Localization of oestradiol, progesterone and oxytocin receptors in the uterus during the oestrous cycle and early pregnancy of the ewe
Authors: Wathes D. C. , Hamon M. 
Published: December 2008

ABSTRACT
Uterine tissue samples were collected from 47 ewes at various stages of the oestrous cycle and early pregnancy (until day 21) and during seasonal anoestrus. Cryostat sections were immunostained to determine the localization of oestradiol and progesterone receptors using specific monoclonal antibodies. Oxytocin receptors were localized by autoradiography in sections from the same ewes using the 125I-labelled oxytocin antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH29]- vasotocin. Plasma progesterone measurements were made during the preceding cycle up to the time of slaughter.
Oestradiol receptor concentrations were maximal in all regions of the tract at oestrus. Immunostaining of the luminal epithelium, superficial glandular epithelium, stroma and myometrium decreased in the early luteal phase but was maintained for longer in the deep glands. Progesterone receptor immunostaining in the luminal epithelium and superficial glands developed in the early luteal phase (days 1–2) with a somewhat later appearance in the deep glands (days 5–7). Progesterone receptor concentrations in the stroma and myometrium also reached a maximum in the early luteal phase. Myometrial staining was clearly maintained throughout the luteal phase whereas stromal staining was variable between ewes. For both oestradiol and progesterone receptors no differences were apparent between pregnant and non-pregnant ewes between days 2 and 12, but pregnant ewes did not show the general increases in oestradiol receptor staining associated with luteolysis on days 14–15.
Oxytocin receptors first developed in the luminal epithelium of non-pregnant ewes on day 14 of the cycle and spread to the superficial glands, caruncular stroma, deep glands and myometrium at oestrus before decreasing in reverse order on days 1–2. Specific binding was not detectable on days 5–12 of the cycle or on days 14 or 21 of pregnancy. The appearance of oxytocin receptors in the luminal epithelium on day 14 preceded that of both the oestradiol and progesterone receptors in the epithelial cells and the fall in plasma progesterone. It was followed by the development of oestradiol and oxytocin receptors in the superficial glands, deep glands, caruncular stroma and myometrium, with the two receptor populations showing a significant positive association in these tissues. The loss of oxytocin receptors in all regions occurred as plasma progesterone levels were increasing, but the association between these two variables was only significant in the superficial glands. The development of progesterone receptors in different tissues could not be explained on the basis of either oestradiol receptor content or plasma progesterone. We conclude that all three receptor populations change in a dynamic manner during the oestrous cycle with variations both between days and between different uterine compartments. The complex pattern of receptor formation and loss suggests that, in addition to the circulating steroid hormone concentrations, local paracrine factors are likely to be involved in their regulation.
Journal of Endocrinology (1993) 138, 479–491