Differential Regulation of Brain Angiotensin II in Genetically Hypertensive and Normotensive Rats after Nephrectomy

To investigate the role of tissue angiotensin II (Ang II) in the maintenance of hypertension after nephrectomy in spontaneously hypertensive rats (SHR), Ang II levels were measured in various tissues of both 12-week-old SHR and normotensive control, Wistar-Kyoto rats (WKY), 48 h after nephrectomy or sham operation. Ang II was determined by radioimmunoassay coupled with high performance liquid chromatography. Nephrectomy caused a decrease of plasma renin activity and plasma Ang II concentration in both SHR and WKY. Aortic Ang II levels were significantly lowered by nephrectomy only in WKY, and not in SHR. Ang II levels in hypothalamic block, brainstem and cerebellum of SHR increased after nephrectomy, whereas those of WKY were unchanged. Intracerebroventricular administration of ceronapril, an angiotensin converting enzyme inhibitor, significantly decreased sustained high blood pressure in SHR 48 h after nephrectomy compared with vehicle administration, whereas intravenous administration had no effect. These results suggest that in spite of the important role of the renal renin-angiotensin system in maintenance of high blood pressure in SHR, control mechanisms may switch to other systems after nephrectomy, and that the increased brain Ang II levels after nephrectomy may be related to these mechanisms.