At first thought the skin is an unlikely culprit in hypertension. However, the skin represents the human body’s largest organ system with an estimated 12-15% of body weight and a surface area of 1-2 square meters making the skin an ideal reservoir for sodium. In 2009 Machnik et al reported an interesting finding in the journal Nature Medicine. This group found that the interstitium of the skin serves a dynamic role in serving as a reservoir to buffer sodium accumulation in intravascular volume and blood pressure. They found that during high-salt feeding, mice accumulated sodium in the subdermal interstitial spaces at hypertonic concentrations. Macrophages sense the hypertonicity leading to expression of tonicity-responsive enhancer binding protein (TonEBP). TonEBP leads to VEGF-C expression which is a potent inducer of lymphatics allowing for a greater reservoir to store sodium. This same group has also reported that tissue sodium content indeed did accumulate in various tissue beds of hypertensive patients using MRI.
Matthew Sparks, MD