182 Brain Research, 222 (1981) 182-186 Elsevier/North-Holland Biomedical Press Brain renin: localization in rat brain synaptosomal fractions AHSAN HUSAIN, ROBERT R. SMEBY, JOHANNA KRONT1RIS-LITOWITZand ROBERT C. SPETH Research Division, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44106 (U.S.A.) (Accepted June 4th, 1981) Key words: brain renin - - synaptosomes - - choline acetyltransferase - - neuronal localization The distribution of brain renin activity was determined in subcellular fractions of rat brain prepared by discontinuous density gradient centrifugation. The highest amounts of brain renin activi- ty occurred in both the light and heavy synaptosomal fractions, while the activity of choline acetyl- transferase was elevated only in the light synaptosomal fraction. These results indicate an intraneu- tonal localization of brain renin. During the last twenty years, the octapeptide angiotensin II, has been shown to produce a variety of effects in the central nervous system such as increased blood pressure 3, induction of thirst 7, vasopressin release 14, and the induction of sodium appetite 1. In addition, specific angiotensin II receptors have also been demonstrated in the central nervous system 2. These effects may be caused either by peripherally genera- ted angiotensin II 6 or by angiotensin II generated within the brain tissue itself s. The latter suggestion is supported by the recent investigations of Osman et al. 16 and Hirose et al. 9 who have shown that a neutral protease present in whole brain extracts forms angiotensin I. This enzyme, which has a pH optimum between 6.5 and 7.016, has been referred to as brain renin 15. It has been partially separated from acid proteases by affinity chromatography on caesin-Sepharose 9 and hemoglobin-SepharosO 0 and also by chromatography on CM-cellulosO 6. In addition, brain renin can be separated from the small quantities of plasma renin contaminating brain preparations ~° and its presence has also been demonstrated in saline-perfused brains 16. A renin-like enzyme has also been shown to occur in the walls of blood vessels 8. Thus, it is not clear whether brain renin originates from the brain microvasculature or from renin containing neurons. This problem must be resolved before a physiological role for the brain renin-angiotensin system can be defined. As a first step towards resolving this problem, we investigated whether brain renin was present in biochemi- cally characterized synaptosomes (pinched-off nerve terminals) prepared from rat brains. A similar approach has been used previously to show the presence of the components of several putative neurotransmitter systems in neurons ~2,22,23. Choline acetyltransferase (CHAT), used by many investigators as a marker enzyme for synaptosomal fractionsS,13,1s, was measured in parallel with brain renin to biochemi- cally characterize the subcellular fractions of brain.