P = .017). The Barriers beliefs were positively correlated only to time on dialysis (r = 0.25 P = .008). Subjects with lower schooling and those of older age tended to consume more discretionary salt (r = -0.27, P = .005; r = 0.23, P = .016, respectively); however, they reported a lower consumption of foods with high salt content (r = 0.25 P = .006; r = -0.27 P = .004).

CONCLUSIONS

Educational interventions aimed at reducing salt consumption for this group must include interventions targeted at different behaviors related to overall salt consumption, the specificities of age, and level of schooling of the patients.

The day-night difference of blood pressure is increased in AT(1A)-receptor knockout mice on a high-sodium diet

BACKGROUND

Abnormal circadian variation of blood pressure (BP) increases cardiovascular risk. In this study, we examined the influence of angiotensin AT(1A) receptors on circadian BP variation, and specifically on its behavioral activity-related and -unrelated components.

METHODS

BP and locomotor activity were recorded by radiotelemetry in AT(1A)-receptor knockout mice (AT(1A)(-/-)) and their wild-type controls (AT(1A)(+/+)) placed on a normal-salt diet (NSD) or high-salt diet (HSD, 3.1% Na).

RESULTS

The 24-h BP was lower in AT(1A)(-/-) than AT(1A)(+/+) mice on a NSD (92 +/- 2 and 118 +/- 2 mm Hg, respectively), whereas the day-night BP difference (DeltaDNBP) was similar between groups (11 +/- 2 and 12 +/- 1 mm Hg, respectively). HSD increased BP by 20 +/- 2 mm Hg and DeltaDNBP by 7 +/- 1 mm Hg in AT(1A)(-/-) mice, without affecting these parameters much in AT(1A)(+/+) mice. The DeltaDNBP increase in AT(1A)(-/-) mice was caused by nondipping BP during the inactive late-dark period. Conversely, BP rise associated with circadian behavioral activation during the early dark period was not altered by HSD in AT(1A)(-/-) mice. The BP change associated with spontaneous ultradian activity-inactivity bouts was also similar between strains on HSD as was the BP rise associated with induced (cage-switch) behavioral activity. Ganglionic or alpha(1)-adrenergic blockade decreased BP in both strains; HSD did not affect this response in AT(1A)(-/-), but abolished it in AT(1A)(+/+) mice.

CONCLUSIONS

AT(1A)-receptor deficiency, when combined with HSD, can increase circadian BP difference in mice. This increase is mediated principally by activity-unrelated factors, such as the nonsuppressibility of basal resting sympathetic tone by HSD, thus suggesting a form of salt-/volume-dependent hypertension.

Pressed for time: the circadian clock and hypertension

Hypertension is a major risk factor for cardiovascular disease and death. The "silent" rise of blood pressure that occurs over time is largely asymptomatic. However, its impact is deafening-causing and exacerbating cardiovascular disease, end-organ damage, and death. The present article addresses recent observations from human and animal studies that provide new insights into how the circadian clock regulates blood pressure, contributes to hypertension, and ultimately evolves vascular disease. Further, the molecular components of the circadian clock and their relationship with locomotor activity, metabolic control, fluid balance, and vascular resistance are discussed with an emphasis on how these novel, circadian clock-controlled mechanisms contribute to hypertension.