Significance of high glucose-6-phosphatase activity in rat oviduct epithelium

To study the origin of glucose in the oviduct fluid, we cytochemically examined glucose-6-phosphatase (G6Pase) activity in rat oviduct. The activity in the whole oviduct was also assayed biochemically. During proestrous, estrous, and metestrous phases, staining reaction for the activity was moderate in the epithelium of the caudal isthmus (CaI) and uterotubal junction (UJ), whereas it was weak in that of the ampulla (A) and cephalic isthmus (CeI). In the diestrous phase, staining reaction in the epithelium of CaI and UJ became strong although it remained weak in that of A and CeI. Reaction product for the activity was localized in the endoplasmic reticulum and nuclear envelope of all cell types in the epithelium. The amount of reaction product in secretory cells was small to moderate in CaI and UJ, and small in A and CeI during proestrus, estrus, and metestrus. In diestrous the amount became abundant in CaI and UJ and moderate in A and CeI. However, the amount in ciliated cells remained small in the four segments during the four phases. The biochemical activity in diestrous was greater than that in proestrus, estrus, or metestrus. This shows that the activity is high in secretory cells in the epithelium of CaI and UJ in the diestrous phase and suggests that the role of the high activity is to release glucose into the oviduct fluid for use by the embryo passing down the CaI and UJ to the uterus.