Autoradiography of angiotensin-converting enzyme in fixed and unfixed rat brain using the specific enzyme inhibitor [ 125I]351A or a polyclonal antibody and [ 125I]staphylococcal protein A

Abstract

Angiotensin-converting enzyme (ACE, kininase II, EC 3.4.15.1) was visualized in unfixed rat brain sections by autoradiography after incubation with a polyclonal goat anti-rabbit lung converting-enzyme antibody and [ 125I]protein A. Paraformaldehyde fixation interfered with the recognition of ACE by its antibody in brain nuclei but not in the choroid plexus. Conversely, incubation of brain sections with the specific ACE inhibitor [ 125I]351A allowed ACE visualization in either unfixed and paraformaldehyde-fixed brain sections, since [ 125I]351A binding was not affected by our fixation conditions. Our results indicate that ACE could be visualized in unfixed brain sections directly by incubation with the specific inhibitor [ 125I]351A or indirectly by radioimmunohistochemistry and autoradiography. Different autoradiographic methods could be used to visualize and quantify ACE in unfixed or fixed tissues.