Progesterone induction of the uterine milk proteins: major secretory proteins of sheep endometrium.

Progesterone induction of the uterine milk proteins (UTMP), the major secretory products of the ovine uterus during pregnancy, was studied in ovariectomized ewes given physiological levels of progesterone for 0, 2, 6, 14, or 30 days. Western blotting of uterine flushes and of endometrial explant culture medium, endometrial RNA analyses on dot and Northern blots, and immunocytochemistry performed on uterine tissue sections demonstrated the presence of low levels of UTMP mRNA and UTMP protein after 6 days of progesterone therapy, and increasing levels of UTMP production and secretion after 14 days. Highest activity was observed at Day 30. The induction of the UTMP progressed from small amounts of antigen present in the supranuclear region of a few epithelial cells in deep and middle-depth regions of uterine glands in the Day 6 progesterone-treatment group to large amounts detected in epithelial cells spread throughout the length of the glands in later groups. UTMP production was also identified in the uteri of intact ewes at Day 16 (but not earlier) of the estrous cycle and during early pregnancy (Days 14 to 22). Production of a protein similar to the UTMP was also noted in the uterus of a pregnant cow. The UTMP provide a good model of a progesterone-responsive secretory protein in a mammal whose synthesis is increased gradually over a period of weeks.