Introduction: High sodium intake is an important risk factor for cardiovascular and renal diseases. However, the role of sodium appetite in the development of salt-sensitive hypertension is not well understood. Hypothesis: We hypothesized that higher sodium appetite indexed by spontaneous sodium intake in a preference test may correlate with salt-sensitive hypertension in male and female adult Wistar rats and alter reflex control of blood pressure (BP). Methods: Male and female Wistar rats, 3 months aged, were individually housed and had free access to food, tap water and saline (1.8% NaCl) solution for 35 days (preference test). Water and saline intake were evaluated daily, between 4:00 and 6:00 pm. Thereafter, animals were anesthetized with ketamine plus xylazine and had femoral artery and vein cannulated for BP evaluation and drug injection. After 72 hours of recovering, BP, heart rate (HR), baroreflex index (BRI) and cardiopulmonary reflex response (CPR) were assessed. Results: Females (N=21) drank 4.2 times more saline (10.6±1.2 female vs. 2.5±0.5 mL/100g b.w. male) and 1.4 times more water (11.7±0.5 female vs. 8.4±0.2 mL/100g b.w. male) than males (N=30). Males had a bimodal distribution of the saline volume intake, with 37% of the animals drinking more than average group intake. Females had a broad distribution of the saline volume intake, with 52% of the animals drinking more than average group intake. Males on preference test had higher BP levels than females (115±1.5 male vs. 109±1.4 mmHg female; p=0.0093; n=12). BP levels of males on preference test were not different of males off preference test (115±1.5 vs. 111±1.4 mmHg respectively; p=0.0596). Sodium appetite was not correlated with BP or BRI in both, male and female (Pearson r correlation). Phenylbiguanide activated CPR (20 µg/kg) was higher in female (-43±3 mmHg) compared to male (-63±3 mmHg) and showed negative correlation with saline intake. Neurogenic pressor activity was indexed by the fall in BP due to hexamethonium (20 mg/kg) injection and no difference was found between males and females, and no correlation was stablished with salt intake. Conclusion: Results suggest that female Wistar rats display smaller BP despite of the greatest salt appetite compared to males and, interestingly, sodium appetite did not correlate with BP levels. The decreased CPR associated with high salt intake may indicate a role for this reflex in cardiovascular control under high salt intake in female rats.
Cardoso et al. (Mon,) studied this question.