Regional changes in the spatio-temporal pattern of progesterone receptor (PR) expression in the guinea-pig genital tract as parturition approaches

Normal parturition in guinea-pig involves changes in responsiveness of the genital tract to estrogen and progesterone. To better characterize endocrine control of guinea-pig parturition, protein and mRNA expression of estrogen receptor-α (ERα) and progesterone receptor (PR) were quantitatively evaluated in lower (LUS) and upper (UUS) uterine segments, cervix (C) and pubic symphyseal ligament (PSL) at three stages of pregnancy (established based on interpubic distance, 0 mm: non-relaxed group, 4–6 mm: 5 days before parturition, 11–14 mm: 1–2 days prepartum) and immediately after parturition. Towards parturition, no changes in PR mRNA levels were recorded in the UUS, whereas the LUS displayed a gradual increase. PR transcripts exhibited decreased levels during parturition in C and PSL. Levels of PR mRNA were increased in the LUS compared with that of the UUS only at parturition. Regarding protein expression during parturition, PR levels decreased in the UUS whereas in the LUS increased. In C and PSL, PR protein expression decreased 1–2 days prepartum and remained low during parturition. None of the regions studied showed changes in mRNA or protein expression of ERα. Therefore, functional regionalization of the guinea-pig genital tract is associated with changes in the spatio-temporal pattern of PR expression as parturition approaches.