Effects of dietary sodium on brain angiotensin II receptors in spontaneously hypertensive rats.

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Abstract
The effects of dietary Na on angiotensin II (AII) receptor sites characteristics in the hypothalamus-thalamus-septum-midbrain (HTSM) region were examined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). A total of 24 SHR and 24 WKY were each divided into 2 groups, which were maintained on high Na diets or low Na diets for 4 wk, respectively. The binding capacity and affinity of the AII receptors were measured by radioreceptor assay. In WKY, the binding capacity of the AII receptors in the high Na group was significantly lower than that in the low Na group. On the ohter hand, the binding capacity of AII receptors was not significantly different between high and low Na groups in SHR. The secretion of arginine vasopressin (AVP) increased significantly in SHR and high Na intake. Apparently, in WKY the decrease of the binding capacity of the AII receptors in the HTSM region in response to a high Na intakes serves to attenuate an osmotical stimulus to AVP secretion. In SHR such a regulatory mechanism as adjusting the binding capacity of the AII receptors is lacking, and this seems to be responsible, at least in part, for the enhanced secreton of AVP on the Na loading.