237. Aquaporins in rat uterine epithelial cells during early pregnancy and in response to progesterone

Abstract

Implantation of the rat blastocyst is a highly regulated process, involving transformation of the uterine environment into one which is receptive to an implanting blastocyst. At the time of implantation, in response to progesterone, there is a dramatic decrease in the amount of uterine luminal fluid leading to close apposition between the luminal epithelium and trophoblastic cells. The rat blastocyst also always implants at the antimesometrial pole of the uterine lumen and currently mechanisms regulating this process are unknown. Aquaporins, a family of transmembrane water channels, are involved in the regulation of water movement across epithelial barriers. We investigated several aquaporins in the rat uterus during early pregnancy using reverse transcriptase PCR. Immunofluorescence and immunogold electron microscopy techniques were then used to investigate the localisation of particular aquaporins including AQP5 in the uterine epithelium during early pregnancy and in ovariectomised rats treated with progesterone. There was an increase in AQP5 molecules in the apical plasma membrane of luminal epithelial cells at the time of implantation, with a greater increase at the mesometrial compared to antimesometrial pole. A similar result was seen in luminal epithelial cells from ovariectomised rats treated with progesterone, however there was no differential concentration between mesometrial and antimesometrial poles, as there was during early pregnancy. It is suggested that the increase in AQP5 protein expression in the apical plasma membrane of luminal epithelial cells is involved in reabsorption of luminal fluid at the time of implantation. Furthermore, the differential concentration of AQP5 on luminal epithelial cells at the time of implantation could lead to the establishment of a fluid gradient within the uterine lumen and hence lead to the asymmetrical implantation position of the rat blastocyst.