Morphology of the endolymphatic sac after an acute endolymphatic in the guinea pig hydrops

The role of the endolymphatic sac (ES) in endolymph volume homeostasis is speculative. The present study investigates changes of the ES's epithelia and luminal filling after induction of an acute endolymphatic hydrops. After microiniection of 1.1 mu l artificial endolymph into scala media of the cochlea, guinea pigs were terminated immediately (n = 6) or after different time intervals; 1/2 h (n = 3), 1 h (n = 4) and 2 h (n = 4). Inner ear specimens were processed for light and/or transmission electron microscopy. The noninjected contralateral ear served as a histological control. Correct injection was confirmed by detection of microspheres in the endolymphatic compartment after the same microinjection procedure. In all specimens, ribosome rich cells and intraluminal macrophages appeared to be actively involved in degradation of homogeneous substance (HS) by secreting lytic enzymes and digestion, respectively. Amazingly, in our study no ES differences were found between injected and non-injected ears and no distinct changes were observed in guinea pigs terminated after different time intervals. The ES's luminal HIS was always present and often to a large extent. This is in contrast with [Hear. Res. 138, 81] dramatic changes were observed. Endolymph volume homeostasis is a complex mechanism, in which the role of HS remains obscure. (c) 2004 Elsevier B.V. All rights reserved.