Increased number of angiotensin II receptors in the subfornical organ of spontaneously hypertensive rats.

Angiotensin II receptors were studied in the brain of spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar-Kyoto rats (WKY) by quantitative autoradiographic methods coupled to computerized microdensitometry and comparison with 125I-standards, after incubation of brain sections with 125I-Sar1-angiotensin II. Binding sites for angiotensin II were highly localized in the subfornical organ. The number of binding sites was higher in the subfornical organ of young (4-week-old) and adult (14-week-old) SHR when compared with WKY rats (young rats: 735 +/- 91 and 444 +/- 85 fmol/mg protein, SHR and WKY, respectively; adult rats: 1390 +/- 64 and 848 +/- 136 fmol/mg protein, SHR and WKY, respectively). Our results suggest that subfornical organ angiotensin II receptors are involved in genetic hypertension in the rat. An increased number of subfornical organ angiotensin II receptors substantiates the idea of an overactive central angiotensin II system in spontaneous hypertension.