Extracellular Fluid Volume Expansion Research Articles

Deoxycorticosterone-acetate salt-sensitive hypertension initiates with intracellular K+ and water loss

Background: Textbook teaching pretends that Na+-driven extracellular fluid and blood volume expansion may cause hypertension. We tested the alternative hypothesis, namely that K+ loss-driven intracellular volume contraction causes hypertension. Methods: We tested the effect of deoxycorticosterone acetate (DOCA; 25 mg pellet) in mice on low Na+ diet (0.02-0.03%) without (tap water), or with Na+ in their drinking water (1% NaCl or 1.44% NaHCO3). We measured BP with radio-telemetry, and analysed body Na+, K+, and water content 2, 6, and 12 days after initiation of DOCA treatment. We monitored food intake, solute and water excretion in urine and stool, and quantified renal and cutaneous blood flow by pulse-wave/laser Doppler spectroscopy. Results: DOCA NaCl treatment initially reduced intracellular K+ and water content, and elevated BP without accompanying Na+ retention. To re-hydrate the intracellular volume space, hypertensive DOCA NaCl−treated mice secondarily replaced lost intracellular K+ by Na+ solutes, increased fluid intake, reduced renal solute-free water clearance, constricted renal blood vessels, and reduced dermal blood flow. Normotensive DOCA NaHCO3-treated mice similarly lost intracellular K+, but immediately compensated by intracellular Na+ accumulation, and therefore experienced no intracellular volume contraction. Without prolonged under-hydration of their K+-space, DOCA NaHCO3-treated mice neither showed augmentation of renal or dermal water conservation, nor vasoconstriction and blood flow reduction, and their BP remained normal despite body Na+ excess. Conclusions: DOCA salt-sensitive hypertension is caused by K+-driven under-hydration, and not by Na+-driven over-hydration. The BP increase is explainable by secondary-adaptive multi-organ water conservation physiology, but not by Na+-driven water excretion physiology. National Medical Research Council (NMRC) of Singapore to the Duke-NUS Medical School, the German Federal Ministry for Economics and Technology/DLR Forschung unter Weltraumbedingungen (Mars500-III; 50WB2024). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 11373: Suppression of Plasma Angiotensin II by GLP-1 in Humans is Independent of Changes in Plasma Angiotensinogen

Introduction: In humans, the natriuretic effect of GLP-1 depends on GLP-1 receptor interaction, is independent of changes in renal blood flow, renin, ANP, and aldosterone but is accompanied by suppression of angiotensin II (ANGII). The mechanism by which GLP-1 reduces ANGII independently of changes in renin is not clarified. Hypothesis: It was hypothesized that GLP-1 suppresses renin substrate, angiotensinogen, in plasma. Methods: To test this proposal, we measured arterial angiotensinogen concentration in biobanked plasma samples from healthy males during a 3-hour GLP-1 infusion that induced natriuresis (1). Samples were from a study with fixed sodium intake where eight healthy men were examined twice in random order during a 3-hour infusion of either GLP-1(1.5 pmol kg -1 min -1 ) or vehicle together with an intravenous infusion of 0.9% NaCl (750 mL/hour). Arterial plasma angiotensinogen was measured in plasma by dilution (1:200) and addition of excess exogenous human renin (Inst. Of Biological Standards UK). After prolonged incubation, ANGI was quantified by radioimmunoassay. Intraassay variation was 9-12%. Results: Arterial plasma angiotensinogen and renin levels decreased similarly and modestly (~15 and ~30%, respectively) after NaCl infusion during both studies whereas ANGII levels decreased significantly (~25%) only during GLP-1 infusion. Conclusions: Suppression of plasma angiotensinogen is less likely to account for GLP-1-mediated ANGII suppression in healthy young males. In perspective, GLP-1 could enhance pathways of ANGII degradation rather than inhibit its formation. 1. Asmar A et al. Extracellular fluid volume expansion uncovers a natriuretic action of GLP-1: a functional GLP-1-renal axis in man. J Clin Endocrinol Metab. 2019 Jul 1;104(7):2509-2519.

1652-P: Suppression of Plasma Angiotensin II by GLP-1 in Humans Is Independent of Changes in Plasma Angiotensinogen

In humans, the natriuretic effect of GLP-1 depends on GLP-1 receptor interaction, is independent of changes in renal blood flow, renin, ANP, and aldosterone but is accompanied by suppression of angiotensin II (ANGII). The mechanism by which GLP-1 reduces ANGII independently of changes in renin is not clarified. It was hypothesized that GLP-1 suppresses renin substrate, angiotensinogen, in plasma. To test this proposal, we measured arterial angiotensinogen concentration in biobanked plasma samples from healthy males during a 3-hour GLP-1 infusion that induced natriuresis (1). Samples were from a study with fixed sodium intake where eight healthy men were examined twice in random order during a 3-hour infusion of either GLP-1(1.5 pmol kg-1 min-1) or vehicle together with an intravenous infusion of 0.9% NaCl (750 mL/hour). Arterial plasma angiotensinogen was measured in plasma by dilution (1:200) and addition of excess exogenous human renin (Inst. of Biological Standards UK). After prolonged incubation, ANGI was quantified by radioimmunoassay. Intraassay variation was 9-12%. Arterial plasma angiotensinogen and renin levels decreased similarly and modestly (~15 and ~30%, respectively) after NaCl infusion during both studies whereas ANGII levels decreased significantly (~25%) only during GLP-1 infusion. Suppression of plasma angiotensinogen is less likely to account for GLP-1-mediated ANGII suppression in healthy young males. In perspective, GLP-1 could enhance pathways of ANGII degradation rather than inhibit its formation. 1. Asmar A et al. Extracellular fluid volume expansion uncovers a natriuretic action of GLP-1: a functional GLP-1-renal axis in man. J Clin Endocrinol Metab. 2019 Jul 1;104(7):2509-2519. Disclosure B.L.Jensen: None. A.Asmar: Research Support; Novo Nordisk A/S.

ABSENT VASOREACTIVE RESPONSE TO HIGH SODIUM INTAKE COINCIDES WITH SALT SENSITIVITY IN CKD PATIENTS

Objective: Chronic kidney disease (CKD) patients are advised to limit salt intake, because of its detrimental effects on blood pressure (BP) and albuminuria. The salt-sensitive BP response in CKD is classically attributed to impaired renal ability to excrete sodium (Na+) resulting in fluid overload. Yet, BP sensitivity to salt is also linked to vasodysfuction, and may even be fluid independent. We aimed to investigate which factor contributes to BP sensitivity to salt in CKD. Design and method: In this randomized crossover study, CKD patients (KDIGO stage G2-3A, proteinuria >0.5 g/d) and healthy controls (HC) followed a 7-day low sodium diet (LSD, <50mmol/d) and high sodium diet (HSD, >200mmol/d), respectively. After each diet, assessment of the hemodynamic profile included daytime BP (Mobil-O-Graph) and cardiac output (CO) measurements (using NexfinTM), by which SVR was calculated accordingly. Extracellular fluid volume (ECV) change was assessed with multi-frequency body impedance spectroscopy (FHCresenius). Results: We included 16 HC (median age 36.0 yrs) and 8 CKD patients (median age 49.5 yrs, and median (IQR) proteinuria 0.6 (0.5-1.1) g/d and plasma creatinine 144 (103 - 167) μmol/l. Dietary salt intervention was successful with median difference in urine Na+ excretion of 242.2 vs 224.6 mmol/day in HC and CKD respectively (p = 0.74). After HSD, the median (IQR) change in systolic BP of patients with CKD was 14 mmHg (4 - 18; p = 0.04), while systolic BP change (4 mmHg (-3 - 8)) in HC was not significant (Fig 1A). After HSD, we observed a significant ECV expansion in both CKD and HC subjects (Fig 1B), but no effect on CO. No associations between HSD-induced BP changes and both ECV and CO were found. Systolic BP increase was correlated with SVR decline in HC, but not in CKD patients (Fig 1C). Conclusions: In contrast to healthy persons, BP salt sensitivity in CKD does not associate with vasodilation. Regarding the absence of differences with ECV and CO between healthy and CKD persons, our data indicate that the incapacity for vasodilation might explain salt sensitivity in CKD.

Urine Di-(2-ethylhexyl) Phthalate Metabolites Are Independently Related to Body Fluid Status in Adults: Results from a U.S. Nationally Representative Survey

Purpose: Di-(2-ethylhexyl) phthalate (DEHP) has been utilized in many daily products for decades. Previous studies have reported that DEHP exposure could induce renin–angiotensin–aldosterone system activation and increase epithelial sodium channel (ENaC) activity, which contributes to extracellular fluid (ECF) volume expansion. However, there is also no previous study to evaluate the association between DEHP exposure and body fluid status. Methods: We selected 1678 subjects (aged ≥18 years) from a National Health and Nutrition Examination Survey (NHANES) in 2003–2004 to determine the relationship between urine DEHP metabolites and body composition (body measures, bioelectrical impedance analysis (BIA)). Results: After weighing the sampling strategy in multiple linear regression analysis, we report that higher levels of DEHP metabolites are correlated with increases in body measures (body weight, body mass index (BMI), waist circumference), BIA parameters (estimated fat mass, percent body fat, ECF, and ECF/intracellular fluid (ICF) ratio) in multiple linear regression analysis. The relationship between DEHP metabolites and the ECF/ICF ratio was more evident in subjects of younger age (20–39 years old), women, non-Hispanic white ethnicity, and subjects who were not active smokers. Conclusion: In addition to being positively correlated with body measures and body fat, we found that urine DEHP metabolites were positively correlated with ECF and the ECF/ICF ratio in the US general adult population. The finding implies that DEHP exposures might increase ECF volume and the ECF/ICF ratio, which may have adverse health outcomes on the cardiovascular system. Further research is needed to clarify the causal relationship.

The Wright Variation of the Darrow‐Yannet Diagram: A New Tool to Teach Water Homeostasis

PurposeTo introduce an expanded version of the Darrow‐Yannet (D‐Y) diagram that can both improve basic understanding of water balance homeostasis and be more specifically applied to specific organ system topics (e.g., gastrointestinal secretion) than can the basic diagram.Introduction and hypothesisSince 1935, the Darrow‐Yannet diagram has been used to teach both water balance and homeostasis. Six models of ECF volume expansion or contraction of hypertonic, isotonic, or hypotonic fluid with subsequent water transfer to or from ICF show how ECF and ICF remain in balance. Yet when osmosis is used later in both gastrointestinal and renal physiology to describe movement of water from spaces that are technically outside the body into or out of part of the extracellular fluid compartment, students sometimes struggle with the concept of osmosis (water diffusion between compartments) not from ECF to ICF but from ECF to OB and back. They must also consider that through both structural characteristics of the epithelium and the autonomic and hormonal control of epithelium function, this water transfer can be considerably modified or even prevented. Because the classic D‐Y has no OB in its illustrations, it cannot be used to show either of these aspects of water balance. The question therefore arose, is there some way to expand the D‐Y diagram to show both, and emphasize other aspects of homeostasis too? The author hypothesized that it could be done.ResultIn the Wright variation of the D‐Y diagram, two changes are made to expand the D‐Y diagram and increase its usefulness. First, an OB compartment of open volume is introduced on the one side of the ECF while keeping ICF on the other side as usual. Second, the epithelial layer between OB and ECF is artificially widened so that it is both more easily visualized and potentially drawn with two cell populations (e.g., secretory vs. absorptive cells lining the duodenal lumen). Though volume is undefined in the OB compartment, osmolarity is defined, ranging from zero (pure water) to immeasurably high (dry), so osmotic OB‐to‐ECF gradients can be seen. Using control of the epithelium to determine whether fluid flows through or not regardless of gradient, nervous and hormonal control of water homeostasis can be shown. Finally, not just water movement but hormonal‐ or autonomic‐controlled ion movement across the epithelium can be graphically shown, showing off an important aspect of homeostasis. Loss of control of these ion movements (e.g., in GI secretory cells in cholera) can also be demonstrated, along with its pathophysiological effect.ConclusionAn expanded D‐Y diagram with an artificially emphasized epithelial layer between an outside‐the‐body (OB) compartment and the extracellular fluid (ECF) has the potential to better illustrate the epithelium’s possible control in expanding or contracting ECF volume prior to ICF change than can a D‐Y diagram alone, both in health and disease.

Determinants of hypokalemia following hypertonic sodium bicarbonate infusion.

The hypokalemic response to alkali infusion has been attributed to the resulting extracellular fluid (ECF) expansion, urinary potassium excretion, and internal potassium shifts, but the dominant mechanism remains uncertain. Hypertonic NaHCO3 infusion (1 N, 5 mmol/kg) to unanesthetized dogs with normal acid-base status or one of the four chronic acid-base disorders decreased plasma potassium concentration ([K+]p) at 30 min in all study groups (Δ[K+]p, - 0.16 to - 0.73 mmol/L), which remained essentially unaltered up to 90-min postinfusion. ECF expansion accounted for only a small fraction of the decrease in ECF potassium content, (K+)e. Urinary potassium losses were large in normals and chronic respiratory acid-base disorders, limited in chronic metabolic alkalosis, and minimal in chronic metabolic acidosis, yet, ongoing kaliuresis did not impact the stability of [K+]p. All five groups experienced a reduction in (K+)e at 30-min postinfusion, Δ(K+)e remaining unchanged thereafter. Intracellular fluid (ICF) potassium content, (K+)i, decreased progressively postinfusion in all groups excluding chronic metabolic acidosis, in which a reduction in (K+)e was accompanied by an increase in (K+)i. We demonstrate that hypokalemia following hypertonic NaHCO3 infusion in intact animals with acidemia, alkalemia, or normal acid-base status and intact or depleted potassium stores is critically dependent on mechanisms of internal potassium balance and not ECF volume expansion or kaliuresis. We envision that the acute NaHCO3 infusion elicits immediate ionic shifts between ECF and ICF leading to hypokalemia. Thereafter, maintenance of a relatively stable, although depressed, [K+]e requires that cells release potassium to counterbalance ongoing urinary potassium losses.

Hypernatremia in the intensive care unit.

Hypernatremia is a relatively frequent electrolyte disorder seen in critically ill patients. As many as 27% of patients in intensive care units (ICUs) develop hypernatremia of variable severity during an ICU stay. Debate among specialists often ensues as to whether to correct hypernatremia or not. Some practitioners, particularly intensivists, believe that correction of hypernatremia with fluids may cause expansion of the extracellular fluid volume (ECFV) thereby worsening ventilation and impeding extubation. Other practitioners, including many nephrologists, do not expect correction of hypernatremia to lead to clinically apparent ECFV expansion, and fear other deleterious effects of hypernatremia. In this review we address the controversy regarding appropriate practice. There are no randomized, clinical trials (RCTs) to guide the administration of electrolyte-free fluid administration in hypernatremic patients. However, there are associations, demonstrated in the literature, suggesting that hypernatremia of any severity will increase the mortality and length of stay in these patients. These associations generally support the practice of correction of hypernatremia. In addition, our knowledge of the distribution of total body water influences us towards correcting hypernatremia as an appropriate therapy. We do not expect that adequate RCTs addressing this question will be performed. Allowing persistence of any degree of hypernatremia is associated with increased mortality, length of stay (LOS) and postdischarge mortality. We expect that proper use of electrolyte-free water intake will avoid adverse outcomes.

Abstract 10884: B-Cell-Mediated Sodium and Water Retention Contributes to Heart Failure Pathogenesis

Background: B-cells have been shown to serve pathogenic roles in heart failure through cardiac-specific monocyte mobilization and autoantibody deposition. Beyond this, we recently showed that mice with hypomorphic c-Myb activity ( c-myb h/h ) have reduced B-cells and that B-cell deficiency is associated with increased sodium- and water-excretion and reduced blood pressure. Here, we determine the relevance of these responses in an experimental model of heart failure. Methods & Results: C57BL/6J wild-type (WT) and B-cell deficient c-myb h/h mice (male and female; aged 10-12 weeks) underwent either: (i) permanent LAD ligation to induce myocardial infarction (MI); or (ii) sham surgery. Echocardiography showed that B-cell deficiency preserved ejection fraction (53±2 vs. 44±2 %; N=6-7/group; P<0.01) and limited pathologic remodeling with reduced LVID (end-diastolic: 4.9±0.1 vs. 5.5±0.1 mm; N=6-7/group; P<0.01; end-systolic: 3.8±0.2 vs. 4.5±0.1 mm; N=6-7/group; P<0.001) at 4-weeks post-MI compared to WT. Heart weight/tibia length and right lung weight/tibia length ratios (g/mm; P<0.01), as well as pleural effusion volumes (μl; P<0.05) were increased post-MI in WT, rather than c-myb h/h mice. Indeed, mice with B-cell deficiency manifest reduced right lung weight/tibia length ratio (0.005±0.000 vs. 0.009±0.001 g/mm; N=5-6/group; P<0.01) and pleural effusion volume (17±6 vs. 55±18 μl; N=6-7/group; P<0.06) post-MI compared to WT. Underlying this decongestion, metabolic cage studies revealed that B-cell deficient mice had sustained increases in 24-h urine volume/body weight and 24-h sodium excretion/body weight ratios, which correlated with ejection fraction 4-weeks post-MI (r=0.53; N=13 pairs; P<0.05; and r=0.50; N=13 pairs; P<0.05, respectively). Conclusion: Together, these data show that B-cells play a role in sodium- and water-retention, and consequently, extracellular fluid volume expansion and congestion post-MI, and suggest that B-cells may represent a therapeutic target in heart failure.

Mineralocorticoid Receptor Antagonists in Diabetic Kidney Disease.

Diabetes mellitus is a global health issue and main cause of chronic kidney disease. Both diseases are also linked through high cardiovascular morbidity and mortality. Diabetic kidney disease (DKD) is present in up to 40% of diabetic patients; therefore, prevention and treatment of DKD are of utmost importance. Much research has been dedicated to the optimization of DKD treatment. In the last few years, mineralocorticoid receptor antagonists (MRA) have experienced a renaissance in this field with the development of non-steroidal MRA. Steroidal MRA have known cardiorenal benefits, but their use is limited by side effects, especially hyperkalemia. Non-steroidal MRA still block the damaging effects of mineralocorticoid receptor overactivation (extracellular fluid volume expansion, inflammation, fibrosis), but with fewer side effects (hormonal, hyperkalemia) than steroidal MRA. This review article summarizes the current knowledge and newer research conducted on MRA in DKD.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms.

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23–Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

Salt sensitivity and hypertension.

Salt sensitivity refers to the physiological trait present in mammals, including humans, by which the blood pressure (BP) of some members of the population exhibits changes parallel to changes in salt intake. It is commoner in elderly, females, Afro-Americans, patients with chronic kidney disease (CKD) and insulin resistance. Increased salt intake promotes an expansion of extracellular fluid volume and increases cardiac output. Salt-sensitive individuals present an abnormal kidney reaction to salt intake; the kidneys retain most of the salt due to an abnormal over-reactivity of sympathetic nervous system and a blunted suppression of renin-angiotensin axis. Moreover, instead of peripheral vascular resistance falling, salt-sensitive subjects present increased vascular resistance due mainly to impaired nitric oxide synthesis in endothelium. Recent studies have shown that part of the dietary salt loading accumulates in skin. Hypertensive and patients with CKD seem to have more sodium in skin comparing to healthy ones. However, we still have not fully explained the link between skin sodium, BP and salt sensitivity. Finally, although salt sensitivity plays a meaningful role in BP pathophysiology, it cannot be used by the physician in everyday patient's care, mainly due to lack of a simple and practical diagnostic test.

1909-P: The Natriuretic Action of Glucagon-Like Peptide-1 in Humans Is Abolished by the GLP-1 Receptor Antagonist Exendin 9-39

We have recently demonstrated that renal extraction of GLP-1 is ∼45% and that extracellular fluid volume expansion in healthy participants uncovered a natriuretic action of GLP-1 probably via a tubular mechanism secondary to suppression of angiotensin II (ANG II) and independent of changes in renal hemodynamics. It is not known whether the high extraction is due to receptor binding. The present study was designed to test the hypotheses that the renal extraction and natriuretic effect of GLP-1 are mediated via GLP-1 receptor. Under fixed sodium intake for 4 days before each study day, 6 healthy male participants were recruited from our recent study1 and examined during a 3-h infusion of GLP-1 (1.5 pmol/kg/min) together with a 3.5-h infusion of the GLP-1 receptor antagonist, exendin 9-39 (Ex 9-39) (900 pmol/kg/min), initiated 30 minutes before start of GLP-1 infusion. Timed urine collections were conducted throughout the experiments. Renal plasma flow (RPF), glomerular filtration rate (GFR), and renal extraction of GLP-1 were measured via Fick’s principle after catheterization of a renal vein. Renal extraction of GLP-1 was ∼45% during infusion of GLP-1 alone and decreased significantly to ∼25% during co-infusion of GLP-1 and Ex 9-39. Urinary sodium and osmolar excretions remained at baseline levels during co-infusion of GLP-1 and Ex 9-39 compared to a mean 2-fold natriuretic effect during GLP-1 infusion alone. Arterial plasma ANG II levels were unaffected during the co-infusions, whereas ANG II decreased significantly during GLP-1 alone. Arterial plasma renin levels decreased similarly on the two study days, and arterial aldosterone levels remained unchanged on both days. RPF and GFR remained unchanged on both days. In conclusion, renal extraction of GLP-1 is partially and natriuresis is fully dependent on GLP-1 receptor activation, probably via GLP-1-mediated ANG II suppression. 1Asmar A et al. J Clin Endocrinol Metab. 2019 Jul 1;104(7):2509-2519. Disclosure A. Asmar: None. P.K. Cramon: None. M. Asmar: None. L. Simonsen: None. S. Madsbad: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Merck Sharp & Dohme Corp., Novo Nordisk A/S, Sanofi-Aventis. Research Support; Self; Boehringer Ingelheim International GmbH, Novo Nordisk A/S. Speaker’s Bureau; Self; AstraZeneca, Boehringer Ingelheim International GmbH, Novo Nordisk A/S. C.M. Sorensen: None. B. Hartmann: None. J.J. Holst: Advisory Panel; Self; AstraZeneca, Merck Sharp & Dohme Corp., Novo Nordisk A/S, Zealand Pharma A/S. Other Relationship; Spouse/Partner; Antag Therapeutics. P. Hovind: None. B.L. Jensen: None. J. Bülow: None.

Altered renal medullary blood flow: A key factor or a parallel event in control of sodium excretion and blood pressure?

In the context of the ongoing debate on the mechanism of blood pressure (BP) regulation and pathophysiology of arterial hypertension ("renocentric" vs "neural" concepts), attention is focused on the putative regulatory role of changes in renal medullary blood flow (MBF). Experimental evidence is analysed with regard to the question whether an elevation of BP and renal perfusion pressure (RPP) is likely to increase MBF due to its impaired autoregulation. It is concluded that such increases have been clearly documented only in rats with extracellular fluid volume expansion. A possible translation of this finding to BP regulation in health and hypertension in humans may only be a matter of speculation. Within the "renocentric" theory, the key event leading to restoration of initial BP level is pressure natriuresis. Its relation to elevation of renal interstitial hydrostatic pressure and to the phenomenon of "wash-out" of renal medullary solutes by increasing MBF is discussed. We also assessed the validity of data supporting the putative mechanism of short-term restoration of elevated BP owing to the release of a vasodilator lipid (medullipin) by the medulla. The structure of the proposed medullary lipid is still undefined, and there is no sound evidence on its mediatory role in lowering elevated BP level. In conclusion, MBF change can hardly be regarded as a crucial event in the regulation of BP: it can be involved in the control of sodium excretion and BP only in some circumstances, although its contributory role cannot be excluded.

Salt-sensitive blood pressure rise in type 1 diabetes patients is accompanied by disturbed skin macrophage influx and lymphatic dilation—a proof-of-concept study

Type 1 diabetes patients are more prone to have hypertension than healthy individuals, possibly mediated by increased blood pressure (BP) sensitivity to high salt intake. The classical concept proposes that the kidney is central in salt-mediated BP rises, by insufficient renal sodium excretion leading to extracellular fluid volume expansion. Recent animal-derived findings, however, propose a causal role for disturbance of macrophage-mediated lymphangiogenesis. Its relevance for humans, specifically type 1 diabetes patients, is unknown. The present study aimed to assess responses of type 1 diabetes patients to a dietary salt load with regard to BP, extracellular fluid volume (using precise iohexol measurements), and CD163+ macrophage and lymphatic capillary density in skin biopsies. Also, macrophage expression of HLA-DR (a proinflammatory marker) and CD206 (an anti-inflammatory marker) was assessed. Type 1 diabetes patients (n = 8) showed a salt-sensitive BP increase without extracellular fluid volume expansion. Whereas healthy controls (n = 12), who had no BP increase, showed increased skin CD163+ and HLA-DR+ macrophages and dilation of lymphatic skin vasculature after the dietary salt load, these changes were absent (and in case of HLA-DR more heterogenic) in type 1 diabetes patients. In conclusion, we show that salt sensitivity in type 1 diabetes patients cannot be explained by the classical concept of extracellular fluid volume expansion. Rather, we open up a potential role for macrophages and the lymphatic system. Future studies on hypertension and diabetes need to scrutinize these phenomena.

Analysis of the critical determinants of renal medullary oxygenation.

We have previously developed a three-dimensional computational model of oxygen transport in the renal medulla. In the present study, we used this model to quantify the sensitivity of renal medullary oxygenation to four of its major known determinants: medullary blood flow (MBF), medullary oxygen consumption rate (V̇o2,M), hemoglobin (Hb) concentration in the blood, and renal perfusion pressure. We also examined medullary oxygenation under special conditions of hydropenia, extracellular fluid volume expansion by infusion of isotonic saline, and hemodilution during cardiopulmonary bypass. Under baseline (normal) conditions, the average medullary tissue Po2 predicted for the whole renal medulla was ~30 mmHg. The periphery of the interbundle region in the outer medulla was identified as the most hypoxic region in the renal medulla, which demonstrates that the model prediction is qualitatively accurate. Medullary oxygenation was most sensitive to changes in renal perfusion pressure followed by Hb, MBF, and V̇o2,M, in that order. The medullary oxygenation also became sensitized by prohypoxic changes in other parameters, leading to a greater fall in medullary tissue Po2 when multiple parameters changed simultaneously. Hydropenia did not induce a significant change in medullary oxygenation compared with the baseline state, while volume expansion resulted in a large increase in inner medulla tissue Po2 (by ~15 mmHg). Under conditions of cardiopulmonary bypass, the renal medulla became severely hypoxic, due to hemodilution, with one-third of the outer stripe of outer medulla tissue having a Po2 of <5 mmHg.

Extracellular fluid volume expansion, arterial stiffness and uncontrolled hypertension in patients with chronic kidney disease.

Hypertension is prevalent in patients with chronic kidney disease (CKD) and is related to extracellular fluid volume (ECFV) expansion. Arterial stiffening is another implication of CKD that can be caused by ECFV expansion. In this study, we hypothesized that CKD patients with uncontrolled hypertension are more likely to be fluid volume expanded than normotensive patients, which in turn is associated with increased arterial stiffness. Adult hypertensive patients with mild-severe CKD (n = 82) were recruited. ECFV was assessed using multifrequency bioimpedance and arterial stiffness by applanation tonometry and oscillometry. Patients with uncontrolled hypertension had fluid volume expansion compared with controls (1.0 ± 1.5 versus 0.0 ± 1.6L, P < 0.001), and had a higher augmentation index (AIx) and pulse wave velocity. Fluid volume expansion was more prevalent in patients with uncontrolled hypertension (58%) than patients who were at target (27%). Fluid volume expansion was correlated with age, AIx and systolic blood pressure. In a binary logistic regression analysis, AIx, age and fluid volume status were independent predictors of uncontrolled hypertension in both univariate and multivariate models. In summary, uncontrolled hypertension among hypertensive CKD patients is associated with ECFV expansion. Our data suggest a relationship between ECFV expansion, increased arterial stiffness and uncontrolled hypertension.

Alterations in regional kidney oxygenation during expansion of extracellular fluid volume in conscious healthy sheep.

Expansion of extracellular fluid volume with crystalloid solutions is a common medical intervention, but its effects on renal cortical and medullary oxygenation are poorly understood. Therefore, we instrumented sheep under general anesthesia to enable continuous measurement of systemic and renal hemodynamics, global renal oxygen delivery and consumption, and intrarenal tissue perfusion and oxygen tension (Po2) in conscious animals ( n = 7). The effects of three sequential intermittent infusions of 500 ml of compound sodium lactate solution, administered at hourly intervals, were determined. Volume expansion induced transient increases in mean arterial pressure (+7 ± 2%), central venous pressure (+50 ± 19%), and cardiac output (+15 ± 3%). There were sustained increases in renal medullary tissue Po2 (+35 ± 10%) despite increases in global renal oxygen consumption (+66 ± 18%) and renal oxygen extraction (+64 ± 8%). Volume expansion did not significantly alter renal blood flow, renal oxygen delivery, or medullary perfusion. The sustained increase in medullary Po2 was paralleled by increased bladder urine Po2 (34 ± 4%). Cortical perfusion and Po2 did not change significantly. Our findings indicate that extracellular fluid volume expansion can increase renal medullary oxygenation, providing a potential mechanistic basis for its use as prophylaxis against iatrogenic acute kidney injury. They also indicate that continuous measurement of bladder urine Po2 could be used to monitor the effects of volume expansion on medullary oxygenation. However, the mechanisms mediating increased medullary oxygenation during volume expansion remain to be determined.

Endothelial factors in the pathogenesis and treatment of chronic kidney disease Part I: General mechanisms: a joint consensus statement from the European Society of Hypertension Working Group on Endothelin and Endothelial Factors and The Japanese Society of Hypertension.

: Kidney damage is a common consequence of arterial hypertension, but is also a cause of atherogenesis. Dysfunction and/or harm of the endothelium in glomeruli and tubular interstitium damage the function of these structures and translates into dynamic changes of filtration fraction, with progressive reduction in glomerular filtration rate, expansion of extracellular fluid volume, abnormal ion balance, and hypoxia, ultimately leading to chronic kidney disease. Considering the key role played by endothelial dysfunction in chronic kidney disease, the Working Group on Endothelin and Endothelial Factors of the European Society of Hypertension and the Japanese Society of Hypertension have critically reviewed available knowledge on the mechanisms underlying endothelial cell injury. This resulted into two articles: in the first, we herein examine the mechanisms by which endothelial factors induce vascular remodeling and the role of different players, including endothelin-1, the renin-angiotensin-aldosterone system and their interactions, and of oxidative stress; in the second, we discuss the role of endothelial dysfunction in the major disease conditions that affect the kidney.

Treatment of Disorders of Sodium Balance in Chronic Kidney Disease.

Extracellular fluid volume expansion is nearly universal in patients with CKD. Such volume expansion has features similar to the syndrome of heart failure with preserved ejection fraction, which not only leads to symptoms but can also lead to further organ damage. Unique treatment challenges are present in this patient population, including low glomerular filtration, which limits sodium chloride filtration, intrinsic tubule predisposition to sodium chloride retention, and proteinuria. In addition, pharmacokinetic considerations alter the disposition of diuretics in patients with CKD and nephrotic syndrome. Maintaining extracellular fluid volume near to normal is often necessary for hypertension treatment in this population, but it may also help prevent progressive cardiovascular and kidney damage. Although powerful diuretics can often accomplish this goal, this often comes at a cost of competing adverse effects. An approach to reduce extracellular fluid volume while avoiding adverse effects, therefore, requires a nuanced yet aggressive therapeutic approach.