Cytosol estrogen and progesterone receptors in bovine endometrium after uterine involution postpartum and in the estrous cycle

Abstract

Cytosol estrogen and progestin receptor (ERC and PRC) concentrations in bovine endometrium were investigated. Samples were taken by biopsy after parturition, when uterine involution was completed but before estrous cycles resumed (postpartum anestrus) and thereafter during the follicular phase and at diestrus. The concentration of cytosol estrogen receptor (ERC) was lower in diestrus (375 fmol/mg protein) than during follicular phase (557 fmol/mg protein, P < 0.01) and postpartum anestrus (544 fmol/mg protein, P < 0.05). During the follicular phase, ERC increased from values measured at proestrus (388 fmol/mg protein) to higher concentrations at estrus (550 fmol/mg protein) and metestrus (700 fmol/mg protein). At the beginning of diestrus, ERC levels were observed to decline ( P < 0.05). Progesterone receptor concentrations during postpartum anestrus (1333 fmol/mg cytosol protein) and during the follicular phase (1405 fmol/mg protein) were significantly higher than in diestrus (794 fmol/mg protein). During the follicular phase, PRC concentrations increased from the level measured at proestrus (865 fmol/mg protein) to higher levels at estrus (1366 fmol/mg protein) and metestrus (1909 fmol/mg protein). The rises between proestrus and metestrus ( P < 0.001), as well as between estrus and metestrus ( P < 0.05), were statistically significant. After formation of the corpus luteum, PRC concentrations diminished in the endometrium. Decreasing concentrations of PRC were observed during diestrus until the onset of proestrus. Changes in the concentrations of PRC and ERC were usually parallel. As in several other species, these results are compatible with the thesis that estrogen induces ERC and PRC, whereas progesterone has an opposite effect. No significant differences in PRC or ERC levels were observed between Ayrshire and Friesian breeds, or different feeding groups.