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(Hypertension. 2006;47:1101.)
© 2006 American Heart Association, Inc.

Original Articles

Extrarenal Na⁺ Balance, Volume, and Blood Pressure Homeostasis in Intact and Ovariectomized Deoxycorticosterone-Acetate Salt Rats

Jens Titze; Friedrich C. Luft; Katharina Bauer; Peter Dietsch; Rainer Lang; Roland Veelken; Hubertus Wagner; Kai-Uwe Eckardt; Karl F. Hilgers

From the Department of Nephrology and Hypertension (J.T., K.B., R.L., R.V., K.-U.E., K.F.H.), Friedrich-Alexander-University, Erlangen-Nürnberg, Germany; Charité Campus Buch (F.C.L.), Franz Volhard Clinic, HELIOS Klinikum-Berlin and Max Delbrück Center for Molecular Medicine, Berlin, Germany; Institute of Biochemistry (P.D.), Charité Campus Benjamin Franklin, Berlin, Germany; Federal Research Centre for Nutrition and Food (H.W.), Kulmbach, Germany.

Correspondence to Jens Titze, Department of Nephrology and Hypertension, Loschgestr. 8, 91054 Erlangen, Germany. E-mail jens.titze{at}rzmail.uni-erlangen.de

Water-free Na⁺ storage may buffer extracellular volume and mean arterial pressure (MAP) in spite of Na⁺ retention. We studied the relationship among internal Na⁺, K⁺, water balance, and MAP in Sprague-Dawley rats, with or without deoxycorticosterone-acetate (DOCA) salt, with or without ovariectomy (OVX). The rats were fed a low-salt (0.1% NaCl) or high-salt (8% NaCl) diet for 5 weeks. DOCA salt increased MAP (161±14 versus 123±4 mm Hg; P<0.05), and DOCA-OVX salt increased MAP further (181±22 mm Hg; P<0.05). DOCA salt increased the total body Na⁺ by &40% to 45%; however, water-free Na⁺ retention by osmotically inactive Na⁺ storage and by osmotically neutral Na⁺/K⁺ exchange allowed the rats to maintain the extracellular volume close to normal. DOCA-OVX salt rats showed similar Na⁺ retention. However, their osmotically inactive Na⁺ storage capacity was greatly reduced and only partially compensated by neutral Na⁺/K⁺ exchange, resulting in greater volume retention despite similar Na⁺ retention. For every 1% wet weight total body water gain, MAP increased by 2.3±0.2 mm Hg in DOCA salt rats and 2.5±0.3 mm Hg in DOCA-OVX salt rats. Because water-free Na⁺ retention buffered total body water content by 8% to 11% wet weight, we conclude that this internal Na⁺ escape buffered MAP. Extrarenal Na⁺ and volume balance seem to play an important role in long-term volume and MAP control.

Key Words: electrolytes • gender • water-electrolyte balance • hypertension, sodium-dependent