The cyclic pattern of the immunocytochemical expression of oestrogen and progesterone receptors in human myometrial and endometrial layers: characterization of the endometrial-subendometrial unit

Immunocytochemistry of oestrogen receptor (ER) and progesterone receptor (P R) expression of the whole uterine muscular wall and the endometrium was pe rformed in order to obtain morphological and functional insights into the r egulation of cyclic uterine peristalsis, which is confined to the endometri um and the subendometrial myometrium and serves functions such as rapid and sustained sperm transport. The study revealed that the subendometrial myom etrium or stratum subvasculare with a predominantly circular arrangement of muscular fibres exhibits a cyclic pattern of ER and PR expression that par allels that of the endometrium, whereas the outer portion of the uterine wa ll composed of the stratum vasculare and supravasculare, which represents t he bulk of the uterine musculature, does not exhibit a cyclic pattern of ER and PR expression. According to ontogenetic and phylogenetic data from the literature, the outer myometrium is of non-paramesonephric origin with fun ctions confined to parturition, while the inner myometrial layer together w ith the glandular epithelium and the stroma of the endometrium is of parame sonephric origin with various functions during the cycle in addition to tho se during pregnancy and parturition, The inner quarter of the stratum vascu lare adjacent to the stratum subvasculare constitutes a transitional zone i n that the cyclicity of receptor staining becomes, in radial direction, gra dually less expressed. Morphologically this zone corresponds to the inner p art of the stratum vasculare where its muscular fibres blend with those of the stratum subvasculare.