Recently, studies have emerged suggesting that the skin plays a role as major Na+ reservoir via regulation of the content of glycosaminoglycans and osmotic gradients. We investigated whether there were electrolyte gradients in skin and where Na+ could be stored to be inactivated from a fluid balance viewpoint. Na+ accumulation was induced in rats by a high salt diet (HSD) (8% NaCl and 1% saline to drink) or by implantation of a deoxycorticosterone acetate (DOCA) tablet (1% saline to drink) using rats on a low salt diet (LSD) (0.1% NaCl) on tap water as control. Na+ and K+ were assessed by ion chromatography in tissue eluates, and the extracellular volume by equilibration of 51Cr‐EDTA. By tangential sectioning of the skin, we found a low Na+ content and extracellular volume in epidermis, both parameters rising by ∼30% and 100%, respectively, in LSD and even more in HSD and DOCA when entering dermis. We found evidence for an extracellular Na+ gradient from epidermis to dermis shown by an estimated concentration in epidermis ∼2 and 4–5 times that of dermis in HSD and DOCA‐salt. There was intracellular storage of Na+ in skin, muscle, and myocardium without a concomitant increase in hydration. Our data suggest that there is a hydration‐dependent high interstitial fluid Na+ concentration that will contribute to the skin barrier and thus be a mechanism for limiting water loss. Salt stress results in intracellular storage of Na+ in exchange with K+ in skeletal muscle and myocardium that may have electromechanical consequences. Key points Studies have suggested that Na+ can be retained or removed without commensurate water retention or loss, and that the skin plays a role as major Na+ reservoir via regulation of the content of glycosaminoglycans and osmotic gradients. In the present study, we investigated whether there were electrolyte gradients in skin and where Na+ could be stored to be inactivated from a fluid balance viewpoint. We used two common models for salt‐sensitive hypertension: high salt and a deoxycorticosterone salt diet. We found a hydration‐dependent high interstitial fluid Na+ concentration that will contribute to the skin barrier and thus be a mechanism for limiting water loss. There was intracellular Na+ storage in muscle and myocardium without a concomitant increase in hydration, comprising storage that may have electromechanical consequences in salt stress.

Background: Recent studies have indicated that sodium storage is influenced by macrophages that secrete VEGF-C (vascular endothelial growth factor) during salt stress thus stimulating lymphangiogenesis, thereby acting as a buffer against increased blood pressure (BP). We aimed to explore the role of dermal lymphatics in BP and sodium homeostasis. Our hypothesis was that mice with reduced dermal lymphatic vessels were more prone to develop salt-sensitive hypertension, and that mice with hyperplastic vessels were protected. Methods: Mice with either hypoplastic (Chy), absent (K14-VEGFR3 [vascular endothelial growth factor receptor 3]-Ig), or hyperplastic (K14-VEGF-C) dermal lymphatic vessels and littermate controls were given high-salt diet (4% NaCl in the chow), deoxycorticosterone acetate (DOCA)-salt diet and 1% saline to drink or nitric oxide blocker diet L-N G -nitro arginine methyl ester (followed by high salt diet). BP was measured by telemetric recording, and tissue sodium content by ion chromatography. Results: In contrast to previous studies, high salt diet did not induce an increase in BP or sodium storage in any of the mouse strains investigated. DOCA-salt, on the other hand, gave an increase in BP in Chy and K14-VEGFR3-Ig not different from their corresponding WT controls. DOCA induced salt storage in skin and muscle, but to the same extent in mice with dysfunctional lymphatic vessels and WT controls. Lymph flow as assessed by tracer washout was not affected by the diet in any of the mouse strains. Conclusions: Our results suggest that dermal lymphatic vessels are not involved in salt storage or blood pressure regulation in these mouse models of salt-sensitive hypertension.

The pathogenesis of hypertension is not well understood, but high sodium intake has been associated with blood pressure (BP) rise. Studies have indicated that sodium can be stored in skin without commensurate water accumulation, and macrophages may secrete VEGF‐C that can stimulate lymphangiogenesis, thereby acting as a buffer against increased BP. Here we aimed to explore the role of dermal lymphatics in BP and sodium homeostasis. Our hypothesis was that mice with reduced dermal lymphatic vessels were more prone to develop salt‐sensitive hypertension, and that mice with hyperplastic vessels were protected against this outcome. Mice with either absent (K14‐VEGFR3‐Ig), hypoplastic (Chy) or hyperplastic (K14‐VEGF‐C) dermal lymphatic vessels and littermate controls were given high salt diet (HSD) (4% NaCl in the chow and 1% saline to drink), DOCA‐salt diet (16mg/week 11‐deoxycorticosterone acetate ‐ 50mg/21 days slow release tablet subcutaneously and 1% saline to drink) or nitric oxide (NO) blocker diet (L‐NAME 0.5mg/ml in drinking water for 3 weeks, followed by one week washout and thereafter 2 weeks HSD). BP was measured by telemetric recording, and tissue sodium content by ion chromatography. In contrast to previous studies, HSD did not induce an increase in BP or sodium storage in any of the mouse strains investigated. DOCA‐salt, on the other hand, induced an increase in mean arterial pressure (MAP) in Chy of 13.4 ± 7.1 (SD) mm Hg (n=4), not different from a corresponding pressure in WT control of 14.7 ± 6.4 mm Hg, n=5. In K14‐VEGFR3‐Ig mice, DOCA raised the MAP 24 ± 12.1 mm Hg (n=6), not different from the corresponding WT control (22.8 ± 8.3 mm Hg, n=7). DOCA induced salt storage in skin and muscle, but to the same extent in mice with dysfunctional lymphatic vessels and WT controls. L‐NAME diet tended to give a higher diastolic pressure in mice lacking dermal lymphatic vessels compared with WT control as suggested by the rise in diastolic BP of 11.6 ± 10.8 (SD) mm Hg (n=9) and 1.9 ± 2.4 (SD) mm Hg (n=6) (p<0.05, One‐way ANOVA), respectively, without a concomitant increase in sodium content in skin or muscle in any of the strains. Our results indicate that there is no association between dermal lymphangiogenesis, sodium accumulation and blood pressure response. The response seen in NO‐blocker diet in mice lacking dermal lymphatic vessels was salt storage independent. This suggests that dermal lymphatic vessels are not involved in salt storage or blood pressure regulation in these mouse models of salt‐sensitive hypertension.

Aims Cardiac energy metabolism is centrally involved in heart failure (HF), although the direction of the metabolic alterations is complex and likely dependent on the particular stage of HF progression. Vascular endothelial growth factor B (VEGF-B) has been shown to modulate metabolic processes and to induce physiological cardiac hypertrophy; thus, it could be cardioprotective in the failing myocardium. This study investigates the role of VEGF-B in cardiac proteomic and metabolic adaptation in HF during aldosterone and high-salt hypertensive challenges. Methods and results Male rats overexpressing the cardiac-specific VEGF-B transgene (VEGF-B TG) were treated for 3 or 6 weeks with deoxycorticosterone-acetate combined with a high-salt (HS) diet (DOCA + HS) to induce hypertension and cardiac damage. Extensive longitudinal echocardiographic studies of HF progression were conducted, starting at baseline. Sham-treated rats served as controls. To evaluate the metabolic alterations associated with HF, cardiac proteomics by mass spectrometry was performed. Hypertrophic non-treated VEGF-B TG hearts demonstrated high oxygen and adenosine triphosphate (ATP) demand with early onset of diastolic dysfunction. Administration of DOCA + HS to VEGF-B TG rats for 6 weeks amplified the progression from cardiac hypertrophy to HF, with a drastic drop in heart ATP concentration. Dobutamine stress echocardiographic analyses uncovered a significantly impaired systolic reserve. Mechanistically, the hallmark of the failing TG heart was an abnormal energy metabolism with decreased mitochondrial ATP, preceding the attenuated cardiac performance and leading to systolic HF. Conclusions This study shows that the VEGF-B TG accelerates metabolic maladaptation which precedes structural cardiomyopathy in experimental hypertension and ultimately leads to systolic HF.

We have previously shown that there is an osmolality and urea gradient from epidermis to dermis and subcutis. This gradient may be a result of the proposed counter‐current mechanism for electrolyte homeostasis in skin. Our aims were to test whether there are gradients in salt concentration in skin generated by counter‐current exchange and whether glycosaminoglycans (GAGs) can store sodium making it ‘inactive’ in relation to fluid exchange and thereby act as buffers during high salt intake. Sprague‐Dawley rats were given low salt diet (LSD, <0.1% NaCl in chow and tap water), high salt diet (HSD, 8% NaCl in chow and 1% saline to drink), and DOCA‐salt diet (50mg/week deoxycorticosterone acetate, 150mg/21 days and 1% saline to drink). Rats were randomly assigned to either LSD (n=15), HSD (n=7) or DOCA salt (n=8) diet for measurements of extracellular volume (ECV) in tangential sequential skin sections. Two weeks into the diet regimen the rats were anesthetized, neprectomized and given the extracellular tracer 51Cr‐EDTA i.v. that was allowed 120 min circulation time. Directly thereafter, shaved back skin was further processed by cutting sequential sections of 40 µm (epidermis) and 100 µm (dermis and subcutis) thickness in a cryostat taking care to avoid evaporation. The skin sections were weighed and counted in a gamma counter and the extracellular volume found as the plasma equivalent space of 51Cr‐EDTA. After counting, the samples were dried until constant weight, then eluted in ultrapure water for seven days. The eluate was analyzed in an ion chromatograph to determine sodium and potassium content in each layer. Sulfated GAGs were determined in whole skin, dermis and subcutis using Blyscan sGAG colorimetric assay to determine sGAG content. When relating sodium content to ECV we found that there was a gradient from epidermis to dermis, and that this gradient was more pronounced in the DOCA rats. The LSD group had a mean sodium of 332.7±194.3 mM in epidermis and 118.3±20.15 mM in the following layer at 140±mM, with corresponding concentrations of 219.2±52 mM and 121.1±41.4 mM in HSD, and 757.8±426.1 mM and 123.7±11.45 mM in DOCA. There was no difference in sulfated GAGs in skin between LSD, HSD and the DOCA salt group in any of the skin regions. Our results suggest that there may be a gradient of salt in the skin with a higher concentration in ECV in epidermis supporting the notion of a counter‐current mechanism. However, our data do not support that an increased concentration of sulfated GAGs contribute to salt buffering during high salt conditions.