SYNTHESIS AND SECRETION OF AN ESTRUS STAGE-SPECIFIC PROTEIN BY RAT UTERUS

A specific protein with an estimated molecular weight of 260 kDa was f ound to be synthesized and secreted into the incubation medium by rat uterus only during the estrus stage of the cycle. This secreted uterin e protein was designated as estrus stage-specific protein (ESP). ESP w as not produced by pregnant, lactating or immature pup rat uteri. Estr adiol administered to ovariectomized rats induced production of ESP wh ich was blocked by the antiestrogen, ICI 182, 780. The present results show that the synthesis and secretion of ESP is regulated by estradio l and this protein maybe involved in blastocyst implantation.