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HINDLIMB-SUSPENSION, WATER DEPRIVATION AND SALT-LOADING AFFECT ANGIOTENSIN-CONVERTING ENZYME (ACE) EXPRESSION IN RAT CHOROID PLEXUS.    E. Vila-Porcile¹, C. Carcenac¹, C. Masseguin¹, J.-M. Gasc² and J. Gabrion¹.  ¹Inst. des Neurosci., UMR CNRS 7624, Univ. P.-&-M. Curie, Paris, France (e.mail: jgabrion@snv.jussieu.fr)., ²INSWEM U36, Collиge de France, Paris.

Angiotensin I-converting enzyme (ACE, EC 3.4.15.1) is a transmembrane ectopeptidase that generates angiotensin II (AII), a vasopressor and aldosterone stimulating peptide, from angiotensin I, and is mainly express-ed in vascular walls, lungs and adrenals but also in choroidal epithelial cells, in brain.  When immunodetected in choroid plexus by immunofluorescence and immunogold methods with the specific polyclonal Y4 anti-body¹, the enzyme is associated to the plasma membrane and asymmetrically distributed at the apical pole of the cells in control rats.  It colocalizes, at the level of microvilli membranes, with angiotensin II, detected with the specific BAII-01 antibody (gift from J. Sealey, Cornell U., NY).  Adaptation to head-down suspension (HDS) induces cellular and molecular alterations in choroidal cells^2,3 in response to central hypovolemia, which results from body fluid shifts. In this study, the choroidal ACE expression was observed also impaired by HDS. ACE was strongly reduced in choroid plexus of rats suspended for 14 days and more again, in rats suspended for 28 days, suggesting that conversion of AI into AII was reduced in these conditions. The altered ACE distribution was restored after a 2-day return to orthostatic position, the enzyme appearing even overexpressed. When detected in choroid plexus of rats after 5 or 7 days of water deprivation or salt-loading (2% NaCl in drinking water), ACE was reduced and heterogeneously distributed under both conditions. The most altered pattern was noted in salt-loaded rats. In all these experimental conditions, known to affect the water balance, most of the choroidal apical proteins were down-regulated. As AII is normally found in CSF, it might be suggested that reduced levels of choroidal ACE noted during such conditions could result in AII decrease in CSF and might be involved in the cerebral fluid balance during hypovolemia.  (Supported by CNES and CNRS funding.) ¹Mounier et al., Kidney Int., 1987, 32:684-690; ² Gabrion et al., Brain Res., 1996, 734:301-315; ³ Davet et al., J. Appl. Physiol., 1998, 84:19-29.