High salt-induced hypertension in B2 knockout mice is corrected by the ETA antagonist, A127722

Dietary sodium induces a redistribution of the tubular metabolic workload

Key points

Body Na⁺ content is tightly controlled by regulated urinary Na⁺ excretion.

The intrarenal mechanisms mediating adaptation to variations in dietary Na⁺ intake are incompletely characterized.

We confirmed and expanded observations in mice that variations in dietary Na⁺ intake do not alter the glomerular filtration rate but alter the total and cell‐surface expression of major Na⁺ transporters all along the kidney tubule.

Low dietary Na⁺ intake increased Na⁺ reabsorption in the proximal tubule and decreased it in more distal kidney tubule segments.

High dietary Na⁺ intake decreased Na⁺ reabsorption in the proximal tubule and increased it in distal segments with lower energetic efficiency.

The abundance of apical transporters and Na⁺ delivery are the main determinants of Na⁺ reabsorption along the kidney tubule.

Tubular O₂ consumption and the efficiency of sodium reabsorption are dependent on sodium diet.

Abstract

Na⁺ excretion by the kidney varies according to dietary Na⁺ intake. We undertook a systematic study of the effects of dietary salt intake on glomerular filtration rate (GFR) and tubular Na⁺ reabsorption. We examined the renal adaptive response in mice subjected to 7 days of a low sodium diet (LSD) containing 0.01% Na⁺, a normal sodium diet (NSD) containing 0.18% Na⁺ and a moderately high sodium diet (HSD) containing 1.25% Na⁺. As expected, LSD did not alter measured GFR and increased the abundance of total and cell‐surface NHE3, NKCC2, NCC, α‐ENaC and cleaved γ‐ENaC compared to NSD. Mathematical modelling predicted that tubular Na⁺ reabsorption increased in the proximal tubule but decreased in the distal nephron because of diminished Na⁺ delivery. This prediction was confirmed by the natriuretic response to diuretics targeting the thick ascending limb, the distal convoluted tubule or the collecting system. On the other hand, HSD did not alter measured GFR but decreased the abundance of the aforementioned transporters compared to NSD. Mathematical modelling predicted that tubular Na⁺ reabsorption decreased in the proximal tubule but increased in distal segments with lower transport efficiency with respect to O₂ consumption. This prediction was confirmed by the natriuretic response to diuretics. The activity of the metabolic sensor adenosine monophosphate‐activated protein kinase (AMPK) was related to the changes in tubular Na⁺ reabsorption. Our data show that fractional Na⁺ reabsorption is distributed differently according to dietary Na⁺ intake and induces changes in tubular O₂ consumption and sodium transport efficiency.

Body Na⁺ content is tightly controlled by regulated urinary Na⁺ excretion.

The intrarenal mechanisms mediating adaptation to variations in dietary Na⁺ intake are incompletely characterized.

We confirmed and expanded observations in mice that variations in dietary Na⁺ intake do not alter the glomerular filtration rate but alter the total and cell‐surface expression of major Na⁺ transporters all along the kidney tubule.

Low dietary Na⁺ intake increased Na⁺ reabsorption in the proximal tubule and decreased it in more distal kidney tubule segments.

High dietary Na⁺ intake decreased Na⁺ reabsorption in the proximal tubule and increased it in distal segments with lower energetic efficiency.

The abundance of apical transporters and Na⁺ delivery are the main determinants of Na⁺ reabsorption along the kidney tubule.

Tubular O₂ consumption and the efficiency of sodium reabsorption are dependent on sodium diet.

Reduced MLH3 Expression in the Syndrome of Gan-Shen Yin Deficiency in Patients with Different Diseases

Traditional Chinese medicine formulates treatment according to body constitution (BC) differentiation. Different constitutions have specific metabolic characteristics and different susceptibility to certain diseases. This study aimed to assess the characteristic genes of gan-shen Yin deficiency constitution in different diseases. Fifty primary liver cancer (PLC) patients, 94 hypertension (HBP) patients, and 100 diabetes mellitus (DM) patients were enrolled and classified into gan-shen Yin deficiency group and non-gan-shen Yin deficiency group according to the body constitution questionnaire to assess the clinical manifestation of patients. The mRNA expressions of 17 genes in PLC patients with gan-shen Yin deficiency were different from those without gan-shen Yin deficiency. However, considering all patients with PLC, HBP, and DM, only MLH3 was significantly lower in gan-shen Yin deficiency group than that in non-gen-shen Yin deficiency. By ROC analysis, the relationship between MLH3 and gan-shen Yin deficiency constitution was confirmed. Treatment of MLH3 (-/- and -/+) mice with Liuweidihuang wan, classical prescriptions for Yin deficiency, partly ameliorates the body constitution of Yin deficiency in MLH3 (-/+) mice, but not in MLH3 (-/-) mice. MLH3 might be one of material bases of gan-shen Yin deficiency constitution.

New insights into sodium transport regulation in the distal nephron: Role of G-protein coupled receptors

The renal handling of Na⁺ balance is a major determinant of the blood pressure (BP) level. The inability of the kidney to excrete the daily load of Na⁺ represents the primary cause of chronic hypertension. Among the different segments that constitute the nephron, those present in the distal part (i.e., the cortical thick ascending limb, the distal convoluted tubule, the connecting and collecting tubules) play a central role in the fine-tuning of renal Na⁺ excretion and are the target of many different regulatory processes that modulate Na⁺ retention more or less efficiently. G-protein coupled receptors (GPCRs) are crucially involved in this regulation and could represent efficient pharmacological targets to control BP levels. In this review, we describe both classical and novel GPCR-dependent regulatory systems that have been shown to modulate renal Na⁺ absorption in the distal nephron. In addition to the multiplicity of the GPCR that regulate Na⁺ excretion, this review also highlights the complexity of these different pathways, and the connections between them.

Acute nitric oxide synthase inhibition and endothelin-1-dependent arterial pressure elevation

Key evidence that endogenous nitric oxide (NO) inhibits the continuous, endothelin (ET)-1-mediated drive to elevate arterial pressure includes demonstrations that ET-1 mediates a significant component of the pressure elevated by acute exposure to NO synthase (NOS) inhibitors. This review examines the characteristics of this pressure elevation in order to elucidate potential mechanisms associated with the negative regulation of ET-1 by NO and, thereby, provide potential insight into the vascular pathophysiology underlying NO dysregulation. We surmise that the magnitude of the ET-1-dependent component of the NOS inhibitor-elevated pressure is (1) independent of underlying arterial pressure and other pressor pathways activated by the NOS inhibitors and (2) dependent on relatively higher NOS inhibitor dose, release of stored and de novo synthesized ET-1, and ET_A receptor-mediated increased vascular resistance. Major implications of these conclusions include: (1) the marked variation of the ET-1-dependent component, i.e., from 0 to 100% of the pressure elevation, reflects the NO-ET-1 regulatory pathway. Thus, NOS inhibitor-mediated, ET-1-dependent pressure elevation in vascular pathophysiologies is an indicator of the level of compromised/enhanced function of this pathway; (2) NO is a more potent inhibitor of ET-1-mediated elevated arterial pressure than other pressor pathways, due in part to inhibition of intravascular pressure-independent release of ET-1. Thus, the ET-1-dependent component of pressure elevation in vascular pathophysiologies associated with NO dysregulation is of greater magnitude at higher levels of compromised NO.

Genetic manipulation and genetic variation of the kallikrein-kinin system: impact on cardiovascular and renal diseases

Genetic manipulation of the kallikrein-kinin system (KKS) in mice, with either gain or loss of function, and study of human genetic variability in KKS components which has been well documented at the phenotypic and genomic level, have allowed recognizing the physiological role of KKS in health and in disease. This role has been especially documented in the cardiovascular system and the kidney. Kinins are produced at slow rate in most organs in resting condition and/or inactivated quickly. Yet the KKS is involved in arterial function and in renal tubular function. In several pathological situations, kinin production increases, kinin receptor synthesis is upregulated, and kinins play an important role, whether beneficial or detrimental, in disease outcome. In the setting of ischemic, diabetic or hemodynamic aggression, kinin release by tissue kallikrein protects against organ damage, through B2 and/or B1 bradykinin receptor activation, depending on organ and disease. This has been well documented for the ischemic or diabetic heart, kidney and skeletal muscle, where KKS activity reduces oxidative stress, limits necrosis or fibrosis and promotes angiogenesis. On the other hand, in some pathological situations where plasma prekallikrein is inappropriately activated, excess kinin release in local or systemic circulation is detrimental, through oedema or hypotension. Putative therapeutic application of these clinical and experimental findings through current pharmacological development is discussed in the chapter.