Postnatal Developmental Expression and Localization of Water Channel Proteins in the Rat Ovary.

Aquaporins (AQPs) are integral membrane proteins that are crucial for maintaining fluid homeostasis in the female reproductive system. This study aimed to determine the immunolocalization and protein expression levels of AQP1, AQP2, AQP3, and AQP4 in rat ovaries at postnatal days 1, 5, 15, 30, and 70. AQP1 immunoreactivity was detected in the cytoplasm and nuclei of oocytes and granulosa cells in follicles on postnatal days 1, 5, and 15. It was found to increase from day 30 onward. AQP2 immunoreactivity was positive only in the zona pellucida from postnatal day 5 onward. The AQP3 immunoreaction was similar to that of AQP1, with a particularly strong reaction in smooth muscle cells located in the walls of blood vessels. AQP4 immunoreactivity was found to be strongly positive in the cytoplasm of oocytes and granulosa cells on the postnatal days examined, and this reaction was higher than that observed in theca and luteal cells. Western blot analysis revealed that AQP1 protein expression levels were high on postnatal days 30 and 70 compared with other postnatal days. These data support the idea that AQPs are local regulators of water metabolism in oogenesis, folliculogenesis, and antrum formation during postnatal development.