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 expression of oestrogen (OR) and progesterone receptors (PR). To determine the effects 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 was used to localize OR and PR, and staining intensity was scored. Moderate staining for the PR was detected in the stroma at proestrus (days 17-20). Expression increased through oestrous, reaching maximal levels by metestrus (days 1-6) (P< 0.05). During diestrus (days 7-16), PR expression was downregulated (P< 0.05). Progesterone receptor expression was detected in the luminal 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 staining compared to intercaruncular stroma (P< 0.05). Reactivity to the OR antibody in cycling animals was detected in the stroma and glandular epithelium. Levels increased through proestrus and oestrous, were maximal during metestrus (P< 0.05), and decreased during diestrus (P< 0.05). Interestingly, there was transient upregulation in the luminal epithelium on day 16 or day 14 (P< 0.05). This was not evident at day 16 of pregnancy, although some OR reactivity was present in stroma and glands. By day 18 of pregnancy OR were undetectable (P< 0.05). Oestrogen-treated ovariectomized animals had increased OR and PR expression in comparison to progesterone treated cows (P< 0.05). Untreated ovariectomized cows showed constitutive steroid receptor expression. These results support the widely accepted role for sex steroids in the regulation of their receptors and indicate that there is paracrine regulation of steroid receptor expression in the bovine uterus. Copyright 2001 Harcourt Publishers Ltd.