Progesterone receptor subtype B is differentially regulated in human endometrial stroma

Two anti-progesterone receptor (PgR) antibodies, a new one specific toPgRB, the other to PgR subtypes A + B, have been used to examine thecellular location of PgR subtypes A and B in normal endometrium throughoutthe menstrual cycle and in early human decidua by standardimmunohistochemical techniques. PgR(A+B) is the receptor detected by theantibody recognizing both isoforms of the receptor. PgRB is the receptordetected by the new antibody specific to the B isoform. Since it is notpossible to raise antibody specific to PgR subtype A, allimmunohistochemical analysis of the PgRA subtype is by subtractiveinference. Thus we refer to PgRA as the subtype responsible for positiveimmunoreactivity when the PgRB subtype cannot be specifically detected.Endometrial biopsies were collected from 40 women with regular menses (n =5 each stage of cycle: menstrual; early, mid and late proliferative;ovulatory; early, mid, and late secretory). Decidual tissue was obtainedfrom 10 women undergoing first trimester surgical termination of pregnancy.As previously reported, the PgR(A+B) antibody stained glandular and stromalnuclei during the proliferative phase but only stromal nuclei during thesecretory phase and early pregnancy. The new PgRB antibody also stainedboth cell types intensely during the proliferative phase, but failed tostain either stromal or glandular nuclei strongly during the secretoryphase and early pregnancy. We concluded that, while both PgR subtypes werepresent in glands and stroma in the proliferative phase, and both subtypeswere dramatically reduced in the glands during the secretory phase, PgRAremained as the predominant type in the stroma during the secretory phaseand early pregnancy. The profound effects of progesterone on endometriumduring the secretory phase and early pregnancy appear to be mediatedprimarily by PgRA in the stroma.