Circadian rhythm of urinary potassium excretion during treatment with an angiotensin receptor blocker

Associations between dietary potassium intake and urinary potassium excretion: a protocol for systematic review and meta-analysis

BACKGROUND

While numerous studies have reported associations between low dietary potassium intake and adverse clinical outcomes, methods to estimate potassium intake, mainly self-reported dietary measures and urinary potassium excretion, entail certain limitations. Self-reported measures are subject to underreporting and overreporting. Urinary potassium excretion is affected by multiple factors including renal function. Revealing the degree of bias inherent in these measures would help accurately assess potassium intake and its association with disease risk. We aim to summarize evidence on the strength of the associations between potassium intake estimated from 24-h urinary potassium excretion and potassium intake estimated from self-reported dietary measures or objective quantification methods in populations with different kidney function levels and age groups. We also aim to identify factors that affect the association strength.

METHODS

We will search for potentially eligible studies that examined associations between self-reported potassium intake, 24-h urinary potassium excretion, and objectively quantified potassium intake, using MEDLINE (PubMed), Embase, Web of Science, and Scopus. Studies on children, adolescents, adults, and the elderly are eligible. Studies of patients on dialysis will be excluded. Collective study results, including a meta-analysis, will be synthesized if an adequate number of studies examining similar dietary potassium intake estimation methods are found. Analyses will be performed separately according to age groups and renal function. For the meta-analysis, fixed-effects or random-effect models will be employed depending on the degree of study heterogeneity to combine across studies the correlation coefficient, ratio, or standardized mean difference for potassium intake, comparing dietary potassium intake based on self-reported or objectively quantified methods and intake based on 24-h urinary potassium excretion. The degree of heterogeneity among included studies will be examined by calculating I2 statistics. To investigate sources of study heterogeneity, random-effects meta-regression analyses will be performed.

DISCUSSION

Revealing the strength of the association between dietary and urinary measures in populations with different levels of kidney function and age groups will enhance researchers' and clinicians' ability to interpret studies that utilize these measures and help establish a more solid evidence base for the role of potassium intake in changing chronic disease risk. Identifying factors that modify the associations between these measures may aid in developing predictive models to estimate actual potassium intake.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022357847.

Sodium balance, circadian BP rhythm, heart rate variability, and intrarenal renin-angiotensin-aldosterone and dopaminergic systems in acute phase of ARB therapy

We have revealed that even in humans, activated intrarenal renin–angiotensin–aldosterone system (RAAS) enhances tubular sodium reabsorption to facilitate salt sensitivity and nondipper rhythm of blood pressure (BP), and that angiotensin receptor blocker (ARB) could increase daytime urinary sodium excretion rate (U_NaV) to produce lower sodium balance and restore nondipper rhythm. However, the sympathetic nervous system and intrarenal dopaminergic system can also contribute to renal sodium handling. A total of 20 patients with chronic kidney disease (61 ± 15 years) underwent 24‐h ambulatory BP monitoring before and during two‐day treatment with ARB, azilsartan. Urinary angiotensinogen excretion rate (U_AGTV, μg/gCre) was measured as intrarenal RAAS; urinary dopamine excretion rate (U_DAV, pg/gCre) as intrarenal dopaminergic system; heart rate variabilities (HRV, calculated from 24‐h Holter‐ECG) of non‐Gaussianity index λ_25s as sympathetic nerve activity; and power of high‐frequency (HF) component or deceleration capacity (DC) as parasympathetic nerve activity. At baseline, glomerular filtration rate correlated inversely with U_AGTV (r = −0.47, P = 0.04) and positively with U_DAV (r = 0.58, P = 0.009). HF was a determinant of night/day BP ratio (β = −0.50, F = 5.8), rather than DC or λ_25s. During the acute phase of ARB treatment, a lower steady sodium balance was not achieved. Increase in daytime U_NaV preceded restoration of BP rhythm, accompanied by decreased U_AGTV (r = −0.88, P = 0.05) and increased U_DAV (r = 0.87, P = 0.05), but with no changes in HRVs. Diminished sodium excretion can cause nondipper BP rhythm. This was attributable to intrarenal RAAS and dopaminergic system and impaired parasympathetic nerve activity. During the acute phase of ARB treatment, cooperative effects of ARB and intrarenal dopaminergic system exert natriuresis to restore circadian BP rhythm.

Addition of hydrochlorothiazide to angiotensin receptor blocker therapy can achieve a lower sodium balance with no acceleration of intrarenal renin angiotensin system in patients with chronic kidney disease

Objective:

Angiotensin receptor blockers (ARBs) produce a lower sodium (Na) balance, and the natriuretic effect is enhanced under Na deprivation, despite falls in blood pressure (BP) and glomerular filtration rate (GFR).

Methods:

The effect of additional hydrochlorothiazide (HCTZ; 12.5 mg/day) to ARB treatment (valsartan; 80 mg/day) on glomerulotubular Na balance was evaluated in 23 patients with chronic kidney disease.

Results:

Add-on HCTZ decreased GFR, tubular Na load, and tubular Na reabsorption (t_Na), although 24-hour urinary Na excretion (U_NaV) remained constant. Daily urinary angiotensinogen excretion (U_AGTV, 152±10→82±17 μg/g Cre) reduced (p=0.02). Changes in tubular Na load (r²=0.26) and t_Na (r²=0.25) correlated with baseline 24-hour U_AGTV. Changes in filtered Na load correlated with changes in nighttime systolic BP (r²=0.17), but not with changes in daytime systolic BP. The change in the t_Na to filtered Na load ratio was influenced by the change in daytime U_NaV (β=−0.67, F=16.8), rather than the change in nighttime U_NaV.

Conclusions:

Lower Na balance was produced by add-on HCTZ to ARB treatment without an increase of intra-renal renin-angiotensin system activity, leading to restoration of nocturnal hypertension. A further study is needed to demonstrate that the reduction of U_AGTV by additional diuretics to ARBs prevents the progression of nephropathy or cardiovascular events.

Molecular bases of circadian rhythmicity in renal physiology and pathology

The physiological processes that maintain body homeostasis oscillate during the day. Diurnal changes characterize kidney functions, comprising regulation of hydro-electrolytic and acid-base balance, reabsorption of small solutes and hormone production. Renal physiology is characterized by 24-h periodicity and contributes to circadian variability of blood pressure levels, related as well to nychthemeral changes of sodium sensitivity, physical activity, vascular tone, autonomic function and neurotransmitter release from sympathetic innervations. The circadian rhythmicity of body physiology is driven by central and peripheral biological clockworks and entrained by the geophysical light/dark cycle. Chronodisruption, defined as the mismatch between environmental-social cues and physiological-behavioral patterns, causes internal desynchronization of periodic functions, leading to pathophysiological mechanisms underlying degenerative, immune related, metabolic and neoplastic diseases. In this review we will address the genetic, molecular and anatomical elements that hardwire circadian rhythmicity in renal physiology and subtend disarray of time-dependent changes in renal pathology.