Increased interstitial osmolality in skin of rats on a high salt diet

Abstract

ALTHOUGH GENERALLY ACCEPTED, RECENT OBSERVATIONS HAVE SUGGESTED THAT EFFECTIVE CLEARANCE OF ELECTROLYTES FROM THE BODY CANNOT BE ACHIEVED BY RENAL EXCRETION ALONE, BUT ALSO RELIES ON EXTRARENAL REGULATORY MECHANISMS INVOLVING SKIN NA+ STORAGE WITHOUT COMMENSURATE WATER RETENTION. TO ASSESS THE TISSUE AND THEREBY THE OSMOLALITY IN THE SKIN MICROENVIRONMENT, WE ADAPTED A TISSUE OSMOMETRY METHOD DEVELOPED FOR USE IN THE BRAIN AND KIDNEY. SAMPLES WERE ISOLATED FROM BACK SKIN OF RATS ON A HIGH SALT DIET (HSD) (8% NACL AND 0.9% SALINE) OR LOW SALT DIET (LSD, <0.1% NACL AND TAP WATER) AND SNAP FROZEN. WHILE STILL FROZEN, ~0.5 MM THICK SAMPLES WERE LATER APPLIED TO A VAPOR PRESSURE OSMOMETER ALONG WITH PLASMA. HSD DID NOT INFLUENCE PLASMA OSMOLALITY (FIG). THE SKIN OSMOLALITY IN LSD WAS NOT DIFFERENT FROM PLASMA, WHEREAS SKIN HSD EXCEEDED SKIN LSD, PLASMA HSD AND LSD OSMOLALITY BY 18–24 MOSMOL/KG (FIG) (P<0.001, ANOVA). OUR RESULTS SHOW FOR THE FIRST TIME THAT ACCUMULATION OF NACL IN SKIN RESULTS IN INTERSTITIAL HYPERTONICITY, AND THAT PLASMA OSMOLALITY IS PARTIALLY UNCOUPLED FROM CHANGES IN THE INTERSTITIUM THAT OCCUR WITH NA+ STORAGE.