Regulation of rat brain angiotensin II (AII) receptors by intravenous AII and low dietary Na +

Abstract

Previous studies have shown the presence of specific AII receptors at several areas of the brain. The purpose of this study was to examine by radioreceptor assay the effect of intravenous AII infusion (5 or 25 ng/kg/min) and low dietary Na + (<8mmol/100g) on AII receptors in five brain regions: the olfactory lobes (OLF), hypothalamus/thalamus/septum (HTS), midbrain (MID), cerebellum (CER) and medulla (MED). Scatchard analysis of binding data from control rats showed significant (P < 0.01ANOVA) differences between brain areas in bothK a (1.54OLF, 1.87HTS, 1.25MID, 1.33MED, 0.77CER× 10 9M −1) and R 0 (321 OLF, 224 HTS, 203 MID, 145 MED, 41 CER fmol/g tissue). Following the i.v. infusion of AII for 4–7 days, marked changes were observed in the areas with a porous BBB, the HTS and MED. Both theK a [3.20 (HTS) and 0.67 (MED) × 10 9M −1] and R 0 [116 (HTS) and 249 (MED) fmol/g tissue] changed. In addition, decreases in R 0 were also observed in the OLF (241 fmol/g tissue) and CER (21 fmol/g tissue), areas which have not been considered as being accessible to blood-borne AII. A low Na + diet for 21–30 days changed theK a and R 0 in all five regions but not in similar directions. Furthermore, with the exception of the OLF the direction of change was not similar to that caused by i.v. infusion of AII. It was concluded that AII receptor sites in the rat brain differ from each other in both receptor properties and in their response to such regulatory factors as AII and Na + depletion. In addition, the division of receptor sites into those within and those outside the BBB appears to lack functional significance since both types were affected by i.v. exogenous AII.