ACTION OF ANGIOTENSIN-CONVERTING ENZYME-INHIBITORS IN RAT-BRAIN - INTERACTION WITH ISOPROTERENOL ASSESSED BY FOS IMMUNOCYTOCHEMISTRY

Low and high doses of angiotensin converting enzyme (ACE) inhibitors h ave been shown either to enhance or suppress, respectively, the water intake of rats induced by acute administration of isoproterenol. In or der to assess the role and sites of action of angiotensin II (Ang II) in this dual action of ACE inhibitors, rats were administered either l ow or high doses of enalapril or captopril, followed by isoproterenol, and were sacrificed 1 h later for determination of Fos-like immunorea ctivity (FLI) in brain. Isoproterenol induced strong FLI in the magnoc ellular paraventricular (PVN) and supraoptic (SON) nuclei, and moderat e staining along the structures of the rostral wall of the lamina term inalis (LT). Low doses of ACE inhibitors either had no effect or sligh tly increased FLI along the LT following isoproterenol. Enalapril redu ced FLI in some other regions, including the parvocellular PVN. In con trast, high doses of ACE inhibitors abolished FLI along the LT, and re duced FLI in the PVN and SON. Captopril, but not enalapril, induced so me FLI in the LT, SON and PVN. The data are discussed in terms of acce ss of ACE inhibitors to the brain, and interactions with structures in volved in Ang-related water intake.