Quantification of an estrogen-dependent cat uterine protein (CUPED) in uterine flushings of estrogen- and progesterone-treated ovariectomized cats by radioimmunoassay.

We previously reported the purification of an estrogen-dependent cat uterine protein (CUPED) and the preparation of a specific anti-CUPED serum in rabbits. Here, we describe a specific radioimmunoassay for CUPED using the purified CUPED and anti-CUPED serum that was utilized to quantify CUPED in daily uterine flushings obtained from steroid-treated ovariectomized cats. The radioimmunoassay was sufficiently sensitive to measure 0.1-100 ng CUPED. CUPED levels were low in untreated ovariectomized cats, increased within one day after the onset of treatment with estradiol, and remained elevated as long as estradiol was unopposed by progesterone. The levels of CUPED decreased when progesterone was added to the treatment regimen either 7, 14, or 28 days after the initiation of estradiol treatment. The data indicate that the presence of CUPED in the uterine flushings is dependent on the presence of estradiol and the absence of progesterone, that CUPED appears in the uterine lumen within one day after the onset of treatment with estradiol, and that the levels of CUPED are sharply reduced within one day of administration of progesterone and become nondetectable after three days.