DISTRIBUTION OF ANGIOTENSIN-II RECEPTOR SUBTYPES IN RAT-BRAIN NUCLEI

Angiotensin II (ANG II) receptor subtypes in rat brain were characterized and quantified by competitive radioligand binding using [I-125]Sar1Ile8 angiotensin II ([I-125]sarilesin) as a tracer and ANG II, sarilesin and the subtype selective ligands DuP 753 (AT1) and CGP 42112A (AT2) as competitors. The distribution of AT1 and AT2 receptors was determined in midbrain, brainstem, hypothalamus as well as in individual hypothalamic and periventricular nuclei. Whereas in midbrain and brainstem the AT1:AT2 ratio was 40%:60% and 70%:30% respectively, the AT1 receptors were by far predominant in hypothalamus and in the nuclei investigated. Interestingly, we found that approximately 25% of the ANG II receptors in hypothalamus did not bind DuP 753 even at 0.1 mM. These sites which bind CGP 42112A, ANG II and sarilesin may represent a third ANG II receptor subtype.