AUTORADIOGRAPHIC EVIDENCE FOR A BRADYKININ ANGIOTENSIN-II RECEPTOR RECEPTOR INTERACTION IN THE RAT-BRAIN/

Using angiotensin II(ANG II) to compete with (3-[I-125]iodotyrosyl-4,S ar(1), Ile(8))ANG-II([I-125]Sar(1), Ile(8))ANG II)) for its binding si tes in the nucleus of the solitary tract (nTS) and the paraventricular hypothalamic nucleus (PV) bradykinin (10 nM) reduced the IC50 value ( 48 nM) of ANG II, an action blocked by the bradykinin B-2 antagonist H OE-140 (100 nM). In contrast, when analysing the high-affinity site (K -d 3.1 nM) for [I-125]ANG II in the nTS bradykinin (10 nM) increased t he K-d value. Thus, a central bradykinin/ANG II receptor interaction m ay exist involving a differential regulation of the high- and low-affi nity ANG II receptors in the nTS. This regulation by bradykinin of ang iotensin receptors in the nTS may help to explain the central vasopres sor effect of bradykinin.