Osmotically inactive skin Na+ storage in rats.
Compared with age-matched men, women are resistant to the hypertensive effects of dietary NaCl; however, after menopause, the incidence of salt-sensitive hypertension is similar in women and men. We recently suggested that osmotically inactive Na+ storage contributes to the development of salt-sensitive hypertension. The connective tissues, including those immediately below the skin that may serve as a reservoir for osmotically inactive Na+ storage, are affected by menopause. We tested the hypothesis that ovariectomy (OVX) might reduce osmotically inactive Na+ storage capacity in the body, particularly in the skin. Male, female-fertile, and female OVX Sprague-Dawley (SD) rats were fed a high (8%)- or low (0.1%)-NaCl diet. The groups received the diet for 4 or 8 wk. At the end of the experiment, subgroups received 0.9% saline infusion and urinary Na+ and K+ excretion was measured. Wet and dry weight (DW), water content in the body and skin, total body Na+ (rTBNa+) and skin Na+ (rSKNa+) content were measured relative to DW by desiccation and dry ashing. There were no gender differences in osmotically inactive Na+ storage in SD rats. All SD rats accumulated Na+ if fed 8% NaCl, but rTBNa+ was lower in OVX rats than in fertile rats on a low (P < 0.001)- and a high (P < 0.05)-salt diet. OVX decreased rSKNa+ (P < 0.01) in the rats. A high-salt diet led to Na+ accumulation (DeltaSKNa+) in the skin in all SD rats. Osmotically inactive skin Na+ accumulation was approximately 66% of DeltaSKNa+ in female and 82% in male-fertile rats, but there was no osmotically inactive Na+ accumulation in OVX rats fed 8% NaCl. We conclude that skin is an osmotically inactive Na+ reservoir that accumulates Na+ when dietary NaCl is excessive. OVX leads to an acquired reduction of osmotically inactive Na+ storage in SD rats that predisposes the rats to volume excess despite a reduced Na+ content relative to body weight.
Titze
Jens
J
Department of Nephrology, Friedrich-Alexander University Erlangen-Nuremberg, Loschgestrasse 8, D-91054 Erlangen, Germany. jus.titze@t-online.de
Lang
Rainer
R
Ilies
Christoph
C
Schwind
Karl H
KH
Kirsch
Karl A
KA
Dietsch
Peter
P
Luft
Friedrich C
FC
Hilgers
Karl F
KF
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001835:Body Weight; D001842:Bone and Bones / Q000378:metabolism; D005260:Female; D008297:Male; D008593:Menopause / Q000502:physiology; D008903:Minerals / Q000378:metabolism; D009318:Natriuresis / Q000502:physiology; D010052:Ovariectomy; D051381:Rats; D020303:Rats, Inbred Dahl; D017207:Rats, Sprague-Dawley; D012727:Sex Characteristics; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000493:pharmacokinetics; D014867:Water / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
D008903:Minerals; D014867:Water; D012965:Sodium Chloride; C028705:bone ash; D012964:Sodium