Vascular supply of the endolymphatic sac. A gross and ultrastructural study in the Mongolian gerbil under normal and experimental conditions.

The vascular network of the gerbilline endolymphatic sac (ES) and its dynamics were studied using different morphological procedures. The normal condition was compared to serum osmotic alterations induced by changing the daily water intake of the animals. The gross morphology was studied after intracardiac injection of Berlin Blue, while light (LM) and transmission electron microscopy (TEM) were applied for the ultrastructural analysis. A rich vascular supply was seen in the intermediate portion of the normal ES, and the presence of micropores and fenestrations confirmed also in this animal species the importance of this region for fluid exchange. The lacunar arrangement of the vessels in the distal portion of the ES, together with the close vicinity of this area to the bone marrow, led to the hypothesis that the distal ES possesses a functional role as blood reservoir. The hyperosmotic condition induced by water deprivation appeared to affect mostly the morphology of the red cells. In some of the capillaries, a thrombus-like occlusion was also evident. This vascular occlusive condition appeared to be partly reversible when water intake was reestablished, although the morphological alterations induced by the hyperosmotic condition to the subepithelial tissue appeared not to be reversible.