Sodium Accumulation and Blood Capillary Rarefaction in the Skin Predispose Spontaneously Hypertensive Rats to Salt Sensitive Hypertension

Potential Role of the Skin in Hypertension Risk Through Water Conservation

Previous basic and clinical investigations have identified various pathogenic factors and determinants of risk that contribute to hypertension. Nevertheless, the pathogenesis of hypertension has not been fully elucidated. Moreover, despite the availability of antihypertensive medications for the management of blood pressure, treatments that address the full spectrum of the pathophysiological defects underpinning hypertension remain to be identified. To further investigate the mechanisms of primary hypertension, it is imperative to consider novel potential aspects, such as fluid management by the skin, in addition to the conventional risk factors. There is a close association between body fluid regulation and blood pressure, and the kidney, which, as the principal organ responsible for body fluid homeostasis, is the primary target for research in the field of hypertension. In addition, the skin functions as a biological barrier, potentially contributing to body fluid regulation. In this review, we propose the hypothesis that changes in skin water conservation are associated with hypertension risk based on recent findings. Further studies are required to clarify whether this novel hypothesis is limited to specific hypertension or applies to physiological blood pressure regulation.

Sodium as an Important Regulator of Immunometabolism

Salt sensitivity concerns blood pressure alterations after a change in salt intake (sodium chloride). The heart is a pump, and vessels are tubes; sodium can affect both. A high salt intake increases cardiac output, promotes vascular dysfunction and capillary rarefaction, and chronically leads to increased systemic vascular resistance. More recent findings suggest that sodium also acts as an important second messenger regulating energy metabolism and cellular functions. Besides endothelial cells and fibroblasts, sodium also affects innate and adaptive immunometabolism, immune cell function, and influences certain microbes and microbiota-derived metabolites. We propose the idea that the definition of salt sensitivity should be expanded beyond high blood pressure to cellular and molecular salt sensitivity.

Contributions of renal water loss and skin water conservation to blood pressure elevation in spontaneously hypertensive rats

We recently reported that skin vasoconstriction to suppress transepidermal water loss (TEWL) leads to hypertension in renal injury model rats with impaired urine concentration ability. In this study, we investigated the pathogenesis of hypertension in spontaneously hypertensive rats (SHRs) from the perspective of renal water loss and skin water conservation. We compared the urinary concentration ability, body sodium and water balance, blood pressure, and TEWL in SHRs and control normotensive Wistar-Kyoto rats (WKYs). SHRs showed significantly higher urine volume and lower urinary osmolality than those of WKYs, while there were no significant differences in water intake, urinary osmolyte excretion, and plasma osmolarity between the groups. SHRs exhibited significantly higher blood pressure, skin sodium content, and lower TEWL compared with those is WKYs. Skin vasodilation, induced by elevating body temperature, increased TEWL in both SHRs and WKYs, and significantly reduced blood pressure in SHRs but not WKYs. These findings suggest that physiological adaptation can reduce dermal water loss in SHRs to compensate for renal water loss. Vasoconstriction required for successful cutaneous water conservation explains SHR hypertension. Renal concentration ability and skin barrier function for water conservation may become a novel therapeutic target for essential hypertension.