1 Early Synthesis of Uterine Proteins After a Decidual Stimulus in the Pseudopregnant Rat

The synthesis of soluble proteins in the uterus of the pseudopregnant rat after decidual induction has been examined by means of a polyacrylamide electrophoretic technique with double-labeling incorporation of amino acids. It has been shown by the incorporation of l HI-leucine into soluble proteins that the endometrial tissue synthesizes a single protein band 1 h after the decidual stimulus. This protein migrates ahead of the bulk of the proteins, and slightly faster than serum albumin during the 6 percent polyacrylamide electrophoretic run. The protein(s) neither shows up when the whole uterus is examined 1, 2, 3, 4 and 5 h after decidual induction nor in the endometrium on day L3 of pseudopregnancy, the day on which the uterus is insensitive to the decidual stimulus. It is suggested that this protein is synthesized only when the endometrial cells differentiate to form the decidual tissue. The antimesometrial region of the endometrium previously subjected to the decidual stimulus seems to show a higher capacity to synthesize this protein than in the mesometrial region of the same stimulated tissue