Restricted dietary sodium intake alters peripheral but not central angiotensin II receptors

Male Sprague-Dawley rats were maintained on either a normal or low-sodium diet for 5 weeks to examine whether dietary sodium restriction alters angiotensin II (Ang II) receptors. The receptor sites in the hypothalamus-thalamus-septum (H-T-S) region of the brain, the adrenal glands and bladder visceral smooth muscle were measured by saturation isotherm binding assays using 125I-Ang II. Compared to control rats, the low-sodium diet group showed a smaller weight gain, reduced water intake, elevated hematocrit, and decreased urinary sodium concentration. In addition, sodium-depleted rats had a 10-fold elevation in plasma renin activity. However, neither binding affinity of 125I-Ang II to the brain H-T-S region nor its density was significantly different between the two groups. In contrast, both the 125I-Ang II binding density and dissociation constant in the adrenal gland were significantly elevated, while the binding density of 125-I-Ang II in the bladder smooth muscle was significantly decreased in the sodium-restricted group. These results suggest that dietary sodium depletion does not alter Ang II receptors in the rat brain areas wherein Ang II exerts the majority of its central actions.