Progesterone stimulation of fluid absorption by the rat uterine gland

The purpose of this study was to test the hypothesis that the steroid environment affects fluid absorption by the uterine glands. Laser scanning confocal microscopy of the distribution of an extracellular marker (fluorescein isothiocyanate-labelled dextran) within rat uterine glands showed that the endometrial glands change their fluid handling characteristics under different hormonal conditions. Under progesterone dominance, the glands showed an amiloride-sensitive dextran accumulation indicating sodium-dependent fluid absorption; however, this was absent in the oestrogen-dominated state. The rate of fluid uptake in the progesterone-stimulated gland opening was estimated to be approximately 1 x 10(-4) cm s(-1), requiring a suction pressure of between 10 and 20 mm Hg at the mucosal surface. This study provides the first direct evidence of fluid absorption by the uterine glands. Such absorption may provide the mechanism for closure of the uterine lumen and immobilization of the blastocyst necessary for implantation.