Several investigators have recently reported that experimental conditions in a mouse model which affect the pressure/volume ratio in the endolymphatic space increase the amount of a stainable substance in the endolymphatic sac (ES) lumen. They suggest that this stainable substance may play an important role in the regulation of pressure/volume homeostasis. The guinea pig is often used as an animal model of experimentally induced endolymphatic hydrops. In this study we interrupted the endolymphatic duct selectively in guinea pigs. The histology of the ES was studied by light microscopy at various time intervals after the operation. The amount of the stainable substance in the ES lumen on the operated side was increased for a few weeks postoperatively. This finding suggests that in the guinea pig model also the stainable substance in the ES lumen is involved in the regulation of pressure/volume homeostasis in the endolymphatic space.
