Detection and quantification of CUPED, an estrogen-dependent uterine protein, in uterine fluid and endometrial tissue of estrous and pregnant cats.

Uterine flushings, media from cultured endometrial explants, and endometrial tissue obtained from estrous and pregnant cats were analyzed for the presence of a previously characterized, high-molecular-weight, estrogen-dependent glycoprotein (CUPED) by polyacrylamide-gel electrophoresis, Western blots, radioimmunoassay, and immunocytochemistry. Elevated levels of CUPED were present within the flushings, media, and tissue of estrous and 3-day postcoital animals. High levels of CUPED were also present in the flushings of 5-day postcoital animals; but the ability of endometrial explants to synthesize CUPED during short-term culture was greatly reduced, and only some of the endometrial glands contained CUPED secretory granules. CUPED was essentially nondetectable in the flushings, media, and tissues of animals pregnant for 7 or more days. Thus CUPED is present within the uterine lumen of the cycling cat at the time of sperm migration through the uterus and also for the first day or two that the developing blastocyst is present within the uterine lumen. The disappearance of CUPED from the tissue and flushings was correlated with the luteal production of progesterone.