Endometrial mRNA expression of oestrogen receptor alpha, progesterone receptor and insulin-like growth factor-I (IGF-I) throughout the bovine oestrous cycle

This study characterized endometrial expression of mRNAs of oestrogen and p rogesterone receptors (ER, PR) and insulin-like growth factor-I (IGF-I) dur ing the oestrous cycle. Seven Holstein heifers that showed standing oestrus on the same day (day 0) were selected and blood samples for oestradiol (E2 ) and progesterone (P4) determinations by RIA were taken daily until day 23 . Endometrial samples were taken by transcervical biopsies on days 0, 5, 12 and 19 for mRNA determination by solution hybridization. The highest endom etrial mRNA levels of ER alpha and PR were observed at oestrus and a declin e was observed already at day 5, which then decreased progressively at the end of the luteal phase. IGF-I mRNA levels were higher at day 0 and 5 than at day 12. At day 19, mRNA levels of ER alpha, PR and IGF-I were the lowest in heifers that were at the end of their luteal phase (n = 4), but were hi gh again in heifers which P4 levels were basal (n = 3). The temporal change s in mRNA endometrial expression of ERa, PR and IGF-I and their relation to the changes in steroid concentrations during the bovine oestrus cycle are described. (C) 2001 Published by Elsevier Science B.V.