Peer review of: Tissue sodium excess is not hypertonic and reflects extracellular volume expansion (2020)

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

Gradients in Na concentration are observed in kidney: hypertonicity in the medulla vs isotonicity in 
the cortex. Elaborate arrangements of renal tubules in combination with specific enrichment of 
active sodium transporters (Na,K-ATPase, Na,K,Cl cotransporters, Na, Cl cotransporters, etc) are 
required for the sodium gradient in addition to enormous flow in tubules and blood vessels. On the 
other hand, structural basis for local hypertonicity in dermis or other non-renal tissues is not known 
casting doubts. This study provides a solid ground for the pessimism based on well performed 
comprehensive analyses of animals and patients. Data presented are all consistent with expansion of 
ECV which is systemic rather than skin specific. Given the lack of evidence for structural or functional 
features required for the maintenance of local hypertonicity in the skin, these data are conceptually 
more plausible. In the end, the study provides an important insight to the issue of non-renal local 
hypertonicty which has been plagued by conflicting reports. 

 

By Hyug Moo Kwon 


Reviewer #2 (Remarks to the Author): 

The manuscript by Rossitto G. et al. showing that salt accumulation in the skin is not water-
independent but isotonic nature is provocative and interesting. Moreover, excess of tissue Na+ upon 
high salt intake is not a skin-specific but systemic phenomenon reflecting an architectural change 
which is attributable to cellular loss and fat distribution. Results of these in vivo and ex vivo 
experiments in hypertensive rats and skin studies in hypertensive subjects are attractive and 
informative, but there are several defects to be resolved. 

1. In SuppFig 8, at variance with aging, Na/K ratio was shifted to the right, despite the sentence “the 
lack of any significant shift in the Na/K ratio suggest a fluid accumulation” 

2. According to the sentence “Office BP was inversely associated with ESD water ---- (Fig4e)”, no data 
of diastolic BP in Fig4e. 

3. Again, “No significant interaction with medications---, positively--, and systolic BP and negatively 
with diastolic BP, mirrored all measures of skin oedema accumulation (Fig4e)”. But, no data of 
systolic and diastolic BP in Fig4e. 
4. “Na+ and K+ were lower and higher in the ESD compared to DD, respectively (Fig4a)”. However, 
the difference of Na+ between ESD and DD (mean+SD), as shown in the red columns, seemed very 
small. Data should be shown by dot. Water content in ESD and DD also be shown. 

5. How do you explain about the opposite vascular responses to SNP between HS diet and 
hypertonic Na+ (Fig3b)? 

6. In Fig4d showing water, Na+ and K+ in ESD with age, how about these parameters in DD? 

7. Some investigators measured the interstitial fluid osmolarity, Na+, and K+ measured by 
microdialysis (Nikpey E et al. Hypertension 69: 660, 2017), and they showed the significant 
differences in either osmolarity or Na+ between interstitial fluid and plasma in both normotensive 
and hypertensive rats. Is there any difference in Na+ concentration between plasma and tissues? 


Reviewer #3 (Remarks to the Author): 


Add reference to TEWL literature (textbook and/or article), such as: 

Joachim Fluhr, Peter Elsner, Enzo Berardesca and Howard I Maibach, Editors. Bioengineering of the 
Skin. Water and the Stratum Corneum, 2nd Edition. CRC Press, Boca Raton, FL, 2005 


Reviewer #4 (Remarks to the Author): 

I read carefully the part of manuscript on the measurements of potassium and sodium by flame 
photometry in tissues. this part is well prepared and the results are analytically acceptable .