Chemical lesion of the circumventricular organs with monosodium glutamate reduces the blood pressure of spontaneously hypertensive but not of one kidney-one clip hypertensive rats.

Subcutaneous injection of monosodium glutamate (MSG) on days 1, 5 and 9 of the experiment (5 g/kg per day) significantly reduced the blood pressure of a group of 10 spontaneously hypertensive rats (SHR) measured 7 and 14 days after treatment (200 +/- 7 mmHg vs 172 +/- 8 mmHg or 185 +/- 3 mmHg, respectively), without affecting that of 11 age-matched Wistar Kyoto (WKY) rats (127 +/- 7 mmHg vs 123 +/- 5 mmHg and 119 +/- 5 mmHg, respectively). Using autoradiographic methods and 125I-Sar1-angiotensin II, receptor binding was shown to be higher in the subfornical organ (SFO) of SHR (332 +/- 31 fmol/mg protein) when compared to WKY rats (240 +/- 30 fmol/mg protein) and similar (222 +/- 21 vs 170 +/- 14 fmol/mg protein) in the paraventricular nucleus (PVN). Binding to angiotensin-converting enzyme (ACE) was evaluated using the ACE inhibitor 125I-351A as ligand. Binding to ACE was lower in SHR in the PVN and the globus pallidus (GP) of SHR when compared to WKY rats (PVN: 111 +/- 9 vs 172 +/- 13 and GP: 163 +/- 2 vs 213 +/- 7 fmol/mg protein) and similar in the SFO, choroid plexus (ChP) and caudate nucleus (CD) of both strains (SFO: 779 +/- 107 vs 805 +/- 169; ChP: 2,780 +/- 210 vs 3,140 +/- 360 and CD: 461 +/- 42 vs 424 +/- 18 fmol/mg protein). No changes in angiotensin II (Ang II) receptor number or binding to ACE were detected in these brain areas after MSG treatment of SHR or WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)