EFFECTS OF DIETARY SODIUM ON BRAIN ANGIOTENSIN II RECEPTORS IN SPONTANEOUSLY HYPERTENSIVE RATS

抄録

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