IMMUNOCYTOCHEMICAL LOCALIZATION AND CHANGES IN ENDOMETRIAL PROGESTIN RECEPTOR PROTEIN DURING THE PORCINE ESTROUS-CYCLE AND EARLY-PREGNANCY

Changes of progesterone receptor (PR) protein and cellular localizatio n in the endometrium were evaluated during the oestrous cycle and earl y pregnancy of the gilt. During the oestrous cycle, the concentration of total PR protein within the endometrium was highest on Days 0-5 and decreased on Day 10. The endometrial concentration of PR reached a na dir on Day 12 and this level was maintained throughout the remainder o f the oestrous cycle (Day 18). In pregnant gilts, the concentration of endometrial PR protein from Day 10 to Day 18 was similar to that in c yclic gilts. Western blot analysis with antiserum specific for the A a nd B isoforms of PR indicated that porcine endometrium expresses both isoforms of PR. Immunostaining was detectable for both the A and B iso forms of PR from Day 0 to Day 12 of the oestrous cycle. However, no st aining was observed on Day 15 and Day 18 of the oestrous cycle or preg nancy Immunocytochemical localization of PR in the endometrium of cycl ic gilts and pregnant gilts indicated that there was intense staining for PR in surface epithelium and glandular epithelium during oestrus ( Day 0) and on Day 5. However, the staining was less intense on Day 7 a nd Day 10 of the oestrous cycle and no epithelial staining was observe d after Day 12. PRs were present in the stroma and myometrium througho ut the oestrous cycle and early pregnancy. The presence of conceptuses during pregnancy did not affect the loss of PR from the uterine epith elium after Day 10 of gestation. Down-regulation of epithelial PR migh t be one factor involved in the timing of luteolysis during the oestro us cycle as well as conceptus growth and placentation during early pre gnancy.