Oestrous cycle and pregnancy effects on the distribution of oestrogen and progesterone receptors in bovine endometrium

Reproductive cyclicity and Pregnancy require cell and tissue specific expre ssion of oestrogen (OR) and progesterone receptors (PR). To determine the e ffects of cycle day and early Pregnancy (days 16-30) on the distribution of OR and PR, uteri were collected from cycling (n = 39), pregnant (n = 14), and steroid-treated ovariectomized cattle (n = 10). Immunohistochemistry wa s used to localize OR and PR, and staining intensity was scored. Moderate s taining for the PR was detected in the stroma at proestrus (days 17-20). Ex pression increased through oestrous, reaching maximal levels by metestrus ( days 1-6) (P <0.05). During diestrus (days 7-16), PR expression was downreg ulated (P <0.05). Progesterone receptor expression was detected in the lumi nal epithelium in one of three animals each at days 3 and 6 of the oestrous cycle. In pregnant animals only, caruncular stroma showed reduced PR stain ing compared to intercaruncular stroma (P <0.05). Reactivity to the OR anti body in cycling animals was detected in the stroma and glandular epithelium . Levels increased through proestrus and oestrous, were maximal during mete strus (P <0.05), and decreased during diestrus (P <0.05). Interestingly, th ere was transient upregulation in the luminal epithelium on day 16 or day 1 4 (P <0.05). This was not evident at day 16 of pregnancy, although some OR reactivity was present in stroma. and glands. BN day 18 of pregnancy OR A e re undetectable (P <0.05). Oestrogen-treated ovariectomized animals had inc reased OR and PR expression in comparison to progesterone treated cows (P < 0.05). Untreated ovariectomized cows showed constitutive steroid receptor e xpression. These results support the widely accepted role for sex steroids in the regulation of their receptors and indicate that there is paracrine r egulation of steroid receptor expression in the bovine uterus. (C) 2001 Har court Publishers Ltd.