Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC225

Poster Communications

Low-sodium diet induces endocrine and hydroelectrolytic changes in male rats

A. S. Mecawi1,2, F. V. Fonseca2, T. Vilhena-Franco1, L. C. Reis2, L. Elias1, J. Antunes-Rodrigues1

1. University of Sao Paulo, Ribeir


The salt intake is a behavior implicated in the integrative regulation of extracellular volume and blood pressure and is directly influenced by changes in sodium homeostasis. The sodium dietary restriction is an interesting noninvasive model to study the sodium appetite. Our aim was investigate the integrative control of salt and water intake balance after dietary sodium restriction. To this, Wistar male rats receive normal- (1% NaCl) or low- (<0.05% NaCl) Na+ diet during four days. Food intake did not differ between normal and low-Na+ diet groups. However, we observed a reduced body weight gain during the four days of low-Na+ diet (20.0 ± 1.9 g/100g vs. 36.2 ± 3.9 g/100g, p < 0.01) associated with a decrease in water intake (9.6 ± 0.8 mL vs. 13.1 ± 0.5 mL, p < 0.05) and a decrease in the extracellular volume as demonstrated by increase in hematocrit (42.8 ± 0.7 % vs. 38.8 ± 0.6 %, p < 0.01) and plasma proteins (7.0 ± 0.1 mg/dL vs. 5.7 ± 0.1 mg/dL, p < 0.001). Additionally the low-Na+ diet induce a decrease in urinary volume (5.4 ± 0.6 mL vs. 7.6 ± 0.5 mL, p < 0.05) and sodium excretion (0.26 ± 0.01 mE/100g/day vs. 1.66 ± 0.07 mE/100g/day, p < 0.01). We observed a discrete decreased arterial pressure (101 ± 1.5 mmHg vs. 105 ± 1.1 mmHg, p < 0.05) without effect in heart rate. There was no effect of low-Na+ diet on plasma atrial natriuretic peptide and vasopressin concentrations. An increase in plasma angiotensin II (119 ± 12 pg/mL vs. 39 ± 11 pg/mL, p < 0.001) and decrease in plasma oxytocin (0.60 ± 0.04 pg/mL vs. 0.99 ± 0.12 pg/mL, p < 0.05) concentrations after low-Na+ diet was observed. These animals also presented an increase in 1.8% NaCl intake at 30 min (0.44 ± 0.05 mL vs. 0.06 ± 0.02 mL, p < 0.05) to 5 hours (1.65 ± 0.13 mL vs. 0.57 ± 0.05 mL, p < 0.001) after four days of low-Na+ diet. Associated to this, low-Na+ diet group also presents an sodium intake-dependent increase in water intake at 1 hour (0.99 ± 0.09 mL vs. 0.49 ± 0.12 mL,p < 0.05) to 5 hours (2.86 ± 0.13 mL vs. 1.64 ± 0.21 mL, p < 0.001). Regarding the sodium appetite, the low-Na+ diet induce an important increase in sodium preference at 30 min (31.4 ± 3.5 % vs. 12.9 ± 4.8 %, p < 0.001) to 5 hours (34.1 ± 1.9 % vs. 22.1 ± 1.9 %, p < 0.01). Our results indicate that sodium appetite control and the strong increase in sodium preference after sodium restriction is dependent on a variety of factors, that could be included the activation of sodium appetite signals (volume/ baroreceptors and peripheral Ang II) and inhibition of sodium satiety signals, as oxytocin.

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