Enhanced endocytotic and transcytotic activity in the rat endometrium prior to embryo implantation.
BACKGROUND
Understanding the mechanisms by which fluid absorption and secretion occur in the endometrium is clinically important since conditions that deregulate this process reduce fertility. It has been suggested that luminal epithelial cells induce a crucial step in the process of embryo implantation called uterine closure via endocytotic fluid uptake. Uterine lumen closure is a key step in the process of embryo implantation and is absent in some infertile strains of mice.


METHODS
To investigate the process of uterine closure a ferritin-based tracer, used as a marker of endocytosis, was injected into the uterine lumen on day 5 of pregnancy when closure occurs.


RESULTS
Unexpectedly, luminal epithelial uptake of tracer was minimal on day 5 of pregnancy discrediting endocytosis as the induction method of uterine closure. In contrast, ferritin was found deep in the stromal portion of the endometrium in pre-pregnant animals.


CONCLUSIONS
We have shown for the first time that uterine closure is not induced by luminal epithelial cell driven endocytosis. Another novel finding of this study was the passage of the tracer ferritin up to 15 cells deep into the endometrium suggesting an as yet unstudied mechanism by which information can be transported from the uterine lumen to the underlying stroma.
Quinn
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Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Institute of Medical Sciences, University of Toronto, 150 Bloor St W, Suite 210, Toronto, ON, Canada, M5G 1X5.
Folkard
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Detmar
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Casper
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D000818:Animals; D002468:Cell Physiological Phenomena; D010064:Embryo Implantation; D004705:Endocytosis; D004717:Endometrium / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D005293:Ferritins / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley
D005293:Ferritins