Dietary salt intake has been investigated in relation to hypertension since the early 20th century.1 Mendelian forms of hypertension have underscored the role of salt intake in the development of hypertension.2 Clinicians have advised patients in terms of their dietary intake and have relied on 24 hour urine collections to verify dietary compliance. 3 Nonetheless, the results have been suboptimal. Clinicians have been limited to measuring Na + in plasma and urine, and the relationship to these sources for determining salt-sensitivity has been disappointing. The issue is important, as salt-sensitivity portends an earlier death. 4 Na + is bound to negatively charged proteoglycans that are very abundant in the skin, the body's largest organ. 5 We showed recently that signaling mechanisms exist in skin that control skin electrolyte storage. 6 When these mechanisms are perturbed, salt-sensitive hypertension results. Translating such findings to humans has been challenging. For that reason, we implemented quantitative 23 Na magnetic resonance imaging ( 23 Na-MRI) to visualize Na + in skin and soft tissues. 7 We reported on rodents measured with 23 Na-MRI and with MR spectroscopy, a small number of normal subjects, and 5 patients with primary aldosteronism, who were studied before and after definitive treatment. We have now extended our observations to larger numbers of normal men and women, as well as to patients with essential hypertension. We believe that 23 Na-MRI shows promise to be of clinical utility in further defining the relationship between salt and hypertension. MethodsWe implemented 23 Na-MRI for quantitative analysis in men; the methods were recently published. 7 We measured Na + content in lower leg muscle and skin with a 23 Na knee-coil (Stark-Contrast, Erlangen, Germany) at 3.0 T with a MRI scanner (Magnetom-Trio, Siemens Healthcare, Erlangen, Germany) using a 2D-FLASH sequence (total acquisition time, TA=13.7 minutes; echo time, TE=2.07 ms; repetition time, TR=100 ms; flip angle, FA=90°; 128 averages, resolution:Abstract-High dietary salt intake is associated with hypertension; the prevalence of salt-sensitive hypertension increases with age. We hypothesized that tissue Na + might accumulate in hypertensive patients and that aging might be accompanied by Na + deposition in tissue. We implemented 23 Na magnetic resonance imaging to measure Na + content of soft tissues in vivo earlier, but had not studied essential hypertension. We report on a cohort of 56 healthy control men and women, and 57 men and women with essential hypertension. The ages ranged from 22 to 90 years.23 Na magnetic resonance imaging measurements were made at the level of the calf. We observed age-dependent increases in Na + content in muscle in men, whereas muscle Na + content did not change with age in women. We estimated water content with conventional MRI and found no age-related increases in muscle water in men, despite remarkable Na + accumulation, indicating water-free Na + storage in muscle. With increasing age, there was ...

The skin interstitium sequesters excess Na + and Cl -in salt-sensitive hypertension. Mononuclear phagocyte system (MPS) cells are recruited to the skin, sense the hypertonic electrolyte accumulation in skin, and activate the tonicity-responsive enhancer-binding protein (TONEBP, also known as NFAT5) to initiate expression and secretion of VEGFC, which enhances electrolyte clearance via cutaneous lymph vessels and increases eNOS expression in blood vessels. It is unclear whether this local MPS response to osmotic stress is important to systemic blood pressure control. Herein, we show that deletion of TonEBP in mouse MPS cells prevents the VEGFC response to a high-salt diet (HSD) and increases blood pressure. Additionally, an antibody that blocks the lymph-endothelial VEGFC receptor, VEGFR3, selectively inhibited MPS-driven increases in cutaneous lymphatic capillary density, led to skin Cl -accumulation, and induced salt-sensitive hypertension. Mice overexpressing soluble VEGFR3 in epidermal keratinocytes exhibited hypoplastic cutaneous lymph capillaries and increased Na + , Cl -, and water retention in skin and salt-sensitive hypertension. Further, we found that HSD elevated skin osmolality above plasma levels. These results suggest that the skin contains a hypertonic interstitial fluid compartment in which MPS cells exert homeostatic and blood pressure-regulatory control by local organization of interstitial electrolyte clearance via TONEBP and VEGFC/VEGFR3-mediated modification of cutaneous lymphatic capillary function.

Summary Immune cells regulate a hypertonic microenvironment in the skin; however, the biological advantage of increased skin Na+ concentrations is unknown. We found that Na+ accumulated at the site of bacterial skin infections in humans and in mice. We used the protozoan parasite Leishmania major as a model of skin-prone macrophage infection to test the hypothesis that skin-Na+ storage facilitates antimicrobial host defense. Activation of macrophages in the presence of high NaCl concentrations modified epigenetic markers and enhanced p38 mitogen-activated protein kinase (p38/MAPK)-dependent nuclear factor of activated T cells 5 (NFAT5) activation. This high-salt response resulted in elevated type-2 nitric oxide synthase (Nos2)-dependent NO production and improved Leishmania major control. Finally, we found that increasing Na+ content in the skin by a high-salt diet boosted activation of macrophages in an Nfat5-dependent manner and promoted cutaneous antimicrobial defense. We suggest that the hypertonic microenvironment could serve as a barrier to infection.

Objective-Obesity is closely linked to the insulin resistance syndrome (IRS), type 2 diabetes, and cardiovascular disease, the primary cause of morbidity and mortality in these patients. Elevated levels of C-reactive protein (CRP) and interleukin-6 (IL-6), indicating chronic subclinical inflammation, have been associated with features of the IRS and incident cardiovascular disease. Methods and Results-We studied the cross-sectional and longitudinal relation of CRP, IL-6, and tumor necrosis factor-␣ (TNF-␣) with features of the IRS in 37 morbidly obese patients with different stages of glucose tolerance before and 14 months after gastric surgery. Weight loss after gastric surgery induced a significant shift from diabetes (37% vs 3%) to impaired glucose tolerance (40% vs 33%) and normal glucose tolerance (23% vs 64% .64 pg/mL, PϽ0.02, respectively), whereas serum levels of TNF-␣ remained unchanged (8.6 and 6.3/18.8 vs 11.7 and 5.8/17.2 pg/mL; NS.). Multiple regression analysis revealed that the decrease in insulin resistance remained independently and significantly correlated with the decrease in IL-6 concentrations (PϽ0.01) and the decrease in body mass index with the decrease in CRP (PϽ0.05), respectively. Conclusions-Weight loss in morbidly obese patients induces a significant decrease of CRP and IL-6 concentrations in association with an improvement of the IRS.

The steady-state concept of Na(+) homeostasis, based on short-term investigations of responses to high salt intake, maintains that dietary Na(+) is rapidly eliminated into urine, thereby achieving constant total-body Na(+) and water content. We introduced the reverse experimental approach by fixing salt intake of men participating in space flight simulations at 12 g, 9 g, and 6 g/day for months and tested for the predicted constancy in urinary excretion and total-body Na(+) content. At constant salt intake, daily Na(+) excretion exhibited aldosterone-dependent, weekly (circaseptan) rhythms, resulting in periodic Na(+) storage. Changes in total-body Na(+) (±200-400 mmol) exhibited longer infradian rhythm periods (about monthly and longer period lengths) without parallel changes in body weight and extracellular water and were directly related to urinary aldosterone excretion and inversely to urinary cortisol, suggesting rhythmic hormonal control. Our findings define rhythmic Na(+) excretory and retention patterns independent of blood pressure or body water, which occur independent of salt intake.