Experimentelle Untersuchungen über die Bedeutung des Renin-Angiotensin-Systems in der Netzhaut - Eine Übersicht

Abstract

BACKGROUND Many peptides now identified in the brain were previously thought of as exclusively peripheral hormones. Among those, the renin-angiotensin system (RAS) is not only found to be of great importance in peripheral vasomotor and electrolyte homeostasis but also acts as neurotransmitter or modulator in the central nervous system. Here we review a number of experiments performed by us pointing to a modulation effect of the RAS unrelated to its vasoactive mechanisms. The biochemical basis as well as the different methods employed will be described in detail. METHODS RAS enzyme activity within the different ocular structures were determined by means of fluorimetric measurements. Possible neurophysiological effects of the RAS on retinal function were established through electroretinographic in-vitro and in-vivo recordings. Immunocytochemical staining was employed to morphologically identify possible sites involved. RESULTS The performed fluorimetric measurements revealed highest Angiotensin-Converting Enzyme (ACE) activity within the neuroretina. Electroretinographic experiments have shown that variation in angiotensin-II activity is followed by reversible, dose-dependent effects on inner retinal signals. Clear evidence was found by immunohistochemistry that there is a discrete subpopulation of angiotensin-positive cells in the inner retina. CONCLUSIONS These findings demonstrate that the Renin-Angiotensin-System has neuronal sources and is physiologically active in the mammalian retina not purely related to vasoactive mechanisms. The RAS effector hormone angiotensin-II might therefore be a putative neurotransmitter in a subpopulation of retinal neurons. Reported side-effects of vasoactive substances, such as ACE-inhibitors on the visual function might be explained hereby.